The effect of steel grade on weight and cost of warren-type welded tubular trusses

The effect of steel grade on the weight and cost of Warren-type welded tubular roof trusses was investigated. For an unbiased comparison, best truss designs were obtained through optimisation. The steel strength investigated ranged from S355 to S960. Costs were calculated based on the features of the trusses. The starting point was the exact geometry of the truss, from which a finite-element model was derived. This approach allowed the resistance and other requirements of design standards of both members and joints to be included as constraints in the optimisation problem. The design variables were the truss height, the locations of joints, the gap width at the joints and the member sections, from a catalogue of cold-formed square tubes. Eurocode 3 requirements were applied. The results of the comparison imply a significant saving in weight when using high-strength steel (HSS), by as much as 50% for S960. The cost reduction was smaller, but still about 20%, for a hybrid solution of S700/S355 for the higher of two investigated load values. It is hoped the results will motivate the use and further investigations of HSSs in building products.