高軸力下で繰返し曲げを受けるH形断面鋼柱の弾塑性座屈モデル

Abstract

1. Introduction In the heavy plant structures such as thermal power plants composed with the braced frame structures, the H-section columns receive cyclic bending moment under high axial forces, and cause local and overall buckling. However, it is difficult to express the collapse characteristics of columns under such conditions with multi-spring models because the yield areas distributes not only at the ends of the columns but along the member. Modeling such columns as detailed FEM with shell-models is still time-consuming and not practical in structural design. To solve such problem, a single-dimensioned macro-member model composed of fiber elements is proposed in this paper. Each element has the hysteresis reflecting local buckling characteristics and hence can express the local and overall buckling phenomena with simple element which can be easily plugged into time-history analyses. The validity of the proposed element is compared with experiments and FEM analyses with shell elements, followed by discussions on their accuracies. 2. Cyclic bending test of H-section columns under interlocking axial loads Cyclic loading tests with bending moment and interlocking axial loads are carried out on two H-section columns with different width-thickness ratios. FEM analyses were also carried out under the same loading conditions and compared with the test results. Generally the maximum buckling forces observed in the test were higher than FEM analyses with shell elements, however, the deterioration ratios are more significant in the test results. 3. FEM analyses with different width-thickness ratios Cyclic behavior of H-section columns with various width-thickness rations under bending moments and high axial forces are researched with constructed FEM analyses. It is confirmed that the deterioration-starting curvature is reduced with higher width-thickness ratios and axial forces. The overall hysteresis are generally covered with the monotonic load-deformation curves. 4. Proposal for a single-dimensioned macro-member model To construct a simple element applicable to time-history analyses for large structures, a single macro-member models composed of fiber elements whose hysteresis reflects the characteristics of local buckling deteriorations. The hysteresis curves are composed of six stages with different simple functions of normalized axial deformation, and deterioration characteristics of the local buckling is expressed by the parameters of width-thickness ratios. 5. Comparison of macro-model results and shell-model results The behaviors of H-section columns are analyzed with the proposed macro-models, and compared with the results of cyclic loading tests and the results by FEM analyses with shell-models. Generally the results of macro-models agrees well with those of tests and shell-model results, except for relatively earlier deterioration after the local buckling. The positions of local buckling and the dissipated plastic energy by the hysteresis were also agreed well with the tests and shell-model results. The results of H-section columns with various width-thickness by FEM analyses with shell-models are also compared with the analyses with the proposed macro-models. Generally the positions of local buckling and the dissipated plastic energy by the hysteresis were agreed well with the results of shell-model. 6. Conclusions 1) The results of shell-models are generally agreed with the test results when the effects of boundary conditions and residual deformation are taken into account. 2) The results of proposed single macro-member models generally agrees with those of shell-models and modified test results, which are considered to be successful to express the characteristics of H-section columns subjected to bending moment and high axial forces.