基于韧性耗散模型的桥墩船撞混合桩损伤定量识别研究

Vessel collision with pier causes inevitably piles in hidden environment damage, which seriously threatens bridge safety. Summarizing existing studies, if taking into account the influence of interaction between steel casing and core concrete of pile, based on the current damage identification technologies, it is unreliable to carry out the damage quantitative identification of hybrid pile (pile with steel casing) under vessel collision, and detection of damage degree of hybrid pile including steel casing influence has been always a challenge in the field of vessel collision with bridge. Based on the important theoretical basis that both damage and toughness of structures are different forms of energy dissipation, this project is aiming at studying the dynamic response mechanism of hybrid pile subjected to vessel collision and interaction between steel casing and core concrete, revealing the internal natural relations between the characteristic change and energy transition and elastic-plastic strain energy dissipation of hybrid piles, establishing the change rule of toughness of hybrid pile under vessel collision, achieving the toughness-based damage evolution law of hybrid pile under vessel collision, searching for an error reducing means for roughness-based damage of hybrid pile, lastly, to establish a new damage quantitative identification method based on toughness dissipation with definite physical meaning, sensitivity to damage and facilitated test, to lay theoretical basis and provide a new way for damage evaluation and life assessment of hybrid pile when bridge piers are subjected to vessel collision.

船撞桥墩导致基桩损伤无法避免，处于隐蔽环境中的基桩损伤严重威胁桥梁安全。综合既有研究表明，若计入钢护筒与核心混凝土相互作用的影响，基于现有损伤识别技术进行桥墩船撞下的混合桩（带钢护筒的基桩）损伤定量诊断将不再可靠，考虑钢护筒影响的混合桩损伤定量识别成为桥梁船撞损伤评估领域的难题。基于结构损伤和韧性变化均是能量耗散不同表现形式的重要理论基础，本项目研究桥墩船撞下混合桩的动态响应机理以及钢护筒与核心混凝土相互作用效应，揭示混合桩力学性态变换与能量转换、弹塑性应变能耗散之间的内在本质关系，建立船撞桥墩混合桩韧性变化规律，实现以韧性表征的桥墩船撞混合桩损伤演化模型，探求损伤韧性表达的误差降低方法，最终构建以具有明确物理意义、对损伤敏感和便于测试的宏观力学参量—韧性的耗散来表征的桥墩船撞混合桩损伤定量识别新方法，为实现桥墩船撞下的混合桩损伤诊断与寿命评估奠定理论基础和提供新手段。

碰撞作用下钢护筒复合桩的动力特性尚未明晰，且由于基桩所处条件的复杂性，发展撞后损伤评估新方法具有重要意义。本项目以建立基于韧性耗散模型的基桩撞后损伤评估方法为最终目标，主要开展了以下研究工作：(1) 开展了钢护筒复合桩的侧向加载试验研究与有限元模拟。探讨钢护筒对基桩性能和破坏模式的影响，并分析其影响机理。结果表明，钢护筒复合桩的力学性能和失效模式严重受制于钢护筒与RC桩等效塑性区对应区域的位置关系；钢护筒-核心混凝土界面力是基桩破坏模态发生改变的直接原因。基于钢护筒的参数研究，提出钢护筒参数优化公式。(2)开展了21根钢护筒复合桩试件的侧向碰撞试验研究。研究参数包括钢护筒长度、冲击能量及上部质量，分析了其对钢护筒复合桩的冲击动力响应、破坏模式、损伤状态的影响。归纳了侧向碰撞下钢护筒复合桩的韧性耗散过程，阐述了韧性耗散过程的三阶段：上升段、下降段和稳定段。(3) 通过扩展数值模拟，分析护筒对基桩侧向碰撞动力响应的影响，揭示了钢护筒对基桩动力特性的影响机理。还比较了不同钢-混界面条件及不同土体刚度对基桩动态响应、损伤状态的影响。结果表明土体刚度和钢-混切向界面条件影响有限，钢护筒与核心混凝土在冲击作用下的相互作用主要通过二者界面间的法向作用力实现。(4) 结合碰撞头撞深、初始动能和桩土系统的静力韧性，提出了碰撞过程中韧性峰值和最大位移预测方法。并以位移为指标，建立了基于韧性角度的钢护筒复合桩受撞后损伤评估方法。本项目研究成果可用于指导船撞作用下桩基础的设计和损伤评估，所提出的基于韧性的损伤评估方法亦可推广至其他构件/结构中应用。