Reinforcement
Reinforced concrete is the most commonly used structural material in engineering construction. Although concrete is strong in resisting compressive stress, it is weak in tension. Hence to withstand tensional stresses, steel is need in concrete. The reinforcement in concrete may be simple bars or rods bend and tied to a given schedule with stirrups. The nominal diameters of bars used at site were T10, T12, T16, T20, T25, T32, R6, R8 and R10. We used Tor steel bars for the reinforcement of columns, beams and slabs. Mild steel bars were used to construct stirrups. Because mild steel bars can be bent easily reinforced concrete consists of reinforcement bars embedded in concrete. It is practically possible to have these two materials combined, because coefficient of thermal expansion for both steel and concrete are approximately equal.
Tor Steel – yield strength – 500 N/mm2 – symbol “T”
Mild Steel – yield strength – 250 N/mm2 – symbol “R”
Bar Mark Notation
Lapping
Lapping is required when a bar isn’t long enough or a joint is required. Normally lapping position is at where near the minimum shear force acting. Those two bars were physically connected and wired together. In this site lap length is 52D, mean 52 times the bar diameter, if both bars are at same diameter. When lapping two bars of different diameters, the lap length is considered as 52 times the smaller diameter. (Figure1.9)
Crank length also define as
1:10 slope
Figure1.9. Lapping
Stirrups
Stirrups are made by tor steel or mild steel that is bent into a rectangular or a circular shape which typically wraps around the main bars of the column or beam. (Figure 1.10) This is done to prevent shear failure which is usually diagonal in case of cracks.
Figure 1.10. Rectangular Stirrup
Clear cover
Clear cover is the distance from the steel bar to the nearest edge of the structure. It was very important to provide a sufficient clear cover to the reinforcement to protect it from corrosion from soil, air, water and also from the fire.
Minimum Concrete Cover for Reinforcement shall be given as below,
• Concrete surfaces protected against weather or aggressive condition - 25mm (interior areas)
• Concrete surfaces exposed to rain or alternate wetting & drying, continuously under water or contact with soil-50mm
Cover blocks were used to maintain the clear cover. They were made up of 1:1 ratio of cement mortar.
Cover blocks must have an extra strength to prevent the breaking them when concreting and vibrating.
Cover blocks should be immersed in water for 28 days to get the maximum strength.
Barcode
Barcode is useful to give details of steel bars, which is included the type of material, diameter, the number bars, location of the bars and bar spacing.
240Y-10-16 -200-T
Here,
6 - No of bars
Y - Type of steel (Y-tor steel, R-mild steel)
10 - Diameter of steel in mm
08 - Bar mark
150 - Spacing between bars
T - Bar location (T-top, B-bottom)
Bar Bending and Scheduling
All the bars were cut by using steel cutter to given bar schedule. The bar schedule has bar mark, spacing, bar length, number of bars, shape and bending dimensions. Then according to our detail drawing of column or beam or slab anchorages were done. So BBS is very convenience to bar bender.
CALCULATION OF WEIGHT OF THE STEEL
When we do the labour payment for the reinforcement work, total length of the reinforcement is necessary to calculate the weight of the steel. For that, weight of the steel per meter can be calculated using following formula.
Weight of the steel per meter = D2 / 162.16 (D- diameter of the bar)
Total weight of the steel = Weight per meter x Total length
ADVANTAGES of Bar Bending Schedule
• Load to the economical bar cutting, reduce bar, cutting wastage.
• Easy to manage reinforcement stock required for identified time duration.
• Help to fabrication of reinforcement with structure.
• To quantify the material usage for billing purpose.
6.3. LAPPING
Reinforcement Check
The consultant engineers were checked the reinforcement arrangement for issuing the approval for concreting. Basically they were checked whether the reinforcement arrangement was prepared according to the structural drawings and specifications. This includes the following important points to be checked.
• Size of the bar
• Length of the bar
• Location of the bar
• Position of the bar
• Number of bars
• Lap lengths
• Correct cover of reinforcements and cover blocks
• Spacing (in slab reinforcements and stirrups)
• Dimensions of the element thickness of a slab, depth and width of a beam
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