V-H-M-T联合作用下桥梁基桩承载特性及其设计计算方法研究

Pile foundations generally bear the action of combined loading in 3D space. Due to the vehicle load differences over the deck, not only vertical loading is exerted on the pile top, but lateral loads (including horizontal forces Hx & Hy and moment loads Mx & My along and transverse the bridge direction,respectively) as well as the torsion T are caused to result in a complicated bearding behavior of piles in bridge engineering. Available 2D analysis methods based on the superposition principle are hard to evaluate the bearing capacity reasonably and tend to bring about engineering accidents. Therefore, according to the bearing mechanism of piles under uniaxial loading, 3D numrical analysis by using ABAQUS and the Probe Test method will first be carried out to simulate the bearing responses of piles under the action of various combinations of V, H, M and T both in one same plane and two orthotropic planes, and to obtain the corresponding failure enveloping lines and face. Then, the coupling effect of various kinds of loading as well as the failure creterion of pile shaft will be discussed in detail. Afterwards, combined loading instruments will be designed and made to finish the static tests of single pile under various combined loading in single-layer and two-layer subsoil, respectively. Based on the measured force and displacement data from the tests, further parameter analysis will be performed to find out the influencing rules by various factors on the bearing capacity of the pile shaft, from which the simplified bearing capacity calculation formula will be derived for application in engineering practice.

工程桩实际多处于空间受力状态，桥梁桩基更因桥面车辆荷载差异等原因，除承受竖向力V外，还在顺桥向与横桥向受到水平力(Hx和Hy)、弯矩(Mx和My)、甚至扭矩T的联合作用，受力性状极为复杂，基于叠加原理的二维分析方法难以合理评估其承载力而可能导致工程事故。为此，本研究首先拟基于单一受荷桩承载特性和ABAQUS有限元平台，采用Probe Test法进行数值模拟实验，获得同一平面内及两正交平面内不同V、H、M或T组合作用时的破坏包络线，进而获得其共同作用时的六自由度空间破坏包络面，据此探讨桩顶荷载耦合作用机理及桩身承载力破坏准则。在此基础上，研制联合加载装置，采用Swipe法完成均质与双层地基中不同组合荷载下的单桩静载模型试验，根据实测荷载-位移曲线，验证理论与数值分析结果，并通过进一步的参数分析，获得荷载类型及其组合形式对桩身承载力的影响规律，由此确定出桩身承载力简化计算公式，供工程设计参考。

桥梁桩基础除承受结构自重(V)以外，还会因车道车辆荷载差异、船只撞击、地震等受到水平力H、弯矩M、甚至扭矩T的共同作用，导致其承载性状极其复杂。常规设计方法多基于二维单一平面内的叠加原理，难以准确评价桩身承载力，甚至偏于不安全，有必要分析荷载联合作用效应，合理确定空间破坏包络面和判定桩身极限承载力。为此，本项目针对受V-H-M-T联合作用的桥梁桩基的承载变形特性问题：. 先基于剪切位移法，考虑桩周土体剪切模量沿深度呈幂函数和指数函数分布，假定桩周土塑性变形自上而下开展，采用Bessel函数转化求解了单、双层地基中受扭桩桩身内力位移的弹性、弹塑性和塑性解析解；引入虚土桩建立桩-土体系的总能量方程，由最小势能原理分别导得桩身及土体的受扭控制方程，进而获得桩身扭转角的有限差分方程式，再将桩周土体视为理想弹塑性材料，给出了塑性状态下的单桩受扭分析方法；引入理想弹塑性荷载传递模型，获得了成层地基中单桩受扭的递推计算方法；考虑桩-土接触面上的位移非协调性，采用剪切位移法建立出桩身位移控制方程，进而导出不同V-T加载顺序下单、双层地基中的桩身内力位移解答；将联合受荷桩转化为考虑耦合机理的一维杆单元，基于m法和凝聚方法导得了具有一般形式的、适合分析H-M-T受荷桩的杆单元刚度矩阵方程，并求得了桩身内力位移分布。. 然后，设计完成了一系列H-T、V-T、V-H-M-T联合受荷桩模型试验，通过自制联合加载和测试装置，获得了不同荷载组合工况下的桩顶荷载-变形曲线、桩身内力位移、破坏模式及承载力包络线，并验证了理论解答的可行性。. 最后，基于ABAQUS分别建立单层与双层地基中桥梁基桩3D有限元分析模型，采用Probe Test法进行对比分析，确定了不同工况下的荷载-位移曲线和破坏包络线，进而给出了桩身承载力简化计算公式，并通过工程实例应用与参数分析给出了桩身长径比与剪切模量、地基土强度、土层厚度、加载路径、荷载组合等因素对桩身变形承载力的影响规律及桩身承载力破坏准则，可供工程设计参考。