Designing against earthquake and progressive collapse: A structural optimization approach applied to composite steel-concrete buildings

The present work presents an optimization procedure for the design of structures able to resist earthquake actions and progressive collapse. An evolutionary optimization algorithm is employed to minimize structural cost subject to conventional design requirements on safety of structural members and structural system resistance against earthquake; additionally, requirements on progressive collapse resistance are imposed to study their effect on the optimal designs attained. A method based on the notional removal of key-elements of a structure is used to direct the optimizer towards identifying a structural design, which provides adequate alternate load paths when local failure occurs in the structure. A numerical application involving the design of a 6-storey composite steel-concrete building demonstrates the effectiveness of the proposed optimization approach. Of particular importance is also the investigation of the variation in the structural cost achieved when progressive collapse resistance constraints are incorporated in the design process. By enforcing the satisfaction of additional design requirements on system resistance and safety against local failure, structural cost is inevitably increased due to the need for extra material weight/volume. This increase is quantitatively explored by comparing designs obtained with and without progressive collapse resistance constraints.