无粘结预应力混凝土梁双重非线性有限元分析

为研究无粘结预应力混凝土受弯构件的荷载-变形特性,用平面应力大变形问题的UL列式法,建立直线配索无粘结预应力混凝土T形截面简支梁的有限元模型,混凝土和钢筋分别采用了Ottosen四参数屈服准则和Von-Mises屈服准则的弹性-完全塑性本构关系;由于相对滑移,无粘结预应力钢束简化为随加载过程不断更新的外力边界条件;用弥散式裂缝模型模拟了混凝土的开裂并用Euler-Newton迭代法求解非线性有限元方程组.用2集中力3分点加载的简支梁试验对有限元模型进行验证,计算和试验所得荷载-挠度曲线及预应力钢束应力增量与荷载关系曲线均具有三折线形特征,且较为吻合,表明所建立的非线性有限元模型是合理和实用的;与不考虑几何非线性因素时的计算结果相比,考虑几何非线性计算所得的荷载-挠度曲线比不考虑几何非线性时更接近实测结果,表明在计算中考虑几何非线性很有必要.

Dual nonlinear FEM analysis of prestressed concrete beam with unbonded tendons

A plane stress large-deformation problem FEM model of prestressed concrete simply-supported beam with straight-line unbonded tendons was established with Updated Lagrangian formulation.Elastic-perfectly plastic constitutive models with Ottosen and Von-Mises criteria were chosen for the concrete and the steel respectively.Unbonded tendons were simplified as varying force boundary conditions while a smeared crack model was introduced to simulate the crack propagation.Nonlinear FEM equations were solved by Euler-Newton iteration method.In order to verify the FEM model,a model beam was loaded to failure by two concentrated loads at 1/3 span,the analytical and experimental load-deflection curve and load-stress-increment curve were all three-segment polygonal function and showed good consistency,which indicates that the nonlinear FEM model is reasonable.Compared with the analytical load-deflection curve neglecting the geometrical non-linearity,the result of the dual nonlinear FEM model is closer to that of the experimental curve,so it's necessary to the reckon in the geometrical non-linearity in FEM model.