The plastic deformation capacity of welded steel hollow section members subjected to bending and combined bending and axial compression is analysed theoretically, and the test results are compared with this theoretical prediction. Steel material used is the newly developed high-strength steel with lower yield ratio. Dimensions of sections are so selected that the maximum strength and deformation capacity are governed by the local buckling of plate elements. In the theoretical prediction, the deformation capacity is related to the width-to-thickness ratios of section elements. Therefore the width-to-thickness ratio limitation can be obtained if the required rotation capacity of member is assigned.
