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

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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.