Collapse Safety Margin And Seismic Loss Assessment Of Concrete Frames Having Equal Construction Cost

In recent years, with the economic development of our country, equipment and properties in buildings are becoming more valuable, thus economic loss caused by the damage of non-structural components is still huge even though the main structure is undamaged. In China, reinforced concrete (RC) frame structures are widely adopted, a considerable number of which locate in high earthquake intensity regions. Due to the complexity of earthquake mechanism, super earthquakes have potential to occur in such regions. If we can, under the premise of same construction cost, improve concrete frames'collapse resistant capacity to the maximum while reducing the seismic economic loss and the post repair time, it would be meaning to lift the seismic economic efficiency of the concrete frame buildings in China. Based on the above considerations, the main work is as follows:(1) With the premise of same construction cost, conventional high-rise concrete frame, high-rise concrete frame with BRBs and isolated high-rise concrete frame are designed according to Chinese Code. Then established are nonlinear finite element analysis models based on OpenSees. The design method and the establishment of models are introduced in detail.(2) According to ATC-63, seismic fragility analyses and collapse margin ratios (CMR) analyses of basic concrete frame and controlled concrete frames having equal construction cost are conducted with incremental dynamic analysis (IDA) method. The case study indicates that with a premise of same construction cost, isolated frame possesses higher safety reserve at each performance level and stronger collapse resistant capacity than BRB frame and basic frame. The quantity and location of BRBs can influence the structural anti-collapse capacity significantly.(3) The global lateral stiffness, minimum modified rigidity-to-gravity ratio and seismic mitigation coefficient are proposed as collapse resistant design parameters of controlled concrete frames with same construction cost. Considering variations of LRB's parameters and BRB's quantity/parameters/placement schemes, dozens of concrete frames are modeled for IDA analyses to unveil the relationship between the design parameters of frames and their CMR values. This study shows that the BRBs should be arranged in weak story, avoiding to be placed at high story intensively. When the global lateral stiffness and minimum modified rigidity-to-gravity ratio of BRB frame are bigger, the collapse resistant capacity of BRB frame is stronger. When the seismic mitigation coefficient is smaller, the collapse resistant capacity of isolated frame is stronger, stronger than the basic frame and the BRB frame with the same construction cost. In view of the above conclusions, the design method of controlled concrete frame which has strongest collapse resistant capacity is proposed.(4) Based on the evaluation method of FEMA P-58 report, combined with the actual situation in China, the seismic economic loss and time loss assessment of basic concrete frame and controlled concrete frame which has equal construction cost are carried out. This study found that BRB frame can lead to 37% seismic economic loss reduction and 38% post repair time reduction, while isolated frame can lead to 68% seismic economic loss reduction and 82% post repair time reduction.According to this study, with the premise of same construction cost, the seismic loss of isolated concrete frame is less than that of the basic concrete frame, while the collapse resistant capacity is also stronger than that of the basic concrete frame. The seismic loss and collapse resistant capacity of the BRB concrete frame are between those of the basic frame and the isolated frame. In order to improve the seismic collapse resistance capacity and seismic economic efficiency, controlled frames having equal construction cost are suitable for popularization and application in China.