Modeling of high-strength composite special moment frames (C-SMFs) for seismic analysis

This paper presents the development and validation of a fiber-based numerical modeling approach that can be used to evaluate the seismic response of high-strength composite special moment frames (C-SMFs). The high-strength C-SFMs consist of: (i) CFT columns made from high-strength materials (Fy ≥ 525 MPa and f'c ≥ 70 MPa), (ii) wide flange (WF) steel beams, and (iii) double split-tee (DST) beam-to-column connections. The fiber-based numerical modeling approach uses fiber-based finite elements to model CFT columns and WF steel beams, and uses spring elements to model DST connections. Consequently, the accuracy of the fiber-based numerical modeling approach depends fundamentally on: (i) uniaxial effective stress-strain (σ-ε) relationships assumed for the fiber-based finite elements modeling high-strength CFT columns and WF beams, and (ii) effective force-displacement (P-∆) relationships assumed for the spring elements modeling DST connections. This paper develops these critical input relationships using a three-step approach. The first step consists of developing and benchmarking detailed 3D nonlinear FEM models of high-strength CFT columns, WF steel beams, and DST connections. The second step consists of conducting parametric studies using the benchmarked FEM models. The third step consists of developing effective σ-ε and P-∆ relationships using results from the parametric studies, and validating these relationships using results from experimental studies. The fiber-based numerical modeling approach for C-SMFs is validated by using them to predict the lateral force-deformation response of C-SMFs subassemblies. The benchmarked numerical modeling approach is recommended for conducting nonlinear time-history analysis of C-SMFs and evaluating their seismic response.