受火浅圆钢拱平面内跳跃失稳与弯曲行为分析

Analysis on the snap-through instability and bending behavior of steel arch under fire

通过ABAQUS有限元数值模拟分析,考察了受火作用浅拱结构平面内的跳跃稳定和弯曲行为。针对温度与集中载荷共同作用的圆钢拱,进行了详细的参数研究,包括载荷比、端部约束刚度、结构几何等对结构行为的影响,讨论了材料塑性效应和热膨胀效应;并根据火灾下截面弯矩与轴力共同作用的广义屈服函数和跳跃失稳的定义判定浅拱的失效模式,对比了不同加载方式对结构临界温度的影响。研究结果表明:在静力载荷和火灾作用下,浅圆钢拱存在两种失效模式,即弯曲失效和跳跃失稳;载荷比由0.2增大到0.9时,结构的临界温度逐渐减小;当载荷比接近1时,微小的载荷增大,临界温度会发生急剧变化,即载荷比越大,钢拱的临界温度越低,抗火能力越弱;对于不同的约束情况,固支拱的抗火能力最强,铰支拱的抗火能力最弱;临界温度随结构几何参数单调变化;另外,静载荷与温度的加载顺序也会对结构的失效行为产生影响。

In this paper, the snap-through stability and bending behavior in the structural plane of shallow arches subjected to fire are examined through ABAQUS finite element numerical simulation analyses. Detailed parameter studies are performed for round steel arches with the interaction of temperature and concentrated load, including the effects of load ratio, end restraint stiffness, and structural geometries on structural behavior. The elasto-plastic effect and thermal expansion effect of materials are discussed. In the fire, the failure mode of shallow arches is determined by the generalized yield function which under the combined effect of bending moment and axial force at section, and the definition of snap-through instability. Effects of different loading ways on the critical temperature of structures are compared also. The research results show that there are two failure modes for shallow round steel arches under the action of static load and fire, i.e. bending failure and snap-through instability. When the load ratio increases from 0.2 to 0.9, the critical temperature of the structure gradually decreases, while the load ratio is close to 1, the micro load increases and the critical temperature changes dramatically. That is, the larger the load ratio, the lower the critical temperature of the steel arch, leading to the weaker of the fire resistance. For different constraints, the fixed arch is superior in fire resistance while the hinged arch is least in fire resistance. However, the critical temperature changes unidirectional with the structural geometric parameters. Besides, the loading sequence of static load and temperature also affects the failure behavior of structures.