RAPID: Large-Scale Shake Table Test to Quantify Seismic Response of Helical Piles in Dry Sand

本快速反应研究（Rapid）项目将通过对加州大学圣地亚哥分校层状土箱中模型桩的振动台试验来研究螺旋桩的地震行为。螺旋桩是一种深地基构件，外观和安装方式都像一个大型钢土螺钉——它们有一个细长的钢轴，顶端有任意数量的圆板，为它们所承载的结构提供支撑。螺旋桩由大扭矩电机旋转入地，并通过板上和轴上的土壤承重提供支撑。它们有很多长度，通常是改造现有建筑或新建城市建筑的基础选择，因为它们占地面积小，对周围结构的干扰最小。螺旋桩虽然在新西兰、日本等地震活跃地区作为基础构件安装，但在美国地震活跃地区尚未得到广泛应用。不可否认，这种缺乏使用是由于没有量化的数据来说明螺旋桩的地震行为。此外，除了2011年克赖斯特彻奇地震的定性“生存”故事外，没有与其他深层基础系统的地震对比。在2011年的一系列地震之后，对克赖斯特彻奇市进行了调查，发现所有在螺旋桩上建造的建筑物/基础设施都受到了最小的结构破坏，然而，绝大多数被谴责的建筑物是在其他基础类型上建造的。国际社会有定性证据证明螺旋桩在地震多发地区表现良好，但工程师们并没有量化“为什么”这些桩是优越的基础元素，不幸的是，螺旋桩在美国地震活跃地区的使用仍然很少。因此，这个项目试图通过在加州大学圣地亚哥分校的大振动台中对螺旋桩进行地震荷载试验，找出“为什么”螺旋桩在地震区表现如此良好。这些数据的产生是特别重要和及时的，因为美国的某些地区现在需要对现有建筑进行抗震改造，但工程师缺乏有关基础系统的数据，以帮助使这些结构更安全。例如，2015年10月，洛杉矶市投票通过了一项地震条例，该条例将要求超过13,000个结构，包括预应力混凝土和软层木结构，进行抗震改造。尽管定性研究（如新西兰和日本）表明，螺旋桩等截面相对较小、锚固能力较高的桩，由于其细长细度、较高的阻尼比、延性和抗端部隆起性，似乎有利于抗震，但由于缺乏定量数据，目前尚无针对此类桩的建筑规范和实践现状。因此，对螺旋桩支承结构的抗震性能进行研究是必要的，这将有助于确保螺旋桩在地震地区的正确应用，并确定螺旋桩在地震地区使用的可量化的效益和/或局限性。该项目将通过向工程师提供全面的螺旋桩实验数据，使他们更好地了解如何设计一个对个人和社区更安全、更有弹性和可持续发展的建筑系统，从而使生活在地震带的人们受益。

This Rapid Response Research (RAPID) project will investigate the seismic behavior of helical piles by means of shake table tests on model piles in the UC San Diego laminar soil box. Helical piles are deep foundation elements that look like, and are installed like, a large steel soil screw - they have a slender steel shaft with any number of round plates at the tip to provide support to the structure they hold. Helical piles are spun into the ground with a large torque motor and provide support through soil bearing on the plates and along the shaft. They come in many lengths and are often the foundation of choice for retrofitting existing buildings or new, urban construction, due to their small footprint and ability to create minimal disturbance to surrounding structures. Although helical piles are installed as foundation elements in seismically active areas such as New Zealand and Japan, they have not been used widely in seismically active areas of the United States. This lack of use is, admittedly, due to having no quantifiable data to illustrate the seismic behavior of helical piles. In addition, there are no side-by-side seismic comparisons to other deep foundation systems available, other than qualitative "survival" stories like those from the 2011 Christchurch earthquake. After the series of earthquakes in 2011, the city of Christchurch was surveyed and it was found that all buildings/infrastructure constructed on helical piles sustained minimal structural damage, however, a large majority of the condemned buildings were constructed on other foundation types. The international community has qualitative proof that helical piles perform well in earthquake prone areas, but engineers have not quantified "why" those piles are superior foundation elements, and unfortunately, helical pile use in seismically active areas within the United States remains minimal. Therefore, this project seeks to find out "why" helical piles seem to behave so well in seismic regions by subjecting them to earthquake loads in the University of California - San Diego's Large Shake Table. These data are especially important and timely to generate because certain areas of the United States are now requiring seismic retrofits of existing buildings, yet engineers have a dearth of data regarding foundation systems to help make these structures safer. For example, in October 2015, the City of Los Angeles voted on a seismic ordinance that will require more than 13,000 structures, both pre-stressed concrete and soft-story wood structures, to be seismically retrofitted. Even though it is known from qualitative studies (e.g., New Zealand and Japan) that piles with comparatively small cross-section and high anchoring capacity, such as helical piles, are beneficial for seismic resistance seemingly due to their slenderness, higher damping ratios, ductility, and resistance to tip uplift, building codes and current state of practice have not been adequately developed for this pile type because no quantitative data exist. Research of seismic behavior of helical pile supported structures is therefore imperative to generate necessary data that will help ensure that helical piles are being correctly applied in seismic areas and establish quantifiable benefits and/or limitations of helical pile use in seismic areas. This project will benefit people living in seismic zones by educating engineers with full-scale helical pile experimental data so that they better understand how to design a building system that is safer, more resilient and sustainable for individuals and the community.