Optimal Partial Safety Factor Calibration of Structure Considering Series System Failure

Partial safety factors (PSFs) given in Indian Code of Practice for plain and reinforced concrete (IS 456: 2000) are the same for live load as well as for dead load for limit states of collapse as well as for limit states for serviceability. However, it is obvious that uncertainty in live load is more compared to dead load. Hence, proper calibration of code is a must for safe and economic design of structure. In this work, considering uncertainty in live load is more, partial safety factors using the first order reliability method are calculated. In the first module, PSFs are calculated for a single limit state function i.e., flexure only for a simply supported beam under UDL. The results show significant variations in PSFs with variations in loadings. In the second module, a set of combined PSFs are obtained using multivariate normal distribution concept for flexure as well as the shear limit state under static loading as well as under dynamic loading for the same simply supported beam. Here also, it is observed that the PSFs vary with variations in loads and changes in geometric properties. To overcome this problem, an optimization has been performed for different live load to dead load ratios using Baker’s approach. Finally, a unique set of PSFs are worked out which is valid for all load ratios under static and dynamic loads. A comparison is also made with IS code specified PSFs, which shows that the proposed set of PSFs yields more economical section than the existing PSFs of IS Code.