05.09: Experiment study on square steel tubular columns: Under compressive axial force with monotonic antisymmetric bending moment

Abstract

ABSTRACTIn Japan, square steel tubular columns are widely used. When the building is subjected to a lateral force, columns will subject axial force with antisymmetric bending moment simultaneously. Therefore, it is important to design the column under these combined loading in the ultimate limit state to guarantee the safety. Recommendation for Limit State Design of Steel Structure (LSD) [1] specifies the requirements for columns to guarantee sufficient strength and ductility. The plastic deformation capacity of the columns that are subjected to the compressive axial force with one end monotonic bending moment are ensured more than 3 by LSD. However, specific deformation capacity of the column that are subjected to the compressive axial force with monotonic antisymmetric bending moment is hardly shown in experimental test. Therefore, it is necessary to gather more data of maximum strength, deformation capacity, and elasto‐plastic behaviour of square steel tubular columns by testing. Moreover, second‐order effects is needed to take into account because high compressive axial force leads to elasto‐plastic instability.In this study, testing where axial force with monotonic antisymmetric bending moment are applied to the columns simultaneously are conducted. Maximum bending moment, deformation capacity, and second‐order effect that will be caused by Pδ moment were evaluated from the test results. Comparison between LSD requirements and test results were also shown.From the test results, followings are found. 1) The plastic deformation capacity of the square steel tubular column will be determined by either local buckling or Pδ moment. 2) When second‐order effects determined the plastic deformation capacity, the plastic deformation capacity R of the columns had a linear relation between N/Ny.λc02. When the value of N/Ny.λc02 is smaller than 0.25, a plastic hinge was formed at the end of the column, and the plastic hinge determined the collapse mechanism. 3) The current LSD limitation provided conservative results, and the plastic deformation capacity greater than 3 was observed even if the limitation was not satisfied.