Optimal lateral stiffness design of composite steel and concrete tall frameworks

This paper presents the optimal lateral stiffness design of composite steel and concrete tall frameworks subject to overall and interstorey drift constraints as well as member sizing limits using an efficient numerical approach developed based on the Optimality Criteria (OC) method. Taking into account the composite interaction between the structural steel and concrete materials, the stiffness-based optimal design problem is first formulated according to the European Code 4 (EC4). The necessary optimality criteria are then derived for the design followed by the construction of an iterative scheme to satisfy these optimality conditions while indirectly optimizing the design problem with multiple constraints. The recursive OC process is then carried out with the initial member sizes obtained from a closed-form solution developed for the similar problem with a single drift constraint. The effectiveness and practicality of the developed optimization approach is further illustrated through a series of framework examples.