Coupled element and structural level optimisation framework for cold-formed steel frames

Abstract

Optimisation of cold-formed steel (CFS) structures can be challenging due to the complex behaviour of thin-walled CFS sections affected by different buckling modes. In this paper, a coupled framework is presented for element and structural level optimisation of CFS portal frames, under serviceability limit state (SLS) and ultimate limit state (ULS) conditions, using Genetic Algorithm. First, CFS lipped-channel beam sections are optimised with respect to their flexural capacity determined in accordance with the effective width method specified in Eurocode 3 (EC3). The relative dimensions of the cross-section are considered as the main design variables, while the EC3 plate dimensions and slenderness limits and a number of manufacturing and end-use constraints are taken into account in the optimisation process. The results show that the optimum CFS sections exhibit significantly higher (up to 84%) ultimate capacity compared to the standard lipped channel sections with the same plate width and thickness. The structural level optimisation is then carried out to obtain the optimal design solution for a long-span CFS portal frame with knee braces under SLS and ULS conditions. Compared to conventional optimisation using standard cross-sections, it is shown that the proposed coupled framework leads to more cost-effective solutions (up to 20% less structural material) by using the more efficient CFS cross-sectional shapes optimised for generic applications. The results also indicate that optimising the frame geometry and knee brace configuration can noticeably improve the structural performance and reduce the required structural weight, especially when both ULS and SLS conditions are considered.

Numerical Evaluation of the Upright Columns with Partial Reinforcement along with the Utilisation of Neural Networks with Combining Feature-Selection Method to Predict the Load and Displacement

“…In this paper, five objective criteria, including correlation coefficient (R 2 ), Pearson's correlation coefficient (PR), Nash-Sutcliffe efficiency (NS), root mean square error (RMSE), mean absolute error (MAE) and Wilmot index (WI) were used to evaluate the accuracy of the results and the reliability of the proposed neural network [29][30][31][32]45]. Nash-Sutcliffe (NS) efficiency is a normalised statistic that determines the relative amount of residual variance compared to the variance of calculation (Nash and Sutcliffe [65]).…”

“…Numerical evaluation of racking systems currently is a typical approach to derive the optimum values of CFS sections and upright characteristics. Two famous numerical approaches including finite strip method and direct strength method were conducted along the genetic algorithm (GA) [25,26] to obtain the best possible upright columns [27][28][29][30]. In this study, various lengths and thicknesses of cold-formed uprights were modelled by ABAQUS with different reinforcement distances.…”

Constrained optimization of anti-symmetric cold-formed steel beam-column sections

“…In another study conducted by Ye et al [31], the compressive capacity of the CFS lipped channel was optimized by considering the interactive local and flexural buckling modes. More recently, a coupled optimization framework at the element and structural levels was developed by Phan et al [36] to find the optimum solutions for the CFS portal frames. They also conducted shape optimization to improve the flexural capacity of the CFS beam members used in bolted moment connections by taking into account the bimoment effects [37].…”

Optimized Design of Cold‐Formed Steel Elements for Serviceability and Ultimate Limit States

“…Although CFS members are susceptible to local/distortional buckling, they can be more economical and efficient compared to their hot-rolled counterparts, due to their inherent advantages, such as a high strength-to-weight ratio, an increased construction speed and greater flexibility in manufacturing various cross-sectional profiles and sizes through a cold-rolling or press-braking process. The flexibility to relatively easily obtain various CFS cross-sectional shapes provides an excellent opportunity to achieve higher load carrying capacities by using more efficient (optimised) design solutions [2,3]. However, optimisation of CFS sections can be a challenging task due to typical manufacturing and end-use constraints and due to the complex behaviour of CFS elements, controlled by combinations of local, distortional and global buckling modes.…”