RCC structure : Beams

by: aayush210789

IDesign Procedure
  Design procedure 
 The procedure for the design of beam may be summarized as follows: 
1. Estimation of loads 
2. Analysis 
3. Design 
1. Estimation of loads 
The loads that get realized on the beams consists of the following: 
  • Self weight of the beam. 
  • Weight of the wall constructed on the beam 
  • The portion of the slab loads which gets transferred to the beams. These slab loads are due to live loads that are acting on the slab dead loads such as self weight of the slab, floor finishes, partitions, false ceiling and some special fixed loads.  
The dead loads are calculated based on the density whereas the live loads are taken from IS: 875 depending on the functional use of the building. 
IIImpose (Live) load - IS 875
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IIIStructural Analysis
 2. Analysis 
For the loads that are acting on the beams, the analysis is done by any standard method to obtain the shear forces and bending moments
IVExample - Analysis of simply supported beam

Deflection of Simply Supported Beam
VCantilever Beam deflection

Cantilever Beam Deflection
 3. Design 
  • Selection of width and depth of the beam. The width of the beam selected shall satisfy the slenderness limits specified in IS 456 : 2000 clause 23.3 to ensure the lateral stability. 
  • Calculation of effective span (le) (Refer clause 22.2, IS 456:2000) 
  • Calculation of loads (w)
  • Calculation of critical moments and shears. The moment and shear that exists at the critical sections are considered for the design. Critical sections are the sections where the values are maximum. Critical section for the moment in a simply supported beam is at the point where the shear force is zero. For continuous beams the critical section for the +ve bending moment is in the span and –ve bending moment is at the support. The critical section for the shear is at the support. 
  • Find the factored shear (Vu) and factored moment (Mu) 
  • Check for the depth based on maximum bending moment. 
  • Considering the section to be nearly balanced section and using the equation Annexure G, IS 456-2000 obtain the value of the required depth required. If the assumed depth “d” is greater than the “required”, it satisfies the depth criteria based on flexure. If the assumed section is less than the” required”, revise the section. 
  • Calculation of steel. As the section is under reinforced, use the equation G.1.1.(b) to obtain the steel. 
  • Check for shear. 
  • Check for developmental length. 
  • Check for deflection. 
  • Check for Ast min, Ast max and distance between the two bars.