最小地震剪力系数对隔震结构抗震性能的影响

Influence of minimum earthquake shear force coefficient on seismic performance of isolation structures

最小地震剪力系数是隔震结构设计的关键控制因素之一。对等效周期为2~6 s的单质点隔震体系在远场地震动(FF地震动)、近场含脉冲地震动(NFWP地震动)和近场不含脉冲地震动(NFWNP地震动)作用下的剪力系数分布特点进行分析,并将其与规程中有关最小地震剪力系数的相关规定进行对比,探寻在不同抗震设防烈度下,不能满足最小地震剪力系数的隔震结构的等效周期范围。以位于我国抗震设防烈度8度区的某隔震结构为例,采用三种不同的设计地震剪力取值方法,设计了6种不同的结构模型。通过模型的弹塑性时程分析,比较了地震动的近远场特性对各模型抗震性能的影响,及其在罕遇地震作用下的性能差异。分析结果表明:地震动的近远场特性对隔震结构的楼层设计剪力影响较大;对不满足最小地震剪力系数要求的隔震结构,采用放大设计地震剪力使其承载力满足最小地震剪力系数的方法,能够有效提高其抗震能力;不考虑最小地震剪力系数对结构设计地震剪力的限制,采用结构的实际地震剪力需求进行设计的隔震结构能够满足地震作用下的承载力和层间位移限值要求。

The minimum earthquake shear force coefficient is one of the key issues in seismic design of isolation structures. The shear force coefficients of single mass isolation models with equivalent periods between 2 s and 6 s under far-field earthquakes, near-field with pulse earthquakes and near-field without pulse earthquakes were calculated, which were compared with the requirement on minimum base shear force in typical Chinese seismic design codes and specifications. The isolation structure periods among which structure shear forces could not meet the minimum shear force were investigated. Then based on an isolation structure located in 8-degree seismic fortification region of China, six building models were designed with three design base shear force demands. With elasto-plastie dynamic analysis, the seismic performances of these buildings under the severe earthquakes were comparatively discussed, as well as the influence of far-field ground motions, near-field with pulse ground motions and near-field without pulse ground motions on the seismic performance. The analytical results indicate that field property has remarkable influence on the design shear forces in isolation structures. Seismic properties of isolation structures, whose design shear forces are lower than the limits of the minimum shear forces, are improved effectively by ampifying the design shear forces to the limit values. Isolation structures can meet the strength demand and drift demand under earthquakes, whose design shear forces can meet shear forces requirement in time history analysis without considering the minimum earthquake shear force coefficients.