Evaluation of loading sequences on testing capacity of concentrically braced frame structures

Static cyclic loading tests are commonly used to evaluate the seismic capacity of a structure. However, different loading sequences would result in different structural behavior. To quantify the effects of loading sequences on the structural capacity, we investigate the experimental behavior of braces in concentrically braced frames (CBF) under different loading sequences. The variables for testing program includes two different pipe sections (different slenderness as well) and three loading protocols, namely, loading sequence for beam-to-column moment connections (LS1), loading sequence for link-to-column connections (LS2) and proposed loading sequence for CBF structures (LS3). After tests, we compare the critical performance parameters of different specimens including the failure modes, maximum deformation, cumulative energy, etc. Test results show that the specimens fracture at different deformation stages under different loading sequences. The specimens accumulate energy the fastest under LS1. The maximum cumulative energy is less correlated to the loading sequences. The test results also show that the rate of cumulative deformation under LS1 is too fast for CBF structures; the rate under LS2, on the contrary, is a little slow for CBF structures. LS3 is more suitable for braces in regard to failure modes, cumulative deformation rate, cumulative energy rate, and deformation amplitude.