Optimization of the Topology of Masonry Units from the Thermal Point of View using a Genetic Algorithm

Masonry enclosures subjected to environment conditions have a considerable economic weight in building construction cost, and are also important when considering thermal and structural behaviour. Also, more accurate, methods of analysis of wall systems create an opportunity to design buildings where masonry walls can be more efficient. In Mediterranean countries like Portugal the use of thick single leaf envelope walls can be an interesting alternative to cavity walls because thermal insulation inserts are expensive components of masonry walls [1]. The use of single leaf external walls is acceptable, as long as the correct material and construction techniques are used and a satisfactory structural behaviour is attained [2]. The use of masonry blocks made with lightweight concrete with expanded clay aggregates is increasing in Portugal. Lightweight concrete expanded clay aggregates exhibit particular properties as good thermal and acoustic behaviour provided by the volume of voids. Unfortunately, compressive strengths of lightweight concretes are lower than normal density concretes and low compressive strength reduces the load that can be carried by walls made of lightweight concretes. Moreover the quantity of lightweight concrete must be limited so the production cost is proportional to its quantity and the cost of transport and laying increases with weight. In this paper we present a computational method to optimize the masonry unit topology according to thermal normative requests. Current techniques for the evaluation of the wall thermal performance are focused on the thermal resistance value of the clear wall area. Finite element twodimensional computer simulations are used to optimize the topology of vertically perforated lightweight concrete masonry units. A developed numerical evolutionary algorithm [3] iterates over the direct analysis performed by the commercial code ABAQUS. The optimal solution presented in this paper exhibits a thermal transmittance of the masonry unit U = 0.54 W/(m2 °C) with an air percentage equal to 42.2%.