考虑长期荷载作用的高强钢管混凝土桥墩撞击下及撞击后力学性能研究

Concrete-filled steel tubes (CFST) have been widely used as bridge piers. By adopting high strength steel in the steel tube, the self-weight of the piers could be effectively reduced and their seismic resistance could be enhanced. As a result, concrete-filled high strength steel tubular (CFHSST) bridge piers have good potentials in engineering applications. The design of bridge pier against impact load is critical for its structural safety during its service life. However, currently there is a lack of research on the impact behavior of CFHSST piers. Studies on the impact behavior of conventional CFST also have some limitations. For instance, there is no sufficient study on the mechanical behavior of post-impact CFST. This project aims at studying the impact resistance and the post-impact behavior of CFHSST piers through experimental, numerical and theoretical investigations. The influence of major parameters, including the impact energy and impact location, is considered. Due to the fact that the long-term load carried by the bridge piers has direct influence on their impact mechanism, the effect of long-term sustained load is a major focus in the study. The contents of the project consist of: 1) the mechanism of long-term loaded CFHSST bridge piers subject to impact load; 2) the resistance and design method of CFHSST bridge piers subject to impact load; 3) the calculation method of residual strength of impacted CFHSST bridge piers. The research outcomes could serve as the basis for the engineering applications and service safety of CFHSST bridge piers, and it also could be used as references to the studies of the impact behavior of conventional CFST.

钢管混凝土已在桥墩中大量应用，其外钢管若使用高强钢，形成高强钢管混凝土，可有效减小桥墩自重，提高其抗震性能，具有良好的工程应用前景。对桥墩进行抗撞击设计对保障其安全服役极为重要，而目前尚缺乏对高强钢管混凝土撞击力学性能的研究，对普通钢管混凝土的撞击研究也存在一定不足，如对其撞击后力学性能的研究尚不充分。本项目以高强钢管混凝土桥墩为对象，通过落锤试验、数值模拟和理论分析，考虑主要参数如撞击能量和撞击位置等的影响，对其撞击下及撞击后力学性能开展系统研究。由于桥墩遭受撞击时承受的长期荷载对其撞击工作机理有直接影响，拟对此进行重点分析。研究内容包括：1）考虑长期荷载作用的高强钢管混凝土桥墩撞击下工作机理；2）高强钢管混凝土桥墩抗撞击承载力及设计方法；3）高强钢管混凝土桥墩撞击后轴压剩余承载力计算方法。研究成果可为高强钢管混凝土桥墩工程应用和安全服役奠定基础，也可为普通钢管混凝土的撞击研究提供参考。

本项目针对考虑长期荷载影响的高强钢管混凝土桥墩在撞击下及撞击后的力学性能，基于试验研究、数值模拟、理论分析和设计方法研究，理清了关键参数对其撞击下和撞击后力学性能的影响规律，明晰了决定其抗撞击承载力和撞击后剩余承载力的力学机制，提出了可用于高强钢管混凝土桥墩抗撞击设计和撞击后剩余承载力评估的简化计算方法。本项目主要研究内容和关键结论如下：1）试验研究共设计了38根圆高强钢管混凝土及26根普通强度钢管混凝土的撞击及静力对比试件，分析了其在撞击荷载下的破坏形态、撞击力时程曲线及挠度时程曲线，及关键参数的影响规律。结果表明，在长期荷载较低时，其对高强钢管混凝土的应力和内力重分布影响较小；撞击荷载下高强钢管混凝土主要呈现弯曲破坏形态，与其在静力加载下的破坏形态较为类似，但相比于静力加载其局部破坏更加明显；在具有同样静力轴压承载力时，高强钢管混凝土的抗撞击承载力要低于普通强度钢管混凝土。2）基于有限元模型的机理分析表明，高强钢管混凝土抗撞击承载力低于同等条件普通钢管混凝土的主要原因是高强钢材的应变率效应要低于普通钢材，而钢材强屈比、截面含钢率、截面直径及撞击速度则是影响高强钢管混凝土动态抗弯承载力的主要因素；在同样的侧向挠度之下，遭受撞击的高强钢管混凝土轴压剩余承载力要低于遭受静力荷载的对比构件，表明侧向挠度和撞击部位的局部损伤对轴压剩余承载力均具有较为显著的影响，是衡量其在撞击后剩余承载力的关键。3）基于机理分析、参数分析和数据拟合，提出了高强钢管混凝土在撞击荷载下的动态抗弯承载力计算方法以及其在撞击后的剩余承载力简化计算方法。简化计算方法可用于设计阶段高强钢管混凝土桥墩的抗撞击承载力设计以及服役阶段遭受撞击荷载之后的剩余承载力评估。