How to calculate quantity of steel for beam ?
Reinforced cement concrete work is usually estimating under two items. The concrete work including centring and shuttering, and binding of steel bars in position is taking under one item in cu.m (cu ft). The steel reinforcement and its bending are taking under a separate item in quintal (cwt). The quantity of steel being small no deduction is making for steel from the volume of concrete. Binding wire is not taking separately but included in item of R.C.C. work.
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Centring and Shuttering
Centring and shuttering may also be taken under a separate item is sq m (sq ft). Bending and binding of steel may also be taken separately in quintal (cwt).
Steel reinforcement is calculating as per actual requirement as laying in position including over-laps, hooks, cranks, etc. It is determining from the detail drawings. If the detail drawings are not available the steel reinforcement may be calculating approximately on the percentage basis of concrete. The density of steel may be taking as 78.5 quintal per cu m or 7.85 grams per cu m (490 lbs per cu ft). The percentage of steel reinforcement depends on the design of the structure. In absence of detail design the percentage for steel concrete may be taking approximately as given below:-
- Lintel, slabs, etc. 0.7 to 1.0%
- Beams 1.0 to 2.0%
- Columns 1.0 to 5.0%
- Foundation raft, footing, etc. 0.5 to 0.5%
For small span and light load less steel is requiring and for bigger span and heavier load greater amount of steel is requiring.
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R.C.C. work may also be taking as complete work in cu m including steel reinforcement and centring, and shuttering, bending of steel to the requiring shape, placing and binding of steel with G.I. wire in position.
The expose surfaces of R.C.C. work are fair finish and the centring and shuttering are made in such a way as to give the surface smooth and even finish. If require thin plastering of rich cement mortar may be apply but the work of plastering is not taking separately nor the thickness of plastering is measure with the concrete.
Same principle is adopting for reinforced brick (R.B.) work but the expose surface of R.B. work is finish with 12 mm thick plastering in 1 : 2 to 1 : 3 cement mortar. The item of plastering is taking separately under separate item.
In R.C.C. work the end or side covers for steel bar may be taking as 4 cm to 5 cm. The bottom and top covers may be taking as 1.2 cm to 2 cm for slab and 2.5 cm to 5 cm for beams.
Hook and Cranked bent up bars
The length of one hook may be taking as 9 Diameter of bar and the total length of straight bar hook at both ends may be taking as L + 18 Diameter.