Fundamental Dynamics of 3-Dimensional Seismic Isolation
Fundamental Dynamics of 3-Dimensional Seismic Isolation
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发表时间：
2017
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通讯作者：
W. Eltahawy;K. Ryan;S. Cesmeci;F. Gordaninejad
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作者：
W. Eltahawy;K. Ryan;S. Cesmeci;F. Gordaninejad
通常选择建筑物的隔震系统来实现更高的抗震性能目标，例如在设计地震事件后继续运行或立即入住。然而，最近的大规模测试表明，如果震动包括会损坏非结构部件和内容物的大垂直加速度分量，则这些目标可能会受到损害。已经进行了一些研究来开发三维隔离系统，该系统可以将结构与地面运动的水平和垂直分量隔离。在一些情况下，系统的提出并没有对目标设计参数进行太多论证。摇摆已被认为是具有 3D 隔离系统的结构的潜在问题，并且已提出复杂的系统来控制摇摆。在本研究中，探讨了具有 3D 隔离系统的结构的基本动态响应。根据 NEHRP 建议开发了代表性强运动地点的目标水平和垂直频谱，并选择了当对所有三个运动分量应用相同的幅度比例因子时最适合目标频谱的水平和垂直地面运动。使用线性隔震支座上的刚性块的简单模型，对各种水平和垂直隔震周期的以下方面进行评估：摇动的响应模式和严重程度、隔震支座中的水平和垂直位移要求，以及结构中水平和垂直加速度相对于地面加速度的衰减。初步结果指出了一些有用的观察结果。例如，仅当水平和垂直隔离周期间隔很近时，摇摆才显得是一个问题。已应用于一些结构的螺旋弹簧隔震系统具有此特性。然而，如果水平隔离周期相对于垂直隔离周期较大，则可以避免麻烦的摇摆。此外，其他研究人员提出了垂直隔离周期为2秒左右的系统，这需要大的位移和阻尼能力。然而，初步结果表明，低至 0.5 秒的垂直隔离时间将有效减弱垂直加速度。限制垂直隔离周期将使 3D 隔离系统的设计在垂直位移能力和避免晃动方面更加可行。
Seismic isolation systems for buildings are generally selected to achieve higher seismic performance objectives, such as continued operation or immediate occupancy following a design earthquake event. However, recent large scale tests have suggested that these objectives may be compromised if the shaking includes large vertical acceleration components that are damaging to the nonstructural components and contents. Some research has been conducted to develop three dimensional isolation systems that can isolate the structure from both the horizontal and vertical components of ground motion. In several cases, systems have been proposed without much justification of the target design parameters. Rocking has been noted as a potential concern for structures with 3D isolation systems, and complex systems have been proposed to control the rocking. In this study, the fundamental dynamic response of structures with 3D isolation systems is explored. Target horizontal and vertical spectra for a representative strong motion site were developed based on NEHRP recommendations, and horizontal and vertical ground motions were selected that best fit the target spectra when the same amplitude scale factor was applied to all three motion components. Using a simple model of a rigid block resting on linear isolation bearings, the following aspects are evaluated for a wide range of horizontal and vertical isolation periods: response modes and severity of rocking, horizontal and vertical displacement demands in the isolation bearings, and attenuation of both horizontal and vertical accelerations in the structure relative to the ground acceleration. Preliminary results point to a number of useful observations. For example, rocking appears to be an issue only if the horizontal and vertical isolation periods are closely spaced. Helical spring isolation systems that have been applied to a few structures have this characteristic. However, if the horizontal isolation period is large relative to the vertical isolation period, troublesome rocking can be avoided. In addition, other researchers have proposed systems with vertical isolation periods on the order of 2 seconds, which require large displacement and damping capacity. However, preliminary results suggest that vertical isolation periods as low as 0.5 seconds will be effective in attenuating the vertical acceleration. Limiting the vertical isolation period will make design of a 3D isolation system more feasible with respect to vertical displacement capacity and avoiding rocking.