STUDY ON BEAM ELEMENTS FOR ELASTOPLASTIC BUCKLING BEHAVIOR OF CHORD MEMBERS IN TRUSS GIRDERS

我们开发了一种梁单元，它可以模拟具有局部损伤的桁架梁的倒塌行为，如弦杆的屈服和屈曲现象。在单元中，最简单的模型被认为是由两个弹性直杆和一个弹塑性旋转弹簧组成的，用于描述弦杆件的屈曲行为。采用考虑轴向力和弯矩共同作用的广义塑性铰模型，估算了回转弹簧屈服后的状态。但广义塑性铰模型与实际情况不一致。在这项研究中，我们提出了一种新型的弹塑性梁单元，它考虑了塑性区大小的变化和包辛格效应。将本单元应用于我们的桁架梁模型，使我们能够准确地模拟实际行为。通过对某桁架梁的有限元分析，得出了硬化特性和塑性区尺寸变化对加固效果的影响。为简化起见，将弹塑性梁单元的截面形状假定为双翼缘截面型。根据上述概念，建立了一种新型的梁单元。假设每个法兰具有具有恒定硬化系数的组合硬化特性。通过与有限元计算结果的比较，验证了该单元的有效性。3.将上述单元推广到具有包辛格效应的材料中。通过与有限元计算结果的对比，验证了扩展方法的有效性。

We have developed a beam element that makes it possible to simulate the collapse behavior of a truss girder with local damages like the yielding and buckling phenomenon of chord members. In the element, the simplest model, which consists of two elastic straight bars and an elastoplastic rotary spring, is considered to represent the buckling behavior of chord members. The condition of the rotary spring after yielding is estimated with the generalized plastic hinge model in which the interaction of axial force and bending moment is taken account. But the generalized plastic hinge model is different from the actual. In this study, we present the new type of an elastoplastic beam element involving the change of plastic region size and the Baushinger effect. Applying the present element to our truss girder model enables us to simulate the actual behavior exactly. We obtained the following results :1.It was shown that the influence of hardening properties and the change of plastic region size via results of a truss girder by FEM. Furthermore, the basic concepts to formulate the influence of the hardening and the plastic region size were clarified.2.For the simplicity, the cross section shape of an elastoplastic beam element was assumed to be the 2-flange section type. According to the above-mentioned concepts, a new type of beam element was formulated. Each flange was assumed to have combined hardening properties with the constant hardening coefficient. The validity of the element was confirmed by comparison with results by FEM.3.We extend the above element to the case of a material with the Baushinger effect. Then we confirmed the validity of the extension by comparison with results by FEM.