Representation of Bidirectional Ground Motions for Design Spectra in Building Codes
Representation of Bidirectional Ground Motions for Design Spectra in Building Codes
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DOI：
10.1193/1.3608001
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发表时间：
2011-08
影响因子：
5
通讯作者：
J. Stewart;M. Eeri;N. Abrahamson;G. Atkinson;J. Baker;D. Boore;Y. Bozorgnia;K. Campbell;C. Comartin;I. M. Idriss;M. Lew;M. Mehrain;J. Moehle;F. Naeim;T. Sabol
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文献类型：
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作者：
J. Stewart;M. Eeri;N. Abrahamson;G. Atkinson;J. Baker;D. Boore;Y. Bozorgnia;K. Campbell;C. Comartin;I. M. Idriss;M. Lew;M. Mehrain;J. Moehle;F. Naeim;T. Sabol
2009年NEHRP条款修改了水平地面运动的定义，从两个分量的谱加速度的几何平均值到单个集中质量振子的峰值响应，无论方向如何。这些最大方向（MD）地面运动是在假设结构的动态特性（例如，刚度、强度）在所有方向上都相同。这种假设对于某些平面内对称结构可能是正确的，然而，大多数结构的响应由沿着沿着特定轴的振动模式支配（例如，建筑物中的纵向和横向轴线），并且通常沿这些轴线的动态特性（尤其是刚度）沿着是不同的。为了实现与NEHRP文件中给出的倒塌风险水平一致的结构设计，我们认为，设计谱应与预期水平的地面运动沿着这些主要响应轴。MD地震动的使用有效地假设最大地震动的方位角与结构的主反应方向一致。因为这是不可能的，设计地震动的发生概率比预期的要低，社会成本很高。我们建议进行调整，以使设计地面运动与目标风险水平兼容。
The 2009 NEHRP Provisions modified the definition of horizontal ground motion from the geometric mean of spectral accelerations for two components to the peak response of a single lumped mass oscillator regardless of direction. These maximum-direction (MD) ground motions operate under the assumption that the dynamic properties of the structure (e.g., stiffness, strength) are identical in all directions. This assumption may be true for some in-plan symmetric structures, however, the response of most structures is dominated by modes of vibration along specific axes (e.g., longitudinal and transverse axes in a building), and often the dynamic properties (especially stiffness) along those axes are distinct. In order to achieve structural designs consistent with the collapse risk level given in the NEHRP documents, we argue that design spectra should be compatible with expected levels of ground motion along those principal response axes. The use of MD ground motions effectively assumes that the azimuth of maximum ground motion coincides with the directions of principal structural response. Because this is unlikely, design ground motions have lower probability of occurrence than intended, with significant societal costs. We recommend adjustments to make design ground motions compatible with target risk levels.