Otimização multiobjetivo de lajes nervuradas de concreto armado com ênfase na redução de custos e na ampliação da vida útil

Abstract

Structural engineering, one of the major areas of study in civil engineering, is based on the search for optimized solutions that can withstand various actions and ensure the balance of buildings, while also aiming to reduce the consumption of materials and, consequently, costs during the design process. Added to this is the need to design procedures to extend the durability of structures throughout their useful life, since premature deterioration of structural elements, in addition to causing discomfort and generating insecurity for users, is one of the main factors that leads to a considerable amount of the construction industry's resources being spent on repairing and maintaining pre-existing structures. Since minimizing costs and maximizing useful life are conflicting objectives, the applicability of multi-objective optimization concepts and techniques becomes evident. To this end, this study aimed to design reinforced concrete ribbed slab floors – economic alternatives in situations that require large spans – in accordance with the guidelines of ABNT NBR 6118:2014 and respecting the restrictions of the ultimate limit states (resistance) and serviceability (stiffness). The optimization, through the application of the mathematical tool SolveXL® – a Microsoft Excel® add-in that uses genetic algorithms –, aimed to minimize the total cost of concrete, steel and formwork, while simultaneously maximizing the service life. The optimized sections were analyzed in four cases in which the spans varied from 5.0 to 8.0 m, in increments of 1.0 m. For each scenario, the concrete strength classes were sequentially alternated, from C25 to C50. The probabilistic prediction of the service life of the optimized ribbed slabs in this study was made based on the model proposed by the Spanish standard Instrucción de Hormigón Estructural (EHE-08), taking as reference the corrosion process of the reinforcement bars due to carbonation.