超高车辆撞击下预应力混凝土空心板桥损伤机理及撞后承载力研究

为研究超高车辆撞击预应力空心板桥的损伤破坏机理及被撞主梁承载力的变化规律，建立精细的预应力空心板桥-双轴卡车碰撞有限元模型，其中车辆模型采用美国国家碰撞分析中心建立的标准双轴卡车模型，并用足尺模型试验结果对空心板桥模型承载力进行验证。分别考虑车辆速度、载质量、超高高度、撞击角度和混凝土强度等因素，采用显式动力分析软件LS-DYNA进行不同参数下超高车辆-桥梁的碰撞分析（共计13种工况）。研究结果表明：在超高车辆撞击作用下，桥梁整体位移和变形较小，空心板桥主要发生局部型损伤，碰撞区域混凝土剥落，部分普通钢筋及预应力钢筋外露甚至屈服退出工作，车辆的碰撞速度、碰撞角度以及结构自身的材料强度对于空心板局部损伤影响较明显；在不同车辆撞击参数下，被撞主梁的竖向抗弯承载能力损失水平都在15%以内，30°角为最不利的撞击角度，损伤结构的承载力下降达14%；混凝土强度为C30时空心板桥撞损后的承载力下降比例要大于C40及C50。在主梁预应力筋因撞击退出工作的情况下，被撞梁的竖向承载性能及变形刚度均明显降低，其中车辆撞击侧预应力底板束失效情况下，竖向承载力仅为损伤前承载力的65%；底板束和腹板束同时失效时，主梁在自重作用下出现整体垮塌。对于预应力空心板桥，需高度重视撞后预应力筋损伤破坏对主梁承载力的影响，在桥梁防撞设计中应予以充分考虑。

Damage Mechanism and Postcollision Bearing Capacity of Prestressed Concrete Hollow Slab Bridge Under Overheight-vehicle Collision

To investigate the damage mechanism and postcollision bearing capacity of prestressed concrete hollow slab bridges subjected to overheight-vehicle collision,a refined prestressed concrete hollow slab bridge-biaxial truck collision finite-element(FE)model was established.Full-scale model test results were used to validate the vertical bearing capacity of the bridge.The vehicle model adopted the standard biaxial truck described by the National Crash Analysis Center in the United States.The explicit dynamic FE software LS-DYNA was employed to conduct the simulation of an overheight-vehicle collision with a bridge in 13cases,with various vehicle impact speeds,vehicle impact masses,vehicle ultrahigh heights,impact angles,and concrete strengths.The results showed that the overall deformation and displacement of the bridge was not significant,and the overheight collision on the bridge mainly caused local damage,such as spalling of concrete,reinforced and prestressed bar yield,and fracture failure.The vehicle impact speeds,impact angles,and concrete strengths had an obvious influence on the local damage of the hollow slab bridge.The loss level of the vertical bearing capacity of the damaged girder was within 15%under different vehicle speeds,masses,overheights,and concrete strengths.A 30°angle was the most unfavorable impact angle under all impact angles investigated,and the ultimate vertical bearing capacity decreased by 14%.The vertical bearing capacity of the damaged girder was reduced more significantly than that of C40and C50when the concrete strength was C30.The vertical bearing capacity and deformation stiffness of the damaged girder decreased obviously once the prestressed bar failed after vehicle collision.Once the prestressed bar on the bottom slab failed,the vertical bearing capacity decreased to 65%.In addition,the bridge could not even bear its own weight when both the prestressed bars failed on the bottom slab and web of the impacted side.Extra attention is needed to quantify the influence of failed prestressed bars on the bearing capacity of bridge and should be fully considered in the anti-collision design of bridge.