Numerical investigation of the cyclic response of CHS braces

The behaviour of seismic-resistant buildings relies heavily upon the inclusion of energy dissipating elements. For concentrically-braced frames, the function of energy dissipation is accomplished by diagonal bracing members, whose performance depends upon both cross-sectional properties and global slenderness. Rectangular hollow sections are traditionally preferred in such applications. However these sections are susceptible to local buckling and, particularly in the case of cold formed tubes, have high residual stresses and reduced corner ductility. Hence as an alternative, this paper focuses on the hysteresis response of hollow circular tubes under cyclic axial loading. The uniformity of the circular cross-section may provide improved performance under cyclic loading over rectangular sections. In this paper, finite element analysis and a damage assessment method are first validated against experimental data on both hot-rolled and cold formed hollow CHS members. A series of parametric investigations is then carried out to access the influence of the local slenderness, global slenderness and steel material type on the hysteresis behaviour. Predictive expressions for displacement ductility and energy dissipation, incorporating both local and global slenderness, are proposed.