Modeling of Restoring Force Characteristics from Collapse Test Data of Frame Structures

During the September 21 (local time) 1999 Chi-Chi Taiwan earthquake, a large number of older buildings built before 1982 sustained severe damage and many others suffered from complete failure. These old buildings, having low ductility RC columns, are known to have poor seismic performance in terms of ductility and energy dissipation capacity during severe seismic events. Therefore, it is the main concerns of structural engineers and, at the same time, benefit of building owners how to retrofit these old buildings to match more strict requirements of the next generation building code to get better odds to survive probable future earthquake events. In this study, an analytical inelastic hysteretic model which includes strength and stiffness deterioration and post-peak behavior with negative stiffness (i.e. collapse behavior) is developed. By observing the result of the collapse test data of RC portal frame structure at NCREE, verification on the proposed hysteretic model with the consideration of post-peak behavior is conducted and modal parameters are identified. Verification is also extended to two simulation cases by C. Lynn (1996). Based on the proposed model, a combination of maximum ductility and residual displacement in the format of a performance matrix is generated to define the system's performance of hazard levels from 475years to 2475years. Hysteretic characteristics including pinching effect, strength deterioration, stiffness degrading, and as well as different period of system are considered.