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# Construction Insitu Rc Suspended Floors Using Bm Bending Moment Formula Maths

## by Dan Ross, Lecturer on Mar 16, 2009

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Practical maths

Practical maths
Construction Insitu RC Suspended Floors using BM Bending moment formula maths

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## Construction Insitu Rc Suspended Floors Using Bm Bending Moment Formula MathsPresentation Transcript

• Reinforced Concrete Suspended Floors and beam design
• Ribbed Floors are used to….
• reduce the overall depth of a traditional cast insitu reinforced concrete beam and slab suspended floor
• The basic concept is to replace the wide spaced deep beams with narrow spaced shallow beams or ribs which will carry only a small amount of slab loading .
• These floors can be designed as one or two way spanning floors.
• One way spanning ribbed floors are sometimes called trough floors
• the two way spanning ribbed floors are called coffered or waffle floors.
• Ribbed floors are usually cast against metal, glass fibre or polypropylene They are made in preformed moulds which are temporarily supported on plywood decking joists and props
• From the following diagram make sure that you note down the joist data then work out the total load per joist
• Answer: Total load (W) per joist = 5m X 0.4m X 2.25 kN/m 2 = 45 kN
• On the following page you should
• Make a note of the bending moment (BM) formula
• Make a note of the data
• Find the depth d , of the joist
• Answer The formula for the Bending moment of a beam is …. Transpose the BM formula to find, d. Answer from standard sizes TN4 Work slowly through the following
• Joist and Beam Sizing for calculating overall dimensions alone is insufficient.
• checks should also be made to satisfy: resistance to deflection
• resistance to shear .
• Deflection — should be minimal to prevent damage to….
• plastered ceilings.
• An allowance of up to 0003 X span is normally acceptable; for the last example this will be:- 0003 X 5000mm = 15mm
• (Use b and d from before) The formula for calculating deflection due to a uniformly distributed load is: Answer Answer TN4 Use the nearest commercial size to find I then find ,d. Answer