Performance-based seismic design of intentionally eccentric IH-treated steel braced frames

Using induction heat (IH) treatment to increase the yield stress of one half of a steel brace section (i.e., a dual-strength steel 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. This paper aims to numerically investigate the seismic performance of steel braced frames using the IH-treated steel sections with intentional eccentricity and establish a performance-based seismic design method for them. More specifically, a physical model is developed to calculate the multiple strength points, as well as the increased post-yielding stiffness of the brace. On the basis of the physical model, mathematical expressions are developed to support the seismic design of the proposed braced frame structures. The high post-yielding stiffness and controllability of the brace response through the effective combination of the IH-treated steel section and eccentricity provide the brace the capability of satisfying multiple strengths and deformation performance objectives offering reduced section sizes. Time-history analysis results under three hazard levels (frequent, design-basis and maximum occurring event) demonstrated that better control is achieved with the proposed bracing system in achieving drift and ductility limitations dissipating more evenly the seismic energy along the height of the structure. A significant reduction of the residual deformation without storey damage concentration was observed at high seismic intensity levels.