火灾下钢筋混凝土受弯构件的非线性分析

Nonlinear Analysis of Reinforced Concrete Flexural Members under Fire

火灾下钢筋混凝土受弯构件的变形非常大,伴随的转动也很大,尤其是单面受火的板,属于典型的大变形问题。基于平截面假定的M-非线性分析方法,以截面中心处的应变ε-和截面曲率为基本变量,建立平衡方程,原理简单,比较适合对火灾下钢筋混凝土受弯构件的简单分析。材料的本构方程中考虑了塑性应变、蠕变应变和热膨胀应变,并采用了有效的热弹塑性积分方案。利用Quasi-Newton方法,进行求解。通过实际编程发现,该方法简单,计算量小,且计算精度能满足工程要求。缺点是需要选择合适的ε-、初值。

Experiments revealed that reinforced flexural concrete members under fire underwent large deformations with large rotations, especially in slabs exposed to fire on one face. Typically it is a large deformation problem. Based on the assumption, the equilibrium equations were developed, regarding strain ε^-： and curvature φ as basic variations. The M-φ nonlinear analysis method is simple in principle, with easy calculations, and so it is suitable for analysis of reinforced concrete flexural members. Constitutive equations include plastic strains, creep strains and thermal strains. Effective integration strategy for Thermal-Elastic--Plastic Models is used. Quasi--Newton methods are adopted for solution. The computations are simple with small calculation amount compared with the finite element method. The computing results are accurate to meet engineering precision requirement. The shortcoming of the present method is that suitable initial values of strain e and curvature φ are required.