Aplicação da otimização ao projeto de estruturas de contraventamento formadas por pórticos planos de concreto armado

Abstract

The search for space usage, coupled with new constructive technologies and advanced computational methods, has resulted in increasingly taller and therefore slender buildings. In these buildings, the system responsible for the absorption of the horizontal actions, ensuring the desired indeslocability level, is a highlight element in the project. An alternative to this system for concrete buildings up to 20 floors is the association of plane frames in two directions with the hypothesis of the high stiffness in the story plan. Considering a structure made up 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. Optimization tools can be used to design these structures, searching, for example, the elements’ dimensions such that requirements for stiffness, resistance, durability, comfort and safety are satisfied and a specific measure of performance is minimized. In the definition of the design variables, a study can be done to identify which parameters can influence significantly the objective function of the optimization problem formulated. It’s important to note that the unit made up of the side-load resisting elements has to be analyzed instead of the elements isolated. 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 to frames using the method of compatibilized frames at the top. The design variables are the compressive strength of concrete and the cross sections dimensions of the columns and beams, all them considered of discreet nature. To define the design variables, a study is conducted to investigate the influence of the relative stiffness of the beams and columns in the side-load resisting system. The objective function of the problem is the total cost of the structure, which is associated to the volume of the structural elements that compose it. Firstly, a linear elastic analysis is used, but the effect of geometric non-linearity will be investigated. The constraints are relative to requirements in the ultimate and service limit states 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 will be evaluated in the applications and the relative contributions of the beams and columns in the stiffness of the moment-resisting frame are compared.