Seismic fragility analysis of the steel frame with new layered assembled joints

Abstract

In order to improve the assembly efficiency of the steel frames, a new fully-bolted core tube joint was proposed in combination with the seismic performance requirements of the joint. Cyclic loading tests were carried out on both new and traditional joints to study their seismic performance, and the joint parameters obtained from the tests were introduced into the overall frame model in SAP2000 to perform Incremental Dynamic Analysis. Based on the single-parameter damage model and the two-parameter damage model, the structural performance level limits were defined, the damage states were classified, and the seismic fragility analysis of the structure was performed. The results showed that the fragility curves of the steel frame with the new joint were enveloped within the fragility curves of the steel frame with the traditional joint under both single and double damage indices, and the collapse resistance reserve factor of the steel frame with new joint was larger. That is, the use of the new joint could reduce the failure probability of the structure under each damage state and improve the collapse resistance of the frame. The median PGA values of the structure based on the single-parameter damage index were smaller than those based on the two-parameter damage index in the LS1 ∼ LS2 limit states, and the opposite was true in the LS3 ∼ LS4 limit states, meaning that the cumulative energy dissipation had an obvious influence on the evaluation of the seismic performance of the structure, and the combination of the two-parameter damage index could better predict the damage degree of the structure. Additionally, increasing the inner sleeve height in the joint domain improved the overall performance and reduced the failure probability of the structure.