Void-filled cold-formed rectangular hollow section braces subjected to large deformation cyclic axial loading

This paper describes a series of tests on empty and void-filled rectangular hollow section (RHS) braces subjected to static and cyclic axial loading. The braces were made from cold-formed C450 (450 MPa nominal yield stress) RHS with two different plate slenderness ratios. The filler material used was normal concrete and light-weight concrete. Two loading protocols were applied, namely Cyclic-Direct (full axial displacement applied and load oscillated) and Cyclic-Incremental (load oscillated at several accumulating axial displacement increments). First-cycle buckling loads were compared with design loads predicted using various national standards. The effects of filler material and section slenderness on the load-deflection response, first cycle peak load, postpeak residual strength, ductility, and energy absorption of void-filled RHS braces are studied in the paper. The effect of the loading scheme is also discussed.