Cal-Reliability Assessment of Failure of Industrial Structural Steel Roof Truss Systems

This research investigated the reliability of a newly designed steel roof truss system of an industrial building to be constructed in one of the major cities in Nigeria. The probabilistic analysis technique was done with the aid of CalREL, a general-purpose structural reliability analysis software program. The longest span truss element (consisting of 73 members), is the most critical in the system, was selected and first analysed using SAP2000 Advanced 12.0.0 finite element analysis (FEA) software program in order to obtain the forces in the steel truss members; this forms part of the inputs required in CalREL. Four load variations (referred to as load ratios in the study) were tested on the selected truss. The strengths of the truss members and other properties were determined as specified in BS 5950-1: 2000. Limit state equations were derived for the calculation of the probability of failure of the individual members of the truss system. A reliability index as a measure of structural performance and related to the probability of failure was developed for all the elements of the truss. The results showed that compression members displayed a noticeable violation of the ultimate limit state requirement, while tension members showed a negligible violation. Sensitivity factors that reflect the relative importance of the individual variables in the design of roof trusses were also presented. The estimated reliability indices also revealed structural members that require immediate redesign; though they appear satisfactory in the level of deterministic design. A probabilistic approach for the reappraisal of new and existing civil structures is well supported by the findings of this investigation.