Building Technology Notes Form 4 2012-2013

7/30/2019 Building Technology Notes Form 4 2012-2013

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Table of Contents

PRELIMINARY SITE WORKS .....................................................................................................1

Factors Affecting the Choice of a Site .........................................................................................1

Reasons for Stripping and Clearing a site .................................................................................... 4

Purpose of Hoarding .................................................................................................................... 5Laying Out of a Small Building ................................................................................................... 7

Purposes of Temporary Shelter ..................................................................................................12The Building Site ...................................................................................................................12

Reasons for Temporary Services ............................................................................................... 14

THE MANUFACTURING OF PORTLAND CEMENT ..............................................................16Portland Cement .........................................................................................................................16

Characteristics of different Types of Cement ............................................................................16

Notable Behaviour of Concrete .................................................................................................17

Characteristics of Aggregates .................................................................................................... 18Requirements of Aggregates ..................................................................................................18

Types of Aggregates .............................................................................................................. 18Importance of Proportioning or Batching ..................................................................................19The total weight of water in the concrete ...................................................................................21

PROPERTIES OF PLASTICS ..................................................................................................21

TIMBER AND TIMBER PRODUCTS .........................................................................................23Softwood and Hardwood Trees .................................................................................................25

Softwoods .................................................................................................................................. 25

Hardwoods .................................................................................................................................25Conversion of Timber ................................................................................................................26

Seasoning of Timber ..................................................................................................................28

Moisture content ........................................................................................................................ 29

Timber Defects ...........................................................................................................................30Wood Preservation .....................................................................................................................33

Production of Manufactured Boards ..........................................................................................35

Lumber Classification ................................................................................................................37FOUNDATIONS ...........................................................................................................................39

Types of Foundations .................................................................................................................40

Excavation and Timbering .........................................................................................................47Types of excavations ..............................................................................................................47

Reduced Level Excavation .......................................................................................................... 48

Trench and Pit Excavations ...........................................................................................................48

Types of Excavation Machines ..............................................................................................49

........................................................................................................................................................ 49Timbering to Excavation ................................................................................................................51

Precautions .....................................................................................................................................56WALLS ..........................................................................................................................................57

Definition ..................................................................................................................................57

Categories of Walls ....................................................................................................................57Types of Walls: ......................................................................................................................57

Definition of a Scaffold .............................................................................................................65


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Two Main Systems of Shoring .................................................................................................. 70

Functional Requirements ........................................................................................................... 71Categories of Floors ...................................................................................................................72

Floor members ...........................................................................................................................75

Important Steps in Constructing a Timber Floor .......................................................................81ROOFS ...........................................................................................................................................82

Definition: ..................................................................................................................................82

Functional Requirements ........................................................................................................... 82

Factors Determining Roof Shape & Design .............................................................................. 82Roof Classifications ...................................................................................................................82

Types of Roofs ...........................................................................................................................82

Advantages of using Roof Trusses ............................................................................................87Parts of a Roof ........................................................................................................................... 88

Technical Words for Parts of a Roof .........................................................................................88

Truss Types ....................................................................................................................................24........................................................................................................................................................ 24

DOORS ..........................................................................................................................................25

Types of Doors ...........................................................................................................................25Door Ironmongery ..................................................................................................................... 28Door Dimensions .......................................................................................................................29

WINDOWS ....................................................................................................................................30

Functions of Windows ...............................................................................................................30Building Regulations for Windows ...........................................................................................30

Technical Terms for parts of a window and frame: ...................................................................30

Types of Windows .....................................................................................................................31Some common terms associated with Stairs ..............................................................................34

Building Regulations regarding Stairs .......................................................................................34

FINISHES ......................................................................................................................................36

Rendering ...................................................................................................................................36Plastering ....................................................................................................................................36

Types of paints ...........................................................................................................................37

Properties of Paints and Varnishes ............................................................................................38Methods of Application ............................................................................................................. 38

The Purpose of Solvents ............................................................................................................ 38

RELATED SERVICES ................................................................................................................. 41The Principles of Plumbing Pipes ..............................................................................................41

Methods of Jointing and Fittings ............................................................................................... 42

The Combine System of Drainage .............................................................................................44The Separate System of Drainage ..............................................................................................44

The Principles of Drain Runs .....................................................................................................44THE BUILDING TEAM AND BUILDING TRADES .................................................................47

The Building Team .................................................................................................................... 47Various Building Trades ............................................................................................................48

HISTORY OF BUILDINGS ..........................................................................................................49

Factors Influencing Building Designs .......................................................................................49Influence of Other Culture on Local Building Styles ................................................................49


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PRELIMINARY SITE WORKS

Factors Affecting the Choice of a Site

Zoning

Zoning is the legal identification of land for a specific use. The general categories ofzoning are:

1. Residential

2. Commercial

3. Industrial4. Agricultural

Zoning helps to assist land developers or owners in recognizing land for use as well as

provide information about the character of the neighbourhood. Lands within a zone may carrydifferent unit cost.

Land use

The owner or client must be sure that the land can be used for the intended purpose.

Although an area might be appropriately zoned, specific plots of lands may have certain

restrictions placed on them as a result of buried services or proposed development, e.g. roads,

gas lines etc.

Ownership

This is certified by a deed (legal document) which must be established before any finaldecision is taken regarding any purchasing of land. Ownership transfer can only be made

between the rightful owner and the purchaser.

Boundaries

Boundaries must be established and supported by a survey drawing before the actual size

of the property can be ascertained. This task is usually carried out by a legal chartered surveyor.

Boundaries are normally marked in such a way that they can be easily identified or re-established. References for markers are called Datum- Points.

Topography

Topography is the shape of the surface of the land. This shape is sometimes referred to

as contour and can be classified as follows:

- flat- undulating

- gently sloped

- steeply sloped

Access

All lands not immediately adjoining a street or public pathway requires some means of

access. This access influences movement on and off site during the construction stages as well

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as during normal occupancy. Where the possibility of trespass exists, access should be legally

established and be adequate.

Shape

When purchasing a piece of land, the shape of the land should reflect the proposed shape

of the structure within the framework of the legal restrictions. Examples of problems commonly

encountered with lands are:1. Too narrow

2. Corners may be too acute or there may be too many corners.

reinforcing steel

street possible building

limitingposition

(a) Narrow Lotlegal limits

(b) High unusable Land Space owing to a

number of and sharpness of corners

Size

Minimum sizes of building lots are usually specified in order that:- Legal requirements of setback and off set distances are satisfied

- The building should occupy the maximum percentage of the total land area as specified

by the authorities for the prescribed zone.- A reasonable sized building is produced.

History

History is the study of past events associated with the use of the site. Historical issuesthat should be of concern to the purchaser are:

1. Water- whether a natural water course, springs or flooding are associated with the site.

2. Dump- whether the site was ever used as a dump.3. Original topography- whether the land was ever filled.

4. Other problems e.g.

o Whether trees were recently removed to accommodate development or

o Underground lines such as electric, gas or telephone.5. Development- This is a measure of clearing and preparation activities associated with a

site. It may also indicate the availability of services to the site.

Unit Cost

Unit cost is the price per metre or foot of the land. Unit cost is normally associated with:

1. Level of development

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2. Available amenities

3. Available Services4. Location

5. Zone

6. Demand

7. Topography

Amenities refer to the degree of comfort associated with the location, and are related to theavailable utilities, health and educational facilities as well as other features such as public

transport, shopping centres and recreation facilities.

Location may influence the unit cost by providing certain advantages such as prevailing winds,

scenic views and general neighbourhood.

Sloping sites

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Reasons for Stripping and Clearing a site

Stripping

This is the removal of the topsoil from the construction area. This area is usually stripped

to a depth of 150 mm, using a bulldozer.

Stripping helps to provide a sound level platform as well as the removal of vegetablematter as well as the removal of termites nests.

Soils containing high levels of vegetable matter tend to:

1. Support plant life2. Be very unstable

3. Affects some building materials

Clearing

Clearing is not necessarily part of stripping but for undeveloped sites, clearing is

essential. Trees which sometimes obstruct the building process, those found to be in the way andat a time obstruct the flow of traffic and must also be removed. The roots that would pose a

problem to the building process or even affect the foundation must be removed as well.Other obstacles like derelict buildings should be removed, because they too hinder the

building process and can cause problems with the foundation.

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Purpose of Hoarding

Hoarding is a part of the temporary facility installed on a construction site. Its primary

function is the enclosure of the construction area to serve as a form of protection to passers by.

This enclosure has other purposes and is developed accordingly.

Public Protection

The local authority has the responsibility for the protection of the public against injury

during any construction work. As such, there are laws requiring the installation of hoarding,particularly where pedestrian traffic is common. Hoarding should provide protection from the

vertical side and overhead as well as permit or provide adequate lighting and ventilation if

required.

Security

The construction site must be secured, especially during evenings, on weekends andpublic holidays.

Material Protection

Hoarding is an ideal way of ensuring some degree of protection against theft andvandalism of materials and installations.

Control

The control of the movement of workers and avoidance of unwanted interruptions anddistractions assist in increasing productivity. All activities should be carried out with

minimum inconvenience. The movement of supply vehicles and receipt of goods should

be planned and controlled at all times.

To keep out stray animals

It is important that stray animals be kept off of the construction site since they can causedisruptions to the building works as well as harm to the workers.

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Laying Out of a Small Building

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Building Layout

The Setting out of a building can be divided into two specific operations:

Establishing a datum peg and transferring required levels to various positions

Establishing the position of the building and setting up profiles (batter boards)

Establishing the position of the building and setting up profilesThe basic requirements for establishing the position of a building are linear measurement

(length), the setting out of right angles and the setting out of curves.

Linear Measurement

A 30m steel tape is most often used for setting out; linen or plastic tape should be

avoided as they are likely to stretch, and this could result in serious errors. If steel tapes are notfully stretched out they can give inaccurate readings. Wherever linear measurements are made

the tape should be held horizontal. For sloping sites the possibility of error is far greater. For

slightly sloping grounds pegs of different lengths may be used. For steeper slopes the tape is heldhorizontally and the measurement is plumbed down to the peg.

Setting out Angles

Right angles can be set out using any one of the following methods:

1. Using a builders Square

2. Using Pythagorass 3:4:5 rule3. Using Site square

Setting out Curves

The methods used to set out a curve will depend on its size and whether its centre point isaccessible or not.

The four main methods are:1. Timber template

2. The radius Rod

3. Triangular frame4. Calculated ordinates

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Layout Procedures for a Small Building

It is essential to obtain a working drawing of the proposed building before any work isstarted. After careful study of this, the builder can then proceed with the layout of the building.

The procedures for setting out a small building are as follows:

1. The building line is established with reference to the setback distance from the centre line

of the road. The line is established by driving in 50mm x 50mm softwood pegs A and Bon or near the side boundaries. Position a nail in the top of the pegs to represent the exact

position of the building line. Strain a line between these two nails.

2. Drive two pegs C and D along the building line to indicate the front corners of the

building and with reference to the side setbacks as indicated on the Working drawing.Drive nails into the top of the pegs to indicate the exact position of the corners on the

building line.

3. Set out lines at right angles to pegs C and D and establish pegs E and F. Drive nails intothe tops of pegs E and F to indicate the exact positions and strain lines between the four

pegs.4. Measure along lines CE and DF to establish pegs G and H, the remaining corners of the

building.

Check lines should be used at this point to determine the accuracy of the layout and adjustments

made where required.

Profile boards can now be set up just clear of the trench runs at all corners and wall intersections

of the building. Ensure that there is adequate clearance space between the position of the trench

and profiles to prevent obstruction to profiles due to excavation procedures. Transfer positionsfrom the setting-out lines on the pegs to the profile boards. Step-off all trenches and block wall

widths and drive nails in these positions. Saw cuts can be used as an alternative to nailing.

Lines can be strained on the nails to indicate trench width and block wall width whenexcavation and blocks are to be layed.

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Purposes of Temporary Shelter

The Building Site

Site Preparations

Before any preparation work can commence the Building regulation/code should bechecked. This is necessary to ensure that the building (commercial or residential) to be erected

complies with the standards laid out in the code. There are zoning laws to be adhered to as theyrelate to:

1. The building line

2. Distance Separation3. Lot line

4. Premise

5. Property Line

6. Setback7. Do a check on the Site Deed

8. Obtain a Building Permit

The Building Line-This is a legally determined boundary that no part of the building can cross.

Distance Separation- This describes the amount of open space between buildings. Open spacehelps to keep fire from spreading from one structure to another and enable good ventilation.

Lot/Property Line- A surveyed and recorded boundary (or monument) that separates one pieceof property from another. In essence, it is the legal boundary that marks a lot or parcel of

property.

Premise- A term used to describe collectively a piece of property as well as any buildings orstructure on it.

Setback-This is the open space required between a building line and the street centre line. Itcould also be used to describe the distance between the sides of a building the lot or rear

boundary lines of a property.

Site Investigation

The purpose of a Site Investigation is to determine beforehand:

Existing trees and buildings on the property or adjacent property

Details such as full data of existing services or the lack of it

Contour lines- natural grade elevations Details of above ground obstruction such as transmission lines

Topography of the site and existing fording (water running underground)

Sewer system availability or the lack of it

The geographic location (with respect to the orientation)

Required Security and Staffing

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Layout

(General site conditions such as soil nature, height of water table, flooding risks, andneighbouring properties, among others).

These factors will to a large extent help the builder in the design and construction processes

of the proposed work.

Soil Investigations

Determines the suitability of the site for the proposed project

Determine an adequate and economical foundation design.

Determine the difficulties that may arise during the construction process and period.

Determine the occurrence and /or causes of all changes in subsoil conditions

Site Preparation Principles

In Site Preparation the builder will require operatives, materials and plant, which must be

carefully controlled so that the operatives have the right machines in the most advantageouspositions, the materials stored in such a way that will allow for easy access and little or no

interference with site circulation, and adequate storage space and site accommodation.

When Planning the Site Layout the following must be taken into consideration:

1. Site activities;

2. Efficiency;3. Movement;

4. Control ;

5. Facilities for health, safety and welfare provision, and

6. Accommodation for staff and storage of materials.

Usually before the proposed site is planned and drawn the prevailing conditions should

be considered these are; the condition and positions of existing roads and the setting out of anytemporary roads considered necessary should be noted and planned. Information regarding the

soil conditions, height of water table and local weather patterns should be obtained preferably

from the meteorological office or from the local authority.

Temporary Shelters

These are required on a building site for the housing of personnel, services, processes andmaterials for the expediting and control of building works, and to cater for illness and accidents

among workers. Consideration should be given to the following:

Statutory Requirements

The construction site is under the control of the factory inspectorate and as such shouldcarry provisions for amenities to workers. Amenities usually include a change room, a lunch

room and sanitary facilities.

Activity Areas

Offices: Normally for large projects site offices and briefing rooms are provided to assist in thedaily administration of the project.

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Workshops: Carpenters, steel benders and some other tradesmen require workshop facilities to

assist in their work. Workshops should be so located as to ensure good control and effectivehandling of materials.

Storage

Warehousing: Warehouses are normally required for storage of delicate components and

fittings. Items normally stored in a warehouse include doors, windows, ceramic receptacles,light fittings, electrical and plumbing appliances etc.

Tools and Equipments Stores: Tradesmen are usually required to carry and secure their own

tools. The main contractor, for special processes may find it necessary to carry a supply of

special tools and equipment which would be available to workmen. The store may also carry

other items that can only be had on special issue. Some of these items are paints, locks and smalltools. Such stores are controlled by a storekeeper or a timekeeper.

Material Stores: Material stores may be provided to protect materials from theft or damage. Thematerial stores are usually close to the appropriate workshop or activity area. Such stores would

carry materials such as reinforcing steel, rough lumber and cement. Special provisions must bemade to ensure that materials are not spoiled or damaged during storage and handling. Inaddition, brittle materials such as tiles require provisions.

Reasons for Temporary Services

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Temporary services relate to the provision of utilities for the purpose of facilitating

construction activities as well as providing conveniences for workers. The supplies normallyinclude gas, water, compressed air, electricity and telephone.

Conveniences

These include conveniences for personnel and work process.

Personnel: Provision under the factories act allows for provision of certain conveniences forworkers. Temporary services assist in the provision of drinking water, adequate lighting and

toilet facilities. Drinking water and toilet facilities should be positioned for quick access thus

reducing idle time.

Work processes: Utilities supplied to the site can be used to drive (power) plant and equipment

or provide ingredients for preparing certain materials.

Examples of supplies used for driving plant and equipment are:A. Air- Pneumatic tools and equipment

B. Oil and Gas- Turbine and hydraulic tools and equipmentC. Electricity- electric tools and equipment

Heat, water and air are used in the following processes:

1. Heat- asphaltic processes

2. Water- making concrete

3. Air- Spray painting, excavating, compacting

Communication

Communication includes physical and verbal contact between the agencies and processesduring the life of the project. Factors to be considered in communication are temporary roads for

access to the site and storage areas, as well as possible telephone or two way radio contacts for

placing orders and dealing with routing administration and contingencies which are important.

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THE MANUFACTURING OF PORTLAND CEMENT

Cement is a substance that binds aggregates together into a very dense material that possesses

great compressive strength.

Portland Cement

Portland cement is used in the manufacturing of concrete and mortar. It may also be usedas a bed for clay and cement tiles. Ordinary Portland Cement is made by mixing ground chalk or

limestone and clay with water to form a semi-liquid mixture, or slurry. Local materials such as

shale may be used instead of clay in the manufacturing of Portland Cement. The slurry isscreened and is passed into a storage tank where it is kept agitated in preparation for passage into

a kiln, which is a rotating cylinder, approx. 90 meters long, inclined at an angle and fired by

pulverized coal or oil.

The slurry is fed into the upper end of the kiln and flows down to the direction of the

heat. As the kiln revolves, it dries the slurry. Water evaporates under this intense temperatureheat (raised to about 1500 Celsius) fusing the materials into a clinker or cement noodles. The

clinker is cooled and ground to a fine powder. A small amount of gypsum is added to retard thesetting time of the cement.

Characteristics of different Types of Cement

Portland Cement is the most commonly used cement since it hardens rapidly. There are

several other cements that can be used for special purposes.

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The ratio of Portland Cement to aggregates varies with the strength requirements for the

concrete. Additives may be put into the mixture or cement to enhance the strength or providesadditional qualities such as quicker drying, waterproofing, resistance to sulphate corrosion etc.

During the manufacturing of cement, various chemical components are produced. This

compound which influences the properties and behaviour of the cement includes:

(1) Strength Development:(2) Setting Time and Heat Production

By varying the components, the properties can be modified. These properties caninfluence the ability of the cement to resist sulphate attack, which is the rate at which cements

sets and heat is produced.

Some types of cements are low heat (used for concreting large masses) and some high heat (for

cold weather conditions).

The five common types of cement used in construction are Types 1, 2, 3, 4, 5

Type 1- Normal

This type is ordinary Portland Cement. It has normal qualities, a reasonable setting timeand is used for general concrete work, when conditions are normal. Such example include:masonry work, filling of pockets, and ordinary strip foundation.

Type 2 Moderate

This type of cement gives off less heat than type 1, and has a moderate resistance tosulphate. It is suitable for use in foundations where there are low levels of sulphate but

offers good resistance to soils with high sulphate level such as those adjacent to chemical

plants.

Type 3 - Low Heat

This type is ideal for use in mass concrete work, such as large foundations or damretaining walls. It develops strength slowly and generates less heat, thus reducing

cracking.

Type 4 - High Early Strength/Rapid Hardening

This type is used when the weather is bad (rainy season), or when formwork has to be

removed early. It develops strength earlier than types 1 and 2.

Type 5 Aluminium

This type contains aluminium ore. It is darker in colour than Normal Portland Cement. It

hardens very rapidly and has great strength.

Notable Behaviour of Concrete

Climatic conditions can influence the setting time of concrete and its used. Formaximum strength development, concrete should be wetted down for 28 days.

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Characteristics of Aggregates

Aggregates generally make up the bulk of the concrete. These are available in fine and

coarse grades. For mortar the size of aggregates is very small ranging from 0-4mm, and forgeneral concrete work the size varies from 5-20mm.

Requirements of Aggregates

All aggregates should be:

clean

free from sediments

sound

strong not easily crushed

well graded

well shaped

Types of Aggregates

Coarse Aggregate

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Gravel This consist of small pieces of stone which are somewhat rounded in shape. It makes

good coarse aggregate because it is hard and closed textured. When using gravel as a coarseaggregate the pebbles should be graded in size. (Source= gravel banks, river beds).

Crushed Stones Trap rock is the hardest and most durable stone that can be crushed and used

for making concrete. This stone is dark, heavy and close-grained, and is of igneous origin.

Granite makes good crushed stone and is less expensive than trap rock. The stone should begraded in sizes 6mm-20mm.

Fine Aggregates

For concrete work these are sand, crushed stones or gravel screening. The most important

of these is sand. Sand is a fine divided material of rock which will pass through a standard 5mm

sieve. Sand is not subjected to disintegration, decay or expansion.

Importance of Proportioning or Batching

Proportioning aids in determining the strength, durability, permeability, workability and

economy of the concrete. Proportioning is essential to ensure a good mix.

Batching is the determination of the exact amount of each ingredient that is placed into a

specific concrete mix.

The following are some results of Batching.

Strength In order to obtain maximum strength, the aggregates must produce little or no

voids in the concrete. This increases the density of the concrete thus increase its strength.

Economy Cost is a major factor in concrete work. Cost is influenced by careless use ofingredients. The most costly ingredient is cement. A poor mix often increases the cost of thejob or reduces the strength of the concrete.

Workability This is the ability of the wet concrete to be placed and worked with ease. This

property is enhanced by the correct proportioning of the cement and aggregates and water-cement ratio.

Volume Batching

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This is generally used but it is a less accurate method of mixing concrete. A measuring

box is used to determine the amount of cement and aggregates. A change in the moisturecontent will impact upon the volume of the materials and affect the quality of the concrete.

Figure 2 showing a diagram of a Gauge or Measuring Box

Batching by Weight

In this method the materials are measured by weight. This is a more reliable system ofbatching than that of volume. Variation in volumes owing to compacting is eliminated whenusing this method.

Water

The water used in the making of concrete must be clean and free from impurities whichcould affect the quality of the concrete. A proportion of water will set up a chemical reaction that

will harden the cement. The rest is required to give the mix workability and will evaporate fromthe mix while it is curing. An excess amount of water will give a porous concrete or reduced

durability and strength.

The water/cement ratio is the amount of water used in the mix and is expressed as:

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The total weight of water in the concrete

Weight of cement

For most mixes, the ratio is between 0.4 and 0.7. Concrete mixes can be expressed as volume

ratios, thus:

1:2:4 = 1 part cement 2 parts fine aggregates and 4 parts coarse aggregates1:5 = 1 part cement and 5 parts all in aggregates

Some common mixes

1: 10 = not a strong mix but it is suitable for filling weak pockets in excavation and for binding

layers

1:8 = slightly better suitable for paths and paving

1:6 = a strong mix suitable for mass concrete

1:3:6 = the weakest mix

1:2:4 = the strongest mix suitable for reinforced concrete

Concrete is a mixture of fine aggregates, coarse aggregates, cement and water that possessesgreat compressive strength.

Mortar is a mixture of cement, sand and water in definite proportion.

Slump test

PROPERTIES OF PLASTICS

Plastic is one of the new building Materials being widely used in the Building Industryand for Domestic Purposes. Such purposes include: - plumbing, electrical fittings and sanitary

appliances. Plastics are usually by products of Petro-Chemicals.

Plastics are usually:-

light weight

easily handled durable

strong for their weight

readily adapted to various situations

Properties of Plastics which make them suitable for usage in Construction Work are:

1. strong

2. light weight

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3. durable

4. pliable/flexible5. easily joined

6. glazable

7. elastic

8. water proof9. rust proof

10. cheap/economical11. soft

Some disadvantages of plastics and precautions to be observed in their use are they:

Can be easily damaged if not properly protected

Have a low melting point

Are easy to crushed under weight

Must be supported when suspended

Have poor chemical resistance to thinners and solvents

Becomes brittle under continuous exposure to variations of weather

Types of Plastics Application

1. Thermo-Plastics Conduits, pressure and non-pressure pipes

2. Polyvinyl Tiles, mouldings

3. Polythene Sheeting, bags

4. Nylon Ropes, coverings, garments

5. Thermo-setting Resins

Uses of Plastics in the Building Construction Industry are:

1. Electrical Installation; Conduits, fittings2. Plumbing

3. Guttering4. Tiles/Floor Finishes

5. Waterproofing; Damp Proof Membrane, drains6. Roofing

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TIMBER AND TIMBER PRODUCTS

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Bark- Every species of tree has its own bark which is a means of identification. The

bark is the outer layer of a tree that protects it. Without it the tree cannot survive.

Cambium layer - This is the growing part of the trunk. Here new cells are constantlydeveloping. Some becoming bark while others become wood.

Medullar Rays - Food is distributed to all parts of the tree by means of these small cells. These

wood cells grow in length radially and can be easily seen in oak, beech, and mahogany.

Annual Rings - The age of the tree can be determined by the counting of these rings, as each

ring represents one year of growth.

Pith or Medulla - This is the core of the tree. It may be sound or solid, but in many cases it is

filled with a cork like substance. It has a dark, brown colour.

Sapwood - Light coloured outer concentric rings of woody tissue that is found next to the

cambium. It contains only a few living cells and functions mainly in the storage of plant food.

Its thickness varies from 13mm to as much 150mm in some species.

Heart wood - The inner concentric rings of woody tissue which consists of inactive cells.

These cells of heartwood may contain many minerals which contribute to its darker colour, great

beauty and resistance.

Bast -The channel that is found between the cambium layer and bark which transport food from

the root to the leaf.

The tree can be regarded as one of natures gift to man. It provides food, shelter and fuel.The tree is a living organism, the components parts performing specific life functions.

Timber is the oldest building material. The growth process of certain species encouragesthe production of various by-products.

To those studying botany a tree is just another plant. To the carpenter and the joiner it is

the plant which produces the material with which he is mainly concerned namely wood or

(timber). The growth of a tree is affected by the soil and by the climate in which it grows.

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Softwood and Hardwood Trees

Commercial timbers are classified into soft woods and hard woods. The most common

method of identifying them is by their leaf. Soft woods have narrow needle like leaves where as

hard woods have a broad leaf.

Softwoods

Soft woods (gymnosperms) are not all soft; some soft woods are very hard e.g. Yew,

pitch pine strong and durable. Soft woods are all for practical purposes, derived from a group of

trees called conifers. Coniferous trees are mainly evergreen and grow chiefly in the northern

cold to temperate zone. Soft woods comprise about 75% of the timber used in the U.K.Soft woods are non- flowering and have needle shaped leaves and naked seeds contained in

cones, their branches normally arises in whorls with more than two at the same level. Even after

the tree is converted, most lumber can be easily identified as hard wood or soft wood. Conifersare simpler and more uniformed in structure than broad leaved trees. They have mainly one type

of cell, the tracheid. These cells appear as regular rows of holes, with the cells formed duringspring and summer (wet seasons) having thin walls and those formed during autumn and winter(dry seasons) have thick walls. It is this difference in the formation of cells that indicates a

years growth or annual rings.

Soft woods main features include:1. They have an open grain texture, which is easier to work on than hard wood.

2. They have a lighter colour than hard wood.

3. They do not shed their leaves seasonally.

4. Their leaves are usually needle or cone shaped.5. They grow quite quickly.

6. The timber produced needs to be protected from the weather by applying paint, varnish or

preservatives.7. They need to be protected from insect attack.

Examples of soft woods are:Douglas fir

Western red cedar

Pitch pine

White pineRed wood

Red pine

Sugar pine

Southern pine

Yellow pine

Caribbean PineAlaska cedar

Honduras cedar

Hardwoods

Hard woods (angiosperms) are not all hard, some hard woods are very soft e.g. balsa.Most hardwoods are deciduous or broad-leaved trees. Hard woods include densest, strongest,

and most durable timbers. Some hard woods contain resins and oil which interfere with the

hardening of paint such as teak. The cheapest hard woods approximate in cost to the more costlysoft woods.

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Hard woods can be recognized by their broad leaves on their branches which usually

grow out at different levels, at the most two at the same level. These trees produce flowers fromwhich their seeds come enclosed in a fruit. These trees grow in cool to tropical climates and may

be deciduous or evergreen.

Hard woods unlike soft woods have a more complex structure with mainly two distinct

cells. One type is fibrous and similar to the tracheid and the other type is known as vessel orpore cells. The latter appears as pores or holes in the end grain, and as vessel lines on

longitudinal surfaces.Cell structure in both soft woods and hard woods affect the grain, texture, density and

figure in these woods. The grain in soft wood is generally straight, the texture is fine and the

figure is plain to pleasing. In hard woods, the grain may be straight, sloping or interlocked. The

texture is fine to coarse because of the size and arrangement of the pores and the figure plain tohighly figured. These are dense hard boards and more difficult to work with tools.

Hard woods main features include:

1. They are harder to work with hand tools than soft wood trees.

2. They are darker in colour or have distinctive colours.3. They shed their leaves seasonally.4. They are slow growing and cannot be cultivated.

5. They are more expensive to use for timber.

6. They are selected for decorative appearance.

Examples of hard woods are:

Mahogany

TamarindTeak

Mora

Green heartBullet wood

Satin wood

Mahoe

Crab woodWallaba

Cedar

OakBirch

Beech

Balsa

Conversion of Timber

Conversion is the process of cutting up timber in marketable sizes. It is a commonfeature that decorative cuts are made during conversion. The two general methods of selling

lumber are plain sawing, (flat or slash sawing) and quarter sawing.

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Plain SawingThe log is slabbed on either two or four sides to form a cant from which other plain

sawed lumber is cut. Plain sawed lumber has several advantages over quarter sawed:

1. More lumber is produced when grain figures are not considered.

2. It dries more rapidly.3. It is cheaper to cut.

4. It has lower unit cost.

Plain sawing (1,2,3,4) and quarter sawing (5,6)

Quarter Sawing

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Quarter sawing can be done any of four methods: radial, tangential, combined radial

tangential and quarter tangential.Quarter sawing has the following advantages:

1. Fewer tendencies to warp or twist.

2. Fewer tendencies to cut or twist.

3. Less shrinkage.4. More durability strength.

5. More attractive grain pattern.6. More rapid kiln drying.

It is used in the manufacture of high class joinery, furniture and quality work. It wears more

evenly when used as flooring.Disadvantage

The method of conversion is time consuming and produces much waste.

Seasoning of Timber

Timber cannot be used for carpentry and joinery immediately after it is converted, sincethere is a lot of moisture present in the wood. A large portion of this sap must be removed, ifdistortion resulting from shrinkage is to be avoided. The process of moisture removal from the

wood is called seasoning. This can be done in either one of two ways: natural or artificial terms

known also as curing or conditioning. It is realized that, the lower the moisture content in thewood the greater its strength.

Natural Seasoning

After conversion, the wet timber is stacked with strips of wood, usually of the same kind,

or stickers separating each layer. This allows proper circulation of air which removes the

moisture. A suitable roof is needed to protect the timber from sun and rain. Air seasoning

reduced the moisture content to about 17% under ideal conditions and even takes up to twoyears. The moisture content must be in equilibrium with that of the atmosphere. The weather

and thickness of the material will vary the length of time required for seasoning. End splits may

be controlled by tacking on straps or metal or wood, or by putting paint wax or oil on the ends ofthe boards.

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Advantages

- High quality of lumber.

Disadvantages- Length of time, limited availability of large quantities.

- May be more costly- Needs more space for drying

- No control over drying process.

Artificial Seasoning

Artificial seasoning has improved greatly and the kiln which is the storage house for it

can now be completely computerized to control the drying process even without attendance or

human inspection. Accurate moisture content readings are readily available at any time. Thematerials are stacked in a similar manner of that of the natural.

Advantages

- Relatively short time

- Early use of material

- May result in greater availability and reduced cost.- Some wood worms are destroyed by the heat

- Moisture content can be controlled to as low as 12%

Disadvantages- Case Hardening

- Rapid drying can cause it to check or become honey combed.

Moisture content

When a tree is felled it contains a great deal of moisture. The timber will need to havesome moisture content, whatever its commercial use is to be. The purpose of drying the timber

is to minimize the subsequent movement when it is used; which means, different uses demands

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different moisture content levels. The timber for internal use should have lower moisture content

than timber which is used externally. This is because internal timber would be reduced by thewarmth of the atmosphere. This can cause excessive shrinkage and possibly other more serious

defects.

Moisture content is always expressed as a percentage of the dry weight of the timber.

The formula used to calculate this formula is:

Wet weight- Dry weight x 100Dry weight

= moisture content (%)

A sample of timber is cut and weighed. This is the wet weight. It is placed in a kiln 100C and

taken out at intervals until no further weight is loss. This is the dry weight. A piece of timber

weighs 132.5gIts dry weight is 108.7g

Moisture content weighs 23.8g% of moisture (23.8/108.7) x 100= 21.9%

Example:

132.5- 108.723.8 x100

108.7

= 21.9%

Timber Defects

A defect is a fault in the timber that will result in some reduction in strength, appearance

which is usually cause by natural elements during growth or during conversion and seasoning

which could and should be avoided.

Natural defects

Knots are caused by branches growing out of the tree in which case the grain in the tree

trunk becomes twisted. Forest grown tree usually have less knot because of lack of sunlight.The branches always start at the centre of the tree at the pith .

Sound Knots

They will not fall out of the position they occupy but they tend to crack. This allows the

inlet of fungus to attack the wood. Provided that they are not too large or close to the edge they

dont posed a problem.

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Dead Knots

These are a source of real weakness, whatever is the size. They are produced when a

branch is broken off before the tree is finish growing. The tree starved this broken off part of the

trunk causing it to die. It is identified by a very dark colour around the decayed knot, making itliable to fall out eventually leaving a knot hole. Such a timber is classified as low grade and is

unsuitable for structural use.

Shakes- Take the form of splits in the wood and detracts from its strength quite considerably.

Heart Shake- These occur in the heart wood of a tree when it is left too long after it has maturedbefore being felled for use. It is due to lack of food.

Checks- These are separation of the wood fibres along the grain. They usually occur along theends of lumber. In artificial seasoning checks are caused by rapid drying.

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Ring Shake- These follow the contour of the growth ring. They usually result fromexcessive

swaying of the tree in high winds bringing about separation of the fibres.

Cup Shake- These are brought about by similar conditions as ring shakes, but without results.They also position themselves in the growth rings.

Star Shake- These are fine cracks in the appearance of a star as a result of the sun drying up the

cellular tissue, when the bark has been damaged or when the timber has been season too quickly.

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Dry Rot- This is caused by a fungus (merious lacrymans) a growth which lives in the wood and

destroys it. It thrives on wood in dark, damp unventilated conditions causing it to dry up anddisintegrate into dust.

Wet Rot- Wet rot (cellar) fungus attacks only wet timber, and is found in damp, poorly

ventilated cellars. The disintegration of timber is due to exposure to alternate wet and dryweather which is favourable conditions for growth of fungus.

Up Sets- This is a form of shake, the cause of which is uncertain. The effect of it is in a zigzag

crack across the grain, where the affected boards are likely to snap very easily under little

pressure. Probable causes are:

1. The tree being struck by lightning during growth.2. The tree falling awkwardly when felled causing a fracture to run through the log.

Bowing- This often results when the boards are stacked with too much distance between

the sticks.

Warp- This is any distortion from the true form and may include any one or a combination of the

following: cup, bow, twist. This is caused by the exposure to the elements and poor stacking inthe process of seasoning and usage.

Cupping

Spring Twist

Wood Preservation

Timber for construction work should be treated in order to increase its ability to resist

fungal and insect attack. Insects break down the cellular structure of the wood and destroy itsstrength and appearance. Timber being exposed needs to be protected.

Timber preservation is costly, extending to the life of the timber. Preservation is cheaper in long

term.

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Some preservatives, such as creosote are used exclusively underground or in roofs where

the material will not be visible. Other types have pleasing effects, example: Cuprinol, Atlas Awhich change the colour of the wood to a light green.

Application requires some care since preservatives are highly toxic and others may attack the

skin.

There are three groups of preservatives:

1. Tar- oil type2. Water solution type

3. Organic solvent type

Tar-oil

These preservatives are distilled from coal tar. Creosote is probably the best know. They

are very efficient but have a strong odour. This can be done by steeping or can be brushedon,

where the lumber becomes saturated after a period of time. It becomes resistant to insect attackand moisture penetration.

Water Solution

Water is used as a vehicle to take the chemical into the timber and afterwards it evaporate

leaving the chemical to fight off attack from sodium fluoride, zinc chloride and copper sulphate

solutions which are commonly used as preservatives but are odourless and can be painted over

quite easily.

Organic Solvents

This can be done as non-pressure and pressure impregnation.

Pressure Treatment

This is done by forcing liquid Wolman Salt under pressure into the timber- this ensuresbetter penetration.

Non-Pressure

Brushing- A suitable material is brushed on the lumber. This is a simple process but slow toallow the liquid to soak in.

Spraying- This is used in areas difficult to get into, such as roof spaces. It is much quicker andeffective than brushing while using a spray gun.

Dipping- The timbers are submerged in a bath of preserving liquid for 5-15 minutes. Excess

preservatives are allowed to drain into the bath which can produce fairly good results.

Steeping- Similar to dipping, however, the timbers are left submerged for at least (2) weeksespecially with solution types of preservatives.

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Production of Manufactured Boards

Ranges of sheet material are widely used in woodworking and building industries. Some

are made from solid timber while others are made from low-grade timber. Standard size for

building boards is 1220 x 2440 mm. Thickness varies according to use.

1 laminboard

2 core

3 blockboard4 battenboard

5 cellular board, cellular plywood

6 composite board7 hardwood plywood

8 mixed plywood

9 softwood plywood10 multi-ply

11 crossbanding12 star formation

13 parallel-grain plies14 single layer chipboard, standard grade chipboard

15 multilayer chipboard

16 peg board, perforated hardboard17 hardboard

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Plywood

Plywood is one the most extensively used boards which is made up of an unequal number

of sheets and veneers called plies. Three- ply plywood consists of three veneer of equal

thickness glued together with the centre or core veneer, having its grain running at right angles to

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the outer veneers. This gives it considerable strength. It has extensive uses which may include

panelling and lining as well as other forms of covering. The grade is usually stamped on theboard by the manufacturer and these must be recognized when deciding the usage of the board.

Int - Denotes for internal use only and indicates that is has been glued together with glue having

low moisture resistance. If such timber is exposed to moist conditions there would a separationof the veneers.

MR- Fair resistance to moisture.

BR- High resistance in exposed conditions because it is boil resistant.

WBP- Indicates that it is weather and boil condition and also in the boat building industry.

Laminated Panels

These panels are constructed of thin layers of material glued together to form special

effects. These panels will resist warping and shrinkage.

Hard Boards

This is yet another of the wood waste product. Hard board are made from wood chips

and logs. The wood is pulped by machine, and bonded with adhesive and finally pressed to a

thickness of 3mm- 6mm. With such a thickness they usually have a width of 1.2m. With lengthsof 2.4 3 m. Their usage includes panelling, wall and floor covering.

Bagasse Board

Bagasse is the residue left after milling cane during the manufacture of sugar. The

material is crushed to a pulp, mixed with adhesive and compressed with a heat treatment. Thisresults in a hard durable board suitable for interior work.

Chip Board

This board makes use of machine chips of wood, glued and compressed into large sheets.The core section consists of larger chips than the surface. A disadvantage is that it is unable to

take a screw. It is used for cheaper range of furniture as well as wall coverings.

Lumber Classification

Lumber is sold by standard cubic measurement, board measure.

Any size over 30mm and 100mm is boards. (31mm thick and 100mm wide)37mm thick is planks

Measurement in length is called linear.

Measurement in length and breadth is called square measure.

Measurement in length, breadth and thickness is called cube measure.

N- Number of pieces in stock.

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T- Thickness in mm.

L- Length in metre.

Note:

- 1 inch=25.44mm

- 1 foot = 304.8mm- 1 metre = 3.281ft

Formula to calculate board in m is:

Foot board measure 10 pieces of 2 x 6 x 120

= 10 x 2 x 6 x 12 012

= 120 FBM

L (M) x W mm x T mm = m3

1000 1000

If L = 5m W = 175mm T= 5mm

Then volume of board or lumber =

5 x 175 x 251000 1000

= 0.02m3

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FOUNDATIONS

The purpose of the foundations is to adequately transfer the load of a structure to suitable

ground and to spread building loads over a sufficient area of soil to avoid undue settlement,particularly unequal settlement.

Foundations should meet the following requirements;(1) Building loads must be supported and transmitted to the ground,

(a) safely; transmit and sustain to the ground the total dead and imposed loads so as

not to cause any settlement or

(b) without causing deflection or deformation of the building;(c) without affecting adjacent buildings.

(2) They must be of such depth or be so constructed as to avoid damage by shrinkage of the

subsoil.

(3) They must be capable of resisting chemicals in the sub-soil.

The explanation of common terms associated with soils in foundation work is given below:

Settlement: Ground movement, which may be caused by:(a) deformation of the soil due to imposed loads.

(b) volume changes of the soil as a result of seasonal conditions.(c) mass movement of the ground unstable areas.

Made Ground: Refuse, excavated rock or soil deposited for the purpose of filling in a

depression or for raising the site above its natural level.

Bearing Pressure: The pressure produced on the ground by the loads.

Bearing Capacity: Safe load per unit area which the ground can carry.

Back Fill: Lateral excavated from site and if suitable used to fill in around the walls andfoundations.

Sub-Soil: Sub-soil lies below the topsoil to a depth about 300 mm.

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Types of Foundations

The types of foundations normally used in construction include strip, raft, short bore pile

and pad. Various types of foundations are used in domestic buildings. The type of foundationsselected depends main~ on two factors:

(1) The total load of the building ("live and "dead" loads).

(2) The nature and bearing capacity of the subsoil.

(3) The design of the building.

Strip Foundation:

The majority of domestic structures have a strip foundation in which a continuous strip of

concrete provides a continuous support under load-bearing walls. This type of foundation iscomposed of plain concrete usually to a mix 1: 3: 6 volumes (1 part cement, 3 parts sand 6 partscoarse aggregate). The thickness of the foundation must not be less than the projection (P) and in

no case less than 150 mm. Reinforcement bars are sometimes used in small domestic building.

These bars strengthen the structure, and make it less vulnerable to earth tremors.

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Deep Strip Foundation

Raft Foundation

Raft foundations cover the entire area of the building and usually extend beyond it. They

consist primarily of a reinforced concrete slab up to 330 mm thick, which is often thickened

under load bearing walls. The level of the base of the raft is usually within 300 mm of the surface

of the ground and the reinforcement is often in the form of two layers of fabric reinforcement,one being near the top and one near the bottom of the slab.

The reinforcement helps to spread the loads and resist tensile stress, which could cause

cracking of the raft.Raft foundations are best suited for use on soft natural ground or fill, or on ground that is

liable to subsidence as in mining areas. The ground at the edge of the raft should be protected

from weather, which can cause erosion or slippage. This can be overcome by:(1) Laying concrete paving around the building

(2) Deepening the edge beam

(3) Laying a field drain in a trench filled with suitable fill as shown

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Raft foundation

Stepped Foundation

On a sloping site the most economic procedure is to use a stepped foundation thusreducing the amount of excavation, back fill, surplus soil removal and trench timbering. The

foundation is stepped to follow the line of the ground and the depth of each step is usually 150 or

225 mm (multiple of brick courses).

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The lap of concrete at the step should not be less than 300 mm. The damp proof course

may also be stepped in a similar manner. Where the slope exceeds one in tenth it is desirab1e touse short bored pile to overcome the sliding tendency.

Stepped foundation

Short Bored Pile

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Short bored piles were devised to provide economical and satisfactory foundations' for

houses built on shrinkable clay. They consist of a series of short concrete pile cast in holes boredin the ground and joined or connected (for load bearing walls) by light beams usually of

reinforced concrete. They have several, advantages over strip foundations:

i. speed of construction

ii. reduced quantity of surplus excavated soiliii. ability to proceed with construction in bad weather

Problems do, however, arise on stony sites or where there are many tree roots.Holes are normally bored to a depth of 2.5 - 3.5 metres by hand or mechanically operated

auger keeping the holes vertical and on the centre 1ine of the beams. The depth will be

determined by the stability and bearing capacity of the clay.

The piles, generally about 300-350 mm in diameter, should be cast immediately after theholes have been bored. A mixture of 1:2:4 concrete is generally used. Short lengths 20 mm

diameter reinforcing bars should be set in the top of each corner pile and bent over to cast in with

the beams. The reinforced concrete beams often 300 x 150 mm' in section, are usually cast informwork, but in some cases are cast in trenches.

The placement of piles is influenced by the shape of the building, the load to be carriedand the load-bearing capacity of the piles. With load bearing walls, piles should be provided atcorners and junctions of walls, with intervening piles placed to give uniform loading and, as far

as possible, to keep ground floor door and window openings mid-way between piles.

Short bored pile foundation

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Pad Foundation

Pad foundations are isolated foundations designed to support columns. The area of

foundation is determined by dividing the column load plus the weight of the foundation by the

allowable bearing capacity of the ground. The thickness of the foundation must not be less thanthe projection from the column (unless reinforced) and must, in any case I not be less than 150

mm. The size of foundation can be reduced by providing steel reinforcement towards the bottomof the foundation running in both directions.

Pad foundation

The area of the pad for a foundation may be calculated by determining the ratio of the load to the

bearing capacity of the soils under laying the structure.

Terminology

Three terms used regularly with foundation construction are explained.

Footing: offsets at the base of a wall to provide a greater bearing area.

Damp proofing: making waterproof by special materials or processes.

Hardcore: broken bricks block or stone consolidated as a foundation for concrete in solid floors.

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Excavation and Timbering

Excavation Works

The excavation for foundations follows after the setting or laying out the building and

fixing of profiles. Excavations take various forms depending upon the type foundation to be laid.

ExcavationThe term excavation means to hollow out. In building terms it means to remove earth to

form a cavity in the ground.

The method of excavation can either be manual or mechanical. Manual excavation is,

used extensively on small domestic structures. The manual process requires hand tools such aspick axe, shovel, digging bars, forks and wheelbarrows.

Types of excavations

1. Over-site Excavation that involves the removal of topsoil up to 300mm deep.

2. Reduced Level Excavation which is carried out below the over-site level to form a level

surface on which to build and can consist of both cutting and filling operations. Thelevel to which the ground is removed is called the formation level.

3. Trench Excavations are narrow excavations that are primarily used for strip foundations

and buried services. Excavation can be carried out by either machine or hand.

Types of Trench Excavations

Battered faced

Vertical or straight faced

Battered Excavation Vertical/Straight Excavation

47

Advantage: Advantage:

No temporary support is required to thesides of the excavation

Minimum amount of soil is removed andtherefore minimum of backfill is required

Disadvantage: Disadvantage:

It incurs extra cost for over excavating and

extra backfilling

The sides of the excavation may require

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Reduced Level Excavation

This is necessary because very few sites are level in their natural state.

On small sites the process is similar as for Site clearance. Bulldozers are used for cut and filloperation and a mechanical shovel plus Lorries are used for cut only operations.

Trench and Pit Excavations

On small sites the hand process can be used but if the depth of excavation exceeds

1.200m some method of removing spoil (soil) from the excavation will have to be employed. Inthis event a trenching machine such as a Back actor could be employed.

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Types of Excavation Machines

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Typical excavation machines include:

1. Bulldozers2. Scrapers

3. Graders4. Tractor Shovel

5. Skimmer

6. Face Shovel

7. Back actor8. Dragline

9. Multi-Purpose Excavators

10. Trenchers

Mechanical - The bulk of major building projects is now performed. The principal machines are:

Dragline: A bucket dragged towards the machine, and it generally excavates below ground

level.

Face Shovel: This digs in deep faces above the level of its wheels or tracks.

Skimmer: This is used for shallow excavation up to 1.5 m deep and is particularly useful for

levelling and roadwork.

Drag Shovel or Back Actor: This digs below its own level and towards itself and is primarily

used for trench excavation.

Drag and Clamshell: This is for moving loose materials.

The Scraper: Operates like an earth plane and carries its scraping with it.

Bulldozer: This is used for, bulk excavation and grading.

Front End Loader and Back Hoe: This is for excavating and moving loose materials.

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Timbering to Excavation

This is the term used to cover temporary supports to the sides of excavations and is

sometimes called planking and strutting. The sides of some excavations will need support to:

Protect the operatives while working in the excavation

Keep the excavation open by acting as a retaining wall to the sides of the trench.

The type and amount of timbering required will depend upon the depth and nature of thesubsoil, weather conditions, type of soil, and the duration of the operations.

Types1. Timbering in firm soils2. Timbering in dry loose soils

3. Timbering in loose wet soils

4. Timbering in hard soils

Safety

When excavating foundations and. drains in soil that is liable to fall away from the sides

of the trench, timbering should be used to prevent this (the soil from falling into the trench).The builder must ensure all trenches are safely timbered or pile sheeted. Apart from the

death or injury, it will result in additional cost to the builder to re-excavate and new damaged

work in the trench should the sides collapse. Proper attention should be given to safety at alltimes. The construction industry has a very high accident rate and everyone in the industry must

be more safety conscious.

Timbering

Timbering is the temporary support used at sides of trenches to prevent caving in. The

support given to sides of the trench depends upon the depth of the trench and the soil conditions.

Weak soils will require more elaborate temporary support.

Terminology

Poling Boards: are vertical members that usually measure 175 mm x 31 mm x 1 m.

Walling Board: Horizontal members placed against the poling boards with cross sectionmeasurement 150 mm x 75 mm. The length varies.

Struts: Horizontal supports placed across the trench to hold the other members in position. They

are spaced at centres between 1.5 m and 2 m along the length of the trench and are usually 100

mm x 100 mm in cross-section.

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Wedges: Sometimes pairs of folding wedges are used between the walling boards and the struts

to take up slackness.

Types of Timbering

1. Open BoardingThis is used for moderately firm ground such as sandy gravel, soft dry chalk, clayey, gravel.

2. Poles and strutsThese are used for moderately firm ground, such as stiff clay, firm gravel and hard chalk. The

poling boards are spaced 1.829 m apart.

3. Close Boarding or Sheeting

This is used for unstable ground such as loose sand, wet soils and made up grounds.

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Timbering in hard soils

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Timbering in loose dry soils

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Timbering in loose wet soils

Safety

Construction regulations state that:1. Heavy loads or machinery likely to cause the collapse of the sides must not be moved close to

the excavation.

2. Open excavations must be fenced off to prevent persons falling into them.3. Approaches to excavations must have warn1ng lights prominently d1splayed at night.

4. No vibration likely to bring about collapse of the sides must be caused close to the excavation

Curing

When concrete is poured it begins to set/cure and as time passes it becomes solid, and at

the same time increases in strength.

The chemical reaction which accompanies the setting of cement and hardening ofconcrete is dependent on the retention of water is known as curing. Exposed concrete should

therefore be sprayed and covered with bubble plastic sheets or quilts of plastic with fibres or

straw or cement bags (sandbags), until it attains maximum strength (cures). To developmaximum strength concrete requires the correct conditions and a certain minimum time,

depending on the temperature. Time ranges from 7 - 28 days for normal Portland cement.

Placing

All form work should be checked, cleaned and oiled before concrete is placed against it.Concrete should not be permitted to fall freely more than one metre. When transported by a

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barrow over rough ground segregation of the materials may occur as larger particles settle to the

bottom of the barrow. This will result in weakened concrete. To prevent or reduce this, usepneumatic wheels to help cushion the shock.

Precautions

1. The area of concreting should be free from all debris.

2. The area of concreting should be washed.3. The mixing bed should be as near as possible to concreting area.

4. The approach of the concreting should be free from all obstruction.

5. Oil the form work to allow ease of striking.

6. Do not allow concrete to fall freely more than one metre.7. Use barrows with pneumatic wheels to reduce segregation of materials.

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WALLS

Definition

This term refers to a unit that is used to sub-divide or partition space.

It is also considered to be a unit that encloses a space thus giving it a degree of protection from

the elements.

Categories of Walls

There are essentially two categories of walls namely:

Load bearing walls and

Non-load bearing walls.

Load bearing Walls

These are walls that are designed to transmit imposed and super-imposed loads in

addition to their own weight to a suitable foundation. They can either be external or internalwalls.

Non-load bearing Walls

These walls are designed to accommodate their own weight in addition to fixings placed

on them. Most often these are used internally.

Functional Requirements for WallsA wall should be:

Fire Resistant;

sound insulated;weather resistant;

thermally insulated;

design to accommodate fixings such as doors and windows or openings, anddesigned to safely transmit all loads encountered to a suitable foundation.

Types of Walls:

Rubble wallsBrick wallsParapet walls

Party walls

Block wallsCavity walls

Timber Framed walls

Dwarf walls

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Concrete walls (In-situ and Prefabricated)

Brick walls

The materials used in the manufacture of bricks is clay or it may be from sand or lime

and are available in a wide variety of strength, types, textures, colors, and special shaped bricks.

In the manufacturing process, the raw material (usually clay) is dug and then prepared

either by weathering or grinding before being mixed with water to the right plastic condition. Itis then formed into the required brick shape using a mould / form before being dried and fired in

a kiln.

Bricks are generally manufactured to a length of 337.5mm, a width of 225mm and a height of112.5 mm.

However, the usual size of bricks for common use is 215 mm in length, width 102.5 mm and aheight of 65 mm where 10 mm of mortar joint thickness is added to 3 faces.

Bonding

This is an arrangement of bricks in a wall, column or pier laid to a set pattern to maintain

an adequate lap. The bond is set along the length of the wall working from each end to ensurethat no vertical joint is above another in consecutive courses.

Purpose of Bonding

Bonding is required:

To ensure that maximum strength is obtain whilst the load to be transmitted through the

wall, column or pier is being distributed.To ensure that there is lateral stability and resistance to side thrusts.

To create an aesthetic (acceptable) appearance.

Types of Bonds

English Bond

This bond is formed by laying alternate courses of stretchers and headers. It is one of the

strongest forms of bonding pattern used.

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English bond details

Flemish Bond

This bond is formed by laying headers and stretchers consecutively in each course. It is

not as strong as English bond but is considered to be aesthetically superior.

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Stretcher Bond

This bond consists of alternate courses of stretchers and is used extensively for block wall

construction.

Parapet Walls

This is a low wall projecting above the level of a roof, bridge or balcony forming a guardor barrier at the edge. Parapets may be exposed to the elements on three faces namely front, rear

and top and will therefore need careful design and construction if they are to be durable and

reliable.

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Party Walls

Party wall is an interior lot line used or adapted for joint service between two buildings.

Cavity Walls

These consist of an outer brick or block leaf or skin separated from an inner brick or

block leaf or skin by an air space called the cavity. These walls provide better thermal insulationand weather resistant than block or brick wall. The two leaves of a cavity are tied together withwall ties at not less than 900mm width and vertical heights of 450mm.

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Cavity wall details

Timber Constructed Walls

Types: -Balloon Framed

Platform Framed

Members:-

Foundation Footing, sill plate, sole plate, studs, Noggins, Top plate, wall plate, trimmerstud, cripple stud, header, window sill.

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Block walls

These are walling units exceeding in length, width or height the dimensions specified for

bricks. They are made from a mixture of cement, sand and marl/crushed stone to specificproportions.

The size of blocks varies depending on their use, but the standard length is given as length 400mm, width from 75 mm up to 215 mm and a height of 200 mm.

Blocks suitable for external solid walls are classified as load bearing and are required to have a

minimum average crushing strength of 2.8N/mm2.

Block walls

CharacteristicsAdequate strength

Good insulation

Low costGood load bearing capabilities

Block walls

The core of blocks assumes more than 25% of its total area/volume. According to theAmerican Society for Testing and Materials (ASTM), blocks are graded based on compressive

strength and range from:

600 psi to be used above grade800 psi used for all exterior walls

Definition of a Scaffold

These are three definitions of a scaffold:

1. A temporary platform either supported from below or suspended from above, on

which workers sit or stand when performing tasks at heights above the ground.

2. A raised wooden framework or platform.3. A temporary structure of timber, boards, etc., for various purposes, as for

supporting workmen and materials in building.

Suspended Scaffolds

Supporting outrigger beams must be able to support 4 times the intended load. To keep ascaffoldfrom falling to the ground, it must be attached to the roof, tied to a secure anchorage, or

secured with counterweights. The suspension ropes and rigging must support at least 6 times the

intended load.1. Counterweights must be attached to secure and strong places on a building so they

wont move.

2. Do not use bags of sand or gravel, masonry blocks, or roofing materials that canflow or move.

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3. Do not use gas-powered equipment or hoists. A hoist must have an automatic

brake for emergencies.4. A 1-point or 2-point suspended scaffold must be tied or secured to prevent

swaying.

Independent Tied Scaffolds

An independent scaffold consists of a platform resting on horizontal tubes, usually called

transoms, which are fixed at 90 to the face of the building and which are secured at both ends to

a row of uprights, or standards, and to horizontal tubes, often called ledgers, running parallel to

the face of the building. An independent scaffold, although it must be tied to the building orstructure, does not rely on it for its strength.

Working platforms and gangways

The scaffold boards which make up a working platform should rest squarely and evenly on

transoms to prevent the risk of tripping. Where the ends of boards meet, transoms must bedoubled and so spaced that no board overhangs by more than four times its thickness. Too muchoverhang will cause the board to tip if you step on it, while too little less than 50 mm will

mean that it is easily dislodged. Normally, each board should have three supports to prevent it

bending or sagging. The space between the edge of the working platform and t

Building Technology Notes Form 4 2012-2013

Documents

Transcript of Building Technology Notes Form 4 2012-2013