In Failure Diagnostic We Can Get Only Reason Of Failure But Not Get The Calculation. How We Know The Failure Calculation Of Column?

IN FAILURE DIAGNOSTIC WE CAN GET ONLY REASON OF FAILURE BUT  NOT GET THE CALCULATION. HOW WE KNOW THE FAILURE CALCULATION OF COLUMN? 

Reply:

RCDC provides the reason for failure in the Failure Diagnostics report. There are multiple type of Failure suggested by RCDC as follows:

1. Axial Failure -  When the Average Stress in Column (Pu / Ag) for Pumax from seismic Load Combination exceeds 0.4 fck, then there is Axial Failure. 
   • This can be tackled by either Increasing the Column Size or by Increasing the Grade of Concrete. As both these parameters are set by user, RCDC cannot modify these parameters and shows as a Failure condition.
2. Joint Flexure Failure - As per Clause 7.2 (IS:13920-2016), for a considered Beam Column Junction, when the Column Capacity is found to be Less the 1.4 Beam Capacity (considering all the beams at the joint), then there is Joint Flexure Failure. 
   • In this case, RCDC tries to increase the Ast provided for Column up to Maximum Pt considering the Max Diameter - Min spacing parameters that are set in RCDC. If still there is failure after increasing the Pt, then RCDC shows it as Failure only. 
   • You can handle this by either increasing the Column sizing or by controlling the moments in beam by providing some partial releases in beam or by decreasing the beam sizing to control the stiffness.
3. Joint Shear Failure - As per Clause 9.1 (IS 13920-2016), the Nominal shear strength of concrete in the Beam - Column Joint is checked as mentioned in the code. Below image for reference:
   • This check depends on the Beam-Column Joint area and the Concrete Grade. So, this can be tackled by either Increasing the Column Size or by Increasing the Grade of Concrete. As, RCDC cannot modify both these parameters it is shown as a Failure condition.
   • 
4. Detailing Failure - This type of Failure occurs in RCDC when the 'Maximum Diameter' and 'Maximum allowable bars' for a column section is provided and still with this configuration of Pt provided is less than the Max Pt allowed. 
   • In this case RCDC has already tried to reach the maximum possible diameter and number of bars. So, this can be further handled from user's end by allowing the Maximum diameter available in the list and / or increasing the Number of Bars for the column section. The number of bars for column section can be increased from the Zone & Rebar settings in RCDC. 
5. Rupture Failure - Modulus of rupture check is performed as per clause 6.2.2 of IS 456-2002. The option of performing this check is available in RCDC as per user’s choice. This check is performed only for the tensile axial force in the column against the tensile capacity of the column. Effect of moment is not considered as this check is for tensile strength of concrete. If the axial tension is more than 0.7xsqrt(fck) then RCDC shows the column failure. It is just a check performed in the RCDC, there is no impact on the final design of the column.
   • In this case, the check is performed only when user selects to perform this check and there is tension in the column.