Builiding Technology 2009 Question 1A

Explain the development stages of construction project

Answer:

A construction project has been defined as the process of ensuring that set and stipulated project objectives such as performance, timely completion and containment of costs within budget are clearly set out from the beginning, monitored and managed throughout the project duration. In any construction project, the project manager is overall in charge and responsible for transforming the goals and visions into a set of project objection formulation and interpreting the design brief and the successful implementation of the project. he has to ensure that each project team member discharge his duties responsibilities and contractual obligations in an efficient, effective, professional, responsible and ethical manner.

In tandem and synchronizing with the rest of the project consortium team, the project manager is responsible for the various stages of implementation that can be categorized as:

Development Stage                              Nature of Plan

1. Inception Stage                          Project Feasibility Plan  

2. Engineering Stage                       Project Preliminary Plan

3. Implementation Stage                 Project Construction Plan

1. Inception Stage

Planning by the client begins as soon as he gets the idea about developing a facility to fulfill certain motives. His early thought process conceptualize the cost, time and benefit implications of the project only when he is convinced about the soundness of his idea does he decide to go ahead with feasibility studies.

The feasibility study team examines the needs of the client and ways to fulfill them. It defines the overall scope of works and breaks it down to various task groups . If develops an outline plan of work and assesses the time and costs of accomplishing the project. This outline plan, developed by the feasibility team during the inception stage, forms the basis for identifying project objectives and developing the project plan.

2. Engineering Stage

Acceptance of the feasibility studies marks the commencement of this stage which involves the preliminary plan making process. Its main aim is to provide direction to the client managers and staff employed during the development phase of the project. The project preliminary plan forms the basis for developing the project construction plan in the implementation stage. The preliminary plan includes the following:

a) A project time schedule and the skeleton network highlights the work dependencies, project milestones and the expected prices and completion time.

b) The project designs and drawings preparation schedule

c) A breakdown of project work into contracts along with a schedule of contracting activities, including the tender preparation period, tender finalization period and contracted works commencement and completion date.

d) A resource preliminary forecast indicating the phased requirement of labor, important materials, plant and machinery.

e) Resources procurement system

f) Project organization and staffing pattern.

g) Preliminary forecast of funds requirement

3. Implementation Stage

This stage is the project construction plan development. The clients entrusts the construction of project to the project management team headed by the project manager or the Resident Engineer. This team maybe from the clients own construction agency or form a client appointed construction management consultant firm or from a suitably organized combination of these. The project manager which is entrusted with the task of developing project construction plan. This plan includes the constructed works plans and the commissioning plans as appreciable. The work programmes are de?ined from the targets set out in the project plan. The project construction plan as well as the contracted works plan further include the following plans:

a) Time Plan: It depicts the schedule of project activities for the completion of the project within the specified time.

b) Resources Plan: It forecasts the required. input resources of men, materials machinery and money for achieving the project completion time target and cost objectives.

c) Plan for controlling project. If encompasses the design of control system, monitoring system, codification system and computerized information system.

Finally, this stage includes the actual execution which is the implementation of the design or concept of plan. Most of the work related to the project is realized at this stage and requires complete attention on the part of the project manager.

Builiding Technology 2008 Question 6B

Explain the following types of cement and elaborate on their properties and usage

1. Ordinary Portland Cement
2. Super Sulphate Cement
3. High Alumina Cement

Answer: 

1. Ordinary Portland Cement

This is a low cost general- purpose cement recommnded for all type of structures, such as columns, beams, floor stabs and other general construction purposes of develops strength sufficiently rapidly for most cement work.

The setting and hardening of ordinary portland cement paste is accompanied by heat liberation. Thus in mass concrete construction such as in dams, where it is difficult for this heat to escape, it becomes necessary to avoid using this type of cement and instead use low-heat portland cement.

For ordinary Portland cement practically all the cement particles will pass 150 um (micron) aperture (BS410 No 100 sieve) and over 95% will pass a 75 mm no 200 siene. Particle size has a bearing on the rapidity of hardening.

The strength which the concrete is made with cement is determined by compression tests on 100mm concrete cubes. For ordinary portland cement, the minimum strength requirements are.

3-day conpressive strength > 8n/mm2

7-day compressive strength > 14n/mm2

Ordinary portland cement concretesnate of hardening may be accelerated by warmth and retarded by cold its resistance to attack by sulphates is generally low its rate of gaining strength, heat of hydration, dujms shrunkage and resistanie to cracking are moderate

2. Super Sulphate Cement

Super sulphate cement is made from well granulated blast furnace slag (80 to 85%), calcium sulphate (10 to 15%) and portland cement (1 to 2%) and is ground finer than portland cement. Thus it has a modified chemical composition.

One of its most important properties is its low total heat of hydration. It is therefore very suitable for construction of dams and other mass concreting work. Concrete made from super sulphate cement may expand y cured in water and may shrink if the concrete is cured in air. Another big advantage of super sulphate cement is its comparatively high resistance to chemical attack by sulphate solutions which are found in some soils.

Super sulphate cement, unlike normal portland cement harden slowly. 

3. High Alumina Cement

High alumina cement is a specially manufactured high early strength cement. High alumina cement is used in small quantities as compared to Portland cement. Its technical importance originates from the special properties such as high early strength. The term high alumina cement refers to the class of hydralic cements, the essential constituents of which are calcium aluminates. High alumina cement is much more expensive than portland cement.

The raw material customarily used for the manufacture of ordinary high alumina cements are limestone and bauxite (rocks of high aluminum content)

High alumina cements are greatly sperior to Portland cements in sulphate resistance, a property that is attributed to the absence of free calcium hydroxide in the hydrated high alumina cements.

Early strength development of high alumina cement (low-silico type) is very evident. The superiority of the strength developing ability of high alumina cements is even more conspicuous when the applied curing temperature is close to the freezing point.

Hydration of tri-calcium alumina does not contribute any strength to the concrete. It is mainly responsible for setting action of the cement. High alumina cement has been banned for structured use in some countries like the UK due to some well publicized structural failures.

Builiding Technology 2008 Question 6A

What is cement? State the functions of cement in concrete mix.

Answer:

Cement is the material used to bind concrete. There are many varieties although Portland cement are the most important and widely used.  They depend on water to set, harden and as known as hydraulic cements when water is added to the cement, chemical reactions take place. The process is exothermic, meaning that heat is given off. The stiffening process subsequently begins and the material begins to harden and develop strength. A mixture of cement and sand and water to form a paste is known as cement mortar, while the product obtained by mixing cement, water, sand and aggregates is cement concrete.  

The ingredient of cement are clay (silica, aluminum oxide and iron oxide) and chalk or limestone. All these materials are finely and intimately mixed and burnt at a chinkering temperature of about 1400c. The chinkens resulting are ground to a fine powder to get cement. During burning and fusion, all the ingredients under chemical combination and from what are known as Bogue compounds. Bogue Compounds are:

1. Tri-calcium silicate, C3S
2. Di-calcium silicate, C2S
3. Tri-calcium aluminate, C3A
4. Tetra-calcium alumino-ferrite, C4AF

The proportion of above stated Bogue compounds vary in various types of cements. Tri-calcium silicate and Di-calcium silicate are the compounds mostly responsible for the strength characteristics of the cement. Concrete is manufactured using cement, aggregates and water. The aggregates usually contain a range of particle sizes, from fine to coarse. Fine aggregate as referred to as sand. The coarse aggregates are usually crushed rock or limestone. The chemical reaction between cement and water is responsible for setting and hardening of cement concrete. Although all materials that go into a concrete mixture are essential, cement is the most important constituent because it is usually the delicate link in the chain.

The function of cement is:

1. Although cement constitutes only about 10% of volume of the concrete mix, its the active portion of the building medium and the only scientifically controlled ingredient of concrete.
2. The extent of hydration of cement and resultant hydrated cement influences the physical properties of concrete. This hinges on the fineness of the cement portion of water and types of cement used. The amount of water in a cement mix must be carefully controlled. if high quality concretes with uniform strength are to be achieved. For this reason, the amount of water contained in the aggregates before they are mixed must also be carefully determined before adding the extra water required for mixing.
3. Bind the sand and course aggregates together. Aggregates help reduce the cost of materials as aggregates are cheaper that cement. They reduce the dry shrinkage and thermal movement and improves resistance to wear by both abrasion and weathering.
4. Fill the voids in between the sand and coarse aggregates particles to form a compact mass.

 

Builiding Technology 2005 Question 3B

Explain the types of building structure suitable for single and double storey houses

Answer:

See model answer to Question 2B of 2010

Builiding Technology 2008 Question 3A

What is the meaning of 'substructure' and 'superstructure' of a building. State the functions and elements of these two structures.

Answer:

The 'substructure' is that part of the building situated below the ground or damp - proof coarse. The purpose of the substructure is to transfer the load from the superstructure to the surrounding ground. An essential part of the substructure is the foundation. The 'superstructure' is normally taken to be that part of the building above the ground on the damp-proof course. Its purpose is to carry the loads imposed on the building though deal and imposed and winds loads and transfer them to the substructure.

The substructure which is usually applied to construction below the ground such as basement and the essential foundation. Thus the substructure though the foundation which is that part of a building which rests directly on or in the ground. It enables the loads of the building to be transferred to the ground below the foundation with exception of solid rock, foundations are built on soils which are capable of being compressed by the imposed load. Thus the functions of the sub-structure though the foundation are:

1. Safely transmit the dead and imposed loads from a building to the soil such that settlement is limited and the ground is not overstressed.

2. Safely distribute the weight of the building over large area so as to avoid over loading of the soil beneath.

3.  Load the sub-stratum evenly and thus prevent uneven settlement.

4. Provide a level surface for building ??persctions

5. Take the structure deep into the ground and thus increase its stability and prevents overturning.

6. Avoid damage from smelling shrinkage or freezing of the subsoil.

7. Resist attack by sulphates or other harmful ??watten in the subsoil.

The stability of a foundation assuming of has been designed satisfactorily will depend upon, how the subsoil on which it rests, behaves under load. This information can be deduced from the report after a soil investigation has been carried out.

The application of a load through the foundation of a building can result in deformation of the ground and some building movement known as settlement. This settlement may not be serious if its uniformly distributed when settlement varies, this produces a condition known as differential settlement which can be lead to the building distorting and in more serious instances, collapse of the structure.

The superstructure of a building may be defined as all elements of the structure situated above and including the damp-proof course. The elements include:

1. Damp-proof courses and membrane.

2. Walls

3. Frame structures

4. Floors

5. Roofs

6. Stains

7. Windows / doors

The conventional superstructure is a framed construction using beams and column to support roof, floor and cladding. Competition between steel and concrete frames is fierce and the popularity of each depends on the ??resiation in piece. the client and architect usually want as much uninterrupted floor space as possible. This is because buildings are priced on floor area and must be flexible enough to accommodate ??vesying internal partition ??anangements as the use may change many times throughout then designed life. Framed structure are good at providing open space floors but they do have the disadvantages of internal columns which reduce internal space and dictate the layout of working areas. One step towards overcoming these disadvantages in medium rise structures is to use composite construction of steel and concrete to achieve long spans. Another popular solution is to use a central core, particularly in mufti-storey structures. The floors are cantilevered from the central core which is used to house lights, stains and service access. There are, of course limits to the spam of such cantilevered floors which limit the size of the building. Props at the end of the cantilevers provided by perimeter columns can greatly increase span but these can affect external appearance.  

Builiding Technology 2005 Question 2B

By using diagrams explain the types of ground water drainage system.

Answer:

Groundwater drainage can be achieved with one of more of the following methods, depending upon the ground conditions:

1. Pumping from open sumps within the excavation

2. Installing well points or ?? wells outside the excavation

3. Sheet piling around the excavation.

1. The first one is the popular method of dewatering the subsoil. This method can be used in most soil types and is economical in operation. Normally sumps are sited within the excavation area, but maybe outside it when large quantities of water have to be pumped. A minimum of two pumps are used on all but the smallest sites.

Pumping From Sumps

The sump is excavated to the fall depth required to drain the excavation before the excavation reaches the level of the groundwater. To prevent loss of soul fines when pumping fillers should be used. Drainage channels should bearing forwards the sumps to prevent water remaining on the surface of the excavation.

2. When the water table is too high or the subsoil is too porous to contain and dispose of the ground water, a system known as well pointing should be considered.

WELL POINTING

Well pointing is a method that uses mechanical wells 75mm in diameter closely spaced in the ground around the excavation water is withdrawn from the well by a suction pump connected to a ring main well points are effective up to 5 meters below the suction pump in lef and therefore at greater depths they well need to be set in stages. Suitable for most Greu??lar  materials and affordable, the well point system is a very popular system used to day. Some 15 to 20 well points can be operated with the same pump.

In excess of 5 meters, deep board wells may be employed ?ere a pump is lowered to the bottom of the deep well to dewater the ground. The bottom of the deep well to dewater the ground. The hole is bo?ed with conventional drilling or bouing machines and steel living is left in place of 300 to 600 mm in diameter. Another steel tube is placed inside the well, in which a submersible pump is placed.

3. Sheet piling is used to seal off the flow of water when there is a layer of impermeable strata below the reduced level. In cases such as this, the water can be virtually sealed off. This form of piling is the most commonly used for permanent and temporary work to control ground water and support excavations steal sheet piles that interlock to form a steel wall, are hammered into the ground are held stable by either candider action or are propped across excavation.


SHEET PILING CUT OFF WALL

It should be noted that this may not work in all circumstances due to the presence of an i?ntesian head of pressure. 

Builiding Technology 2010 Question 1A

State the requirements for the foundation of a building

Answer:

The foundation is part of the construction where the base of a building meets the ground. Foundation are usually placed below ground level because the surrounding ground provides

1. Stability

2. Protection against impact

3. Protection from the extremes of weather such as excessive rain or drought


Foundations are divided into 2 types

1. Natural foundation. This is the ground under earth the base of the building after the excavations are completed.

2. Artificial foundation. The structure that lies between the building and the natural foundation.

In order the design a safe, yet economical foundation for a building on a particular site, it is necessary to determination loads on the foundation which are:

1. Dead loads - which are the structure of the building including the wells, roofs, ceilings, fittings, plumbing, etc

2. Live loads which are the people living of working in the building together with the furniture, fitting and machines, etc.

3. Wind loads which are the impact on the roof and exterior walls of the building and transmitted down to the foundation.

The foundation is also determined from the type of soil which can be discovered through trial hole excavations.

The artificial foundation is to transfer the building loads to the ground and speeds the load evenly across it. This prevents settlement or building movement which might cause instability and endanger the occupants.

With the above facts in mind, the requirement for the foundation of a building are:

1. The foundation do not rest on made up or previously used ground. This is because the made up ground is non loading bearing. This will likely result in uneven settlement of the building, causing cracks or structural damage to it.

2. The subsoil on which the foundation of the building rests, is of consistent textile hand or weak spots can cause uneven settlement and lead to structural damages.

3. Should strip foundation be selected as the foundation of a building and this is common for low rise buildings, the walls of these buildings must be c?? on the strip foundation. This ensures that the bearing pressure on the foundation is evenly distributed.

4. The foundation are wide enough and deep enough to avoid soil movement that could cause instability. Depending on soil conditions, the maximum depth may be 900mm. Building regulations suggest the suitable minimum width for strip foundations. The concrete must be at least as thick as its projection from the base of the wall.



As shown in diagram above, the thickness D is recommended to be 150mm or more. D Should also be equal to P or more. P is the projection from the base of the wall to the side. This ensure the pressure of the building load is being distributed at an angle of 45% and covers the maximum area.

5. In situation where stepped foundation are being employed, a higher foundation projects ?? and meet a lower foundation for a minimum distance of 300mm or slopping ground.



This is to ensure that the foundation is strong enough to take on the building loads especially at the point where the foundation is 'stepped'.

Above flow chart summarizes the requirements for the foundation of a building and how to ?? at the right choice of a foundation.