Effects of out-of-plane stiffness and inelastic behavior of diaphragms on the behavior of SSTF systems

The design and analysis methodologies for steel staggered truss framing (SSTF) systems commonly employ the rigid diaphragm assumption which neglects the out-of-plane stiffness and inelastic behavior of diaphragms. This results in erroneous predictions of yielding mechanisms and overly underestimated predictions of base shear forces. In this work, seismic response analyses and nonlinear pushover analyses were performed on an 8-story SSTF structure and a reference steel moment framing structure incorporating distinct diaphragm modelling methods utilizing rigid membrane elements, homogeneous shell elements, and multi-layered shell elements, respectively. Comparative analyses of the obtained natural periods, base shears, story drifts, and yielding mechanisms revealed that the out-of-plane stiffness of diaphragms significantly contributes to the lateral stiffness of SSTF systems in the direction parallel to trusses, and the inelastic behavior of diaphragm affected the failure modes of SSTF systems. Lastly, the diaphragm actions on SSTF systems were further verified by comparing the experimental results of a tested 1/3-scale SSTF specimen and the analysis results of the counterpart analysis model with the distinct diaphragm modelling methods. Design considerations about the diaphragm modelling were given, which facilitates acquiring the precise predictions of the lateral responses and yielding mechanisms of SSTF systems.