The design and seismic performance of low-rise long-span frames with semi-rigid connections

Moment-resisting steel frames are used frequently in low-rise and mid-rise buildings located in high seismic areas due to their high ductility and economic solutions. In these type of structures, strong-column weak-beam design requirements result in larger column sections and overdesign in low-rise long-span buildings. To mitigate this problem, moment-resisting steel frames with energy-dissipative semi-rigid/partial strength connections can be used as an alternative to perimeter frames. By using energy-dissipative semi-rigid connections, the strong-column weak-beam requirement is eliminated and more economical column sections are used. In this study, a three-span three-bay frame with 7 and 9 m span lengths is designed with semi-rigid connections having four different capacities in high seismic zones. Their seismic performance is evaluated analytically under three different earthquake levels by modeling connections with two different moment-hardening ratios and two different hysteretic behavior models. The design with reduced connection capacity resulted in an increase in the beam weights, a decrease in the column weights and an overall decrease in the structural weight. The seismic performances of 26 sample frames are evaluated with pushover and dynamic analyses under 25 real strong ground motion records. All of the sample frames satisfied the acceptance criteria and showed reliable performance under earthquake loading. The overdesign problem in low-rise long span-buildings is eliminated to some extent without using the perimeter frame approach. Furthermore, under some specific ground motion records, the top displacements in semi-rigid frames become lower than those of their rigid counterparts.