What is the basis for only 20% of vertical reinforcement is considered for the calculation of Shear capacity (Tc)?
Based on the IS 456, Only tension reinforcement is to be considered for shear capacity (Tc) calculation. We can assume at- least 30 to 40% reinforcement would be under tension in a given load combinations. Also, the effective depth as per code is suggested to be considered as 0.8 x the total depth for the shear calculation. Considering both the criteria, it is assumed that the only 20% of the main reinforcement of entire wall would be in tension. It is also very difficult to identify the % tension reinforcement in wall for combination which is critical in shear. This has been discussed with the professor on the code panel in technical presentation of IS 13920-2016 and suggested to use only 20%of the main reinforcement in the shear calculation.