Optimum Location of Outrigger–Belt Truss in High-Rise Buildings against Blast Loading Using Nonlinear Dynamic Analysis and Genetic Algorithm

Abstract

Performance assessment of tall buildings against blast loading is considered a crucial aspect of safe structural design. In this regard, the selection of the optimum positions for structural elements plays an important role. Achieving the best locations of outriggers by dynamic analysis of all possible cases will lead to excessive computational effort. As an alternative approach, using genetic algorithms (GAs), which is proposed in this paper, demands fewer structural dynamic analyses to achieve the optimum configuration. The mathematical formulation is presented to predict the optimum positions of outriggers against blast loading. In the GA algorithm, the positions of outriggers in tall buildings with 20, 30, and 40 stories were optimized against 4 blast scenarios. The sampled structures were modeled using OpenSees considering material and geometry nonlinearity. The GA code was developed using MATLAB and linked with the OpenSees tool as the structural analysis core. To affect the blast loading on sampled structures, the empirical formulation of blast-induced pressure is used. The maximum structural interstory drift ratio (MIDR) is considered as the objective function. To present the results in a practical manner, the formulations to predict the optimum positions are proposed. In the proposed formulation, the optimum relative positions of second and third outriggers are considered as outputs ( h 1 / H total and h 2 / H total ), and the blast scaled distance ( Z ) and number of stories ( N ) are considered as input variables. The nonlinear regression, based on simulated data, calculated using the bootstrap technique, is applied to present the final formulation with minimum prediction error. Based on the results, linear combination of N , Z 2 , and N × ln ( Z ) is proposed as the most suitable relationship. The proposed formulation was tested for 2 new sample buildings with 25 and 35 stories. The accuracy of the proposed formulation was verified through comparison of the predicted best locations of outriggers with those calculated using the nonlinear dynamic analysis.