Optimal lateral resisting systems for high-rise buildings under seismic excitations

It is generally presumed that the design of tall buildings is mainly dictated by wind loads rather than seismic actions because of the high flexibility and, therefore, long natural periods. However, slender buildings exhibit a complex dynamic behavior, and the involvement of higher modes can result in higher flexural and shear demands than expected. Overlooking the importance of strength, stiffness, and stability requirements in seismic design of tall buildings can thus leads to excessive damage, large residual deformations, and even failure. In this regard, since pure rigid frames alone are not sufficient to withstand lateral loads, as those due to earthquakes, bracing systems are often introduced to stiffen the steel frameworks of tall buildings. The design of lateral bracing systems, in turn, calls for the selection of a suitable pattern for the diagonals arrangement, which is commonly performed through trial-and-error procedures that can require many iteration cycles. It is too evident that this approach does not neither ensure the convergence towards a design solution able to fulfill all requirements, nor the achievement of an optimal solution that minimizes the consumption of structural material and thus the total construction costs. In this context, topology optimization might represent an effective tool for improving the design of tall buildings under earthquake. Therefore, a topology optimization methodology is here presented to support the selection of the most effective design solution for the lateral bracing systems of tall buildings, in such a way to meet minimum weight requirement while ensuring the highest structural performance. Specifically, a density-based approach is adopted to establish an optimization design procedure able to generate optimal lateral-resisting systems for tall buildings subjected to earthquakes. The optimum design is formulated in terms of minimum compliance, also to facilitate the comparison of the material distribution results with those already available in the literature. Numerical results presented in this work are concerned with two-dimensional case studies, which are envisioned as part of realistic tall buildings.