预应力混凝土梁桥过火后的材料性能

Material properties of prestressed concrete girder bridge after exposed to fire

火场最高温度、持续时间、扩散条件以及高温下混凝爆裂等因素增加了利用温度获得材料性能的难度。针对火灾后评估预应力混凝土梁桥时需快速、准确、真实地获得其材料性能的需求,对在役高速公路预应力混凝土桥梁过火后拆除的32块空心板进行表观分类和材料试验,通过实测过火后材料性能,获得常用检测指标与材料性能的关系,并利用极限承载能力试验及有限元模拟验证其适用性。结果表明:混凝土高温爆裂剥落,致使空心板截面损失,并进一步降低该区域混凝土及预应力钢绞线强度,是导致该截面抗弯承载能力降低的主要原因;当过火后混凝土剥落深度超过2/3钢绞线净保护层时,混凝土抗压强度、预应力钢筋线拉伸强度折减系数达0.7,将严重影响结构极限承载能力;火灾作用将改变空心板极限破坏形态,由延性转为脆性破坏;利用常规检测指标与材料性能的折减关系,并结合有限元模拟分析过火后预应力空心板梁的极限承载能力,满足工程精度。

The factors such as maximum temperature,duration,diffusion condition and concrete bursting at high temperature increase the difficulty of obtaining material properties by using temperature.In order to quickly obtain the real performance parameters of the materials of the pre-stressed concrete beam bridge in the post-disaster bridge evaluation,the appearance classification and material test of 32 hollow slabs demolished after the fire of the existing beam bridge in a highway were carried out.The relationship between the commonly used testing indexes and the properties of materials is obtained by measuring the properties of materials after fire.The applicability of these indexes is verified by the ultimate bearing capacity test and finite element simulation.The results show cracking and spalling of concrete at high temperature not only results in significant loss of section,but also significantly reduces the strength of concrete and prestressing steel strand in this area,which leads to the reduction of bearing capacity.When the spalling depth of concrete exceeds 2/3 of the net protective layer of steel strand after overfire,the reduction coefficient of compressive strength and tensile strength of pre-stressed steel wire reaches 0.7,which will seriously affect the ultimate bearing capacity.Fire action will change the ultimate failure form of hollow slab from ductility to brittleness.The ultimate bearing capacity of the prestressed hollow beam after fire is analyzed by using the reduction relationship between the conventional inspection indexes and the material properties,and the finite element simulation,so as to meet the engineering precision.