整体式桥台桥梁新型桩基隔震体系工作机理和计算方法研究

The durability of bridge expansion joints and bearings could be solved by the integral-abutment bridge (IAB) concept. The seismic behaviors of IAB is becoming an important task. In the pile-isolation hereby proposed the upper part of the pile is released from the surrounding soil using a pre-hole, and so obtaining an increment in the fundamental period of the bridge. In meantime dissipative filler materials in the pre-hole is proposed to be used to reduce the seismic response of the system. In the research, different modelling strategies of the pile-isolation including the soil-structure will be proposed and evaluated. The accuracy of simply beam models based on Nonlinear Winkler Foundation applied to the pile-isolation for IABs will be studied and compared to more accurate 3D continuum models and related p-y curves will be investigated. Moreover shacking table tests will be developed to confirm and validate the model and p-y curves adopted. A design theory for the Pile-Isolation will be defined based on an optimization procedure able to consider together both static and dynamic conditions under different limit states. The research results will provide the mechanical behavior of a new type of base isolation system called PILE ISOLATION that can be a reliable and economical way to protect bridges against earthquake and can help the spread of Iabs typology.

整体式桥台桥梁较好地解决了桥梁伸缩缝和支座耐久性的重要问题，其抗震性能也受到广泛关注。桩基隔震体系采用预扩孔内填充耗能材料的方式使桩基上部一定长度范围内的桩身与桩周土隔离，增大桥梁的基本周期并降低结构的地震响应。提出适用于考虑桥梁-桥台-土整体性的整体式桥台桥梁新型基础隔振体系，拟采用理论和试验研究的方法针对其抗震工作机理和力学性能进行研究。试验与理论结合分析阻尼材料耗能特性和力学性能，开展桩基础隔振整体式桥台的振动台试验和实际场地试验，基于非线性winkler梁模型研究相应的p-y曲线，与精细的三维有限元分析进行对比研究，并与振动台试验进行相互验证；进行隔振桩体系优化研究，分析静力和动力作用下的不同极限状态并提出优化准则；提出整体式桥台新型隔振设计理论。研究成果将揭示整体式桥台桥梁桩基隔震体系的工作机理，使其成为一种有效且经济的整体式桥台桥梁抗震防护方法，有助于整体式桥台桥梁的发展。

整体式桥台桥梁较好地解决了桥梁伸缩缝和支座带来的整体性与可持续耐久性不足等问题，但同时也带来了桥台混凝土桩基抗震性能不足问题。在混凝土桩顶部区域扩孔并填充阻尼材料以形成扩孔隔震桩是提高桥台桩基抗震性能较好的选择。为此，本项目针对扩孔隔震桩-土相互作用机理开展了理论分析、试验研究、数值模拟和优化分析等工作，在此基础上给出了简化设计计算方法。本项目研究成果可为我国地震区大量桥梁的建设和改造时应用带扩孔隔震混凝土桩的整体式桥台桥梁提供理论基础。本项目主要研究内容及成果总结如下：.（1）开展了土-橡胶混合物的材性试验，探明扩孔内填充材料的力学特性。.（2）通过拟静力试验与三维实体有限元模拟发现，扩孔隔震桩可提高桩-土体系的耗能能力；填充松散颗粒状橡胶颗粒的耗能效果优于填充泡沫。通过修正双曲线型p-y曲线的初始刚度和桩周土极限抗力可拟合得到适用于扩孔隔震桩-土相互作用的静力p-y曲线。.（3）通过试验与三维实体有限元模拟探明了不同缩尺比例对于扩孔隔震桩-土相互作用的影响规律。.（4）通过地震模拟振动台试验与三维实体有限元模拟发现，扩孔隔震桩可显著提高桩-土体系的阻尼比。同时，通过修正静力p-y曲线的初始刚度和桩周土极限抗力拟合得到了适用于扩孔隔震桩-土相互作用的动力p-y曲线。.（5）基于非线性温克尔地基梁法和有限差分法，提出了扩孔隔震桩-土相互作用的理论滞回曲线计算模型，开展了足尺扩孔隔震桩-土相互作用的滞回性能优化分析，获得了最优扩孔深度为桩长的0.1～0.15。.（6）通过开展一系列非线性动力分析获得考虑扩孔隔震桩-土相互作用的整体式桥台桥梁的弹塑性反应谱和地震作用折减系数。结果表明，采用扩孔隔震桩可显著减小整体桥上部结构的位移时程响应；当温克尔地基梁特征长度约等于10m且温克尔地基梁特征长度与桩长比值约等于1时，桩-土体系的耗能性能最佳；若扩孔深度与桩长之比大于0.15，地震作用折减系数可取为1.4。