Seismic Performance Analysis Of Storey-adding Structure With Buckling-restrained Brace

With the further development of urbanization process in China, the situation of population increase, housing and commercial land shortage day by day, and education, medical treatment and the transport infrastructure relative deficiency appeared in many large and medium-sized cities. So the example of adding layers on the top of the existing structure becomes more and more popular, and steel adding layers gets rapid development because of its light weight, small earthquake action, convenience during construction.According to "Code for seismic design of buildings" GB50011-2010, steel framed structures, steel frame-epicenter-braced structures and steel frame-eccentric-braced structures are the three main structure type uesd widely in multi-story and tall steel structure building. The lateral stiffness of steel framed structure is limited. If the house height is higher, or under bigger horizontal force, the lateral displacement of the structure will be larger. So it is not easy to meet the requirements of the corresponding standard. Steel frame-epicenter-braced structures can resist the horizontal force caused by small and medium earthquake. Because its ductility is general, it is difficult to resist the big earthquake. Besides epicenter brace will happen buckling phenomenon in the excessive axial pressure, which affects the seismic performance. Due to the existence of the energy-dissipating beam-segment, absorbed the energy during the earthquake, ductility of steel frame-eccentric-braced structure is better. But after the big earthquake, repairment is difficult, and maintenance cost is high. In this case, buckling-restrainted brace is developed, which will not buckle under pressure, and dissipate energy after the steel yield stess.As a new type of energy dissipation system, structural engineer in many countries has paied much more attention to the frame structure with buckling-restrainted brace. But the current research is focused on the steel frame structures with buckling-restrainted brace, and the research on storey-adding structues with buckling-restrainted brace is rare.In order to further study seimic performance of storey-adding structure with buckling-restrainted barce, combined with an inpatient building expansion project, by the finite element analysis software MIDAS/Gen, this paper discusses buckling-restrainted brace from four aspects.1. Through the spectrum analysis in MIDAS/Gen under frequently earthquake, the contrast analysis of the seismic performance was done between storey-adding structure with buckling-restrained brace and with common epicenter brace. The results show that two kinds of structure are safe, their seismic performance is basic consistent, and buckling-restrained brace dose not reflect its superiority.2. Through time-history analysis in MIDAS/Gen under different seismic intensity, the contrast analysis was done between storey-adding structure with buckling-restrained brace and with common epicenter brace in the same steel quantity. The results show that storey-adding structure with buckling-restrained brace can reduce rotation of story drift by about20%, displacement of the top floor by12%, base shear force, and make structure damage degree reduce by one level under fortification, rarely and great earthquake.3. Through the time-history analysis under the earthquake waves with different strength, the research of working performance on buckling-restrained brace was done. The results show that buckling-restrained brace is in elastic stage under frequently earthquake, and basically do not dissipate energy; buckling-restrained brace is partly in elastic-plastic stage under fortification earthquake, and energy-dissipating is medium; buckling-restraint brace is in elastic-plastic stage under rarely earthquake, hysteretic curve is full, and energy dissipation performance is good.4. Through the seismic performance analysis of storey-adding structure with buckling-restrained brace based on the characteristics of ground motion, the results show the pulse-like earthquake and long duration earthquake, compared to the non-pulse-like earthquake and general duration earthquake, can make rotation of story drift increase about20%and10%separately under rarely earthquake, and about40%and30%separately under great earthquake.