Study on Plastic Design Method of Staggered Truss Structure with Two-Side Connecting Steel Plates

The staggered truss framing (STF) structural system is an efficient, practical and highly economical framing system, and it follows the trend of building industrialization. The STF structural system has been widely used in areas of low earthquake risk, and the merits make this system attractive in moderate to high seismic regions. The truss can be a hybrid truss, a vierendeel truss or a pratt truss. Compared with the vierendeel truss and the pratt truss, the hybrid truss is the most widely used because of its moderate rigidity and its vierendeel panel which can be set as an inner corridor. Existing tests have shown that the hybrid STF structural system has good mechanical performance but poor seismic performance and weak energy consumption capacity, and the soft storey problem is prone to occur. To enhance the seismic behaviour of STF structural systems, this paper proposed a ductile STF structure in which two-side connecting steel plates (TSCSPs) are set in the middle of the truss span and the middle span is taken as an energy dissipation section to dissipate energy. The ductile STF structure is called the two-side connecting steel plate-staggered truss framing (TSCSP-STF) structure. The steel plates of energy dissipation section would not buckle nor yield under frequent earthquakes, while only the steel plates would yield and dissipate energy under major and infrequent earthquakes. The non-dissipative sections of the truss remain elastic. In this way, the ductility and energy dissipation capacity of the traditional hybrid STF structure can be improved, and the instability and brittle failure of the web members can be mitigated or avoided.
The calculation method for the shear capacity demands of the TSCSP was derived from analyzing the shear capacity demands of the energy dissipation section. Assuming TSCSP as eccentric cross brace, we established a simplified analysis model of the TSCSP-STF structure, and then the plastic design method and process of the system. Further, a 10-story TSCSP-STF structure and a 10-story hybrid STF structure were designed with the same design conditions and nearly the same steel consumption. The design goal was to make both structures deplete the energy consumption capacity of the energy dissipation section. The seismic behaviours of the two specimens were investigated by the mode-superposition response spectrum method and Pushover analysis method.
The analysis results showed that:under the action of frequent earthquakes, the components can maintain elasticity, while under the action of major and infrequent earthquakes, the energy dissipation components can fully dissipate the seismic energy and protect the other components from damage. The plastic hinges of STF specimen were concentrated at the ends of vierendeel chords, and evenly distributed along the height of the building. The plastic hinges of TSCSP-STF specimen mainly appeared on the ties and struts of the energy dissipation sections, and the distribution was also relatively uniform. Both the TSCSP-STF structure and the hybrid STF structure designed according to the plastic design method can meet the requirements of the code for load-carrying capacity, deformation and stability under major and infrequent earthquakes. The drift of TSCSP-STF specimen was more uniformly distributed, reducing the possibility of soft-story, and has relatively better ductility.