How to determine the quantity of Reinforced Concrete & Rate Analysis
The rate analysis of reinforced concrete is done with the following steps :-
1- Computation of number of labour and equipment, quantity of materials, miscellaneous items necessary for a specific quantity of reinforced concrete.
2- Ascertainment of structural component for which the rate analysis should be accomplished. It happens because of the amount of RFT differs for slabs, beams, columns, or foundation. Generally, the quantity of other materials like cement and aggregate remains equivalent for the similar mixture design. For labour, the rates for RFT work will be adjusted for various structural components since the amount of reinforcement steel is altered. The quantity of materials like cement, sand and coarse aggregates is adjusted as per the mix design, as for instance, M15 (1:2:4), M20 (1:1.5:3), M25, M30 and so on.
After that, the rate analysis for 1 m3 of reinforced concrete should have been worked out.
Step 1: Computation of Materials:
Materials contain: cement, sand, coarse aggregate and steel reinforcement. As for instance, suppose the mix design is M20 (1:1.5:3). The necessary dry volume of total materials is taken as 1.54 times the wet volume of concrete, as there are voids in sand and aggregates. So, the total volume of required materials is taken as 1.54 m3 for 1 m3 of wet concrete.
1) No. of Cement Bags:
Volume of cement necessary for 1 m3 of concrete = [1 x 1.54] / [1 + 1.5 + 3] =0.28 m3
Number of bags of cement = Volume of cement necessary for 1 m3 of concrete / (volume of one bag of cement = 0.0347 m3) = 0.28 / 0.0347 = 8.07 bags.
2) Volume of Sand:
Volume of sand necessary for 1 m3 of concrete = [1.5 x 1.54] / [1 + 1.5 + 3] =0.42 m3
3) Volume of Coarse Aggregate
Volume of coarse aggregate necessary for 1 m3 of concrete = [3 x 1.54] / [1 + 1.5 + 3] =0.84 m3
4) Amount of Steel Reinforcement:
The types of structural element will find out the quantity of steel necessary.
The amount of necessary steel is measured with the following two approaches:
(a) Based on the structural drawings, the total weight of necessary steel is divided with total volume of concrete for different components. It provides the weight of reinforcement for each cubic meter of concrete.
(b) Approximate method by assuming the percentage of reinforcement provided below. These values are modified for several structures and previous experiences.
• For slabs = 1.0 % of concrete volume.
• For Beam = 2 % concrete volume.
• For column = 2.5 % of concrete volume.
Suppose, the reinforcement essential is 2.5%, weight of steel= [2.5 / [100 x 1] x 7850] = 196.25 kg.
Step 2: Labour and Equipement Requirement for 1 m3 of reinforced concrete
Labours are provided to execute a specific job within certain days:
• Mason: One mason is necessary for 0.37 days.
• Labour: One Unskilled labour is necessary for 3.5 days.
• Water carrier: One water carrier is necessary for 1.39 days.
• Bar Bender: One bar bender is necessary for 100 kg of steel as for 1 day.
• Mixer Operator: One mixer operator is necessary for 0.0714 days.
• Vibrator Operator: One vibrator operator is necessary for 0.0714 days.
Equipment and other charges are taken as a percentage of total material and Labour cost. Consider it as 7%.