Effect of serviceability limits on optimal design of steel portal frames

The design of hot-rolled steel portal frames can be sensitive to serviceability deflections. In such cases, in order to reduce frame deflections, practitioners can increase the size of the haunch and/or the sizes of the steel standard sections used for the column and rafter members of the frame. This paper investigates the effect of such serviceability deflection on the optimal design of steel portal frames, using evolutionary algorithms that optimizes frame weight, taking into account both ultimate as well as serviceability limit states. The results show that heuristic search methods, namely, real-coded and real-coded niching genetic algorithms are efficient and reliable. The niching strategy results in a 66.7% reduction in the computational time. It is shown that serviceability deflections, as recommended by the Steel Construction Institute, govern the design of a 30 m span portal frame, where material cost increases by 27% compared to an ultimate limit state design only.