Weight optimization of steel trusses for industrial buildings

Abstract

AB Associates is a study bureau that performs stability studies and designs steel structures. Trusses are often an economical solution to support the roof of a steel industrial building. One of the main costs in the construction of a truss structure is the material cost of the steel. Since this cost depends largely on the weight of the elements, this thesis will combine both shape and size optimization to minimize the total weight, thus attempting to obtain the most economical solution. This thesis will analyze truss models subject to wind load, snow load, roof load and self-weight, by means of computer aided structural software. The optimizations will be performed for spans with lengths varying from 25m up to 35m. For each length, the height of the truss will vary between 1.25m and 2m. for each situation, the smallest possible cross-section will be selected for each element. The optimization results show that when only the truss itself is optimized, the weight is inversely proportional to the height. However, when the columns of the structure are optimized as well, the optimal height of the truss will not always be the largest anymore. An analysis of the failure modes shows that the critical elements will fail in ULS (buckling or tension), before the SLS constraints (deflection and displacement) are reached.