Otimização da estrutura de contraventamento de edifícios em concreto armado formada por pórticos planos

Abstract

The search for space usage, coupled with new constructive technologies and advanced calculation methods for reinforced concrete, has resulted in increasingly taller and therefore slender buildings. In these buildings, the side-load resisting structure, responsible for the absorption of the horizontal actions, ensuring the desired stability level, is a highlight element in the project. In systems with beams, an alternative to the side-load resisting system for reinforced concrete buildings up to 20 floors is the consideration of moment-resisting plane frames in two directions. In case of flat slabs, there may be the necessity of an independent structure to the side-load resisting, for example, the usage of shear walls. It seems to be attractive a design tool that allow an automatic and optimized choice of the side-load resisting system considering both structural efficiency and cost, in addition the evaluation of the side-load resisting elements together and not just in isolation. Considering a structure composed of moment-resisting frames, a methodology must to be adopted to distribute the wind action to the system frames, which its own distribution depends on the moment-resisting frames’ stiffness involved. In this work, a formulation for the optimization of side-load resisting structures of reinforced concrete buildings made up of moment-resisting plane frames is presented. The wind action is distributed on frames using the method of compatibilized frames at the top. The design variables are the cross sections dimensions of the columns and beams, all them considered of discreet nature. It’s intended to investigate the influence of the relative stiffness of the beams and columns in the side-load resisting system, allowing that the model generate solutions to both slabs with beams and without beams. Functions associated to the concrete volume of the side-load resisting structures are used as objective function. The analysis is linear elastic and the constraints are relative to the instability parameters according to the Brazilian Standard NBR 6118:2014. The wind action is defined based on NBR 6123:1988 and the rigid diaphragm hypothesis is adopted for the behavior of the last floor slabs aiming the wind action distribution. The use of bio-inspired algorithms is evaluated in the applications and the relative contributions of the beams and columns in the stiffness of the moment-resisting frame are compared.