幅厚比の大きいH形断面曲げ材の変形挙動予測に関する研究

抄録

The use of thin-walled welded I-section members have proved to be a practical solution to achieve the best possible economy in construction of prefabricated large-span low-rise building frames in steel. In the. design of such frames against strong earthquake motions, however, it is required to have accurate estimates of those deformation capacities of the members which are governed by local or lateral buckling or by both buckling modes frequently appearing, simultaneously. This paper presents a study for predicting moment-rotation relationships for thin-walled I-section beams and beam-columns after local and/or lateral buckling, when axial loads on these members are relatively low. Firstly, an analysis based on yield line theory was attempted. The numerical results were compared with experimental results, which demonstrated a good agreement between them. Secondly, simple empirical formulas that were capable of predicting moment degradation curves after the maximum moments were devised and proposed on the basis of a number of numerical analyses performed over the parameter space covered by the database. Finally, a method to distinguish between members failing in a local buckling mode and those failing in a lateral buckling mode was discussed. By applying this method, an empirical formula to predict a, boundary of member dimensions between which either of local or lateral buckling became decisive of the rotation capacity of members was proposed.