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

RAPID：大规模振动台试验量化干砂中螺旋桩的地震响应

• 批准号: 1624153
• 负责人: Amy Cerato
• 金额: $ 13.32万
• 依托单位: University of Oklahoma Norman Campus
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-03-01 至 2019-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1624153&HistoricalAwards=false
• 关键词: RAPID; Large; Scale; Shake; Table

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.

本快速反应研究（RAPID）项目将通过在加州大学圣地亚哥分校层状土箱中对模型桩进行振动台试验来研究螺旋桩的抗震性能。 螺旋桩是深基础元件，看起来和安装都像一个大型钢土螺丝-它们有一个细长的钢轴，顶端有任意数量的圆板，为它们所支撑的结构提供支撑。 螺旋桩通过大扭矩电机旋入地面，并通过板上和沿着轴的土壤支承提供支撑。 它们有多种长度，通常是改造现有建筑或新城市建设的首选基础，因为它们占地面积小，对周围结构的干扰最小。 虽然螺旋桩作为基础元件安装在地震活跃地区，如新西兰和日本，他们还没有被广泛使用在美国的地震活跃地区。无可否认，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，除了像2011年基督城地震那样的定性“生存”故事外，没有与其他深基础系统进行并排地震比较。 在2011年的一系列地震之后，对基督城进行了调查，发现所有在螺旋桩上建造的建筑物/基础设施的结构损坏都很小，但是，绝大多数被谴责的建筑物是在其他基础类型上建造的。 国际社会有定性的证据表明，螺旋桩在地震多发地区表现良好，但工程师们还没有量化“为什么”这些桩是上级基础元素，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，该项目试图找出“为什么”螺旋桩似乎在地震区表现得如此之好，使他们在加州-圣地亚哥大学的大型振动台地震荷载。 这些数据是特别重要和及时生成的，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抗震条例，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。即使从定性研究中得知（例如，新西兰和日本），具有相对小的横截面和高锚固能力的桩，如螺旋桩，似乎有利于抗震，因为它们的细长，更高的阻尼比，延性和抗端部上拔，建筑规范和目前的实践状态还没有充分开发这种桩类型，因为没有定量数据存在。因此，螺旋桩支撑结构的抗震性能的研究是必要的，以产生必要的数据，这将有助于确保螺旋桩被正确地应用在地震区，并建立可量化的好处和/或螺旋桩在地震区使用的限制。 该项目将通过向工程师提供全尺寸螺旋桩实验数据，使他们更好地了解如何设计一个对个人和社区更安全，更具弹性和可持续性的建筑系统，从而使生活在地震区的人们受益。