STUDENTS INDUSTRIAL WORK EXPERIENCE

 

The SIWES was established as a result of the realization by the Federal Government, in 1971, of the need to introduce a new dimension to the quality and standard of education obtained in the country in order to achieve the much needed technological advancement; because it has been shown that a correlation exists between a country’s level of economic and technological development, and its level of investment in manpower development (Oniyide, 2000). Some of the objectives of SIWES are:

·         To provide, for the students, opportunities to be involved in the practical aspect of their respective disciplines; thus, bridging the gap between the theoretical aspect taught in the class and the real world situations.

·         To expose students to latest developments and technological innovations in their chosen professions.

·         To prepare students for industrial working environments they are likely to meet after graduation.

1.2              The Company

Reid Crowther Nigeria Limited is an employee-owned Canadian company that has being offering comprehensive engineering services for over 10 years, with the mission to provide Quality Engineering and Project Management Services using creative and innovative solutions that are responsive to client and public needs by applying the art of engineering to solve everyday problems.

The areas of specialisation of the company can be grouped into five main areas, namely: Environmental, Municipal, Transportation, Building and Industrial engineering. Specifically, these include Water Supply and Distribution, Wastewater Collection and Treatment, Solid Waste Management, Marine and Road Transportation, Harbour works, Drainage, Flood Protection, Environmental Impact Assessments, Geographical Information System (GIS).

The company started operations in Nigeria in 1986 with its office in Lagos alone, but various jobs, through which it has demonstrated its expertise, had created offices in other parts of the country such as Warri, Abuja, Ondo and Ekiti states. The company’s staff strength is about 200, made up of expatriates and indigenes.

The company has demonstrated its expertise in a number of major projects such as the Redesigning and Supervision of Lagos State Water Distribution System, Consultancy service for Otamiri River Water Supply Project, Mapping for Rapid Transit System in Lagos, Upgrading of Sewage Treatment Plant and Disposal of Treated Effluent and Stormwater for Chevron’s estate at Satellite Town, Front-End Engineering and Master Plan Design for Potable Water at Chevron Nigeria Limited (CNL) Escravos Terminal, Design Modification of Sewage Collection and Treatment Plant at Chevron Nigeria Limited (CNL) Escravos Terminal, Water Supply System Rehabilitation in Federal Capital Territory, Ondo and Ekiti states for the Federal Government, and so on.

Reid Crowther has the vision of constantly demonstrating its high degree of competence as an international consultant in all engineering projects, and is committed to impart the Nigerian environment as well.

1.3              Objective and Scope of the Report

The objective of this report is to present, in details, the various activities carried out by the trainee at Reid Crowther Nigeria Limited from March 2002 to August 2002 as well as provide the general background knowledge about the aspects of Civil Engineering applied while undergoing the SIWES programme.

For the reasons stated above, the report covers only the extent of work, in brief, that has been done before the trainee was involved in the various projects; as well as background engineering knowledge applied in these projects, except in cases where other engineering knowledge not applied cannot but be mentioned, because they are intertwined with the knowledge applied in these projects, and in such cases they are very brief. Consequently, no mention is made of any further activities carried out in these projects after the trainee’s completion of training.

 LITERATURE STUDY

            This chapter is to serve as a preparatory background of knowledge for the practical training that the trainee went through. It provides elementary knowledge of supply and the design processes of water schemes; design processes of reinforced concrete structural units; application of geographical information studies.

2.1              Water Supply and Design Processes

2.1.1    Water Supply Processes

Water is essential to life, it also serves as a reference liquid in science, as the medium for countless chemical reactions and as the conveyor of the vital substances, which it needs-- mineral salts, organic molecules (Laing, 1973). This makes issues about water to be such important to man’s life that it cannot be pushed aside. These issues are briefly explained in the following sections.

(a)                How much water is needed?

Hammer and Hammer, Jr. (1996) states that the amount of water needed by a community depends on industrial use, climate, economic, social as well as locality conditions.

It is convenient to divide water consumption, according to Twort et al (1985), into the following categories:

·         Domestic: In-house uses such as drinking, cooking, sanitation, house cleaning, car and clothes washing, garden watering, etc.

·         Economic: Industrial usage in factories, power stations, etc; commercial usage in shops, offices, restaurants, etc; institutional usage in schools, hospitals, government offices, etc.

·         Agricultural: Use of water for crops, livestock, horticulture, dairies etc.

·         Public: Usage of water in public parks, for sewer flushing, fire fighting, etc.

·         Losses: Consumer wastages (leakages and wastages from consumers’ premises, misuse or unnecessarily wasteful use of water by consumers); distribution losses (leakages and overflows from service reservoir, leakages from mains, service connections, valves and washouts); metering and other losses.

Since all these categories of water consumption do not apply to all design situations, Twort et al (op. cit.) further explained that it is expedient that a consumption survey (or, its trend be determined) be carried out to investigate likely losses from a system, consumers’ lifestyle, forecast future demand based on population, and come up with an average daily demand (ADD) per capita.

Thereafter, a maximum daily demand (MDD) is computed. It is usually expressed as either a percentage of the ADD or, simply, a multiplying factor of ADD. This factor ranges from 110 to 200%.

Also, the peak hourly flowrate is calculated, depending on the size of area to be served and the nature of demand. This applies flow factors, as well, to the ADD—it ranges from 2.0 to 4.0. This is to cater for peak demand during peak flow period, usually in the morning (5.30 a.m-9a.m) and the evening (6p.m.-9p.m.). Peaking factors, as they are called, are not just chosen on the basis of water demand, it must relate to other factors in consideration such as future upgrading.

Upon an accurate estimation of daily demand, the design process moves to the next stage of locating water source(s) that will guarantee that demand and proximity to the location of the consumers.

(b)               Sourcing for water

In assessing the water resources, the modern approach is to consider all the possible means of development, and to examine, comprehensively, the hydrology of the catchment involved. Twort et al (op. cit.) listed the full range of possible developments as follows:

(1)               Surface water

·         River intake,

·         Reservoir for direct supply,

·         Reservoir for indirect gravity or pumped inflow, and

·         Tanks fed by collected rainfall.

(2)               Groundwater

·         Springs, and

·         Wells and boreholes.

(3)               Water Reclamation

·         Reuse of treated sewage effluent.

The evaluation of a source involves an inventory of all water available including rainfall, losses, catchment areas etc. To do this, a hydrological survey, if necessary, must be conducted in which all flows into and out of the catchment are quantified and balanced, so ensuring that all have been accounted for. The parameters to be measured for a particular catchment will be as follows:

(i)                 Inflows (or Gains)—These include precipitation, surface runoff into the area, groundwater movement into the area, etc.

(ii)               Outflows (or Losses)—These include evaporation and transpiration, surface runoff out of the area, groundwater movement out of the area, irrigation abstractions, etc.

(iii)             Storage—This includes soil moisture changes, change in contents of impounding reservoir and aquifer storage changes.

In summary, a water evaluation survey provides a means of understanding water use in catchment area, checking that catchment are adequate and accurate, and quantifying average resources. In choosing between sources of supply, the main factors, according to Laing (op. cit.), to be considered are quality of the available water, quantity of the water required, regularity of flow, and cost of finding, transporting, treating, and distributing water.

(c)        Estimation of yield

            No source, according to Twort et al (op. cit.), can be said to have a fixed yield because catchment conditions and consumer requirements change with time. It is essential that a water engineer be able to appraise the net yield—water remaining for supply after any compensation water or residual flow has been left for other riparian interests—of a catchment prior to planning any new development. The basic requirement of a catchment to be chosen as a source is that its net yield must be able to meet the MDD in excess, other factors being constant.

            In estimating the yield of a source, the nature and type of the source plays an important role. In estimating the yield of a surface yield, it necessary to obtain and study the record of rainfall data, analyse results of runoff measurements at location concerned (Adewumi, 2000). Furthermore, hydrographs are to be studied in order to forecast a future critical event, as well as preparing contingency plans for an existing source; and to provide a convenient tool for the rapid and consistent testing of a variety of schemes to find their likely critical drawdown period and associated yield. If all these do not guarantee the design requirements in terms of demand, especially during dry periods, Twort et al (op. cit.) advised that the option of excess water storage in high flow period should be considered, such as damming the site.

            For underground source, there are two distinct ways in which well or borehole yields can be estimated (Twort et al, op.cit.). The first concentrates on well hydraulics and installed pumping plant; while the second attempts to predict yield from the hydrogeology of the borehole site and the contributing catchment. The aim of these methods is to attain the ideal yield, whereby the source output is safely maximised with no more than is necessary in the way of pumps. Whatever technique is employed, water quality information of source must be obtained to indicate whether saline water has been struck or some other characteristics have been observed which makes the yield, however large, useless for the designed purpose(s). Care must therefore be taken when estimating groundwater yield that the result does not imply a steady encroachment of coastal seawater into the aquifer or that a poor quality water zone of the aquifer will be drawn upon.

            For the borehole yield to be established as being suitable for the design conditions, a pumping test needs to be carried out with the following objectives:

·         To find the abstraction limit of the hole and the rate at which the water level falls with time;

·         To define the discharge-pumping level relationship in order to choose an efficient permanent pump;

·         To monitor the effect of the use of source on the local environment;

·         To determine the aquifer’s permeability and storage characteristics.

Where the aquifer is confined under pressure by an impermeable layer above it, steadier rates will prevail; so, also, in riverbank aquifers. For unconfined aquifers, a test sequence for investigation is recommended (Twort et al, op. cit.). Once it is guaranteed that the borehole discharge estimate will satisfactorily meet the MDD, over a period of years, a borehole is sunk, and developed by pumping.

On a general note, whichever source chosen, the basic requirement is that it must be able to meet the MDD, as well as allow a cost-effective treatment option guaranteed to produce water that meets the Drinking Water Quality Standards/Guidelines.

(d)               Analysis of Raw Water

Depending on many circumstances, the presence of various substances in raw water and their significances vary. A thorough consideration of raw water quality, and sampling frequency in conditions of limited resources is important and a prelude to choosing a treatment process of raw water to be supplied to a community. The likely substances, or conditions, according to Twort et al (op. cit.), that may be present in raw water, and needs consideration, are:

·         Acidity

·         Alkalinity

·         Aluminium

·         Ammoniacal compounds

·         Arsenic

·         Biochemical Oxygen Demand (BOD)

·         Calcium

·         Carbon dioxide

·         Chloride salts

·         Chlorine

·         Colour

·         Copper

·         Corrosive Quality

·         Cyanide

·         Fluoride

·         Hardness

·         Iron

·         Lead

·         Magnesium

·         Manganese

·         Nitrite and Nitrate

·         Organic matter

·         pH value

·         Sodium

·         Sulphates

·         Suspended Solids (SS)

·         Taste and Odour

·         Turbidity

·         Zinc

(e)        Drinking Water Quality Standards/Guidelines

            It is a generally accepted fact that life is dependent on water and that water exists in nature in many forms—clouds, rain, snow, ice, and fog; however, strictly speaking, chemically pure water does not exist for any appreciable length of time in nature. Even while falling as rain, water picks up small amount of gases, ions, dust, and particulate matter from the atmosphere. Then as it flows over or through the surface layers of the earth, it dissolves and carries with it some of almost everything it touches, including that which is dumped into it by man.

            All these impurities, Twort et al (op. cit.) stated, may give water a bad taste, colour, odour, or cloudy appearance (turbidity), and cause hardness, corrosiveness, etc. They may transmit disease. Many of these impurities are removed or rendered harmless, however, in municipal drinking water treatment plants in order to provide ‘pure’ water to consumers.

            ‘Pure’ water means different things to different people. One way of establishing, and assuring the purity and safety of water, which is generally acceptable to all and sundry, is to set a standard—a definite rule, principle, or measurement that is established by governmental authority—for various contaminants. Thus, we have the 1993 Guidelines for Drinking Water Quality by World Health Organisation (WHO), 1986 Drinking Water Regulations by United States Environmental Protection Agency (US EPA), 1989 Water Quality Regulations by United Kingdom, 1999 National Guidelines and Standards for Water Quality in Nigeria by Federal Environmental Protection Agency (FEPA), etc. There is no international standard for drinking water quality, according to WHO (1993a), in order to allow the use of a risk-benefit approach, which would allow nations to establish their own standards and regulations that takes into consideration peculiar local conditions; all with the primary aim of ensuring the protection of public health.

            WHO (op. cit.) further stated that water is evaluated for quality in terms of its:

(1)        Physical Properties:

·         Turbidity—suspended particles

·         Taste

·         Odour

·         Colour

(2)        Chemical Properties: Inorganic and organic compounds dissolved in water that are harmful.

(3)         Microbiological Properties: Pathogens, especially coliform bacteria.

There are two categories of standards, namely:

(i)                 Primary Standards—based on health criteria; and

(ii)               Secondary Standards—based on aesthetic and non-aesthetic conditions.

For all standards, there are guide limits/levels for various water qualities. These are defined as follows:

·      Maximum Contaminant Levels (MCL)—The highest level of a contaminant that is allowed in drinking water. MCLs are enforceable standards.

·      Maximum Contaminant Level Goal (MCLG)—The level of a contaminant in drinking water below which there is no known or expected risk of health. MCLGs allow for a margin of safety and are non-enforceable public health goals; rather they are intended as guidelines. They are also known as Secondary Maximum Contaminant Level (SMCL).

·      Maximum Residual Disinfectant Level (MRDL)—The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.

(f)        Water Treatment Methods

            According to American Water Works Association (AWWA) (1984), the main function of water treatment is to provide a continuous supply of safe, good-tasting, and cold drinking water that is free of contaminants that can cause disease or be toxic to a consumer. The water must also be free of unpleasant things such as colour, turbidity and odour.

            Therefore, the water treatment processes used in any specific instance must take into account the quality and nature of the raw water supply source. The intensity of treatment must depend on the degree of contamination of the source water (WHO, 1993b). This implies that, according to Lo (1999), the fundamental purpose of water treatment is to protect the consumer from pathogens and impurities in the water that may be offensive or injurious to human health; and to bring raw water up to drinking water quality standards.

            Since there are three categories of contaminants in raw water, there are, correspondingly, three categories of treatment to bring raw water to the required condition, safe for human consumption and use (Twort et al, op. cit.). These are:

(1)   Physical Treatment Processes: These processes entail the use of physical means to treat water in terms of its physical/aesthetic properties, which are mostly visible to the naked eyes. They include Screening, Aeration, Sedimentation, Filtration, and Distillation.

(2)   Chemical Treatment Processes: These processes involve the addition of chemicals to neutralize the effects of harmful organic and inorganic compounds dissolved in the raw water. It involves Chlorine, Coagulation and Flocculation, Ozonation, Fluoridation, etc.

(3)   Biological Treatment Processes: These involve the use of biological means to remove pathogens and other microbial organisms that cannot be removed by the two processes above. They use impermeable membranes, basically, to achieve this. They include Reverse Osmosis, Micro-filters, etc, according to Turner (1998).

It is quite possible for any of the treatment process to perform more than one category mentioned above. For instance, filtration is basically a physical treatment process; it can also allow the purification of water contaminated by pathogenic bacteria (Twort et al, op. cit.).

            The basic processes of the water treatment are briefly explained below.

Screening: This is to remove relatively large floating and suspended solids/debris. This is done through the use of screens which may be coarse (above 25mm perforations) for removing sticks and other solids which cannot pass through it; and/or fine (below 25mm) to remove fine particles that pass through the coarse screens, but should not go through the plant (Reynolds, 1991).

Aeration: Twort et al (op. cit.) explained that aeration is basically used to:

·         To increase the dissolved oxygen (DO) content of the water.

·         To reduce taste and odour caused by dissolved gases in the water, such as hydrogen sulphide, and also to oxidise and remove organic matter.

·         To decrease the carbon dioxide content of a water and thereby reduce its corrosiveness and raise its pH value.

·         To convert iron and manganese from their soluble states to their insoluble states, and thereby cause them to precipitate so that they may be removed by infiltration.

To achieve this goals, four main types of aerators commonly used are free-fall, spray, injection and, surface aerators.

Plain Sedimentation: Basically, sedimentation tanks are designed to reduce the velocity of flow of water so as to permit suspended solids to settle out of the water by gravity. Plain sedimentation is to allow raw water settle in tanks for a period of 6-8 hours so that large and settleable SS will be removed by gravity alone—without the use of chemicals (Lo, op. cit.). Twort et al (op. cit.) explained that they are designed for continuous supply and the velocity of flow through the tank being sufficiently low to permit gravitational settlement of the SS to occur, say maximum velocity of 10cm/s for particle’s diameter not greater than 1mm.

Chemical Coagulation and Flocculation: Lo (op. cit.) explained that chemical coagulation is the addition of chemicals (coagulants) into water in a mixing tank so as to encourage the non-settleable solids to coagulate into large particles (chemical flocs) that will more easily settle; while flocculation is a gently mixing process that induces particle collision and allow the formation of large particles of floc. This takes about 15 – 20 minutes to complete. Twort et al (op. cit.) further explained that these floc particles could thereafter be removed either by sedimentation and/or filtration. The commonest coagulant is Aluminium Sulphate, usually referred to as ‘alum’; others include Sodium Aluminate, Ferrous Sulphate, etc.

Chemically assisted Sedimentation: This, according to Reynolds (op. cit.), is the last stage of the process called clarification—the first two stages (coagulation and flocculation) having been explained above. Sedimentation takes place in a sedimentation, or settling, tank in which the produced chemical flocs settle out by gravity. This implies that the primary function of a sedimentation tank is to provide settled water with the lowest possible turbidity level, thereby decrease the loading on subsequent treatment processes.

            Reynolds (op. cit.) further stressed that efficient sedimentation tanks must be designed to have a sludge collection system. This is necessary, because as the water move slowly through the tank with low velocity and turbulence, the solid flocs settle to the bottom of the tank and the accumulation of these solids on the floor of the tank forms what is called sludge. It is now the function of the sludge collection system to remove the sludge periodically so that the tank can continue to supply low-load water to subsequent treatment processes.

Filtration: Reynolds (op. cit.) explains that the primary purpose of the filtration process is to remove suspended materials (measured in turbidity) from water. This suspended material can be floc that hadn’t settled out in the sedimentation tank, microorganisms, and any chemical precipitates such as iron and manganese. These suspended materials are removed when the water from the sedimentation tanks passes through the filter media—usually beds of granular and fine materials, such as anthracite coal, sand, gravel, etc.

            The filtration process has two types, Twort et al (op. cit.) explained. These are Rapid Sand filtration and the Slow Sand filtration. It is established (Lo, op. cit.; Twort et al, op. cit.) that the purpose of rapid sand filtration is to filter out, quickly, chemical flocs that fail to settle in the previous sedimentation tank. The filtered water is normally free of particles and turbidity; and the removal of the particles is largely by physical action. Though, Twort et al (op. cit.) mentioned that with some contaminated waters, the oxidation of ammonia to nitrate could occur when the water passes through rapid sand filters.

            Slow sand filter, on the other hand, passes water slowly through a bed of sands (Twort et al, op. cit.). It is an effective method devised for the purification of bulk waters contaminated by pathogenic bacteria. Pathogens and turbidity are removed by natural die-off, biological action, and filtering. The incoming water is led gently on to the filter bed and percolates downwards, then the water is expected to maintain the design rate of flow through the bed. However, as suspended material in the raw water is deposited on to the surface of the bed, organic and inorganic materials build up on the surface of the sand and increase the friction loss through the bed, thereby reducing the efficiency of the filter. To maintain the efficiency, there is need for periodic cleaning of the bed through scraping, backwashing etc.

            The slow sand filter does not act by a simple straining process. Twort et al (op. cit.) explained that it works by a combination of both straining and microbiological action of which the latter is more important. Van de Vlaed (1955) gave a clear account of the details of the purification process. It distinguishes three zones of purification in the bird—the surface coatings, the ‘autotrophic’ zone existing a few millimetres below the surface coating, and the ‘heterotrophic’ zone that is extended some 300mm into the bed.

            As the incoming water into the filter bed passes through it, during the first few weeks, the upper layers of sand grains become coated with a reddish-brown sticky deposit of partly decomposed organic matter together with iron, manganese, aluminium and silica. This coating tends to absorb organic matter existing in colloidal state. After some weeks, there exists in the uppermost layer of the sand a film of algae, bacteria, and protozoa, to which are added the finely divided suspended material, and other organic matter deposited by the incoming water. This film acts as an extremely fine, meshed straining mat.

            A few millimetres below this film is the autotrophic zone, where the growing plant breaks down organic matter and uses up available nitrogen, phosphates, and carbon dioxide, providing oxygen in their place. The filtrate thus becomes oxidised at this stage.

            Below this again, a still more important action takes place in the heterotrophic zone, which extends some 300mm into the bed. Here the bacteria multiply to very large numbers so that the breakdown of organic matter is completed, resulting in the presence of only simple inorganic substances and unobjectionable salts. The bacteria act not only to break down organic matter but also to destroy each other and so tend to maintain a balance of life native to the filter so that the resulting filtrate is uniform.

            The advantages of slow sand filters, according to Twort et al (op. cit.), provided that the water they treat, either directly, following storage, or following rapid gravity filters, has relatively good physical and chemical characteristics, then they will produce excellent-quality water. It is efficient in the removal of viruses from contaminated reservoir waters. It allows for easier and cheaper disposal of chemical sludge from coagulation plants.

            The limitation of slow sand filter is that it does not materially reduce the ‘true colour’ of water (The term ‘true colour’ may be taken as the colour of the filtrate after removing colloidal clay). Thus, they are only suitable for dealing with waters of relatively low colour. Also, slow sand filter cannot be expected to be effective in removing any high concentration of manganese in solution. They are also not very suitable for dealing with any substantial amount of finely divided inorganic suspended matter.

Disinfection: This is a means of disinfecting the filtered water so that all pathogenic bacteria will become killed, literally. In the true sense, disinfection means the reduction of organisms in water to such low levels that no infection of disease results when the water is used for domestic purposes (Twort et al. op. cit.).

            The efficacy of any disinfection process depends upon the water being treated beforehand having a high degree of purity, as disinfectants will be neutralised to a greater or lesser extent by organic matter and readily oxidisable compounds in water. Micro-organisms that are aggregated or are adsorbed to particulate matter will also be partly protected from disinfection, and there are many instances of disinfection failing to destroy waterborne pathogens and faecal bacteria when the turbidity was greater than 5 NTU[1]. It is therefore essential that the treatment processes preceding terminal disinfection be always operated to produce water with a mean turbidity not exceeding 1 NTU and maximum of 5 NTU in any water sample. Normal conditions of chlorination (i.e. a free residual chlorine of 0.5 mg/l, at least 30 minutes contact time, pH less than 8.0, and water turbidity of less than 1 NTU) can bring about 99% reduction of E. coli and certain viruses, but not the cysts of parasitic protozoa (WHO, 1993b).

            Twort et al (op. cit.) stated that the commonly used disinfectants are:

·      Chlorine,

·      Chloramine,

·      Sodium Hypochlorite,

·      Ozone,

·      Ultraviolet radiation, and

·      Iodine.

Reynolds (op. cit.) explained that when chlorine is added to water, it forms hypochlorous acid, one of the two forms of free chlorine. Chlorine combines with impurities in the water and enough chlorine must be added to react with these impurities to the point where the addition of chlorine results in free chlorine, meaning it has react with everything it is going to react with. The free chlorine indicates enough chlorine is available to disinfect the water. It is important to note that the effectiveness of chlorination depends on five factors—concentration, contact time, temperature, pH and substances in the water. The destruction of organisms is directly related to the concentration and contact time.

(g)        Miscellaneous Water Treatment methods:

            (i)            Fluoridation—This is the addition of fluoride into water, when they are found to be in short supply of fluoride. This is necessary to strengthen the dental care of baby infants and reduce the incidence of dental caries (Lo, op. cit.; Twort et al, op. cit.).

          (ii)            Softening—This is a means of removing/reducing the hardness of water, caused by high concentration of metallic ions, such as Ca, Mg, etc (Lo, op. cit.).

        (iii)            Use of Package plants—The type mentioned here is the Davnor BioSand Filter System. It is based on a unique intermittently operated slow sand filtration process where the flow through the filter does not need to be continuous to achieve the objectives. It can remove pathogenic organisms as well as taste, odour, turbidity etc (Manz, 2001).

        (iv)            Reverse Osmosis—Osmosis is a natural phenomenon in which a liquid (water, in this case) passes through a semi-permeable membrane from a relatively dilute solution towards a more concentrated solution. This flow produces a membrane pressure called the osmotic pressure. If pressure is applied on the more concentrated solution, and if that pressure extends the osmotic pressure, water flows through the membrane from the more concentrated solution to the more dilute solution. This reversed process of osmosis is called Reverse Osmosis, which removes up to 98% of dissolved minerals. To perform this reversed process, a pump is used to pressurise the feedwater flow through the membrane.

(h)        Storage System

            Twort et al (op. cit.) explained that the storage system is an important part of any water treatment and supply system. It has two main functions:

·         To balance the fluctuating demand from the distribution system against the output from the source.

·         To act as a safeguard for the continuance of the supply, should there be any breakdown at the source or on the main trunk pipelines.

·         To provide adequate contact time for the chlorine added to do its job of disinfection before the treated water is distributed to the consumers.

            If the service storage system is to be of maximum value, as a safeguard to the undertaking against breakdown, then it should be positioned as near as possible to the area of demand. From the service storage tanks, the distribution system should spread directly, with such ramification of mains that no single breakage could cause a severe interruption to the continuity of the supply. There should be sufficient interconnection between the distribution mains that, should a breakdown of any one of the mains occur, a supply may still be maintained by rerouting the water.

            Hammer and Hammer Jr. (op. cit.) explained that storage system may be provided by the use of elevated tanks, underground basins, or covered reservoirs. The advantage of elevated tank is the pressure derived from holding water higher than the surrounding terrain. The elevation at which it is desirable to position a service reservoir depends upon the distance of the reservoir from the distribution area, the elevation of the highest building to be supplied, and the influence of corresponding pump selected.

            The factors influencing depth for a given storage, according to Twort et al (op. cit.), are:

            (i)               Depth at which suitable foundation conditions are encountered,

          (ii)               Depth at which outlet mains must be laid,

        (iii)               Topography of site,

        (iv)               Volume of storage.

In designing a storage system, the following are the salient features to be taken care of, where applicable, are depth and shape of storage tanks, roofing of the tanks, walls, access manholes, etc.

            Generally, storage systems are made from any of these materials—metals, plastic, and concrete. Whatever the material from which it is produced, storage systems must be watertight, i.e. no leakage, in order to be able to adequately supply the needed demand.

(i)         Distribution Network

            WHO (1993b) explained that the distribution network transports water from the place of treatment to the consumers. Its design and size will be governed by the topography, location and size of the community. The aim of any distribution network should always be to ensure that consumers receive a sufficient and uninterrupted supply, and that contamination is not introduced in transit.

            Distribution network, according to Hammer and Hammer Jr. (op. cit.), includes a network of mains with storage reservoirs, booster, pumping stations (if needed), fire hydrants, service connections as well as fittings. 

Twort et al (op. cit.) stated that pipes, for the mains, are made of different materials. These include:

·      Copper pipes—They are expensive, but are strong, durable, resistant to corrosion, easily jointed, and capable of withstanding high internal pressures.

·      Steel pipes—They are widely used because they are one of the cheapest forms of pipes and can sustain high pressure.

·      uPVC pipes—This means unplasticized polyvinyl chloride pipes. It is used mostly for cold water service piping, because it is not wholly suitable for working environment with temperatures above 20⁰C. They are corrosion-resistant, light to handle, and easy to join.

·      Polyethylene pipes—Polyethylene is a thermoplastic material, which softens with heat. Polyethylene pipes are light in weight and flexible, resistant to abrasion and corrosion, and have a better impact resistance at low temperature than uPVC pipes do. Three types of this pipe are available for water supply purposes: low density polyethylene (LDPE), medium density polyethylene (MDPE), and high density polyethylene (HDPE).

·      Concrete pipes—As the name implies, they are pipes made from concrete. They are types of it, as well: Prestressed concrete pipes-noted for its higher pressure resistance; Reinforced concrete pipes-similar to Prestressed pipes, advantageous for relatively high head mains, resistance to abrasion, etc.

The choice of pipe to be used for a main, according to Twort et al (op. cit.), depends on the locality conditions, capacity of mains, cost, length of mains needed, appropriate resistance coefficients, etc.

            Fittings of a water distribution network, according to Twort et al (op. cit.), are all the necessary accessories needed to ensure that the distribution network meets its objectives. They include:

·         Adaptors

·         Bends—used to change the direction of flow in a main. They are usually 90⁰, 45⁰, 22.5⁰, 11.25⁰.

·         Valves—are installed throughout the water distribution network, as well as in the treatment plant and the storage system. This is to control the magnitude and direction of water flow. The various types, according to functions, are Gate valves, Check valves, etc (Hammer and Hammer Jr., op. cit.).

·         Fire hydrants—They provide access to underground water mains for the purpose of extinguishing fires, flushing out the water mains (Hammer and Hammer Jr., op. cit.).

·         Pumps—They are used for a variety of functions in water. Low-lift pumps are used to elevate water from a source to treatment plant, usually. High-lift pumps are used to discharge water to various outlets of the distribution network; depending on other factors such as size of community, length, height of discharge, etc.

o   The power output of a pump is the work done per unit time in lifting water to a higher elevation. The efficiency of a pump is the ratio of the power output to the power input. Mathematically, (Hammer and Hammer Jr., op. cit.).

o   e_p == P_o / P_i                                                    (2.1)

where: e_p = efficiency of pump, dimensionless;

P_o = power output, horsepower (or kilowatts)_;

P_i = power input, horsepower (or kilowatts).

·         Service Connection—Hammer and Hammer Jr. (op. cit.) explained that the service connections into a property includes a corporation stop tapped into the water main, a service to a gate valve at the curb, as well as a water metre and the metre box, which houses the metre.

2.1.2        Flow Process Design

This is the aspect that applies the basic principles of hydraulics in determining the unknown design parameters of water supply process—such as mains’ sizes, pipe types, flowrate, power of pumps, size of storage sizes, etc.—from the known design parameters—such as population of consumer, distances, per capita consumption, etc.

This process, according to Reid Crowther (2001), can be subdivided into four main parts:

·         Design of mains,

·         Design of pumps,

·         Design of storage facilities, and

·         Design of treatment plant.

In hydraulics, there are both empirical formulae and fundamental equations to solve various problems. These empirical formulae work well for the practical situations for which they were intended; however, there are occasions where the incorrect use of an empirical formula may lead to gross error in calculations (Twort et al, op. cit.).

Design of Mains

This entails the determination of the diameters of the pipes, given the flowrate, Q, and limiting velocity, V. This is done by using the relationship among the flowrate of fluid, velocity, and the cross-sectional area of flow, given by equation 2.2:

            Q = A x V                                                           (2.2)

where  Q = quantity of water flowing per unit time (cubic metres per seconds,  m³/s)

            V = velocity of flow (metres per second, m/s)

            A = cross-sectional area of flow (square metres, m²)

This formula is known as the continuity equation. It states that “for an incompressible fluid”, such as water, “if the cross-sectional area decreases, the velocity of flow must increase; conversely, if the area increases, the velocity must decrease” (Hammer and Hammer Jr., op. cit.)

            Having determined the values of Q and V, A is calculated. From the value of A, the diameter, d, of the pipe is determined from geometrical formula:

                        D =√ (4 x A)/ ∏                                                 (2.3)

Design of Pumps

            The design of pumps involves determining the working conditions for which the pumps will operate. These include calculating, for any given flowrate,

(i)                 The total head, H;

(ii)               The power of the pump.

Total Head, H: This is the sum of the elevation head, pressure head, velocity head, and the head losses in flow. The total head is also known as the total energy of a flow.

For an ideal, incompressible fluid flow, the total head (with metres as unit) is calculated from the Bernoulli equation, according to Featherstone and Nalluri (1982),

            Z + (P/ρg) + (V²/2g) = C                                   (2.4)

where C = constant

            Z = elevation above datum

            P = pressure

            V = velocity of flow

            g = acceleration due to gravity

            ρ = density of fluid

That is, the total energy, at all points, along a steady continuous streamline of an ideal incompressible fluid flow is constant. Simply stated, it is the sum of the elevation head, pressure head, and velocity head; thus the constant C can be replaced with E—total energy. Twort et al (op. cit.) however cautioned that the limitations of this equation must be carefully noted. It applies only to steady flow, and to flow where no energy is lost through friction.

For a real fluid flow, Featherstone and Nalluri (op. cit.), stated that the Bernoulli equation can be modified by (i) introducing a loss term in the equation 2.4, which would take into account the energy expended in overcoming other resistances due to changes in section, fittings, etc; and (ii) by correcting the velocity energy term for true velocity distribution. The frictional losses depend upon the type of flow, the roughness of the interior surface of the pipe.

Therefore, the modified Bernoulli’s equation for real incompressible fluid flow, for two points, is

Z₁ + (P₁/ρg) + (α₁V₁²/2g) = Z₂ + (P₂/ρg) + (α₂V₂²/2g) + h_f         (2.5)

where h_f = total head losses (significantly, frictional losses of the pipe)

           α = velocity correction factor.

Therefore, total head, H is determined from

H = Z + (P/ρg) + (αV²/2g)                                                    (2.6)

In computing the value of h_f, for a given pipeline, there are generally two types of formulae, namely: the dimensionally correct, and the empirical. Twort et al (op. cit.) stated.

            The dimensionally correct one is the Darcy’s equation:

                        h_f = (f x l x V²)   (2 x g x d)                                        (2.7)

                        where: h_f = head loss (m head of water)

                                      f = Darcy’s coefficient of friction

                                      l = length of the pipeline in metres

                                    V = velocity of flow (m/s)

                                     d = diameter of pipe (m)

The value of f is related to the relative roughness of the pipe material and the fluid flow characteristics (Hammer and Hammer, op. cit.).

            The empirical formulae are Hazen-Williams formula and the Manning’s equation, however, the former is more popular, Twort et al (op. cit.) stated. Hazen-Williams formula is

                        h_f = (6.78 x l x (V/C)^1.85) / (d^1.165)                              (2.8)

                       

where:   C = coefficient of pipe

                                      l = length of pipe

                                     d = diameter of pipe

It can also be written, conveniently, according to Bouthillier (1981), as

                        h_f = R x L x Q^1.85                                                         (2.9)

                        where: R = resistance coefficient for a particular diameter,

                                    L = length in kilometres,

                                    Q = flowrate, or discharge in Litres/minute

The actual power of the pump is calculated from, according to Al-Layla (1977),

                        P_a = P_t / e_p                                                                                 (2.10)

            But,     P_t = ρ x g x Q x H                                                      (2.11)

                        where:                 P_t = theoretical power of pump, or power output (kW)

ρ  = density (kg/m³)

g  = acceleration due to gravity (m/s²)

Q = flowrate (m³/s)

H = total head (m)

P_a= actual power of pump, or power input (kW)       

                                    e_p= efficiency of pump.

Design of Storage System

            The basic thing to be done here is determining the total volume of water to be supplied to the community per day, and getting an appropriate tank size that can supply the same volume.  Madu (2001) explained that this has to do with the discretion of the designer, in collaboration with list of standard tank sizes from manufacturers.

Design of the Treatment Process Facility

            Madu (op. cit.) explained that, having carried out the quality analysis of the raw water, the treatment process, on the one hand, is designed to take the raw water through the step-by-step treatment methods that will remove the contaminants, or supply sufficient substances as the case may be, to ensure that the treated water meets the drinking water quality standards.

            On the other hand, the treatment plant structures/facility needed to be designed as well. This involves the structural analysis of various units of the treatment plant such as aeration tank walls and beds, filtration walls and beds, etc. All these come after the capacity and treatment rate of plant has been calculated, in order to get the volume required and the corresponding forces that will act.

2.2              Reinforced Concrete Design

2.2.1    Introduction

A structure is an assembly of members each of which is subjected to bending or direct force (either tensile or compressive) or to a combination of both. These primary influences may be accompanied by shearing forces and sometimes by torsion – all of which cannot be adequately resisted by concrete, thus the concept of reinforced concrete.

Reinforced Concrete is a combination of two dissimilar but complementary materials, namely: concrete and steel (Oyenuga, 2001). Concrete has considerable crushing strength, is durable, has good fire resistance; but has a poor tensile stress, and fair strength in shear. On the other hand, steel has good tensile properties, poor resistance to fire (due to rapid loss of strength under high temperature), and is very good both in shear and compression. Thus, a combination of these materials results in good tensile and compressive strength, durability and good resistance to fire and shear.

To every action of loading on any member of a structure, there is a consequential reaction as a result of the combination of concrete and steel. The method of combining these materials (concrete and steel) in the most economical way on one hand, and safety on the other hand, is referred to as reinforced concrete design (commonly referred to as design or structural design). This means that, according to Reynolds and Steedman (1988), design entails the calculation of, or by other means of assessing, and providing resistance against the moments, forces, and other effects on the members (i.e. analysis of structures).

2.2.2        Design Objectives

The aim of structural design is the achievement of an acceptable probability that structures being designed will perform satisfactorily during their intended life (British Standards Institution (BSI), 1997). With an appropriate degree of safety, they should sustain all the loads and deformations of normal construction and use, and have adequate durability and resistance to the effects of misuse and fire.

From the foregoing, according to Oyenuga (op. cit.), a good structural design must satisfy the following functional objectives:

·         Under the worst combination of loading, the structure must be safe.

·         Under the working condition, the deformation of the structure must not impair the appearance, durability and/or performance of the structure – i.e. fits for its intended use.

·         The structure must be economical – the factor of safety should not be too large to the extent that the cost of the structure becomes prohibitive with no additional advantage(s).

Achieving these potentially conflicting objectives calls for experience and good sense of engineering, as well as leads to an efficiently designed structure.

An efficiently-designed structure is one in which the members are arranged in such a way that the weights, loads, and forces are transmitted to the foundation by the cheapest means consistent with the intended use of structure and the nature of the site (Reynolds and Steedman, op.cit.). Efficient design means more than providing suitable sizes for the concrete member and the provision of the calculated amount of reinforcement in an economical manner. It implies that the bars can be easily placed, that reinforcement is provided to resist the secondary forces inherent in monolithic construction, and that resistance is provided against all likely causes of damage to the structure. That is to say, experience and good judgement may do as much towards the production of safe and economical structures as calculations.

In summary, these objectives call for good assessment/estimation of the intending loads, right choice, quality, and proportion of materials, and sound workmanship. The realisation of these requires conformity to clearly defined criteria for materials, production, workmanship, and, also, maintenance and use of the structure in service. All these requirements are borne out of experience—from a study of existing structures and from comparison of alternative designs.

2.2.3        Design Methods

To achieve the objectives of design, according to Ojo (2000), the following methods can be adopted:

(a)        By dividing the ultimate strengths of materials with certain factor (factor of safety) to provide design stress (strength). This method is called elastic method of design (or permissible stress method/modular-ratio method).

(b)        By multiplying the load that the structure can withstand with certain factor of safety to give the working load. This is called the load-factor method.

(c)        Limit state method combines the advantages of the two methods above by applying factor of safety to both the materials and loads. This method also allows a varied factor of safety for various types of loading conditions.

The limit state design is based on the limit state approach or philosophy – the achievement of acceptable probabilities that the structure being designed will not become unfit for its intended use. This means that all criteria relevant to both safety and serviceability are considered in the design process so as to make sure that the structure does not reach a limit state. An easy and usual approach is to design on the most critical limit state, and then to check that the remaining limit states will not be reached.

There are two types of limit state in structural design, namely:

 (i) Ultimate limit state (ULS) – the limit state that ensures that the structure is safe under the worst loading condition. This ensures resistance against collapse, buckling, stability or overturning, and other accidental/special hazards such as earthquake, explosion or fire.

(ii) Serviceability limit state (SLS) – the limit state that ensures that the structure is fit for normal use, i.e. serviceable. This is to ensure that the structure will not fail during service. It takes care of deflection, cracking, fatigue, vibration, durability, lightning, etc.

Except in water-retaining structures, the ULS is generally critical for reinforced concrete structures, while SLS conditions are checked. However, in prestressed concrete[2] design, serviceability conditions are the basis for designing with checks on the ULS conditions (BSI, op.cit.).

            Structural design is largely controlled by regulations or codes (but, even within such bounds, the designer must exercise good judgement in his interpretation of the requirements, endeavouring to grasp the spirit of the requirements rather than to design to the minimum allowed by the clauses of the codes). The various methods of design highlighted above formed the basis of these codes. In Nigeria, the most prominent of these codes is ‘Structural Use of Concrete’ (BS 8110: Parts 1, 2, and 3), which is based on the limit state design method as stated in clause 2.1.2 of the code. Others include ‘The Structural Use of Normal Reinforced Concrete in Buildings’ (CP 114), which is partly based on the load-factor method, and ‘The Structural Use of Concrete’ (CP 110: Parts 1, 2, and 3).

2.2.4        Reinforced Concrete Members

A reinforced concrete structural member may be subjected to any (or all, in worst condition) of the structural failures – flexural, buckling, shear or torsion – depending on the type of member it is and its location in the structure. Thus, it is imperative to understand the importance/necessity of the various structural members, which are briefly outlined in this section as follows:

(a)        Beam:  This is a horizontal member of the whole structure with a rectangular cross-section usually. It, in most cases, supports the loads on the slab, the self-weight of the slab, and its own self-weight – all of which are transmitted to the nearest vertical member, such as column or wall (load-bearing). Beams, generally, resist flexural loading.

            The fundamental principle involved in the design of a reinforced concrete beam, according to Nilsor (1997), is that, at any cross-section, there exist internal forces that can be resolved into components normal and tangential to the section. Those components that are normal to the section are the bending stresses (tension on one side of the neutral axis and compression on the other) – their function is to resist bending moments at the section. The tangential components are known as the shear stresses (they resist the transverse or shear forces).

            In reinforced concrete beams, the concrete usually resists the compressive forces and the steel the tensile forces. Hence, the longitudinal reinforcing steels are located close to the tension face to resist the tension force; and, usually, additional steel bars (shear links) are used to resist inclined tensile stresses caused by the shear force in the beam. However, reinforcement is also used for resisting compressive forces primarily where it is desired to reduce the cross-sectional dimensions of compression members. Even if no such necessity exists, a minimum amount of reinforcement must be placed in all compression members to safeguard them against the effects of accidental bending moments (Nilsor, op. cit.).

            In general, for the most effective reinforcing action, it is essential that steel and concrete deform together, i.e. that there be a sufficiently strong bond between the two materials to ensure that no relative movements of the steel bars and the surrounding concrete occur.

            Design of reinforced concrete beams can be classified based on various factors. Based on reinforcement type, it could either be singly reinforced (only tension reinforcement is provided) or doubly reinforced (tension as well as compression reinforcement is provided). Based on structural shape and role, it may be classified into simply supported, continuous, flanged, and cantilever.

(b)        Column:    Primarily, columns are compression members, although some may be subjected to bending either due to their slenderness or due to their asymmetric loading from beams (Oyenuga, op. cit.). Reinforced concrete columns are generally either rectangular in cross-section with separate links, or circular – and, in some cases, polygonal.

            Fundamentally, columns can be categorised as:

·         Axially loaded column – when it supports approximately symmetrical beam arrangement.

·         Uniaxial column – when it supports direct loading and bending in one direction.

·         Biaxial column – when it supports a concentric loading and bending acting about two axes that are mutually at right angles.

Also, columns can be classified based on its end conditions as:

·         Braced column – when wall, bracing or buttressing, designed to resist all lateral forces in that plane, laterally supports it.

·         Unbraced column – when it is not laterally supported by wall, bracing or buttressing.

Furthermore, columns can be categorised, based on the ratio of its effective length to its cross-sectional dimensions, as:

·         Short column – when the ratios l_ex/h and/or l_ey/b are/is less than 15 (braced) and 10 (unbraced), where:

l_ex = effective height in respect of the major axis

l_ey = effective height in respect of the minor axis

h  = depth of cross-section measured in the plane under consideration

b  = width of a column (i.e. dimension of the cross-section perpendicular to h).

·         Slender column – when both the ratios l_ex/h and/or l_ey/b are/is greater than 15 (braced) and 10 (unbraced).

(c)        Slab:    A slab is a reinforced concrete member that, more often than not, is subjected to shear (Oyenuga, op. cit.). Because slab is generally a horizontal member, its design centres more on flexure rather than direct shear.

            Generally, slabs are similar to beams except that:

·         a width of 1.0m is generally assumed to as to make for a simplified design

·         the section is usually rectangular, hence no flanges

·         shear is generally not considered unless where concentrated or point loads predominate, and the slab is thicker than 200mm.

There are various types of slab, and the type to be preferred may depend on: (i) the span of the slab, (ii) the use of the space, which may determine the span, (iii) the load to be carried, and (iv) the architectural aesthetics required.

The various types include:

·         Solid slab (cantilever, simply-supported, continuous, one-way, and two-way)

·         Ribbed slab

·         Flat slab

·         Waffle slab

Slab directly carries the load imposed on it and its own self-weight (all in the form of uniformly distributed loads) and is supported by walls, beams and/or columns. Solid slabs are the commonest, especially in residential areas.

(d)       Wall:    Generally, this is a vertical load-bearing member whose length exceeds four times its thickness. A reinforced concrete wall is one with a minimum reinforcement not less than 0.4% of the area of concrete (BSI, op. cit.). According to Reynolds and Steedman (op. cit.), a braced wall is one where lateral stability of entire structure, at right angles to plane of wall being considered, is provided by walls (or other means) designed to resist all lateral forces; otherwise, the wall is unbraced. Whether braced or unbraced, a wall can further be classified as either being slender or stocky based on its slenderness ratio[3]. Thus, a stocky wall is one whose slenderness ratio does not exceed 15 (braced) or 10 (unbraced); while a slender wall is any one other than stocky, i.e. greater than 15 (braced) and greater than 10 (unbraced).

(e)        Foundation:     They are horizontal or vertical members supporting the entire structure and transmitting the loads to the soil below. They are sub-structures supporting the superstructures of columns, beams, walls, slabs, and roofs (Oyenuga, op. cit.). Generally, foundations can be broadly classified as either shallow or deep. These encompass the various types, namely: pad footing, strip footing, raft foundation, pile foundation, displacement foundation, strap foundation, e.t.c. The choice of foundation type depends, primarily, on the magnitude of load to be transmitted from the superstructure and the permissible bearing capacity of the soil. The selected foundation type must satisfy two fundamental and independent requirements:

·         The factor of safety against shear failure of the supporting soil must be adequate.

·         The settlement should neither cause any unacceptable damage nor interfere with function/use of the structure.

(i)         Pad footing:     This is most common of all the reinforced concrete footings. It supports columns and transmits the loads to the soil evenly. It is usually square in plan, but where there is a large moment acting about one axis, it may be more economical to have a rectangular base. It may be axially or eccentrically loaded. When axially loaded, the reactions to design ultimate loads may be assumed to be uniformly distributed (i.e. load per unit area). When eccentrically loaded, the reactions may be assumed to vary linearly across the base. It should be noted that the actual pressure distribution depends on the soil type, and the critical section is taken as that at the face of the column being supported (MacGinley and Choo, 1990).

(ii)        Strip footing:    Mosley et al (1999) states that strip foundation is commonly used under walls or under a line of closely spaced columns. Even if it were possible to have individual bases, it is often simpler and more economical to excavate and construct the formwork for a continuous base. In the general case of a wall footing in which the load is uniformly distributed throughout its length, the principal bending moments are due to the transverse cantilever action of the projecting portion of the footing (Reynolds and Steedman, op. cit.).

            For a reinforced concrete wall, the critical section occurs at the face of the wall; hence, the thickness of the footing should be such that the safe shearing stress is not exceeded. Whether the footing is designed for transverse bending or not, if the safe ground pressure is low, longitudinal reinforcement should be inserted to resist possible longitudinal bending moments due to unequal settlement and non-uniformity of the load. One method of providing the amount of longitudinal reinforcement required for unequal settlement is to design the footing to span over a cavity (or area of soft ground) from 1m to 1.5m according to the nature of the ground.

Generally, the loads for foundation design must be expressed both in the SLS and ULS. The ground bearing capacity is generally expressed in working state (SLS); hence, the area of foundation required to sustain the load must be defined based on working state. Once the area has been obtained, the net pressure exerted on the soil is calculated based on the ULS. All loads are obtained from ULS approach.

(f)        Retaining Wall:           Retaining wall is usually required to resist a combination of earth and hydrostatic loads (Mosley et al, op. cit.). Simply put, retaining wall is a structure used to retain earth, which could not be able stand vertically unsupported (MacGinley and Choo, op. cit.). According to Oyenuga (op. cit.), they are useful within the built environment, especially at bridge sites, riverbank areas, ground with sloppy terrain, e.t.c.

            A retaining wall is essentially a vertical, cantilever structure, and when it is constructed in reinforced concrete, it can be a cantilevered slab, a wall with counterforts, or a sheet-pile wall (Reynolds and Steedman, op. cit.). In general, concrete retaining walls may be considered in terms of three basic categories:

·         Gravity wall – usually constructed of mass concrete, and relies on self-weight to satisfy stability requirements both in respect of overturning and sliding.

·         Counterfort wall – it is the combination of a wall and counterforts. Stability is provided by the weight of the wall and the backfill of the retained material.

·         Cantilever wall – it is a vertical cantilever spanning from a rigid base and relies on the bending strength of the cantilevered slab above the base, as well as the weight of backfill on the base, where applicable, to provide stability.

The principal factors to be considered, generally, are stability against overturning, bearing pressures on the ground, resistance to sliding, and internal resistance to bending moments, and shearing forces. Mosley et al (op. cit.) advises that the back faces of retaining walls will usually be subjected to hydrostatic forces from groundwater. This can be reduced by the provision of drainage path at the face of the wall. It is usual practice to provide such drain by a layer of porous medium with pipes to remove the water, or by providing ‘weep-holes’ at regular intervals in the wall.

(g)        Drainage Channel:      This is an open box culvert-like structure used to transport water or liquid from an unwanted area to a point of discharge. The channel must be strong enough to resist vertical and horizontal pressures from the earth and other superimposed loads. Generally, there are only two conditions to considered:

·         When the channel is empty, full load and surcharge on the channel walls’ sides, the weight of the walls, and maximum earth pressure on the walls.

·         When the channel is full, minimum load on the walls, minimum earth pressure on the walls, the weight of the walls, maximum horizontal pressure from water in the channel.

In some circumstances, these conditions may not produce the maximum positive or negative bending moments at any particular section; hence, the effect of every probable combination should be considered.

2.2.5    Design Process

This is, generally, a series of steps that are taken to realise the design objective(s) of a structure. It considers design as a whole, including design for durability, construction and use in service. The realisation of the design objectives, through the design process, requires conformity to clearly defined criteria for materials, production, workmanship and, also, maintenance and use of the structure in service. The design process, chronologically, involves careful estimation of foreseeable loads, analysis of the structure, design procedures to be followed in arriving at concrete and reinforcement parameters, production of a good clear detail drawing and preparation of reinforcement schedule. Each of the series of steps is concisely explained as follows:

2.2.5.1 Load Estimation:       The loads acting on a structure are permanent (or dead) loads, and imposed (live) loads, which include wind load.

·         Dead Loads include the self-weights of the structure being considered, and any permanent fixtures, partitions, finishes, superstructures and so on.

·         Live loads include any external loads imposed upon the structure when it is serving its normal purpose. They vary in magnitude. They are moving loads that would be supported by the structure. They include weights of occupants, furniture, etc. Also, they include wind load caused by the effect of wind on the structure. The accurate assessment of the actual and probable loads is an important factor in the production of an efficient structural design (Reynolds and Steedman, op. cit.).

To arrive at the dead load of a member, Oyenuga (op. cit.) notes that preliminary sizing has to be done and the weight is calculated such that a slight change in the member size will not attract a re-design of the structure. All given values should represent the actual forces, weights of materials. The primary dead load is usually the weight of the concrete, which literatures generally agree to be 24kN/m³. The weight of the other materials to be included as dead loads can be obtained from appropriate texts. Appendix A gives the weights of common construction materials. The sum of all the individual weights of the construction materials to be used permanently in the structure gives the characteristic dead load (G_k). Likewise, the sum of all the individual intensity of expected moving loads on the structure gives the characteristic imposed load (Q_k).

In accordance with the philosophy of the ULS, so as to ensure adequate safety of structure, partial factors of safety are applied to the characteristic loads. These factors are not rigid because of the dynamic nature of various load combinations. The standard factors for various combinations of loads are as outlined in Table 2.1. It is seen from the

Table 2.1        Load Combinations and their Values of Partial Factor of Safety for the ULS

                        (Source: BSI, op. cit.)

Load Combination	Load Type
	Dead		Imposed		Earth and Water Pressure	Wind
	Adverse[4]	Beneficial[5]	Adverse	Beneficial
1. Dead and Imposed (and earth and water pressure)	1.4	1.0	1.6	0	1,4	--
2.  Dead and Wind (and earth and water pressure)	1.4	1.0	--	--	1.4	1.4
3.  Dead and wind and imposed (and earth and water pressure)	1.2	1.2	1.2	1.2	1.2	1.2

table that adequate factor is provided for various load combinations in order to achieve the ULS requirements.

Thus the design load, for a given type of loading, can be obtained from the sum of G_kγ and Q_kγ, where γ is the appropriate factor of safety (BSI, op. cit.). This is true, generally, for beams, columns, slabs and walls. In general, Oyenuga (op. cit.) points out that γ is introduced to take account of unconsidered possible increase in load, inaccurate assessment of load effects, unforeseen stress distribution and variations in dimensional accuracy, and the impression of the limit state being considered.

2.2.5.2 Analysis of Structure:          This is the determination of the forces and moments as well as deformation that results from the action of loads (Oladepo, 2001). Tebedge (1983) defines it as the “process of determining the response of a structure due to specific loadings in order to satisfy the essential requirements of function, safety, economy and, sometimes, aesthetics. This response is usually measured by calculating the reactions, internal forces in the members and the displacements of the structures.” Since the structure is made up of different members joined together, the analysis that must be carried out to justify the design of a structure can be broken into two stages as follows:

·         Analysis of the structure (the structure as a unit)

·         Analysis of the structure (parts of the structure)

The analysis of the structure, as a whole component, is very tedious and laborious, and the advantages may not worth the efforts (Oyenuga, op. cit.). Thus, the analysis is easily dealt with by considering the various sections.

The primary objective of structural analysis is to obtain a set of internal forces and moments throughout the structure that are in equilibrium with the design loads for the required loading combinations (BSI, op. cit.). To obtain this set of internal forces and moments, the determination of the static determinacy of the structure is an essential pre-requisite. A structure can either be statically determinate[6] or statically indeterminate[7].

Basically, the static determinacy of a structure is determined by the following equation:

n = r – e                                                                  (2.12)

                                    where  n = number of redundants

                                                r = number of reactions

                                                e = number of equations of static equilibrium (e = 3)

Hence, if a section of the structure is found to be statically determinate (such as in the case of beams, lintels, e.t.c.), the internal forces and moments are obtained from basic equations of static equilibrium. However, if the section(s) is (are) found to be statically indeterminate, the internal forces and moments are obtained from appropriate method(s) of analysis of indeterminate structures.

Oladepo (op. cit.) explains that there are, generally, two methods of solving

indeterminate structures, namely: (a) the plastic method, and (b) the elastic method. The elastic method of analysis of indeterminate structures can further be divided into:

                        (i)         Classic methods, and

                        (ii)        Matrix methods.

Under the classical methods, we have the moment-area method, virtual work method, moment distribution method, slope-deflection method (SDM), three-moment equations' method, column analogy method, e.t.c. Under the matrix method, we have flexibility (force) method, and stiffness (displacement) method.

            The choice of method to be used depends on its suitability to the type of problem concerned and, to some extent, on its appeal to the particular designer involved (Reynolds and Steedman, op. cit.). Moreover, the method(s) of analysis to be used should be based on as accurate a representation of the structure as is reasonably practicable. For the author of this report, the SDM is the easiest. It forms the basis of the stiffness matrix method. In the SDM, the rotations (i.e. slopes) and relative joint translations/displacements constitute the unknowns. The moments at the joints are expressed in terms of these quantities in the form of the slope deflection equations. These moments are obtained as the solutions of the resulting slope deflection equations, and back-substitution of the rotation and displacement into the original slope-deflection equations. The slope deflections, for two ends A & B of a section of the structure, are:

            M_AB = M_FAB + 2EI/L (2θ_A + θ_B - 3∆/L)                        (2.13)

          M_BA = M_FBA + 2EI/L (θ_A + 2θ_B - 3∆/L)                        (2.14)

where         M_AB and M_BA are the end moments produced at ends A and B respectively,

                   M_FAB  and M_FBA are the fixed end moments (FEM[8])

                   EI = flexural rigidity of the member

                   L = length of the member

                   θ_A= slope of deformed member AB at A = ∫_A M/EI

                   θ_B = slope of deformed member AB at B = ∫_B M/EI

                   E = modulus of elasticity of the material

                   I = moment of inertia of member AB at section

                   ∆ = relative movement of supports

Reynolds and Steedman (op. cit.) points out that the principles of the SDM for analysing a restrained (indeterminate structural) member are that the difference in slope between any two points in the length of the member is equal to the area of the M/EI diagram between these two points. Moreover, that the distance of any point on the member from a line drawn tangentially to the elastic curve at any other point, the distance being measured normal to the moment (taken about the first point) of the M/EI diagram between these two points.

            It may suffice to round off this section in this way: calculating the shearing forces, bending moments, slopes and deflections caused by a load in a structural member, by any method of structural analysis, ensures that the design loads are in equilibrium. The analytical procedure involves transforming the whole section to line diagrams in such a way that, under ultimate load conditions, the inelastic deformations at the critical sections remain within the limits that the sections can withstand. While, under working loads, the deformations are insufficient to cause excessive deflection or cracking or both.

2.2.5.3 Design Procedure:       This section gives the procedures of design methods that will, in general, ensure that for reinforced concrete structures, the objectives set out in section 2.2.2 above are met. These procedures assume the use of normal-weight aggregate, and are extracts of the provisions in BS 8110 1997: Part 1. However, in certain cases, the recommendations of the appropriate clauses of the code may be inappropriate, it is thus incumbent on the engineer to adopt a more suitable method having regard to, and satisfactorily for, the nature of the member in question (BSI, op. cit. – clause 3.1.1.).

            The most important characteristic of any structural member is its actual strength, which must be large enough to resist all foreseeable loads that may act on it during the life of the structure without failure or other distresses (Nilsor, op. cit.). It is logical therefore to proportion members (i.e. to select concrete dimensions and reinforcement) so that members’ strengths are adequate to resist certain hypothetical design loads, significantly above loads expected actually to occur in service. This is the perspective of the limit state method of design.

            Reynolds and Steedman (op. cit.) explains that, when designing in accordance with limit-state principles as embodied in BS 8110, each reinforced concrete section is first designed to meet the most critical limit state and then checked to ensure that the remaining limit states are not reached. For the majority of sections, the critical condition considered is the ULS – at which the strength of each section is assessed on the basis of conditions at failure. When the member has been designed to meet this limit-state, it should be checked to ensure compliance with the requirements of the various SLS such as deflection and cracking.

            However, since certain serviceability requirements (e.g. the selection of an adequate span/effective depth ratio to prevent excessive deflection and choice of a suitable bar spacing to prevent excessive cracks occurring) clearly also influence the strength of the section, the actual design process eventually involves the simultaneous consideration of requirements for various limit states. Nevertheless, the normal process in preparing a design is to ensure that the actual strength of each section at failure is adequate, while also complying with the necessary requirements for serviceability.

            Having identified the critical limit state that governs the design procedures, another vital consideration in the design process is the durability of the concrete. According to BSI (op. cit), as contained in clause 3.1.5.1, a durable concrete element is one that is designed and constructed to protect the embedded metal from corrosion and to perform satisfactorily in the working environment for the life-time of the structure. To achieve this, it is necessary to consider many interrelated factors at various stages in the design process (even construction process), particularly in formulating the design procedures.

            The factors influencing durability of concrete, inter alia, include:

·         Design and detailing of the structure (clause 3.1.5.2.1)

·         The cover to the embedded steel (clauses 3.3)

·         Exposure conditions (clause 3.3.4)

Specifically important is the depth of concrete cover provided to protect the steel in concrete against corrosion. The code provisions for nominal cover limiting values to meet durability requirements is outlined in Table 2.2 below, as contained in Table 3.3 of the code. It would be seen from the table that various degree of exposure for concrete has corresponding nominal cover requirement so as to provide an acceptable durability properties in the concrete.

            Having explained the general preambles to design procedures, it is pertinent to outline specific design steps of the various reinforced concrete structural members, which are dealt with as follows:

Table 2.2        Nominal Cover to all Reinforcement (including links) to meet Durability Requirements (See Note 1)

                        (Excerpted from: BSI, op. cit.).

Conditions of Exposure	Nominal Cover (Dimensions in millimetres)
Mild	25	20	20	20	25
Moderate	__	35	30	25	20
Severe	__	__	40	30	25
Very Severe	__	__	50	40	30
Most Severe	__	__	__	__	50
Abrasive	__	__	__	See Notes 2	See Notes 2
Maximum free water/cement ratio	0.65	0.60	0.55	0.50	0.45
Minimum cement content (kg/m3)	275	300	325	350	400
Lowest grade of strength	C30	C35	C40	C45	C50

(a)        Rectangular Beam:    A rectangular beam can be simply supported or continuous. Simply supported beams are often encountered as lintels, braces between walls, e.t.c.  The design procedures include:

·         Choose beam dimensions – In most cases, the working drawings would have specified these dimensions.

·         Determine the effective depth, d, from:

d = h – cover – Ǿ/2 – link diameter                                (2.15)

where d = effective depth of beam

h = overall depth of beam

Ǿ = diameter of steel reinforcement

·         Compare the design ultimate moment, M (obtained from the analysis of sections) with the ultimate moment of resistance of concrete, M_u.

M_u = 0.156f_cubd²                                                                (2.16)

            where f_cu = characteristic strength of concrete after 28 days

            If M > M_u (or M = M_u), then compression and tension reinforcements are both provided; else, only tension reinforcement is required – subsequent steps are for this case.

·         Obtain the lever arm, z from:

Z = d {0.5 + √( 0.25 – K/0.9)}                                   (2.17)

where z ≤  0.95d

            K = M/bd²f_cu                                                       (2.18)

·         Calculate the area of steel reinforcement in tension, A_s from:

            A_s = M/0.95f_yz                                                             (2.19)

·         A check is then made to ensure that the area of steel reinforcement provided conforms to the provisions for minimum percentage of reinforcement required by the code as stated in clause 3.12.5.3, as well as that for maximum percentage of reinforcement as stated in clause 3.12.6.1.

·         Check for shear stress and design for shear reinforcement where found inadequate. The design shear stress, ν, at any cross-section is calculated from

ν = V/bd                                                                   (2.20)

where        V = maximum shear force

                  b = breadth of section

According to clause 3.4.5.2, in no case should ν exceed 0.8√ f_cu or 5N/mm², whichever is the lesser of the two values. Then, the value of ν is checked against the design concrete shear stress, ν_c obtained from:

               ν_c = [0.79 {100A_s/(b_vd)^1/3{400/d}^1/4]/ λ_m                 (2.21)

where λ_m= 1.25 (partial factor of safety for material)

                              100A_s/(b_vd) should not be taken as greater than 3

                              400/d should not be taken as less than 1.

Thus, shear reinforcement should be provided in accordance with clause 3.4.5.3 and Table 3.7 of the code.

·         Check for local or anchorage bond stresses as required by provisions of clauses 3.12.8.1 – 3.12.8.4. The bond stress, f_b, is calculated from

f_b = F_s/(∏Ǿ_eL)                                                              (2.22)

where         F_s = force in the bar or group of bars

                        Ǿ_e = effective bar size

            L = anchorage length

Values for design ultimate bond stress, f_bu, may be obtained from

            f_bu = ß√f_cu                                                                     (2.23)

          where ß = coefficient dependent on bar type (Table 3.26 of code).

(b)        Axially loaded Column:         The design procedure for a rectangular, short, unbraced, axially loaded column is as follows:

·         Determine the ultimate axial load, N, from the analysis of sections

·         Calculate the area of steel reinforcement from

N = 0.4f_cubh + (0.8f_y – 0.4f_cu)A_sc                                    (2.24)

where  h = depth of cross-section measured in the plane under consideration

            f_y = characteristic strength of steel

            A_sc = area of vertical reinforcement

Therefore, A_sc = (N – 0.4f_cubh)/(0.8f_y – 0.4f_cu)                      (2.25)

Should equation 2.25 results in a negative value (i.e. 0.4f_cubh exceeds N), then the minimum reinforcement required by clause 3.12.5.3 is provided.

·                     No check for shear is required, provided that M/N does not exceed 0.6h, and ν does not exceed the maximum value given in clause 3.4.5.12.

·                     Also, no check is necessary if, in the direction and at the level considered, the average value of l_e/h is not more than 30 for all columns (clause 3.8.5.6).

(c)        Simply supported one-way Slab:        This is a slab carrying predominantly uniform loads. It is designed on the assumption that it consists of a series of rectangular beams 1m wide spanning between supporting beams or walls. Having satisfied the conditions of clause 3.5.2.3, the deign load obtained from structural analysis is turned to a uniformly distributed loads (kN/m), then the design procedure is as follows:

·         Determine the ultimate moment, M from

M = wl²/8                                                                          (2.26)

where              w = uniformly distributed load along the shorter span (kN/m)

                        l = effective span of slab (the same as that for beam in clause 3.4.1.2)

·         Determine the effective depth, d from equation 2.15, if the dimensions have been specified in the working drawings.

·         Determine M/bd²

·         Determine K = M/(bd²f_cu)

·         Determine z from the lever arm equation

Z = d {0.5 + √ (0.25 – K/0.9)}                                   (2.27)

·         Calculate the area of steel reinforcement, A_st from

A_st = M/(0.95f_yz)                                                         (2.28)

·         Check the A_srequired against the A_smin using the provisions of clause 3.12.5.3

·         Determine A_sprovided for main reinforcement and the appropriate spacing taking into consideration the rules of section 3.12.11.

·         Provide minimum reinforcement as distribution reinforcement.

·         Check for deflection through

f_s =⅔f_y * (A_srequired/A_sprovided) * β^-1                     (2.29)

where  β = moment redistribution ratio (=1)

            f_s = estimated design service stress

Modification factor, m.f., is then calculated from

m.f. = 0.5 + ((477 - f_s)/(120 * (0.9 + M/bd²))) ≤ 2.0         (2.30)

Limiting span/effective depth ratio = Basic span/effective depth ratio * m.f.

Actual span/effective depth ratio = Span / effective depth

If actual span/effective depth ratio < limiting span/effective depth ratio, deflection is o.k. Else (i.e. if actual span/effective depth ratio > limiting span/effective depth ratio), the section is redesigned either by providing more than required reinforcement so as to increase limiting value or increasing thickness of slab so as to reduce actual value.

·         Check for shear, as is the case in the section for beam.

(d)       Reinforced Concrete Wall:     Reynolds and Steedman (op. cit.) explains that the design procedures for reinforced concrete walls are similar to those for columns. In the case of reinforced concrete walls, the design axial force, according to BSI (op. cit.), may be calculated on the assumption that the beams and/or slabs transmitting loads into the wall are simply supported.

            Furthermore, considerations must be given to the appropriate conditions stated in section 3.9.3 of the code.

(e)        Pad Footing:   Unlike the structural member already discussed earlier, the design procedure for pad footings involve the two limit states simultaneously. The ground bearing capacity is generally expressed at the working state (SLS); hence, the area of the foundation required to sustain the estimated load must be determined based on the working loads. Thereafter, the exerted pressure is then expressed in the SLS (Oyenuga, op. cit.).

            Having decided the shape of the footing (specifically from the working drawings), the design procedures are as follows:

·         Calculate the plan area of the footing using the permissible bearing pressure of soil and the critical loading arrangement for the SLS.

·         With the appropriate values for the thickness (h) and the effective depth (d), check that the shear stress at the column face is less than 5N/mm² or 0.8√f_cu, whichever is the lesser value.

·         Check the thickness for punching shear, compared with that provided in the code.

·         Determine the ultimate net pressure at the ULS, through dividing the design ultimate loads by the area provided.

·         Express the ultimate net pressure in the form of a udl, and obtain a corresponding ultimate design moment using the simple cantilever equation:

M = wl²/2                                                  (2.31)

            where  l = distance from the column’s centre to the edge of the slab.

·         Determine the reinforcement required to resist bending in the same way for beams

·         Make a more accurate check of the punching shear, having established ν_c precisely, according to section 3.7.7 of the code.

·         Check the shear stress at critical sections. It must be noted, as stated in clause 3.11.2.2, that the critical section in an isolated pad footing is taken as that at the face of the column or wall supported. Also, the punching shear zone is considered as the critical perimeter around the column (i.e. the perimeter at 1.5d from the column).

(f)        Cantilever Retaining Wall:     The design procedures for a cantilever retaining wall are generally in two stages, namely:  Stability analysis – ULS, and Bearing Pressure analysis – SLS. It is well established (Oyenuga, op. cit.; Mosley et al, op. cit.; MacGinley and Choo, op. cit.) that the stability requirements are in terms of resistance to sliding and overturning: the effect of the balancing forces must outweigh that of the sliding forces, and the overturning moments generated by the sliding forces must be adequately resisted by the moments generated by the counter-balancing forces. Also, the bearing pressure conditions require that the ultimate pressures at the heel and toe of the base must not exceed the allowable bearing pressure of the soil.

The step-by-step procedure of the fundamental design principle above are as follows:

·         Determine the active pressure, P_a from

P_a = K_a * γ * H                                                             (2.32)

where K_a = coefficient of active pressure

For situation where angle of slope of retained material, β = 0, therefore

            K_a = tan² (45 – θ/2) ≡ (1 – Sin θ)/(1 + Sin θ)            (2.33)

          θ = angle of repose (internal friction) of soil

·         Transform all pressures to forces by multiplying with their respective area of pressure diagram.

·         Determine the sum of vertical forces and horizontal forces respectively.

·         Check for stability as follows:

(i)                 Sliding            

μ(1.0 * N) ≥ 1.6H_f

                                    where N = total vertical forces

                                                H_f = total horizontal forces

                                                μ = coefficient of friction

(ii)               Overturning

Resisting moment/Overturning moment ≥ 2.0

where Resisting moment = sum of moments of each of the vertical forces about a point A, and

Overturning moment = sum of moments of each of the horizontal forces about a    point A.

            The values – 1.6 and 2.0 – are conservative factors of safety.

·         Calculate the bearing pressures on the ground under the base and compare these with the permissible bearing pressures.

P = N/BD ± 6M/BD²                                                   (2.34)

P₁ = N/BD + 6M/BD²                                                 (2.35)

P₂ = N/BD – 6M/BD²                                                  (2.36)

P₁ and P₂ are the upper and lower limit values, respectively, of the bearing pressure at any point along the base. P₁ and P₂, to satisfy bearing pressure requirements, must be less than the permissible bearing pressure of soil.

·         Calculate the moments on members of the entire structure and, consequently, determine the area of reinforcement required in each of them.

·         Check for deflection, shear, and crack conditions on the wall and heel.

(g)        Drainage Box Culvert:           The design procedure for this member is similar to that of retaining wall, except that the units are just subject to pressures due to earth material outside and the pressure exerted by the liquid inside.

            Once the end moments have been determined from the appropriate method of structural analysis, the critical moment on each member is determined analytically. Then, the amount of reinforcement required to make the structure perform satisfactorily is provided. To achieve this requires experience and good engineering judgement. Because, though stability against floatation is important, the proportion of reinforcement and concrete must fulfil the requirements of leak-proof, deflection and freedom from cracking.

2.2.5.4 Detailing:        This is the presentation of the results of the design calculations in diagrammatic form for the purpose of executing the project (Oyenuga, op. cit.). One may wonder, “After a demanding design calculations, why is detailing necessary?” Boughton (1971) answers, “because of the composition of the construction industry, there is danger in just conveying the wishes of the design engineer to other members of the construction team in any way”. Thus, to ensure that the possibility of error in conveying ideas, it is advisable that the contractor should know the precise requirements with regard to sizes and positioning of reinforcement, cover thickness, concrete strengths, e.t.c. The detail drawing gives all this information and will normally also provide dimensions and outlines of the structural unit.

            Since there is a known variation in the experience of steel reinforcement fixers, it is essential that a detail drawing is easy to read and understand. It is of little use, Boughton (op. cit.) emphasises, to produce a drawing that looks impressive to an engineer but cannot be fully understood by the man actually placing and fixing the reinforcement. Structural designers, especially engineering students, must not forget the basic fact that the detail drawing is the only positive link between the design engineer and the contractor; and that the site visit and meetings are of secondary importance to good, clear detail drawings.

            A detailed drawing and a thorough working knowledge of reinforced concrete detailing are of vital importance to any reinforced concrete design project. Indeed, the detailing knowledge and requirement can often affect the basic design method. Thus, detail drawing, as well as calculations, should be thoroughly checked (specifically, more). Since with calculations, a safety factor on the behaviour of the structure can compensate for an error, whereas a wrongly placed system of reinforcement or the omission of some bars due to badly produced drawing can lead to local failure.

            Boughton (op. cit.) lists the following vital points that must be indicated on a good, clear detail drawings:

·         A reasonable scale should be adopted for each unit.

·         Grid lines, where used, should run in sequence on plans, numbers, e.t.c. (from top to bottom) and letters A, B, C, e.t.c. (from left to right) so that beams and columns can be easily referenced when shown in isolation on detail drawings, or called up on schedule sheets.

·         Plans, elevations and sections should be clearly defined.

·         Sections through plans should always, also, be taken in a uniform direction, usually left downward.

·         Dimension lines of structural units, where no general layout drawing is provided, should always be taken outside the member to avoid confusion; however, a general layout drawing is preferable in which case the reinforcement drawing will not show unit dimensions.

·         For clarity sake, section’s outline should be in thicker line form other than those of the plans and elevations.

·         Reinforcement should be in heavy line since it is the most important item on the drawing.

·         An indication of the reinforcement with one (or two, if alternate) typical bar only in full should be shown on plans and elevations. The bar should also be fully located on either plan or section.

·         Bars should be called up separately for each unit, and not repeated where a similar bar is used in another unit on the same drawing.

·         Bars should be referenced in their likely order of placing to make the steel reinforcement fixers’ job more straightforward.

·         Each drawing should start from bar mark 1.

·         Cover should be shown on the section where it varies from one unit to another on a drawing. Where it is constant, it can be called up in the notes.

·         Where only one type of reinforcement is used throughout a drawing, it is unnecessary to indicate its type on every set of bars since it can be called up in the notes’ column.

·         Certain standard abbreviations can be used in calling up reinforcement, e.g.

For type of reinforcement:

(i)                 Mild Steel bars ----------- R

(ii)               High Tension bars ------- Y

For placement of reinforcement:

(i)                 Bottom face --------------- B

(ii)               Top face ------------------- T

(iii)             Near face ------------------ N. F.

(iv)             Far face -------------------- F. F.

(v)               Each face ------------------ E. F.

(vi)             Both ways ----------------- B. W.

For arrangement of reinforcement:

(i)                 c/c --------------------------- Centre to centre

(ii)               thro’out --------------------- Throughout

(N. B. All these should be mentioned in the notes’ column.)

• The bar mark and size should be grouped in a single numeral where the diameter precedes the bar mark.
• Spacing of reinforcement should be in 25mm increments from 50mm above.
• Normal bar diameters used should be of the order: 6, 8, 10, 12, 16, 20, 25, 32 and 40mm.
• Bars should be called up in the following manner: No. required/ Type of steel/ Diameter or size/ Bar mark/ spacing (if required)/ location/ any special consideration, e.g. 20 – R1205 – 150 c/c T means 20 no. of mild steel bars of 12mm diameter, bar mark 5, are required at 150mm centre to centre at the top of the slab.

Reynolds and Steedman (op. cit.) points out that it has long been realised that the calculated strength of a reinforced concrete member cannot be attained unless the reinforcement it contains is detailed effectively and efficiently. Unless reinforcement bars are detailed correctly, tests show that the actual strength of reinforced concrete member is considerably lower than calculations indicate. Apart from observing the points that make for a good detail drawing, considerations must be given to few interconnected salient factors that can make detailing to be effective and efficient. Basically, one must know the length and size of bars that would bring about efficient construction.

For instance, as few different sizes of bars as possible should be used, thus reducing the number of bars to be bent and placed. Also, the longest bar economically obtainable should be used, but regard should be paid to the facility with which a long bar can be transported and placed in position. Moreover, over certain lengths, it is more economical to lap two bars than to buy long bars, as there are standard length for various diameters of bar.

2.2.5.5 Scheduling of Steel Reinforcement:   It is the method by which steel reinforcements are given dimensions and markings, so that information on quantity, shape and size can be provided for supply (Boughton, op. cit.). It is also referred to as bar bending schedule. The method of scheduling should be uniform throughout the bar bending schedules for any structure. Thus, all scheduling of reinforcement must conform to BS 4466: 1969[9].

            Generally, a bar bending schedule sheet should contain the following information:

• Member – the location in which the bar is used.
• Bar mark – the number of the bar in its sequence on the detail drawing.
• Type and size – the type of steel used and its diameter.
• Number of members – the number of identical units, which can occur in each member.
• Total number – the number of members × the number of bars in each member.
• Length of each bar – the overall length in metres and millimetres allowing for bending tolerances e.t.c. This should always be rounded off to the nearest 5mm.
• Shape  -- this shows the bending of the bar with critical dimensions indicated.
• Dimension columns – these relate to the dimension letters shown in shape’s picture.

It must be noted that the preparation of bar bending schedule, as part of the detail drawings, is the responsibility of the engineer (Boughton, op. cit.). Schedule sheets are used, not only by the steel supplier and steel fixers; but, also, by the quantity surveyor in order to prepare the bill of quantities (BOQ). Bar shapes should be within the range of preferred shapes shown in BS 4466(op. cit.), since bending of steel contributes considerably to the cost of reinforcement. Thus, angle cranks should be avoided, particularly on larger diameters bars, except where absolutely necessary. Bar lengths should remain within easily manageable sizes, where possible, must not exceed the maximum lengths produced by steel reinforcement manufacturers. Bar numbers should run in sequence and should not be repeated for separate bars. In general, the objective of the bar schedule is to make everybody’s job, in the construction team, a little easier.

2.3              Geographical Information System (GIS)

2.3.1        Introduction

All forms of human activity include, and involve, a measure of geography. Whether you are a geologist seeking a well of the ‘black gold’ or a transport planner looking for the shortest and easiest route between two places, the problems you will face are the age old question of geography: where, when and how.

We, as human beings, possess a certain understanding of our immediate surroundings, i.e. our neighbourhoods and communities, through a natural sense of place. However, as we increase the scale of our vision to a local, national or international scope, our knowledge and ability to relate things decreases significantly. At such stage, it becomes a daunting task for us to make decisions based on the conflicting data obtained from our environmental features.

 Nowadays, GIS technology allows us to gather and organise, analyse and manipulate, and interpret large volumes of data about geographical features in a way that greatly enhances making a well-informed decision.

2.3.2    Definition of GIS

            Basically, GIS Development Centre (2000) explains that GIS is an acronym for specific terms:

·         Geographical – This term is used because GIS tend to deal primarily with ‘geographical’, ‘spatial’ or ‘graphical’ features. The features can be referenced or related to a specific location in space. The features may be physical, cultural or economic in nature. Features on a map, for instance, are pictorial representations of spatial objects in the real world.

·         Information – This represents the large volumes of data, which are usually handled within a GIS. Every geographical object has their particular set of data, which cannot be represented in full details on the map. Hence, all these data have to be associated with the corresponding spatial object so that the map can be complete. When these data are associated with respective graphical feature, they get transformed to information. This implies that all information is data, but all data are not information.

·         System – This term is used to represent the approach taken by GIS, whereby complex features are broken down into their component parts for ease of understanding and handling; but are considered to form an integrated whole.

Foote and Lynch (1995) state that, because of its vast areas of application, there is no single universal definition for GIS as a technology. Thus, various definitions have evolved from the various aspects of GIS.  It will be worthwhile to look at some of these definitions so as to get a proper understanding of the technology.

A GIS is an information system that is designed to work with data referenced by spatial or geographical coordinates (Star and Estes, 1990). In other words, it is both a database system with specific capabilities for spatially referenced data as well as a set of operations for working with data. GIS Development Centre (op. cit.) defines GIS as a computer-based information system used to digitally represent and analyse the geographic features present on the Earth’s surface and the attributes/events (non-spatial attributes linked to the geography under study) that take place on it. GIS is a set of tools for collecting, storing, transforming and displaying geographically referenced spatial data with its corresponding attribute information to meet a specific requirement (Chouchan, 2002). From another viewpoint, Environmental System Research Institute (ESRI) (1990) defines GIS as an “organised collection/integration of computer hardware, software, geographic data and personnel designed to efficiently capture, store, update, manipulate, analyse and display all forms of geographically referenced information”.

            From all these definitions, it will be noted that, “every object/feature present on the Earth’s surface can be geo-referenced” is the fundamental key of associating any database to GIS; and that the ultimate objective of GIS is the capturing, storing, checking, integrating, manipulating, analysing and displaying of these geographical data, which are spatially referenced to the Earth (Chouchan, op. cit.).

2.3.3    Fundamental of GIS

            GIS is a special-purpose digital database in which a common spatial coordinate system is the primary means of reference. Thus, a comprehensive GIS, according to Burrough (1986), requires a means of:

(i)         Data input from maps, aerial photogrammetry, satellites, surveys and other sources.

(ii)        Data storage, retrieval and query.

(iii)       Data transformation, analysis and modelling.

(iv)       Data reporting such as maps, reports, plans, e.t.c.

Thus, GIS is an integrating technology, by linking a number of discrete technologies into a whole entity that is greater than the sum of its parts. This entails the components of GIS, devices needed for GIS, associated technologies for GIS, and so on.

2.3.3.1 Components of GIS

GIS Development Centre (op. cit.) explains that GIS consists of five key components listed below:

·         Hardware

·         Software

·         Data

·         People

·         Method

This is as illustrated in Figure 2.1 below. As clearly shown on Figure 2.1, it is seen that the GIS is a process that needs each of the components to be effective in carrying out the purpose for which it was built.

(a)        Hardware – It consists of the computer devices and the computer system in which the GIS will run. The computer and its peripherals form the backbone of the GIS technology. The choice of hardware is influenced by the size of data and the project type. It may include some, or all, of these: monitor, mouse, keyboard, Central Processing Unit (CPU), scanners, digitiser, printer, plotter, e.t.c.

(b)        Software – The GIS software provides the functions and tools needed to store, analyse and display geographic information. The common softwares in use are MapInfo, ArcView, AutoCAD Mapping, e.t.c. The software available can be said to be application-defined. If the user intends to carry out extensive analysis on GIS, the ArcView is the preferred option.

(c)        Data – It is a collection of attributes (numeric, alphanumeric, figures, pictures) about entities (things, events, and activities). It contains an explicit geographic reference, such as latitude and longitude coordinates or an implicit reference, such as address, owner’s name, area, etc.

(d)       People – GIS users range from technical specialists, who design and maintain the system, to those who can use it to help them perform their every day’s work. The people who use can be broadly into two classes, but the more important is the class of CAD/GIS analysts, whose works are to vectorise the map objects.

(e)        Method – And above all, a successful GIS operates according to a well designed plans and business rules, which are the models and operating principles unique to each organisation. There are various techniques used for map creation and further usage for any project. The map creation can either be automated raster to vector creator, or it can be manually vectorised using the scanned images. The source of these digital maps can either be map prepared by any survey agency or satellite imagery.

2.3.3.2 GIS’s Associated Technologies

A GIS, as earlier defined, is a computer-based system that is used to digitally reproduce and analyse the features present on the earth’s surface and the events/activities that take place on it. In the light of the fact that almost 70% of these data has geographical reference as its denominator, it becomes pertinent to understand, or be familiar, with the technological means by which data can be represented geographically. These technologies include Global Positioning System (GPS), Remote Sensing, e.t.c; each is briefly explained below.

(a)        GPS:    The GPS consists of 24 Earth-orbiting satellites. These satellites, in function with a GPS receiver, allow the determination of the precise longitude, latitude and altitude of any feature anywhere on the surface of the earth (Brain and Harris, 2002).

            The GPS satellites determine the coordinates by which each feature is geographically referenced from the basic concept of trilateration. Trilateration is a basic geometric principle that allows a point to be located if its distances from other already determined locations are known.

            The strength of a GPS receiver lies in its ability to find the receiver’s distance from four (or more) GPS satellites. Once it determines its distance from the four satellites, the receiver can calculate its exact location and altitude on Earth. If the receiver can only find three satellites, then it can use an imaginary sphere to represent the Earth and can give you location information (latitude and longitude), but no altitude information. For a GPS receiver to know the location of any feature, it has to determine two things:

·         The location of at least three satellites from the feature.

·         The distance between the feature and each of the satellites.

            To measure distances, GPS satellites send out radio signals that the GPS receiver can detect. The receiver measures the amount of time it takes for the signal to travel from the satellite to the receiver; and knowing that the signals, being electromagnetic radiations, travel at the speed of light (3.0 x 10⁸m/s), the receiver can then basically calculate the distance between the satellites and the feature. Although, some complex mathematical models of a wide range of atmospheric conditions are involved (Brain and Harris, op. cit.). To find the satellites, the receiver simply stores an almanac that tells it where every satellite should be at any given time.

            The most essential function of the GPS receiver is to pick up the transmissions of at least four satellites and combine the information in those transmissions with the information in its almanac so that it can automatically determine the receiver’s position on Earth (invariably that of the feature, since the receiver is placed on it). Thus, the basic information that GPS receiver provides is the latitude, longitude and altitude of its current position.

            Hence, GPS has evolved to become a vital technology to acquire raw, positional data that can be inputted into GIS database. These data are the coordinates of the feature/point on the Earth’s surface in the form of latitude[10] and longitude[11] and altitude.

(b)        Remote Sensing:          This is the science and art of obtaining useful information (spatial, spectral, temporal) about an object, area or a point through the analysis and interpretation of image data acquired by a recording device that is not in physical, intimate contact with the object, area or point under surveillance (Chouchan, op. cit.). Simply put, Remote Sensing is any means, other than direct observation, that determines the attributes and location of a feature. This implies that, without direct contact, some means of transferring information through space must be utilised. In remote sensing, information transfer is accomplished by using electromagnetic radiation.

            Remote Sensing is a complementary technology to aerial photogrammetry, whereby ‘remotely sensed’ information gathered by satellites in outer space is used for geographical analysis and cartographic production. Hence, remote sensing technology is also an important tool for the collection of geo-spatial data of an entity for use in GIS, which analyses and manages these data.

            Remote Sensing produces large volumes of spatial data, which can be handled only by efficient geographic handling and processing system that will transform these data into useable information. GIS utilises these maps as its primary source of spatial data and Remote Sensing produces such spatial data in the form of maps. A typical of such maps from Remote Sensing is the map showing the coastal areas of Lagos State as shown in Figure 2.2. The map is taken by one of the various remote sensing satellites to observe and collate the major roads in Lagos and Victoria Islands. As seen from the map, the features range from barely visible to invisible, because of the altitude of the remote sensing satellites and the sizes of the features.

            The proliferation of GIS is explained by its unique ability to assimilate data from widely divergent sources, to analyse trends over time, and to spatially evaluate impacts caused by development. This implies that GIS, to be effective, needs the experience and knowledge of its operators/analysts; since GIS is an extension of people’s analytical thinking. It has no in-built solutions for any spatial problems! Its work depends upon the outlined processes by the analysts. Thus far, GIS has been explained the challenge now is how it works – the process.

2.3.4    GIS Process

            GIS involves complete understanding about patterns, space and processes needed to solve a problem. It is a tool acting as a means to achieve certain objectives quickly and effectively. Its applicability is realised when the user fully understands the overall spatial concept by which GIS operates and analyses his specific application in the light of that established process. This process is what is to be explained here.

            Two important similar terms, but different really in GIS, are data and information. Data is a collection of attributes (numeric, alphanumeric, figures, pictures) about entities (things, events, activities). On the other hand, information is the

organisation of data such that it is valuable for analysis, evaluation and decision-making. In other words, information is processed data. This implies that data, in its raw form, is not useful directly to the user. Hence, GIS involves the transformation of data to information. The process by which GIS does that entails problem definition, data acquisition, data structuring and analysis, interpretation of results, and decision-making information.

2.3.4.1 Problem Definition

            GIS application is basically the customisation of existing GIS software to meet specific needs. The needs may be as simple as a set of preferences that are stored for each user, or they may be a very complex query that selects a group of layers, identify features of interest, etc. Hence, considering the vast areas of application, every GIS user must define the problem that (s)he wants to solve with the aid of GIS tool. A clear-cut definition of the problem(s) will assist in determining, at the start, whether or not the basic functions of GIS can solve it. If not, it can be programmed using the GIS macro-language for complex problems (Wahi, 2000).

            Moreover, a clear-cut problem definition will help to fashion out the best ways to go about the remaining stages of the GIS process, so as to arrive at a well-informed decision and achieve the objectives. It will determine the sources of data, its method of collection, etc. It will help to identify what parameters play a significant role in the selection of spatial facts and what parameters do not.

2.3.4.2 Data Acquisition

            As it can be observed from the foregoing discussion, without data there can be no GIS; because it is a technology that is data-driven. As a result, there is the need to acquire the required data from the most appropriate and reliable source in conformity with the problem definition. Data acquisition is the process of identifying data sources, collecting data, verifying collected data and inputting the verified data (Burrough, op. cit.).

            The sources of data can be grouped into primary source (field work) and secondary source (other means of getting data). Usually, primary source of data is adopted. Primary source involves getting the required data from the exact location of interests, i.e. mainly by site surveys.

            To carryout site surveys, the method of data collection must be identified. Data can be collected by manual (traditional) method of survey, remote sensing, use of GPS, or photogrammetry. For simplicity and cost-effectiveness, manual method is predominant in this part of the world. Surveys are conducted by technical personnel, who use compass, linear measurement devices, and maps to establish spatial location, extract spatial data, observe and record aspatial data (attributes of the spatial feature).

            Upon collection of the required data (spatial and aspatial), these data need to be verified so as to improve its accuracy. Importantly, the primary requirement for the source data is that the locations for the variables are known. These locations can be annotated by x, y and z coordinate of longitude, latitude and altitude (elevation). The verification of the data must entail identifying the essential and correct data, and filtering out the irrelevant data. This stage is very important to the GIS process, because the reliability of GIS mainly depends upon the accuracy of the data collected, the way it is integrated and displayed for the purpose of extracting information for decision-making (Chouchan, op. cit.). Thus, the verification of the collected data must ensure the completeness, accuracy and consistency of these data.

            The stage of data verification prepares the data to be acceptable to the GIS database. This acceptance is by inputting them into the database. Data input involves transforming the data from ‘physical’ form to ‘digital’ form. It entails keyboard entry of aspatial attributes and locational data into the system, scanning the field information into the system (i.e. converting the data from an existing map to a digital, raster representation), use of digitiser, etc. The choice of mode of data input depends on the type of data source, the database model of the GIS (scanning is easier for raster representation, while digitising is for vector representation), density of data, etc.

            The success of the data acquisition stage results in a prepared data format that can be analysed modelled and restructured to achieve the desired objectives, leading to well-informed decisions.

2.3.4.3 Data Structuring and Analysis

            Data structuring, in GIS, involves storage, retrieval and manipulation of data, so that they can be analysed on certain basis. The GIS has a data of multiple information layers that can be manipulated, to evaluate relationships among the desired elements in a computer system. GIS uses layers, called ‘themes’, to overlay different types of information. Each theme represents a category of information. This is illustrated in Figure 2.3. From the diagram, it can be seen that GIS database handles large volume of data, process them and transform them into a wide variety of usable information: geographical, social, political, environmental and demographic. Moreover, each layer has been carefully overlaid on the others so that every location is precisely matched to its corresponding locations on all the other maps (Foote and Lynch, op. cit.).

             GIS stores these layers, connected by a common geographical frame of reference, and allows the information displayed on the different layers to be compared and analysed in combination. Not all analyses will require using all of the map layers simultaneously; hence, this simple yet powerful mode of abstraction – GIS – allows the users to capture on the information that are of interest to them. For instance, with regards to figure 2.3, users may want to consider the relationship between the layers of land use and infrastructure. Furthermore, information from two or more layers might be combined and then transformed into a new layer for use in subsequent analyses.

            In general, the analysis functions of GIS use the spatial and aspatial data in the database to answer questions about the real world, based on the objectives of the process (i.e. the problem definition). The analysis facilitates study of real-world processes developing and applying models. Such models illuminate the underlying trends in geographical data, and thus make new information available. Essentially, the objective of geographical data analysed is to transform data into useful information to satisfy the requirements or objectives of decision-makers at all levels. An important use of the analysis is the possibility of predicting events in another location or at another point in time. A major method of data analysis is the database query. Database query simply asks to see already stored information in the GIS database. The query may be by attribute (relational data) or by geometry (locational data). The database query is usually performed by a sophisticated function known as Standard Query Language (SQL) to search a GIS database.

            The power of GIS, as it has been explained, lies in its ability to identify relationships between features based on their locations and their attributes. Upon analysis of these data, the results are displayed – waiting for them to be acted upon. For users to act on these results, they must be able to interpret them.

2.3.4.4 Interpretation of Results

            GIS results are displayed in the form of digital maps, which are produced from the layers of data stored in the GIS database. These layers are stored using one of two distinctly different data models, known as raster and vector.

            In raster model, according to GIS Development Centre (op. cit.), a feature is defined as set of cells on a grid. All of the cells on the grid are of the same shape and size, and each one is identified by a coordinate location and a value which acts as its identifier (features are represented by a cell or a group of cells that share the same identifier). In vector model, a feature is represented as a collection of begin and end points used to define a set of points, lines or polygons, which describes the shape and size of the feature. The vector model is particularly useful for representing highly discrete data types such as roads, building and the like.

            These digital maps represent geographical features or other spatial phenomenon by graphically conveying information about locations and attributes. Locational information describes the position of particular geographical features on the Earth’s surface, as well as the spatial relationship between the features. Attribute information describes characteristics of the geographical features represented such as its name, or number, and quantitative information such as its area or length. Locational information is usually represented by:

·         Point Feature – for discrete feature represented as single location. It defines map object too small to show as a line, e.g. tree, telephone pole, etc.

·         Line Feature – is a set of connected, ordered coordinates representing the linear shape of a map object that may be too narrow to be displayed as an area, such as roads, fence, etc.

·         Area Feature – is a closed figure with length and width, whose boundary enclosed a homogeneous area, such as lake, state, etc.

In addition to feature locations and their attributes, other technical characteristics that define maps and their uses, and that aids in the correct interpretation of GIS results, are:

·         Map Scale – This indicates how much the given area has been reduced. The map scale, or extent of magnification, is expressed as a ratio. A typical type I sthe representative fraction of the form:

1: X implies that ‘1’ is a single unit of distance on the map, and ‘X’ is the distance on the ground. Examples are 1:1250, 1:250,000, etc.

·         Map Accuracy – This refers to the relationship between the geographical position on a map and its real-world position measured on the surface of the Earth. Many factors are responsible for this, including quality of source data, map scale, etc. The most important issue to remember about map accuracy is that the more accurate the map, the more it costs in time and money to develop.

·         Map Extent – The aerial extent of map is the area on the Earth’s surface represented on the map. It is the limit of the area covered, usually defined by rectangle just large enough to include all mapped features. The size of the study area depends on the map scale. The smaller the scale, the larger the area covered.

The stage of interpretation of result of analyses makes GIS more of mapping software that links information about where things are with information about what things are like, so as to give a better understanding of things.

2.3.4.5 Decision-Making Information

            The old adage “better information leads to better decisions” is as true for GIS as it is for other information systems. A GIS, however, is not an automated decision-making system but a tool to query and analyse map data in support of the decision-making process. To get that information, you need the right set of tools, which GIS provide.

            The decision on where, when and how to develop a land-use policy, locate a landfill, or a sewage treatment facility, build a water treatment plant, all involve a process that rely heavily not only on the understanding of critical environmental, socio-cultural, political factors, etc; but also the ability to integrate these factors into a common decision-making process for well-informed decision to be taken. Almost all of the questions and issues faced in real-world situations have a geographical component in them. Questions such as when, how, why, or what, all have an obvious or hidden geographical component. Therefore, a GIS with its ability to link and display different data sets on the basis of a common geography apparently becomes the perfect set of tools for supporting a decision-making process.

2.3.5    Application of GIS ( to Civil Engineering)

            GIS’s are being used widely applied to Natural Environment, Built Environment, and Human Environment. GIS applications can be undertaken only when three-piece geographical information are collected and stored for every aspect under study: what is it, where is it and how is it related to other aspect (GIS Development Centre, op. cit.). GIS technology has enabled us to integrate social, economic, demographic and environmental database, and to understand the complexities and interrelationships between features of natural and human environments.

            For Civil Engineering purposes, GIS is used in the following areas:

·         Planning and maintenance of transportation facilities including roadways and railways, bridges and tunnels, air and sea ports; as well as improving the efficiency of transportation means.

·         Land Use planning – this involves zoning policies, land acquisition, maintenance and regulation of ownership of land development regulations.

·         Facilities Management – this includes locating and improving the state of facilities, such as locating underground networks of pipes and water distribution.

·         Project Monitoring and Supervision.

GIS applications are extensive. GIS is now used in research and business for a wide range of expertise including environmental resource analysis, tax assessment, real estate analysis, archaeological analysis, natural resources management, street network etc.

VILLAGES’ WATER SUPPLY SCHEMES

3.1       Project Background

CNL is planning to provide potable water to a variety of villages in its area of operation. Thus, CNL contracted Reid Crowther, in 1999, to come up with a feasibility report on the project. Reid Crowther carried out the feasibility study with an affirmative result for the supply of water to the project area.

The project area is situated in the River Niger delta in Delta State. The project area is generally swampy and covered with mangroves, containing numerous river sub-channels. Villages are mostly constructed on small man-made or natural islands. Access into the villages is by boat or canoe.

CNL approved the report, and Reid Crowther was retained to carry out the preliminary design for the Villages’ Water Supply Scheme with the objective to provide water to the quality that meets WHO Recommendations. The preliminary design process, as required by CNL, commenced in July 2001. The villages are divided into schemes for easy design process and coordination. Scheme1 includes Tisun, KoloKolo, Deghele and Bateren; Scheme 2 includes Opia and Ikenyan; Scheme 3 includes Makaraba and Okoyitoru; while Scheme 4 includes Adagbraza and Asantuwagbene. Each design process is centred on each scheme taking the best arrangement of the water supply units which best minimise cost and allows for easy construction process, without jeopardising the objective of the project.

            After submitting the preliminary design report, CNL undertook an evaluation, in collaboration with the villages of the implications of the various options Reid Crowther developed for the villages. This resulted in a set of local considerations needed to be included in a revised design report to be prepared by Reid Crowther.

            A series of correspondence ensued between CNL and Reid Crowther on those issues between August 2001 and April 2002. This led to the production of Revision A of the design report on the Villages’ Water Supply Scheme, which the trainee was actively involved in, as illustrated in Figure 3.1. As it can be seen from the figure, the flow process involves abstraction from borehole, aeration, filtration, chlorination, storage and distribution.

PROPERTY IDENTIFICATION EXERCISE FOR LAGOS STATE

4.1              Project Background

Generally, big cities have big problems. From New York, Paris, London, Banjul, Beijing, Johannesburg, to Lagos, the list of mega cities is growing steadily. Among these, Lagos is ranked to be among the largest metropolitan cities in the world alongside such places as Los Angeles, Mexico city, Delhi and Peking. It is estimated, by international organisations, that Lagos, currently, is a city of about 15million people. Also, by projection, that Lagos would be home to about 25million people by the year 2015. At that time, Lagos would be the third largest city in the world behind Tokyo and Mumbai. These high figures pose great problems to government in making life meaningful to the residents (popularly called Lagosians).

In order to effectively plan for the provisions of infrastructure, such as improved health and welfare facilities, good network of roads, controlled use of land resources, improved environmental facilities, and so on, the Lagos State Government initiated the Property Identification Exercise (PIE) in February 2001. The project was contracted out to Reid Crowther through its subsidiary company (LRC Nigeria Limited).

To effectively tackle the complex and conflicting aspects of Lagos as an entity, Reid Crowther set up a GIS database for Lagos State’s geographic information on land development. This implies that the whole exercise revolves around data – its collection, storage, integration, retrieval and transformation – to arrive at well-informed decision-making policies on the geographical entity called Lagos State.

            Considering the kind of society we are in, it has been agreed, right from the onset, to employ the simplest techniques to achieve the objectives of the project. Thus, against its wish of using the latest technologies such as GPS and RS, LRC has to employ manual method of data collection including taking of photographs to run the GIS process.

4.2              Work Carried Out and Experience Gained

The work carried out under the PIE project includes:

·         Spot location of map features on site.

·         Collection of geometrical data and other relevant information pertaining to land parcels and their usage.

·         Analysis and verification of field data for upgrading old maps to show existing features on site.

·         Input of field data into GIS database.

·         Updating and maintenance of GIS database.

The experience gained from this project revolves around a technology that is data-driven. It includes paying careful attention to minute details of data, understanding the dynamics of data, methods of collection and analysis of data, application of GIS to manage engineering projects, map reading and importance of site visits to get proper interpretation of data.

ISSUES ON CIVIL ENGINEERING PRACTICE

            Civil Engineering, as an entity, is a widely ranged profession encompassing many individually demanding disciplines such as Structural Engineering, Geotechnical Engineering, Transportation Engineering and Environmental Engineering. In spite of these various disciplines, civil engineering practice is generally of two types in all the disciplines, viz: Consultancy and Construction.

            To lack training and experience in any of these types of practice, even if

well-versed in the other, depicts the non-completeness of one’s practice of the civil engineering profession.

            In order to gain a complete experience of this profession, the trainee undertook the last two months of the 6-month industrial training on a construction site; having been trained in the consultancy field during the first four months of the training. The work carried out and experience gained on the construction field is outlined in the following section; thereafter, other important issues of civil engineering practice experienced in the consultancy field are explained.

5.1              Construction Site Experience

The construction site experience was gained during the construction of a two-storey building located in one of Lagos suburbs. The construction of the building was handled by a small-scale (1-man-owned) construction company, whose owner is closely connected to the client (also, an individual). At the time the trainee joined this site, construction had almost reached the finishing stage, whereby only a few concrete structures were yet to be cast. Simultaneously, the company was also handling the partial demolition of an existing structure in another suburb of Lagos.

Hence, the trainee had to shuttle between the two sites in order to have a wide range of experience. In all, the work carried out includes:

• Casting of parapet wall of the roof structure
• Casting of roof beams
• Gauging, plastering and screeding works
• Estimation of batching quantities of constructional materials
• Construction of roof structure
• Supervision of partial demolition of existing structure and reconstruction to fit new design.

The experience gained during this time of the construction field includes:

• Handling and organisation of manpower (i.e. labourers) for construction activities
• Handling and placing of concrete
• For thickness such as that of parapet wall (about 75mm and below), reinforcements are placed at the centre of the structure’s cross-section.
• Understanding of locations where L-beams and T-beams are used in building structure.
• Quality control of building construction.
• Use and condition for use of ‘upstand’ beam and drop beam, where headroom requirement is important or not.

In summary, the construction field is a necessity for the completeness of the practice of civil engineering practice. It can be referred to as ‘battling and overcoming reality’ to achieve set designs (the consultancy’s output).  On the construction field, engineering personnel are expected to be creative, innovative, to manage independent teams and to have the potentials to manage disciplines outside their own specialist area. Above all, to have a grip on the manpower (i.e. labourers), they should be able to exercise professional judgement at all times.

5.2              Developments in Civil Engineering Practice

The way a discipline such as civil engineering is practiced as a profession and the impact it has on society will clearly depend on its evolution as a technical subject, and, in particular, the way it is taught and how its values are passed on to new members of the profession.

This peculiarity of engineering distinguishes it from science. Science evolved mainly as a search for understanding and knowledge (often grandly designed as a search for truth). However, engineering is about creating new product or service – i.e. a new design. Since there is usually a large range of options that can meet each desirable design, it effectively becomes a search for compromise (Davies, 2002). Thus, the difference between scientists and engineers is that scientists will artificially constrain their world until they have something they can handle and then deal with that; however, engineers have to deal with the reality of what is, and this includes people, who have the capacity to do the unexpected.

Moreover, engineering professionals have a duty to keep their knowledge current. One key issue for engineering is how to make use of new technology, such as information technology, to improve the effectiveness of more ‘traditional’ engineering and to take it forward to tackle the massive challenges in the future.

This is very important for a successful practice of the engineering profession. It is evident that engineering students of this generation are more computer literate than their counterparts of previous generations. This is reflected in their approach to information retrieval and knowledge assimilation. They do not expect to work on drawing boards. Their tool of first recourse is the computer, and the first place they would think of looking for information is the Internet. As such, everything has to be balanced up; because, computers are very good at storing and manipulating data but are still poor at creating knowledge. Humans, on the other hand, have the ability to create knowledge by processing information from a variety of sources.

Perhaps a better perspective of the practice of engineering is the one that combines the best attributes of computer-based data manipulation to assist humans in their pursuit of knowledge. In other words, computer should be seen as tools that help engineers do their jobs and not doing the job for engineers. The evolution of technicians/draughtsmen into computer-aided drawing (CAD) operators is a classic example. The arrival of CAD software meant that many of the people previously known as technicians leave the profession and CAD operators took became ‘draughtsmen’. But, unlike the modern-day generation of CAD operators, the old draughtsmen knew how structures behave, because they were the ones detailing the reinforced concrete and the structural steelwork. They could spot potential problems as well as identify savings at an early stage of the project life span through their acquired knowledge as draughtsmen/technicians in the real sense.

Unfortunately, the wrong application of technology has led to the loss of their skills in the engineering profession. It has left a vacuum of knowledge, which is difficult to replace and it now adds more to the responsibilities of the design engineer. Gone are the days when the design engineer would pass his engineering judgements to the technicians/draughtsmen and, in most cases, the latter would produce a clear and detailed drawings without the assistance of the former. Nowadays, with CAD operators, the engineer has to vet drawings so as to ensure that his ideas are properly and correctly stated in the drawings! As such, the only safe method of passing engineering knowledge to students of engineering is that they should be equipped to thrive in whatever working environment they find themselves; and that engineering professionals must know more about their subjects than their clients or the general public and, therefore, there are responsibilities that go with knowledge. This was an issue that the trainee battled with in his training in the consultancy field, as most CAD works had to be vetted again, because of the knowledge of the CAD operator.

5.3              Principles of Project Management

5.3.1        Introduction

Every construction project is different. On one hand, no two projects are the same in respect of stakeholders, the finished product or its environment; however, on the other hand, all projects have a greater or lesser commonality of the processes used to create them. Projects have large numbers of different participants, each of whom have their own goals and perceptions as to what constitutes success both for the project itself and for themselves as organisations.

The key to achieving satisfaction is therefore to optimise alignment of these potentially conflicting objectives by ensuring initial understanding and “buy in” by all the project stakeholders to clearly define project success factors. Agreeing on, and then achieving these common objectives is the essence of Partnering/Teamwork approach in project management. This approach is highly dependent on mutual attitudes of mind, open communication, trust and cooperation. It is founded on an agreed strategy and built by working together on a fair basis to implement integrated project processes (Blockley and Godfrey, 2000).

Processes are what we do to get what we want. The output of a process is a product such as a new design for a facility. Thus, there is a great benefit by thinking of everything as a process. Many complex engineering problems involve using the ‘ing’ form, i.e. planning, designing, calculating and checking. Then, the attributes are identified by asking questions based on who, what, why, when, how and where. The answers to the ‘why’ questions drive the process – they are the reasons for the change and they define what is important. The answers to ‘what’, ‘when’ and ‘where’ questions are the descriptors – they are the state variables. The ‘how’ questions define the method – the transformations.

The implication is that decisions on facility management, data management, construction methods, e.t.c., taken through this approach will become more effective. How? We engineers often neglect the why questions. Hence, we sometimes do not appreciate what the client really wants. Of course, he wants our building, roads, e.t.c—but the structure is only something he needs on the way to getting what he really wants, which is to add value to his life and business.

Partnering is best considered as a business ethic that can be adopted for all projects regardless of procurement route or contractual form. It needs to be emphasised. Working in a team requires that all team-mates have a dependable perception of each other and mutual recognition that the outcome will be better than working separately in competition. To achieve this, in a project, it is necessary to:

·         Take an interest in each other.

·         Work together to earn trust.

·         Share knowledge and information.

·         Understand and measure as dependably as possible the benefits of partnering.

Unlike sport (which is win – lose), engineers must strive for win – wins in project implementation. Thinking win-win is not a technique, but a philosophy of life. Adversarial approaches need to be replaced by teamwork/partnering, trust has to push aside suspicion. It is important to separate the people from the problem, focus on interest (and not on positions) to identify options for mutual benefits.

The seven pillars that support the ‘partnering’ approach to successful project management are: Strategy, Membership/Stakeholders, Equity, Integration, Benchmarks, Project Process and Feedback. It must be noted that benchmarking of outcomes is used to provide feedback and to, thereby, foster continuous improvement in product and services; and, most importantly, in relationship between satisfied stakeholders. This, in turn, promotes ongoing profitable business (equity) for all concerned (Smith, 2002).

CONCLUSION AND RECOMMENDATIONS

7.1              Conclusion

SIWES was established to provide opportunities for students to be involved in the practical aspect of their respective disciplines in the industrial working environments.

            During the 6-month industrial training, the trainee gained a wide range of experience from the various projects implemented and assignments undertaken such as the flow process design of the Villages’ Water Supply Schemes, design of reinforced concrete members, application of GIS to land-use development and construction site activities. All the experience gained help to fulfil the objectives of SIWES.

            From all these, it is evident that good design results when there is harmony among the artistic, the scientific and the practical facets of civil engineering.  Moreover, civil engineering consultancy is a multi-disciplinary practice that offers a vast array of general and specialist services to the construction industry.

7.2              Recommendations

Having gone through the 6-month industrial training, the trainee has the following suggestions for the effectiveness of SIWES:

·         Trainees should endeavour always to be involved two types of civil engineering practice (i.e. consultancy and construction). This really goes a long way to ensure the completeness of one’s experience in this profession.

·         Companies should show more commitment to the training of engineering students so as to improve the quality of training given.

·         Government should endeavour to improve business relationships with companies that have SIWES students, as a way of adding importance to the scheme, in reality.