双自由度含阻尼体系的地震入射方向性效应

Seismic incident directionality effect of a bi-degree-of-freedom damped system

多维地震动对结构的入射方向具有不确定性,易导致结构出现入射方向性震害,而采用现有抗震设计方法仍无法保证结构在任意入射方向下的地震安全。为此,研究水平地震动分量随入射方向的重组关系,发现两个正交水平分量在入射方向变化后有复杂的重组机制,以这种机制作为地震动分类和选择的依据。以双自由度含阻尼体系为对象,利用统计学方法建立谱响应放大系数预测模型,该模型是基于传统激励方法、考虑入射方向不确定性且持有自定义的保证率;并利用预测模型对双自由度含阻尼体系开展大量参数分析,分析参数包括结构基本周期、双轴周期比、阻尼和场地类型。结果表明:对于地震动入射方向对结构响应的影响程度(以谱响应放大系数表征),结构基本周期越大,双轴周期比越小,影响程度越大;双轴的阻尼比越大或二者越接近,影响程度越小;影响程度在不同场地条件下是基本稳定的。所建立的谱响应放大系数预测模型可用于结构的多维抗震设计。

The incident direction of multi-dimensional ground motion on the structure is uncertain,which is easy to lead to the incident directional earthquake damage of structures.Existing seismic design methods still cannot ensure the seismic safety of structures in any incident direction.Therefore,the recombination relationship of horizontal ground motion components with respect to the incident direction was studied.The results show that the two orthogonal horizontal components have a complex recombination mechanism after the incident direction changes.This mechanism will be used as the basis for the classification and selection of ground motion.Taking a bi-degree-of-freedom damped system(BDOF-DS)as the object,the spectral response amplification factor(SRAF)prediction model is generated by using a statistical method.This SRAF prediction model is based on the traditional excitation method,considers the uncertainty of the incident direction,and holds an owner-defined confidence level.A large number of parameter analyses are performed on the BDOF-DS using the SRAF prediction model,and the parameters include structural period,biaxial period ratio,damping,and site type.It is indicated that for the influence of incident direction on the structural response(quantitatively characterized by the SRAF),the larger the fundamental period of the structure,the smaller the biaxial period ratio,and the greater the influence degree.The greater the damping ratios of the two axes are,or the closer the two ratios are,the smaller the influence degree is.The influence is basically stable under different site conditions.The SRAF prediction model will be applicable for the multi-dimensional seismic design of structures.