考虑震级影响的规范阻尼修正系数评估

规范采用阻尼修正系数(DMF)调整阻尼比不同于5%时的弹性反应谱,然而未考虑矩震级的影响.美欧规范DMF是基于位移反应谱,而中国规范DMF是基于绝对加速度反应谱.对同类场地不同矩震级范围内DMF的统计分析表明,除E类场地外,矩震级Mw6.5时,基于位移反应谱的中值DMF与美欧规范值比较接近,基于绝对加速度反应谱的中值DMF与中国规范值比较接近;而矩震级Mw=5.5～6.5时,中值DMF与各规范值有明显差异,采用规范DMF是偏于不安全的.对E类场地,规范DMF多数情况下稍偏于保守.最后,利用非线性回归分析,提出了不同矩震级范围时各类场地DMF表达式.

Evaluation of Damping Modification Factors in Codes with a Consideration of Effect of Earthquake Magnitude

Damping modification factors (DMF) are used in current codes to adjust elastic response spectral values corresponding to 5% of viscous damping to other damping levels. However, the impact of moment magnitude (Mw) is not considered in codes. The DMF in the NEHRP 2003 and Eurocode 8 are derived from displacement response spectra while those in the China 2010 are obtained from absolute acceleration response spectra. Based on the DMF for different moment magnitude ranges computed from seismic records located at the same site class, except for site Class E, statistical analysis of results shows that the median DMF for Mw>6.5 derived from displacement response spectra are close to those values in NEHRP 2003 and Eurocode 8 while those derived from absolute acceleration response spectra are similar to those values in China 2010. However, the DMF for Mw=5.5~6.5 are obviously different from those values in codes, further, the DMF in codes are probably unsafe. Besides, for site Class E, the DMF in codes are in most cases slightly conservative. Finally, nonlinear regression analyses are used to develop expressions for DMF corresponding to various site classes and moment magnitude ranges.