Effect of serviceability limits on optimal design of steel portal frames

Abstract

The design of hot-rolled steel portal frames can be sensitive to serviceability deflection limits. In such cases, in order to reduce frame deflections, practitioners increase the size of the eaves haunch and / or the sizes of the steel sections used for the column and rafter members of the frame. This paper investigates the effect of such deflection limits using a real-coded niching genetic algorithm (RC-NGA) that optimizes frame weight, taking into account both ultimate as well as serviceability limit states. The results show that the proposed GA is efficient and reliable. Two different sets of serviceability deflection limits are then considered: deflection limits recommended by the Steel Construction Institute (SCI), which is based on control of differential deflections, and other deflection limits based on suggestions by industry. Parametric studies are carried out on frames with spans ranging between 15 m to 50 m and column heights between 5 m to 10 m. It is demonstrated that for a 50 m span frame, use of the SCI recommended deflection limits can lead to frame weights that are around twice as heavy as compared to designs without these limits

Optimal design of cold-formed steel portal frames for stressed-skin action using genetic algorithm

“…Additional details and results including the optimized section sizes are available in Ref. [5]. Table 6(a) summarizes the optimal solution of the frame for both the rigid and semi-rigid joint assumptions.…”

“…As the joints were assumed rigid, the cost of the brackets was not included in the design optimization. In the optimum design of steel portal frames, many studies focused on designing portal frames using hot-rolled rather than cold-formed steel, in which genetic algorithm was successfully adopted as an optimizer [3][4][5], as well as other methods, such as nonlinear programming, sequential algorithm [6][7][8].…”

Design Optimization of Long-Span Cold-Formed Steel Portal Frames Accounting for Effect of Knee Brace Joint Configuration

“…The application of genetic algorithm (GA) for optimizing hot-rolled steel portal frame buildings was considered in the literature [8][9][10][11][12]. The robustness and reliability were successfully achieved through a number of runs.…”

Optimal Fire Design of Steel Tapered Portal Frames

“…It would be favourable to understand clearly from economical point-of-view how cheaper or more reliable frames can be designed and constructed. A number of studies [1][2][3][4][5][6][7][8] exist related to the optimization of regular or tapered portal frames considering only gravitational and meteorological loads in order to achieve a more economic design usually by minimizing the weight or the initial cost of the structure. However, since the introduction of European standards, designers have to satisfy the reliability of structures according to stricter requirements.…”