Reliability-based calibration for punching shear reduction factor for FRP reinforced slabs

Punching shear capacity of fiber-reinforced polymer (FRP) reinforced slabs (RC)is usually predicted using theoretical models obtained from design codes and standards. In the load and resistance factored design (LRFD) approach, a reduction factor is applied to the member capacity as an implicit safety measure. The same reduction factors calibrated for conventional steel reinforced slabs are used for FRP reinforced slabs in design equations of existing codes. To accommodate for the specific properties and modes of failure of FRP slabs, a reliability analysis using Monte Carlo simulation (MCS) with a specific target reliability index (βT) was conducted to calibrate the LRFD design approach reduction factors for punching shear resistance formulas available in ACI 440.1R-15, JSCE.b-1997 and CAN-CSA-S806-12 codes.The conducted analysis has shown that ACI 440.1R-15 provided a conservative estimate for FRP slabs capacity in punching shear. It was concluded that using any reduction factor up to a 3.5 reliability index (5x10-6, probability of failure) is unnecessary. On the other hand, estimation using JSCE.b-1997 and CAN-CSA-S806-12 was more accurate. The calibrated reduction factors for these codes were close to the ones provided. For the CAN-CSA-S806-12 code, the calculated reduction factor was 0.75 with βT=3 and 0.6 for βT=3.5. These values are close to the estimated by CAN/CSA-12, which was 0.65 with βT=3.1. The calculated reduction factor for the JSCE code equation was 0.8 with βT=3 and 0.7 with βT=3.5. A unified reduction factor of 0.7 is proposed to be used for CAN/CSA-12 and JSCE codes equations that satisfy a reliability index of more than 3 for both codes within the practical range of the applied loads.