Seismic design of steel frames with intentionally eccentric induction-heat treated steel braces

Using induction heat treatment to increase the yield stress of one half of a steel brace section as well as inducing intentional eccentricity along the brace length has been experimentally proven to increase the limited post-yielding stiffness exhibited by concentrically braced steel structures. The high-post yielding stiffness and controllability of the brace response through the two material components and eccentricity provides the brace the capability of satisfying multiple displacement performance objectives offering a reduced section size. Design expressions that describe the mechanical behaviour of the bracing system are developed. The seismic performance of steel braced frames using the two-component composite steel braces with intentional eccentricity is investigated and a direct displacement-based design method (DDBD) is proposed in order to support their implementation to building structures. The design method is validated through a verification study performed on the theoretical design of a 4-storey office building and seismic performance is assessed through dynamic non-linear time history analysis (NTHA). Time-history analysis results demonstrate that a better control is achieved with the proposed bracing system for achieving drift and ductility limitations.