Structural Concrete, Vol. 9, no. 3, September 2008
Analysis and cost optimisation of prestressed concrete joists in beam-block floors
Vanessa Cristina de Castilho, Universidade Federal de Uberlandia, Brazil
Maria Cristina Vidigal de Lima, Universidade Federal de Uberlandia, Brazil
The overall production costs of precast concrete elements are important to quantify. Analyses of the constructive stages of these elements, however, may more realistically lead to a function representing production, transport, assembly and casting costs. This article investigates the cost minimisation problems of joists in beam-block floors using a heuristic method known as genetic algorithm (GA) and a conventional method known as generalised reduced gradient (GRG2). The continuous variables considered in the problem were prestressed reinforcements in the three levels, distance between reinforcements, concrete layer strength, distance between joists, concrete layer thickness and degree of redistribution of the continuous slabs' negative moments. Based on the results, the heuristic method was found to be effective in identifying the solution for precast element cost minimisation problems. The performance of the cost function vis-à-vis market alterations was evaluated considering the influence of concrete, reinforcement and labour prices.
