A study on the probabilistic safety assessment of the truss structure designed by the LRFD code

Abstract

The probabilistic analyses provide a more rational approach for the safety assessment of structures since they consider the uncertainties in the calculations. Consequently, the design specifications of engineering structures are gradually transformed from the allowable stress design to the reliability-based specifications such as load and resistance factors design (LRFD) or partial safety factor design. The partial safety factors and the load andresistance factors provided in the reliability-based design codes are successfully determined from probabilistic frameworks. However, these specifications are classified into semi-probabilistic-based codes because no probabilistic analysis is required in the design practice. Thus, the actual reliability index of the design solutions maynot be as close to the target value as expected. This study employs the fully probabilistic analysis as an additional analysis to examine the reliability index of an LRFD-based design of the truss structure. A planar truss,which is designed following the semi-probabilistic code, is thoroughly examined. Several feasible sections are first designed using the LRFD code. Then, the actual reliability indexes of truss structures are evaluated to check if they meet the target reliability index specified in the reliability-based design codes. The tension and compression members concerning the strength limit state and the maximum deflection presenting for service ability are investigated as representative performances. The results of the probabilistic analyses indicate thatthe reliability indexes for the strength limit state are higher than the target value stipulated in the LRFD code. Compared to the tension members, more redundancy in terms of reliability index is observed for compression elements, although they are both designed at the limit state. Moreover, the reliability index obtained for theserviceability limit state is strongly dependent on the component (i.e., floor or roof) where the truss is utilized.