Relating Seismic Design Level and Seismic Performance: Fragility-Based Investigation of RC Moment-Resisting Frame Buildings in China

Analytical fragility analyses are conducted to investigate the impact of seismic design level on the seismic performance of RC moment-resisting frame buildings designed according to the provisions of the current Chinese seismic code. Four groups of buildings of low-to-mid height (3, 5, 8, and 10 stories) are studied, each of which accounts for diverse levels of seismic design, namely, precode, low code, medium code, and high code. Fragility relationships are derived for each building using nonlinear time-history analyses with 100 real ground-motion records. The results show that the buildings designed for a higher seismic code level exhibit less fragility as improving the seismic design level leads to a raised fragility median and a reduced fragility dispersion. Data on the reference seismic hazards with the probabilities of exceedance of 10 and 2-3% in 50 years show that almost all the buildings can satisfy the performance requirements of reparability and no collapse, respectively. However, the damage limitation performance objective, which is associated with 63.2% in 50-year hazard, cannot be satisfactorily achieved by medium-code and high-code buildings. The enhancement of structural resistance caused by the improvement of seismic design level is counteracted by the simultaneously increased seismic action; therefore, the limit-state probabilities of the buildings at the corresponding reference earthquakes are not decreased but increased accordingly. The current Chinese seismic design code seems conservative because the buildings show marginal potential of suffering serious damages endangering life when subjected to the seismic hazard level higher than it was designed for. Thus, it is possible to account for larger anticipated nonlinear behavior in the definition of seismic design force. (C) 2017 American Society of Civil Engineers.