火灾后钢筋混凝土连续梁力学性能的计算分析

A Numerical Approach for Calculating the Mechanical Performance of the Fire damaged Reinforced Concrete Continuous Beams

摘要:

为研究火灾后钢筋混凝土连续梁力学性能，对已有试验结果进行理论分析，并提出计算火灾后构件力学性能简化算法.试验设置1根受火梁及1根对比梁，依据ISO834标准升温曲线对受火梁开展升温试验，静置后，进行受火梁及对比梁常温静载试验.根据实际升温曲线，利用有限元软件对受火梁温度场进行计算，结合常温及火灾损伤后材料力学性能，分析出截面弯矩曲率关系，得出截面抗弯刚度，继而计算出受火连续梁及对比连续梁的弯矩及位移.结果表明：当截面受压区直接受火时，刚度及承载力都有较大降低，其中刚度下降更加显著，当截面受拉区直接受火时，刚度及承载力变化较小；受火梁与对比梁相比，梁弯矩明显更多地向加载点分配，最终导致梁出铰顺序不同，随着荷载增加，常温梁中支座先屈服，继而加载点截面屈服，而受火梁加载点截面先于中支座截面屈服.计算结果与试验结果吻合较好，同时对比分析了传统的计算连续梁的方法，表明其不适用于预测火灾后损伤的连续梁力学性能.

Abstract:

To study the mechanical performance of reinforced concrete continuous beams after fire, a theoretical analysis on test results was carried out and a simplified algorithm was proposed for engineering practice. The experiment included standard ISO834 fire test on a two span beam and subsequent static load tests at ambient temperature on the fire damaged beam and a reference beam. Based on the measured temperature curve, the temperature distribution of the fire exposed beam was computed by the finite element method. According to the stress strain relationship of fire damaged concrete and rebar, the moment curvature relationship of the beam section and the bending stiffness of the beam were obtained. Furthermore, the moment distribution and deformation performance of both the reference beam and fire damaged beam were predicted. The computing results demonstrate that, when the compressive region of beam is subjected to elevated temperatures, bending stiffness and flexural strength will be both decreased and bending stiffness will decline more significantly; however, when the tensile region of the beam is subjected to fire, bending stiffness and flexural strength will decrease much slightly. Compared to the reference beam, the fire damaged beam is found in computing transiting more moment to the mid span. Additionally, computing result shows the plastic hinge appears firstly at the mid span point and then near the middle support point of two span beam, which is totally different from the reference beam. The computing results have excellent agreements with the test observation. Also it is proved the traditional algorithm for continuous beam in ambient is not suitable in predicting the behavior of fire damaged counterpart.