Design Optimization of Strongback Braced Steel Frames Incorporating a Novel Drift Uniformity Constraint

This study investigates the optimal seismic design of a six-story steel frame equipped with three Strongback bracing configurations, characterized by brace-to-beam intersection ratios of , , and  of the span. A Genetic Algorithm (GA) developed in MATLAB was integrated with OpenSees to perform linear static analyses while enforcing a set of design constraints, one of which is a newly introduced drift-uniformity constraint aimed at regulating the distribution of inter-story drifts. A comparative assessment of the three configurations reveals distinct behavioral trends. In the unconstrained optimization, the differences in total structural weight among the configurations remain moderate ۰.۶۱% between  and  span, ۱۲.۲۷% between  and , and ۱۱.۷۳% between  and . When the drift-uniformity constraint is included, these differences increase to ۴.۱۷%, ۲۵.۵۶%, and ۲۸.۵۵%, respectively, highlighting the pronounced sensitivity of Strongback systems to geometric configuration and showing that brace-to-beam intersection location plays a decisive role in their stiffness-redistribution behavior. The effect of the drift-uniformity constraint varies across the three configurations: it leads to weight reductions of ۲.۴۷% and ۶.۹۵% in the - and -span arrangements, respectively, while producing a moderate increase of ۱۴.۹۶% for the    span case. Despite this variation, all three systems exhibit improved drift profiles when the constraint is applied. Overall, the findings demonstrate that geometric configuration strongly influences the efficiency of Strongback action, and the proposed drift-uniformity constraint serves as an effective and novel design feature capable of refining drift distribution while maintaining competitive structural weight.

کلیدواژه ها:

Optimization ، Strong back ، steel structure ، GA (Genetic Algorithm)