Performance of Rocking Systems on Shallow Improved Sand: Shaking Table Testing
Performance of Rocking Systems on Shallow Improved Sand: Shaking Table Testing
复制标题
摇摆系统在浅层改良砂上的性能：振动台测试
DOI：
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发表时间：
2015
影响因子：
3
通讯作者：
I. Anastasopoulos
中科院分区：
文献类型：
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作者：
A. Tsatsis;I. Anastasopoulos
最近的研究强调了地震震动过程中非弹性地基响应的潜在好处。根据一种新兴的抗震设计方案，称为摇摆隔离，基础是故意设计不足，以促进摇摆和限制传递到结构的惯性。这种容量设计的逆转可以改善抗震性能，大大增加安全裕度。然而，这种好处是以永久沉降和旋转为代价的，这可能威胁到地震后的功能。如果垂直荷载FSV的安全系数足够大，则这种不希望的变形可以保持在容许限度内。在这种情况下，响应是上升为主的，沉降的积累可能是有限的。然而，这并不总是可行的，因为土壤特性可能并不理想。浅层土壤改良可能是一个可行的解决方案，因此值得研究。其效率与摇摆的性质有关，摇摆倾向于使浅应力球移动。为此，进行了一系列振动台试验，使用一个理想化的细长桥墩作为概念原型。研究了两个系统，它们都位于宽度为B的正方形基础上。第一个对应于轻载结构，第二个对应于重载结构。这两个系统首先在贫瘠和理想的土壤条件下进行测试，以证明土壤改良的必要性。然后，通过调查它们在深度z/B = 0.5和1的土壤结皮上的性能来研究浅层土壤改良的效率。结果表明，z/B = 1的致密砂壳足以实现与致密砂的理想情况实际相同的性能。根据设计要求，也可以考虑较浅的z/B = 0.5的改进层。土的改良效果随着旋转振幅的增大而提高，随着地震动周期数的增加而提高。
Recent studies have highlighted the potential benefits of inelastic foundation response during seismic shaking. According to an emerging seismic design scheme, termed rocking isolation, the foundation is intentionally under–designed to promote rocking and limit the inertia transmitted to the structure. Such reversal of capacity design may improve the seismic performance, drastically increasing the safety margins. However, the benefit comes at the expense of permanent settlement and rotation, which may threaten post-earthquake functionality. Such undesired deformation can be maintained within tolerable limits, provided that the safety factor against vertical loading FSV is adequately large. In such a case, the response is uplifting–dominated and the accumulation of settlement can be limited. However, this is not always feasible as the soil properties may not be ideal. Shallow soil improvement may offer a viable solution and is therefore worth investigating. Its efficiency is related to the nature of rocking, which tends to mobilize a shallow stress bulb. To this end, a series of shaking table tests are conducted, using an idealized slender bridge pier as conceptual prototype. Two systems are studied, both lying on a square foundation of width B. The first corresponds to a lightly-loaded and the second to a heavily-loaded structure. The two systems are first tested on poor and ideal soil conditions to demonstrate the necessity for soil improvement. Then, the efficiency of shallow soil improvement is studied by investigating their performance on soil crusts of depth z/B = 0.5 and 1. It is shown that a z/B = 1 dense sand crust is enough to achieve practically the same performance with the ideal case of dense sand. A shallower z/B = 0.5 improvement layer may also be considered, depending on design requirements. The efficiency of the soil improvement is ameliorated with the increase of rotation amplitude, and with the number of the cycles of the seismic motion.