落物竖向冲击下PC装配式简支箱梁桥动力响应及损伤分析

为评估落物(重型货物、落石)竖向冲击下的桥梁工作性能,以跨径30 m的预应力混凝土装配式箱梁桥为对象,建立精细化结构模型并与足尺模型试验结果进行对比验证; 采用显式动力分析方法对落物冲击多片式箱梁的动力响应和损伤发展过程进行分析,探讨了不同坠落冲击位置、冲击能量以及冲击角度等因素下桥梁的损伤特征和发展规律。结果表明:落物冲击作用可导致箱梁同时出现整体和局部型损伤,损伤过程可分为初始碰撞、损伤扩展和最终稳定3个阶段; 横向冲击位置由中梁转至边梁,受冲击梁体的损伤逐渐严重,梁体的位移和支反力显著增长; 落物冲击位置由跨中移动至支点处,破坏模式逐渐由弯曲型转变为剪切型,冲击梁体的位移和支反力逐渐减小; 随着冲击能量的增加,受冲击的主梁损伤明显加重,对未受冲击的主梁损伤影响较小,钢筋应力、碰撞力、受冲击主梁支反力和位移呈增长趋势,当冲击能量超过391.9 kJ时,纵向钢筋屈服; 落物角度变化会影响碰撞接触面积,接触面积减小,被冲击梁体的损伤分布区域、支反力和位移也会明显减小,但是局部接触区域的损伤更为严重; 落物冲击参数对于桥梁的损伤影响明显,加固维护时需要根据其特定的损伤分布特征采取相应措施。

Dynamic Response and Damage Analysis of Simply Supported PC Prefabricated Box Girder Bridge Under Vertical Impact of Dropped Cargo

The 30 m span prestressed concrete prefabricated box girder bridge was taken as study example to evaluate the working performance of bridge under vertical impact(heavy dropped cargo, rockfall). The refined finite element(FE)model of bridge structure was established and also verified by full-scale model test results. The dynamic response and damage evolution of multi box girder bridge was investigated by explicit dynamic analysis under dropped cargo impact. The damage feature and mechanism of the bridge were analyzed under different impact positions, energies angles of dropped cargo. The results show that the impact load will lead to both overall and local damage, and the damage process can be classified into three stages, including initial impact stage, damage progress stage and final stable stage. The impacted girder suffers more severe damage, and the displacement and reaction force increase significantly as that the impact position moves from middle girder to side ones. As the impact position transfers from mid-span to support end, the damage pattern of the impacted beam varies from flexural failure to shear failure, and the displacement and support reaction decrease as well. As the impact energy increases, the impacted girder exhibits more severe damage while the non-impacted girder is less influenced, and the rebar stress, impact force, reaction force and displacement of the impacted girder also significantly increase. The longitudinal rebar yields when the impact energy exceeds 391.9 kJ. The impact contact area varies with the cargo falling angle. The damage range, reaction force and vertical displacement reduce significantly if the cargo contact area decreases, whereas the local damage is more severe. The impact parameters of dropped cargo have great influence on the bridge damage, and the corresponding reinforced maintenance measures should be adopted according to the specific damage characters.