ED5001FP Reinforced Concrete Detailing and Design Training Notes 2015 PDF

Institute of Technical Education Training Notes Higher Nitec in Civil & Structural Engineering ED5001FP Reinforced Concrete Detailing and Design Date : 1st Sept 2015 Copyright, Institute of Technical Education ...

Institute of Technical Education Training Notes Higher Nitec in Civil & Structural Engineering ED5001FP Reinforced Concrete Detailing and Design Date : 1st Sept 2015 Copyright, Institute of Technical Education  ED5001FP Training Notes CONTENT Unit Title Page 1 Interpret Drawing 1.1 Different types of construction drawings 4 1.2 Setting out Building on Site 4 1.3 Preliminary Work 6 2 Structural Layout Plans 2.1 Structural Framing Process 7 2.2 Authority submission 7 3 Piling 3.1 Different Types of Piles 10 3.2 Types of Equipment & Method for Pile Construction 14 3.3 Methods of Pile Load Testing 24 3.4 Design Purpose And Requirement Of Pile Cap 27 4 Reinforced Concrete Floor 4.1 Different Types Of Slab 33 4.2 Curtailment of bars for slab 36 5 Reinforced Concrete Beam 5.1 Distance Between Bars 45 5.2 Concrete Cover 46 5.3 Area of Reinforcement 46 5.4 Curtailment of Bar for Beam 57 Institute of Technical Education Page 1  ED5001FP Training Notes Unit Title Page 6 Reinforced Concrete Column & Schedule 6.1 Structural Behavior for Column 62 6.2 Column Failure Modes 63 6.3 Column Schedule and Loading Plan 64 5 Formwork and Falsework einforced Concrete Core Walls 7.1 Falsework 71 7.2 Formwork 71 8 Reinforced Concrete Walls 74 9 Precast Concrete Construction 9.1 Connections 80 9.2 Advantages And Limitations 81 9.3 Prefabrication Process 81 10 Pre-stressed Construction 10.1 Pre-tensioned and Post-tensioned 85 11 Construction Productivity 90 Institute of Technical Education Page 2  ED5001FP Training Notes Institute of Technical Education Page 3  ED5001FP Training Notes Unit 1 : INTERPRET DRAWINGS Unit 1.1 : DIFFERENT TYPES OF CONSTRUCTION DRAWINGS In general, for any kind of construction project, there are four types of construction drawings namely:  Architectural drawing  Civil & Structural drawing  Mechanical & Electrical drawing (M&E  Survey plan / Topography drawing Purpose of Construction Drawing Architectural drawing will be created first, to transform client requirement into drawing. Through architectural drawing structural, M&E drawing will be produced using that as the base. In structural drawing, all the structural members requires to support the whole structure will be captured, together with details, such as connection details, reinforcement etc. Further, within the external work plan, items such as drains, roads, culverts will be designed for and indicated in the drawing. Mechanical & Electrical drawing will incorporate all the mechanical and electrical system, such as air conditioning, water & gas piping under mechanical while lighting and lift under electrical drawing. For survey plan / topography drawing, it will show the height of ground level of the proposed building and its surrounding. Prior to commencement of construction, all the drawing needs to be approved by authorities. Upon completion of the project, all drawing will need to submit into the authorities to capture all the amendment made during construction, this is termed as-built drawings. Unit 1.2 : Setting out Building on Site After the project has been designed and tendered, selection of contractor has been finalized, the first activity for the contractor to do is to carry out a pre-conditioned survey. It is to ascertain the surrounding environment as well as the site condition before the construction work is carried out. Photos and reports will be documented to prevent any conflict in the future. After the preconditioned survey, the contractor will carry out site setting out, to mark out the location of the boundary given to them as well as the structure to be constructed. Institute of Technical Education Page 4  ED5001FP Training Notes Purpose of Setting Out  For all the construction work, setting out is required to mark out the proposed area for construction. General instruments used for setting out  Steel tapes or linen tapes  40 or 50 mm square wooden pegs about 0.5 or 0.75 m long  paint (red and blue)  Staff (leveling)  Theodolite  Hammer  Nails  Wooden profiles  Hemp lines Project Personnel involved for Construction Project  Construction is an organizational process, which mainly involves planning the use of resources such as operatives, materials, machines and similar aids, and the activities of design, manufacture and construction.  In general, for all the construction project, besides the client, it requires the following personnel :  The consultant mainly concerns with the size and disposition of the space within the “envelope” of the structure and the services needed to make it operative.  The contractor who is responsible for the nature and sequence of erection operations / construction, as well as the physical construction of the project.  The sub-contractor / specialists, an independent producer of components for different trades Types of construction activities  Preliminary works and setting out  Excavation, piling and substructure construction  Superstructure construction  Mechanical & Electrical work  Architectural work  External works (Drain, culvert, driveway, landscape etc) Institute of Technical Education Page 5  ED5001FP Training Notes Unit 1.3 : Preliminary Work i Access to site  Good clear access to site improves efficient and successful contracting  Position the access so that vehicles using the access will not interfere with the free flow of traffic on the road.  Construct temporary crossing e.g. culvert or bridge over the drain ii Traffic routes for equipment  Provide temporary roads in large site  Temporary road network should provide for turning of large vehicles for entering and leaving the site without disrupting work in progress. iii Storage of materials  Locate storage areas in a manner such that delivery vehicles will not disrupt site traffic and to avoid double handling and awkward access for delivery trucks  The aggregate and cement stores should be adjusted to the mixing plant, allowing sufficient access for delivery trucks to unload at the batching area iv Location of site office  Must be able to provide maximum visual control from the site office over the site, storage areas and all access road.  The administrative area and conference room should be large enough to accommodate people working in the site as well as for discussion  Electrical, telephone services and drainage facilities are required. v Sheds for bar bending and formwork fabrication  Site workshops adjoining the respective storage areas for easy accessibility.  Have sufficient space for equipment and circulation. vi Fencing and hoardings  To control the delivery and removal of materials from the site by controlled entry and exit points.  To prevent unauthorized persons entering the site. Institute of Technical Education Page 6  ED5001FP Training Notes Unit 2 : Structural Layout Plans Unit 2.1 : Structural Framing Process Structural framing refers to placing column, beam, slab, wall, or any other structural components , using architectural drawing as the base, to ensure the proposed building is safely supported structurally. Columns and walls will be placed first, followed by beams and slabs and any other structural components. After the framing is finalized, detailed drawing and design will be proceeded. Unit 2.2 : Authority Submission Before carrying out any building works, the owner shall appoint Qualified Persons (QPs) to submit the structural plans and the building plans to the Building & Construction Authority (BCA) for approval. The first item to be obtained is written permission from the URA. Thereafter, QPs will prepare the building plans, consult the relevant technical departments and incorporate their requirements onto the building plans. Building & Construction Authority will approve the building plans within one week if submission is in order. All the submission will be through the Corenet e-Submission System. This can be done before or after the submission of building plans, a professional engineer shall submit structural plans to the BCA for approval. This must be carried out prior to commencement of any structural work. Further to this, a permit to commence works from the BCA must be obtained after structural plan is approved and planning permission is obtained. Progress report of the building works needs to be submitted at regular intervals to the BCA after commencement of works Below lists the technical departments generally involved in the approval of building plans:  Fire Safety & Shelter Department (FSSD);  Central Building Plan Unit, Pollution Control Department (CBPU, PCD);  Land Transport Authority, Roads & Transport (LTA, RT);  Land Transport Authority, Vehicle Parking (LTA, VP);  Land Transport Authority, Rails (LTA, Rails); Institute of Technical Education Page 7  ED5001FP Training Notes  National Parks Board (Nparks);  Ministry of Education (MOE);  Preservation of Monuments Board. If there are any material changes to the approved plans, QP must obtain approval before carrying out the proposed amendment on site. The application procedure is similar to the above mentioned. Material changes refer to those that affect the key structural elements of the structure to such an extent that re-design of the key structural elements is required. Where the changes are immaterial, the qualified person for structural works can proceed with the changes on site without prior approval. However, he must keep and maintain a record of all changes and incorporate them in the record structural plans subsequently. Immaterial changes refer to those not affecting any key structural elements; or if they affect the key structural elements, the effects are localised in nature and re-design of the key structural elements is not required. Institute of Technical Education Page 8  ED5001FP Training Notes Revision Questions for Unit 1 and 2 Institute of Technical Education Page 9  ED5001FP Training Notes UNIT 3 : PILES Pile foundations are the part of a structure used to carry and transfer the load of the structure to the bearing ground located at some depth below ground surface. The main components of the foundation are the pile cap and the piles. Piles are long and slender members which transfer the load to deeper soil or rock of high bearing capacity avoiding shallow soil of low bearing capacity The main types of materials used for piles are Wood, steel and concrete. Unit 3.1 : Different types of piles Piles are generally classified into two main types :  Displacement Piles / Driven Piles Displacement piles are piles which are driven into the soil, thus displacing the soil. They include those piles which are preformed, partially preformed or are driven-in-situ. i Bakau pile and Tanalised pile  In rectangular planks formed by bolting together three rectangular planks  Mainly used as closed boarding in trenching  Shapes as birdsmouth formed by bolting together doubled bevelled planks  Tongue and grooved joint formed by bolting together three rectangular planks  Such piles are extensively used in countries where timber is plentiful for temporary structures 250 250 75 450 ii Precast concrete pile iii Pre-stressed concrete pile  Generally rectangular with either tongue and grooved or birdsmouth shaped sides to form interlock  Foot of the pile is bevelled to assist in the driving  When pile is to be driven in hard strata, a metal shoe is used  Joints are usually grouted up to ensure water tightness Institute of Technical Education Page 10  ED5001FP Training Notes  Used for permanent work that incorporated into completed structure 20mm bar grouted in 200 100 400 400 200 400 key 100 Steel straps 115 Cast steel 150 Driving shoes 90 200 Institute of Technical Education Page 11  ED5001FP Training Notes iv Steel piles such as H-section  The two main types of steel sheet piles used are “Frodingham” and “Larssen”  Available in length of 9m to 26m  May be increased in length by splicing on an extra length of pile with fish plates or by use of site welding  Used as permanent retaining walls in dock, harbour, embankments, river banks and sea defence works Larssen sheet Overlapping Frodingham Interlocking Institute of Technical Education Page 12  ED5001FP Training Notes  Replacement Piles / Bored Piles Replacement piles or bored piles are piles formed by removing a column of soil and replacing it with in-situ concrete and in the case of composite piles, with precast and cast-in-situ concrete. i Percussion Bored Pile ii Rotary Bored Pile iii Micropile There is another type of pile, combination of driven and bored pile, termed as Driven-in- situ Concrete Piles or Franki driven in situ pile. It is suitable where a weak strata overlies a firm strata. Advantages and disadvantages of the two main types of piles are : i Displacement Piles Advantages  The quality and workmanship of the piles can be controlled. Disadvantages  Difficulty in transporting the complete length of piles especially through congested streets.  The driving process generates unacceptable noise and vibration.  Difficult to maneuver the long piles around urban area. ii Replacement Piles Advantages  Strata of soil can be explored and examined before construction.  No difficulty in transporting.  Lesser noise and vibration level Disadvantages  Replacement piles are cast-in-situ and therefore more difficult to construct and control. Institute of Technical Education Page 13  ED5001FP Training Notes Factors Determining the Choice of Piles  Cost effectiveness and expediency of installation  Soil Condition  Loadings  Presence of high water table which causes problems in constructing traditional foundation  Differential settlement Unit 3.2 : Types of Equipment and Methods for Pile Construction 3.2.1 Equipment for Driven Piles Construction A pile driver is a mechanical device used to drive piles into soil to provide foundation support for buildings or other structures. One traditional type of pile driver includes a heavy weight placed between guides so that it is able to freely slide up and down in a single line. It is placed upon a pile. The weight is raised, which may involve the use of hydraulics, steam, diesel, or manual labour. When the weight reaches its highest point it is then released and smashes on to the pile in order to drive it into the ground i Percussion Piles are usually installed by percussion method. In certain cases where underground obstructions such as large boulders are encountered, special shoes (i.e. conical, oslo point or pipe shoe) or pre-augering may be necessary. The driving hammer type (hydraulic or diesel) and size must be carefully selected to install the piles successfully without any damage to the pile itself. Two plumb guides at right angles to each other are normally used to ensure verticality of the pile during driving. Spirit levels and theodolites have also been proven useful Institute of Technical Education Page 14  ED5001FP Training Notes ii Vibratory Hydraulic vibration hammer is pile driver-extractor constructing machine that widely used for kinds of foundation construction projects. It uses its periodic vibration force to liquefy the surrounding soil so as to reduce the friction resistance to the pile, and enable the pile to enter the soil layer by making use of the pile weight and pile hammer weight, and pressing downward when necessary. It works in low noise with good pile-sinking effect, and it can work underwater. The hammer can be easily installed to the arm of the digging machine and can be driven by the hydraulic system of the digging machine. It is very easy to operate. It has unique hydraulic oil piping system and strong and long-lasting vibration force, with efficiency more than 90%. iii Hydraulic A hydraulic hammer is a modern type of piling hammer used in place of diesel and air hammers for driving steel pipe, precast concrete, and timber piles. Hydraulic hammers are more environmentally acceptable than the older, less efficient hammers as they generate less noise and pollutants. Institute of Technical Education Page 15  ED5001FP Training Notes iv The Mandrel The Mandrel is a heavy steel sheet that cradles the vinyl sheet and carries it into the ground. The Mandrel is then extracted, leaving the vinyl sheet in the ground. This technique is often used to install a low cost vinyl sheet deep in the ground as a remediation seepage barrier or cut-off wall v Alternative Methods Jetting Jetting involves the displacement of soil beneath the pile by high pressure jet of water. The pile is then sink under the action of its own weight. Screwing By attaching a large blade at the lower end of the pile, it can be screwed into the ground. Jacking This technique is useful where there is lack of headroom. In this case, pile is joined in short length by welding and inserted into ground by jacking it against a solid support located over the pile. Institute of Technical Education Page 16  ED5001FP Training Notes 3.2.2 Driving in Panels Two pairs of sheet are pitched and are driven to partial penetration at the end of each section of sheeting.. Two steel or timber walings are then bolted to these sheets to provide the guide for the remaining sheets which make up the panel and the panel comes in 12 to 24 sheets. The end pairs remain partially driven to provide a support to the adjacent panels. After which the panels itself proides the guide for the final driving of these sheets. Walings Driving in Panels Process of Withdrawing Sheet piles Holes are pre-drilled in the ends of the steel sheet piles. This not only allows for anchorage of the driving head but also facilitates the withdrawal. Additional benefit gained in both driving and removal of the piles if joints are well greased prior to driving. The ease of withdrawal depends on the nature of the soil, the depth of penetration into the ground and the method of driving.In order to avoid damage to the top of the pile, a special cap or extractor jaws should be used. Lightweight trench sheeting can frequently be extracted by the upward pull of a crane. Fot large pile sections, vibrators or an inverted double-acting hammer should be used in conjunction with a crane. When piles are driven by hydraulics system, then extraction can be effected by the same machine, with the rams wrking in the opposite direction. Institute of Technical Education Page 17  ED5001FP Training Notes 3.2.3 Installation Techniques of Driven piles i Prefabricated Driven Pile/Precast Concrete Pile  Precast Concrete piles are usually square in cross-section.  The concrete are normally reinforced or prestressed and manufactured in a casting yard.  The concrete used for these piles is usually of high strength to resist the stresses set up by the heavy driving forces.  In addition to the main reinforcement, links must be provided throughout with the centres closer at the head and shoe to resist the effects of driving.  A helmet must be provided over the head.  The installation of these piles is carried out using a pile driving rig and a suitable hammer.  Pre-tensioned, pre-fabricated piles are especially suitable for installation in very soft soils where significant tensile stress may be exerted during pile driving. Applications  Structures (bridges and viaducts)  Multi-storey buildings  Structures and buildings where the lowest elevation is below the water table, so that the piles are subjected to tensile stress due to under-pressure. ii Franki Driven Cast-in-Situ Piles  Installation Process i A plug of sand / stone is placed in the piling tube and compacted with a hammer. ii The tube is driven by applying blows of the drop hammer iii On reaching the founding level the tube is held by the extracting gear while the plus is expelled using blows of the hammer. iv Relatively dry concrete are expelled from the toe of the tube thus forming an enlarged base. v The reinforcing cage is placed in the tube which is then filled with high slump concrete. vi The tube is extracted by means of the extraction gear.  Advantages  The Franki pile is often a very economical system  There is an extensive range of pile sizes  The Franki pile has an excellent load / deflection performance Institute of Technical Education Page 18  ED5001FP Training Notes  Noise levels are relatively low  The Franki pile has excellent tension load capacity 3.2.4 Installation Techniques of Replacement/Bored Piles i Percussion Bored Pile Bored pile is another type of reinforced concrete pile which is used to support high building which has heavy vertical load. Bored pile is a cast- in-place concrete pile A hole is formed by dropping a digging tool which is a percussion cutter. When the tool is lifted up it brings some of the soil with it. As the hole is formed steel tubes which are made up of 1m lengths are screwed together are driven into the hole. When a firm stratum has been reached, a reinforcement cage is lowered and as the concrete is placed the steel tube is withdrawn. A B C D  Tube lining tamped into ground  Percussion cutter formed a hole by dropping and digging  When tool is lifted soil is lifted  When firm strata is  Hole is lined with reached , reinforcement steel tube is lowered  Concrete is poured Institute of Technical Education Page 19 and steel tube is  ED5001FP Training Notes ii Rotary Bored Pile The clay is extracted by the use of an open flight helical auger, which when rotated fills the flight with spoil. When the flights are filled, the auger is removed from the hole and the soil is deposited at a dump and the operation is repeated. Steel tubes are used if soil conditions demand. The tube are removed when the reinforcing cage has been positioned and as the concrete are being bored. Lining withdrawn as concrete lining level A rises Kelly bar B C D Shell lining through Non-cohesive non-cohesive soil soil Cohesive Soil  Soil is extracted using open flight helical auger  Reaming tool  Reinforcement cage is  Soil fills the auger which (enlarging) is is then lifted  Reaming completed lowered used to enlarge  Concrete is poured and  Steel tubes are used the base compacted where soil condition demands  Steel tubes are withdrawn Institute of Technical Education Page 20  ED5001FP Training Notes iii Micropile  Micropile is small diameter piles constructed by the drilling process and are often keyed into rock.  There is various diameter of micropile can be found in the market ranging from 100mm to 250mm.  Construction of mircropile is similar to any type of bored piles  It can be used in different soil condition as shown below: 1) Shallow Bedrock 2) Boulders and Cavities 3) Intermediate Hard Strata 4) Underpinning  In the past micropile was only used when the ground conditions warranted it because of considerations on cost and speed. Micropile is slow because of the drilling and flushing process, it might takes minutes or hours to complete.  But the trend is such, micropile is now gaining greater popularity and getting wider acceptance because of the requirement to comply with no noise and low vibration regulations, expecially in congested environments. It is widely used in housing area, school, hospital or any location which doesn’t allow to make noise while pile driving process. Institute of Technical Education Page 21  ED5001FP Training Notes iv Contiguous Bored Piles/Secant Piles Closely spaced bored piles can be used to form a retaining wall, perhaps for the construction of a deep basement or a cut and cover tunnel. The piles may be constructed so that they virtually touch each other (contiguous). The gaps between the piles can be grouted to form a watertight retaining wall. Alternatively (secant piles) every other pile may be constructed, with their centres less than two diameters apart. In-fill piles are then bored, cutting into the adjacent piles to form a continuous structure. To aid construction, the first sets of piles may be cast with a lower grade of concrete. These may not be load-bearing and act as ‘seals’ between the main load bearing piles. As the piles interlock, this form of construction leads to a more efficient form of structure. During excavation of the soil, the piles will generally require propping before the permanent floor and/or roof structure are completed. Because of the form of construction, the exposed piles will be fairly rough in appearance. Thus, in most cases, an inner wall, which may or may not be structural, will be built or some decorative surface applied, e.g. sprayed concrete or cladding. A method of drainage will generally be required between the piles and any inner wall. Institute of Technical Education Page 22  ED5001FP Training Notes 3.2.5 Equipment for Bored Piles Construction Basically a bored piling frame consists of three main components, namely A. The kelly bar B. A turntable C. The auger  Pile Frame a) Pile frame is used for guiding the pile during driving. b) It is made of tapered tower composed of steel. c) The members of the pile frame are:-  The leader  The sill  The winch. d) The leaders are two parallel members on the front of the frame which is used to guide the pile driving head. e) The sill is the horizontal member that rest on the ground and some are capable of swivelled. f) The winch is seated on the sill and has two drum fixed at the top, one drum for the hammer and the other for the pile. Institute of Technical Education Page 23  ED5001FP Training Notes Unit 3.3 : Methods of pile load testing Pile load test are usually carried out that one or some of the following reasons are fulfilled:  To obtain back-figured soil data that will enable other piles to be designed.  To confirm pile lengths and hence contract costs before the client is committed to overall job costs.  To counter-check results from geotechnical and pile driving formulae  To determine the load-settlement behaviour of a pile, especially in the region of the anticipated working load that the data can be used in prediction of group settlement.  To verify structural soundness of the pile. Institute of Technical Education Page 24  ED5001FP Training Notes 3.3.1 Constant Rate of Penetration (CRP) In the CRP (constant rate of penetration) method, test pile is jacked into the soil, the load being adjusted to give constant rate of downward movement to the pile. This is maintained until point of failure is reached. Failure of the pile is defined in to two ways that as the load at which the pile continues to move downward without further increase in load, or according to the BS, the load which the penetration reaches a value equal to one-tenth of the diameter of the pile at the base. In the cases of where compression tests are being carried out, the following methods are usually employed to apply the load or downward force on the pile:- A platform is constructed on the head of the pile on which a mass of heavy material, termed "kentledge" is placed. Or a bridge, carried on temporary supports, is constructed over the test pile and loaded with kentledge. The ram of a hydraulic jack, placed on the pile head, bears on a cross-head beneath the bridge beams, so that a total reaction equal to the weight of the bridge and its load may be obtained. Test being carried out Institute of Technical Education Page 25  ED5001FP Training Notes 3.3.2 Maintained Increment Load Test (MLT) The Maintained Increment Load Test, kentledge or adjacent tension piles or soil anchors are used to provide a reaction for the test load applied by jacking(s) placed over the pile being tested. The load is increased in definite steps, and is sustained at each level of loading until all settlements has either stop or does not exceed a specified amount of in a certain given period of time. Test Load Arrangement using Kentledge Institute of Technical Education Page 26  ED5001FP Training Notes Unit 3.4 : Design purpose and requirement of pile cap  A pile cap is a thick concrete mat that rests, slab or connecting beam which covers the heads of a group of piles tying them together so that the structural load is distributed and they act as a single unit.  The pile cap distributes the load from the columns, to the piles.  A similar structure to a pile cap is a "raft", which is a foundation floor resting directly on bedrock.  A metal cap which is placed, as temporary protection, over the head of a precast pile while it is being driven into the ground. Normally, pile foundations consist of pile cap and a group of piles. The pile cap distributes the applied load to the individual piles which, in turn,. transfer the load to the bearing ground. The individual piles are spaced and connected to the pile cap or tie beams and trimmed in order to connect the pile to the structure at cut-off level, and depending on the type of structure and eccentricity of the load, they can be arranged in different patterns. Figure bellow illustrates the three basic formation of pile groups. Institute of Technical Education Page 27  ED5001FP Training Notes a) PILE GROUP CONSIST OF ONLY b) PILE GROUP CONSIST OF BOTH c) SYMMETRICALLY ARRANGED VERTICAL PILES VERTICAL AND RAKING PILES VERTICAL AND RAKING PILES Basic formation of pile groups Q = Vertically applied load H = Horizontally applied load The stiffness of the pile cap will influence the distribution of structural loads to the individual piles. The thickness of the pile cap must be at least four times the width of an individual pile to cause a significant influence on the stiffness of the foundation. A ridgid cap can be assumed if the stiffness of the cap is 10 or more times greater than the stiffness of the individual piles, as generally true for massive concrete caps. A rigid cap can usually be assumed for gravity type hydraulic structures. Institute of Technical Education Page 28  ED5001FP Training Notes Anchorage & Lapping Length For 500 Grade steel , table below gives typical anchorage and lap lengths for ‘good’ and ‘poor’ bond conditions. Lap lengths provided (for nominal bars, etc.) should not be less than 15 times the bar size or 200mm, whichever is greater. Starter bars for columns should have a minimum horizontal leg of 450mm to ensure that the compression forces can be transmitted to the foundation. General Details of Pile Cap Institute of Technical Education Page 29  ED5001FP Training Notes Standard pile caps’ configuration of reinforcement that is normally adopted for standard pile caps is shown below : Bar spacing (EC2, Clause 9.8) Minimum spacing - 75mm (bars 40mm sizes and greater: 100mm) Pairs of bars: 100mm When considering the minimum spacing of bars of 32mm size or greater, allowance must be made for lapping of bars. Maximum spacing: 200mm Maximum spacing When Ast is 0.5% or less – 300mm; Between 0.5% and 1.0% – 225mm; 1.0% Ast or greater – 175mm Institute of Technical Education Page 30  ED5001FP Training Notes Mindmap for Unit 3 – Piles Institute of Technical Education Page 31  ED5001FP Training Notes Revision Questions for Unit 3 - Piles Institute of Technical Education Page 32  ED5001FP Training Notes Unit 4 : Reinforced Concrete Floor In building, slabs are generally used for floors and roofs and placed horizontally but they may be sloped to make ramps as used in multi-storey car parks or similar constructions. A staircase may be considered to be a sloped and cranked slab. One feature of a slab is that its width is usually much greater than its depth whereas a beam is generally deeper than its width. Slabs should be detailed in plan with sufficient sections to show the level of each layer of reinforcement. Minimum concrete cover to be 20mm or diameter of the bar whichever is the greater. Unit 4.1 : Different Types of Slab There are TWO main group of slabs namely :  Non-suspended slab  Suspended Slab 4.1.1 Non-suspended slab It is directly supported by the ground and prone to shrinkage cracking. Being non-structural member, the reinforcement for the slab is to provide mesh reinforcement in the top of the slab (25mm cover) to prevent cracking. The construction of non-suspended slab will be as follow : i) Hardcore bed  to fill in any small pockets which have formed during over site excavations.  to provide a firm and level base on which to place an over site concrete bed.  to help spread any point loads over a greater area.  to act against capillary action of moisture within the soil.  to resist the growth of vegetation. Hardcore is usually laid in 100 to 150 mm layers to the required depth and it is important that each layer is well compacted, usually with a rammer or a roller, if necessary, to prevent any unacceptable settlement beneath the solid floor. Institute of Technical Education Page 33  ED5001FP Training Notes ii) Blinding  to even off the surface of hardcore if a damp-proof membrane is to be placed under the concrete bed or a reinforced concrete bed.  prevent the damp-proof membrane from being punctured by the rough and open- textured surface of hardcore and  provide a true surface from which the reinforcement can be positioned Blinding generally consists of a layer of sand 25-50 mm thick or a 50-75 mm layer of weak concrete if a true surface for reinforced concrete is required. iii) Damp-proof membrane The membrane's purpose is to prevent dampness from the ground entering the building through the concrete slab. The material should stay intact without tearing or puncturing even when workers walk over it while they fix reinforcement in the floors and lay concrete. The membrane should be turned up at the edges to meet and blend with the damp-proof course (dpc) in walls to prevent any penetration of moisture by capillary action at edges of the bed (Fig. 1). Suitable materials for damp-proof membranes are:  Waterproof building papers.  Heavy-duty polythene sheet.  Hot poured bitumen - should be at least 3 mm thick.  Cold applied bitumen/rubber emulsions - should be applied in not less than 3 coats.  Asphalt - could be dual purpose finish and damp-proof membrane. The position of a damp-proof membrane, whether above or below the concrete bed, is a matter of individual choice. A membrane placed above the bed is the easiest method from a practical aspect and is therefore generally used. A membrane placed below the bed has 2 advantages: (i) it will keep the concrete bed dry and in so doing will make the bed a better thermal insulator, and (ii) during construction, it will act as a separating layer preventing leakage of the cement matrix into the hardcore layer which could result in a weak concrete mix. Institute of Technical Education Page 34  ED5001FP Training Notes iv) Concrete bed or slab 4.1.2 Suspended slab The common types of suspended floor slab are:  One way slab  Two way slab  Cantilever slab  Flat slab One Way Slab Slab spanning in one direction only, reinforcement is placed in one direction with distribution bars introduced at right angle to hold the main bars in position while concreting. The symbol used in structural drawing for one-way spanning slab is Two way spanning slab Two way spanning slabs are supported on four sides of beam. Each beam carries part of the load, the remainder of the load being carried by the beams which span in the other direction. Main bars are provided in two directions at right angle to resist the bending stress. The symbol used in structural drawing for two-way spanning slab is denoted as Cantilever slab It is supported by one beam only. Main bars should be provided at top of supports & curtailed at ½ span of the slab and at bottom of mid-span. Distribution bars to be provided as in simply supported slab. For top layer of bars over supports, distribution steel to be placed at bottom of top main steel.The symbol used in structural drawing for cantilever slab is denoted as Institute of Technical Education Page 35  ED5001FP Training Notes Flat Slab Flat slab floor has uniform thickness, supported by columns only. No beam is required. The heads of the columns are expanded (mushroom-headed columns) to provide adequate resistance to compression stresses in the bottom of the slab. This column heads will be square or circular depending upon the shape of the columns. In some circumstances it is necessary to thicken the slab over this cup to form what is termed a drop panel. It is normally used in situations where the loads are heavy and are uniformly distributed over the whole floor. It is, therefore, suitable for such building types as warehouses and car park. Unit 4.2 : Curtailment of bar for Slab A reinforcing bar is terminated for one or more of the following reasons: a) to fit the member b) to economise on steel c) to make construction easier d) stock lengths of bars The surface condition of the bar will also affect the anchorage bond; the rougher the surface the better the bond between the concrete and the steel. As the magnitude of the bending moment on a beam decreases along its length, the area of bending reinforcement is reduced by curtailing bars, as they are no longer required. Each curtailed bar should extend beyond the point at which it is no longer needed so that it is well anchored into the concrete. Curtailment for slab based on British standard will be as such : Institute of Technical Education Page 36  ED5001FP Training Notes (D) END SUPPORT DETAILS Institute of Technical Education Page 37  ED5001FP Training Notes Based on EURO Code : One and Two way slab Span and internal support Minimum pitch distance for bars is recommended to be 75mm (100mm for laps) Maximum pitch of bars : Main bars :3h≤400mm (in areas of concentrated loads 2h≤250mm) Secondary bars : 3.5h ≤ 450mm ( in areas of concentrated loads 3h≤400mm) Institute of Technical Education Page 38  ED5001FP Training Notes Cantilevered Slab Institute of Technical Education Page 39  ED5001FP Training Notes One and Two Way Slabs External Unrestrained Support Institute of Technical Education Page 40  ED5001FP Training Notes One and Two Way Slabs External Restrained Support Institute of Technical Education Page 41  ED5001FP Training Notes In general, when there is opening for mechanical and electrical services, the following details will be used : British Standard : For EuroCode , the trimming bars to be extended 45 minimum Institute of Technical Education Page 42  ED5001FP Training Notes British Standard : For EuroCode , the trimming bars to be extended 45 minimum British Standard : For EuroCode , the trimming bars to be extended 45 minimum Institute of Technical Education Page 43  ED5001FP Training Notes Revision Questions for Unit 4 - Slab Institute of Technical Education Page 44  ED5001FP Training Notes Unit 5 : Reinforced Concrete Beam Unit 5.1 Distance Between Bars The required minimum bar spacing are aimed primarily :  to obtain adequate compaction and bond  to ensure that the space between top bars is sufficient for vibrators to be used, which is commonly of 40mm diameter or more Individual bars or pairs of bars one above the other: Minimum horizontal pitch  75mm (sufficient space must be allowed for insertion of poker vibrator)  100mm for pairs of bars Minimum vertical pitch  25mm or bar diameter, whichever is greater Maximum pitch distance  Tension bars, assuming service stress is at 310MPa, maximum spacing = 165mm  Compression bars, 300mm Beam with depth 1000mm or more For beams with a total depth of 1000mm or more additional reinforcement is required to control cracking in the side of faces of the beam. As a simplification bars (16mm) should be placed along the sides inside the links at a maximum pitch of 250mm. Link spacing Minimum pitch 100mm or [50 + 12.5 (No. of legs)]mm, whichever is greater. This ensures that the space taken up by links along the beam is not overlooked. Maximum pitch 300mm or 0.75d or 12 × diameter of compression bar, whichever is least. Maximum lateral pitch of legs 600mm or 0.75d. The distance of a tension or compression bar from a vertical leg should not be greater than 150mm. Institute of Technical Education Page 45  ED5001FP Training Notes Unit 5.2 Concrete Cover Cover to steel reinforcement is necessary to ensure:  The bond of the steel with the concrete so that both steel and concrete are effective in resisting the applied forces.  It is also necessary to prevent corrosion of the steel reinforcement and to resist damage by fire. Accordance to Eurocode , (EC2, Clause 4.4.1.3) For Beam & Column: Internal use: 30mm + Δcdev (Concrete inside buildings with low air humidity) External use: 35mm + Δcdev (Corrosion induced by carbonation) For Slab & Wall: Internal use : 15mm or bar diameter + ∆Cdev , whichever is greater External use : 35mm + ∆Cdev For Foundation : Large foundations, pile caps, pad and wall footings: 75mm Bottom cover for piled foundations: 100mm The extra cover recognises that piles project into the cap and the reinforcement mat is laid on them. Earth face: 45mm + Δcdev External exposed face: 35mm + Δcdev (other than earth faces) Internal face: (25mm or bar size) + Δcdev, whichever is the larger. This refers to the top of ground slabs, inside trenches, etc. ∆Cdev = Allowance deviation in design, 0 to 10mm Unit 5.3 Area of Reinforcement Minimum Area of Reinforcement For most purposes, thermal and shrinkage cracking may be controlled within acceptable limits by use of minimum reinforcement quantities specified by Eurocode, although requirements of water-retaining structures will be more stringent. Slab For concrete Grade 30/37 and fyk = 500 MPa As, min 0.0015 bt d Preferred minimum diameter: 10mm. Beam Tension reinforcement For concrete Grade 30/37 and fyk = 500MPa As, min 0.0015 bt d Institute of Technical Education Page 46  ED5001FP Training Notes where bt is the mean width of the tension zone; d is the effective depth Compression reinforcement Asc,min 0.002 Ac Transverse reinforcement in top flange As, min 0.0015 hf l where hf is depth of flange; l is the span of the beam Minimum diameter 12mm Links Asw/s bw H 0.085% where Asw is the cross-sectional area of the 2 legs of link bw is the average breadth of concrete below the upper flange s is the spacing of link (≤15 of main compression bars) Preferred minimum diameter 8mm Column 0.002Ac or 0.10 NEd/fyd, whichever is greater where Ac is the area of concrete; NEd is the design axial compression force; fyd is the design yield strength Recommended minimum bar diameter is 16mm Wall Vertical reinforcement - 0.002 Ac (half placed in each face) Minimum bar diameter to ensure robust cage: 12mm Horizontal reinforcement (in each face) - 25% of the vertical reinforcement or 0.001 Ac whichever is greater Preferred minimum bar diameter: ¼ × diameter of vertical bars. Maximum Area of Reinforcement For Beam, slab and wall , Maximum percentage of gross cross section: 0.04 Ac For Column, Maximum area of reinforcement should not exceed0.04 Ac unless it can be shown that any resulting congestion of reinforcement does not hinder the ease of construction. At laps the maximum area of reinforcement should not exceed 0.08 Ac. Institute of Technical Education Page 47  ED5001FP Training Notes Limit State Design The design of each individual member or section of member must satisfy two separate criteria: i) The ultimate limit state, which ensures that the probability of the whole or part of the structure failing is acceptably low. Hence, it concerns the safety of people and structure. ii) The limit state of serviceability, which satisfactory behavior under service load (or working) loads. It concerns with the functioning of structure under normal use, comfort of people , appearance of the construction works. Loads Actions/loads onto the structure shall be classified by their variation in time as follows: Permanent actions (G), e.g. self weight of structures, fixed equipment and road surfacing, and indirect actions caused by shrinkage and uneven settlements; Variable actions (Q), e.g. imposed loads on building floors, beam and roofs, wind actions or snow loads; Accidental actions (A), e.g. explosion or impact from vehicles In accordance to Eurcode, building is categorize accordance to the usage as below: Category Specific Use Example Imposed Loads on floor, balconies and stairs in buildings (kN/m2) A Areas for domestic Rooms in residential buildings, 1.5 to 2.0 (Floor) and residential hospitals, hotels and hostels 2.0 to 4 (Stairs) activities 2.5 to 4(Balconies) B Office areas 2.0 to 3.0 C Areas where people C1: Area with tables e.g areas in 2.0 to 3.0 may congregate schools, cafes, dining halls, (with the exception receotions of areas defined C2: Areas with fixed seats e.g 3.0 to 4.0 under caregory A, areas in churches, theatres, B, and D) lecture halls, assembly hall C3: Areas without obstacles for 3.0 to 5.0 moving people: e.g. areas in museums, exhibition room, access areas in public and administration buildings C4 Areas with possible physical 4.5 to 5.0 activities: e.g dance halls, stages C5: Area susceptible to large 5.0 to 7.5 crowds, e.g. in buildings for public events like concert halls, sports hall D Shopping area Areas in general retail shops 4.0 to 5.0 Institute of Technical Education Page 48  ED5001FP Training Notes Partial Safety Factor for Load Design load is obtained by multiplying the characteristic load by a partial safety factor which is introduced to take account of : a) possible unusual increase in loads b) inaccurate assessment of effects of loads c) variations in dimensional accuracy achieved in construction, and d) the importance of the limit state being considered In EC2 Cl 5.1.3, Table 1.10a, load combination and their partial safety factor is as follows: 1.35Gk + 1.5 Qk or 1.35Gk + 1.5 Wk In EC2 Cl 5.1.3, Table 1.10a, load combination 1.35Gk+1.5Qk+0.75Wk or 1.35Gk+1.05Qk+1.5Wk ( determine which is the more important load factor) Gk = Permanent Load / Dead Load Qk = Variable Load / Imposed Load Wk = Wind Load Partial Safety factor for Material The characteristic strength refers to the strength of the set of test pieces. Some loss of strength of the materials could occur during construction, due to segregation in transport, inadequate compaction, bad curing, etc. These effects are allowed for in design by applying a partial safety factor for strength. For concrete, ‫ ال‬c = 1.5 For steel, ‫ ال‬s = 1.15 Institute of Technical Education Page 49  ED5001FP Training Notes Design of Singly Reinforced Rectangular Beam Section Institute of Technical Education Page 50  ED5001FP Training Notes Design Procedure 1. Calculate K = M/bd2fck 2. Check if K ≤ K lim -> Compression steel is not required 3. Determine the lever – arm , z , from the equation : 0.5 √ 0.25 /1.134 4. Calculate the required area of steel: As=M/0.87fykZ 5. Select bar sizes. Check if area is within the required limits (maximum and minimum) Institute of Technical Education Page 51  ED5001FP Training Notes Practice Questions for distance between bar Institute of Technical Education Page 52  ED5001FP Training Notes Practice Questions for Area of Reinforcement Required Institute of Technical Education Page 53  ED5001FP Training Notes Practice Questions for Limit State Loading Calculation & Bending Moment, Shear Force Institute of Technical Education Page 54  ED5001FP Training Notes Practice Questions for Design of Singly Reinforced Concrete Beam Sections Institute of Technical Education Page 55  ED5001FP Training Notes Bar Table (Area of Bars) Sectional area of groups of bars (mm2) Bar Number of bars Size (mm) 1 2 3 4 5 6 7 8 9 10 6 28.3 56.6 84.9 113 142 170 198 226 255 283 8 50.3 101 151 201 252 302 352 402 453 503 10 78.5 157 236 314 393 471 550 628 707 785 12 113 226 339 452 566 679 792 905 1020 1130 16 201 402 603 804 1010 1210 1410 1610 1810 2010 20 314 628 943 1260 1570 1890 2200 2510 2830 3140 25 491 982 1470 1960 2450 2950 3440 3930 4420 4910 32 804 1610 2410 3220 4020 4830 5630 6430 7240 8040 40 1260 2510 3770 5030 6280 7540 8800 10100 11300 12600 Sectional areas per metre width for various bar spacings(mm2) Bar Spacing of bar Size (mm) 50 75 100 125 150 175 200 250 300 6 566 377 283 226 189 162 142 113 94.3 8 1010 671 503 402 335 287 252 201 168 10 1570 1050 785 628 523 449 393 314 262 12 2260 1510 1130 905 754 646 566 452 377 16 4020 2680 2010 1610 1340 1150 1010 804 670 20 6280 4190 3140 2510 2090 1800 1570 1260 1050 25 9820 6550 4910 3930 3270 2810 2450 1960 1640 32 16100 10700 8040 6430 5360 4600 4020 3220 2680 40 25100 16800 12600 10100 8380 7180 6280 5030 4190 Institute of Technical Education Page 56  ED5001FP Training Notes Unit 5.4 Curtailment of Bar for Beam Accordance to Eurocode Hanger bars At least 20% of maximum support area or sufficient for compression area required, whichever is greater, should be carried to 25mm from each support. Diameter: 16mm (recommended size). Top bars at internal support (Simplified rules) At least 60% of the maximum support area should continue to a point where the hanger bars are sufficient, plus a tension lap, or to a point of zero moment if the nominal hanger bars do not satisfy the minimum spacing rules for tension reinforcement. Where no information is given concerning curtailment, this reinforcement should extend 0.25L from the support face. No reinforcement should extend less than 0.15L from the support face, nor 45 times the bar diameter from the support face, whichever is greater, where L is the effective span of beam. Bottom splice bars at internal support The area should not be less than the minimum percentage required. At least 30% of the maximum span area should be supplied, if the simplified rules are used. Bottom bars in span (Simplified rules) The area should not be less than the minimum percentage required. At least 30% of maximum span area for continuous beams and 50% of maximum span area for simply supported beams, is continued to 25mm from the support. The remainder extends to within 0.15L of internal supports, 0.1L of exterior supports and 0.08L of simply supported beam supports. The point of support may be considered up to d/2 inside the face. U-bars at end of beam These should provide the tension area required for support moment or 30% of maximum span area (50% for simple supports), if the simplified rules are used, whichever is greater. The length of the top leg of the bar should be calculated in the same way as for internal support bars. The bottom leg of the bar extends to the same distance into the span as for internal support splice bars. Institute of Technical Education Page 57  ED5001FP Training Notes Institute of Technical Education Page 58  ED5001FP Training Notes Beam Span and Support Details Institute of Technical Education Page 59  ED5001FP Training Notes Cantilevered Beam Institute of Technical Education Page 60  ED5001FP Training Notes Accordance to British Standard Institute of Technical Education Page 61  ED5001FP Training Notes Unit 6 : Reinforced Concrete Column & Schedule Columns in a structure carry the loads from the beams and slabs down to the foundations, and therefore they are primarily compression members, although they may also have to resist bending forces due to the continuity of the structure. Other compression members are often termed "columns" because of the similar stress conditions. Materials used for column:  In ancient time, columns were constructed of stone, some out of a single piece of stone, usually by turning on a lathe-like apparatus.  In modern time, columns are constructed out of steel, in-situ or precast concrete, or brick. Extension of Column  When a column is too long to be built or transported in one piece, it has to be extended or spliced at the construction site.  A reinforced concrete column is extended by having the steel reinforcing bars protrude a few inches or feet above the top of the concrete, then placing the next level of reinforcing bars to overlap, and pouring the concrete of the next level.  A steel column is extended by welding or bolting splice plates on the flanges and webs or walls of the columns to provide a few inches or feet of load transfer from the upper to the lower column section.  A timber column is usually extended by the use of a steel tube or wrapped-around sheet-metal plate bolted onto the two connecting timber sections. Unit 6.1 : Structural Behavior for Columns Column is classified in the following manners: i) Braced Column  When the lateral loads are resisted by walls or some other form of bracing.  With a braced column the axial forces and moments are caused by the dead and imposed load only. ii) Unbraced Column  Where the lateral loads are resisted by the bending action of the columns. Institute of Technical Education Page 62  ED5001FP Training Notes  An unbraced column the loading arrangements which include the effects of the lateral loads must also be considered iii) Short and Slender Column Accordance to British Standard and Eurocode, there is differences to categorized the above, it is summarized as per the table below : Unit 6.2 : Column Failure Modes i) Crushing Short columns usually fail by the material crushing. Every building material can withstand a distinct amount of compressive stress before it crushes. This value has been determined by laboratory tests and is known as the compressive strength of a material. ii) Buckling A slender column is liable to fail by buckling. The end moment on a slender column cause it to deflect sideways, it means that the column will probably fail in bending! As a column is loaded, it is likely to bend about the weak axis of the cross-section. A column buckles when it bends about an axis. This is a stability failure. When long columns are buckled, most of them are broken into two pieces of columns of different length. For an intermediate length compression member, kneeling occurs when some areas yield before buckling, as shown in the figure below Institute of Technical Education Page 63  ED5001FP Training Notes In summary, the failure of a compression member has to do with the strength and stiffness of the material and the geometry (slenderness ratio) of the member. Whether a compression member is considered short, intermediate, or long depends on these factors Unit 6.3 : Column Schedule and Loading Plan A column schedule displays a series as a set of vertical bars that are grouped by category. Column schedules are useful for showing data changes over a period of time or for illustrating comparisons among items, and displays series as sets of vertical bars with varying beginning and end points. Loading plan is used to capture all the loads transferred from roof to pilecap level. The total load for each pilecap / pile group will be indicated next to the respective column / wall position. This amount will be used for the design of column, pilecap and piles. Institute of Technical Education Page 64  ED5001FP Training Notes Bar Spacing Preferred minimum spacing Main bars - 75mm (bars 40mm size and greater: 100mm) Pairs of bars - 100mm When considering the minimum spacing of bars of 32mm size or greater, allowance must be made for lapping of bars. Preferred maximum spacing Compression bars - 300mm, provided that all main bars in the compression zone are within 150mm of a restrained bar Tension bars - 175mm Anchorage & Lap Length Minimum anchorage length - Greater of 10 or 100mm For 500 Grade steel Link The size of link should be the greater of a quarter the maximum size of longitudinal bar and 8mm An overall enclosing link is required together with additional restraining links for alternate main bars or bundle of bars. Provided that all other main bars in the compression zone are within 150mm of a restrained bar no other links are required. Otherwise additional links should be added to satisfy this requirement. Additional links are not required for circular columns. Institute of Technical Education Page 65  ED5001FP Training Notes Maximum spacing of links The least of: 20 times the size of the longitudinal bars, or the lesser dimension of the column, or 400mm. Column Bottom Details: Institute of Technical Education Page 66  ED5001FP Training Notes Column Intermediate Details Institute of Technical Education Page 67  ED5001FP Training Notes Column Intermediate Details – off set or stepped column Institute of Technical Education Page 68  ED5001FP Training Notes Top Details A : Detail ‘A’ applies when slab depth is not less than: – 200 using 20 size of column bars – 250 using 25 size of column bars – 300 using 32 size of column bars otherwise Detail ‘B’ applies Details B Institute of Technical Education Page 69  ED5001FP Training Notes Revision Questions for Unit 6 - Column Institute of Technical Education Page 70  ED5001FP Training Notes Unit 7 : Formwork and Falsework Unit 7.1 : Falsework Falsework consists of temporary structures used in construction to support structures in order to hold the component in place until it is constructed and able to support itself. Falsework also includes temporary support structures for formwork and scaffolding to give workers access to the structure being constructed. It consists of the following:  Formwork covers all types of moulds for cast-in-situ concrete  Mould boxes for precast concerte units such as lintels, wndow sills and coping  Shuttering refers only to the flat panels which are fixed together to support and make the formwork complete  Centering refers to shuttering for circular members such as arches Unit 7.2 : Formwork Formwork is the term given to either temporary or permanent moulds into which concrete or similar materials are poured. Formwork sometimes also known as shuttering or casing is the boarding or sheeting which is erected to contain and mould the wet concrete during the placing or initial hardening. It consists of :  Soldier - The strong stiff vertical member supporting and stiff anchoring vertical forms.  Tie - Steel bolts of wires which anchor the form faces in vertical work together. Generally used in conjunction with spacers  Struts - Compression members designed to hold the formwork stable Materials used for making Formwork i timber ii steel iii fiberglass iv plastic General Requirements of Formwork i Srength The formwork should be strong enough to carry  The dead weight of concrete  The live load from men and machines used in the placing of the concrete  The impact loading caused by concrete being discharged into the fomwork Institute of Technical Education Page 71  ED5001FP Training Notes ii Alignment For good alignment the joints should be smooth and no surface irregularities should be apparent on the finish unit iii Surface Finish Surface finish of concrete may be  Smooth  Textured  Exposed aggregates Type of finishes may be achieved by the use of different surfaces on the formwork iv Economy In order to keep the waste of formwork to a minimum the correct usage and repeated reuse must be considered v Rigidity vi Tightness vii Durability viii Ease of Placing concrete ix Ease of Stripping Precaution before “Striking Formwork” Before formwork can be removed the concrete must have :-  Sufficient strength to support itself  Sufficient surface hardness to resist damage  Sufficient curing to give a reasonable colour finish to the concrete (too soon an exposure to the atmosphere will cause discolouring) Treatment of Formwork i The nature and treatment of working faces of formwork will affect the surface of the concrete. ii The nature of treatment includes the following:  All working surface should be treated with mould oil to prevent concrete adhering to them  For exposed aggregate surface a retarding liquid may be