Safety evaluation of frames with PR connections

An efficient nonlinear stochastic finite-element method is proposed for the design of frame structures, specifically applicable to steel structures. The assumed stress-based finite-element method is used to compute nonlinear structural responses and the corresponding response gradients. Nonlinearities due to geometry, material, and partially restrained (PR) connections are considered in the algorithm. Elastoplastlc material behavior is considered and the PR connections are modeled by the four-parameter Richard model. The material properties, geometry, connections parameters, and external loads are considered to be random variables. Both the strength and serviceability limit states are considered. The efficiency, robustness, desirability, and application potential of the method are demonstrated by two examples. Several observations with design implications can be made from these examples. Frames designed for strength may not be safe when serviceability is considered. The presence of PR connections makes the frame more flexible, and serviceability could become the governing limit state. It is essential to properly consider the PR connections in the analysis and design of frames, since design forces change significantly. In many cases, the member sizes may change considerably. The assumption that the connections are rigid, which is routinely used in the profession, is not appropriate. The proposed algorithm can be used as an alternative to the currently available methods to analyze and design frames, and to evaluate the corresponding reliabilities. The design is expected to be more efficient using this approach.