预应力混凝土连续梁板抗火性能非线性分析

Nonlinear finite element analysis of fire resistance performance for prestressed concrete continuous beams and slabs

摘要:

为模拟预应力混凝土连续梁板在火灾下的受力全过程,认为火灾下预应力混凝土梁板截面总应变符合平截面假定,基于混凝土、普通钢筋和预应力筋的耦合本构关系,用t时刻的混凝土应力计算t+1时刻混凝土的瞬态热应变、高温徐变,钢筋与预应力筋采用相同的解耦方法,可求得火灾下预应力混凝土梁板的弯矩-曲率曲线;对支座反力进行迭代求解,计算梁板在曲率与支座反力共同作用下的弯矩、挠度和支座位移,直至支座位移满足变形协调方程,进而对截面曲率积分可求得火灾下连续梁板的变形;编制的计算程序得到了抗火试验结果的验证.研究结果表明:支座和相邻跨的约束对连续梁板的耐火极限影响显著,相同条件下,边跨的跨中变形较中间跨大.

Abstract:

A numerical model to simulate loading process of prestressed concrete(PC) continuous beams and slabs at elevated temperature is presented. It is considered that plane sections before bending remain plane after bending. Based on the thermal-mechanical coupling constitutive models of concrete, reinforcing and prestressing steels, the transient strain, creep strain in concrete at time t+1 could be calculated by the stress in concrete at the former step. The coupled constitutive model of concrete could be decoupled, and the reinforcing and prestressing steels were calculated by the same way. Therefore, the moment-curvature relationships of PC beams and slabs subjected to fire can be calculated. The moment of flexure, deflection and support displacement of the beams and slabs imposed by curvature and support reaction together was calculated respectively. The support reaction was calculated by the iteration method until the deflection compatibility equation at the support was satisfied, and the deflection of continuous beams and slabs could be obtained. The deflection of PC continuous beams and slabs subjected to fire calculated by the computer program is verified by correlative fire resistance experiments. Through these studies, it is shown that support and span restraint effect has significant influence on the fire resistance of PC continuous beams and slabs. The mid-span deflection in side spans is larger than that in inner spans.