توسعه تیرهای فولادی به شکل سرد کارآمد
Abstract
1. Introduction
2. Eurocode design principals
3. Problem definition
4. Big Bang-Big Crunch algorithm
5. Optimum design of CFS beams
6. Analytical investigation
7. Summary and conclusions
Acknowledgment
References
Abstract
Cold-formed steel (CFS) elements are increasingly used as main structural members in modern construction practice. While flexibility of CFS cross-sectional shape allows achieving higher load carrying capacities by using more efficient shapes, obtaining optimum design solutions can be a challenging task due to end-use constraints and complex behaviour of CFS elements controlled by local, global and distortional buckling modes. This study aims to develop a practical methodology for optimum design of CFS beam sections with maximum flexural strength and minimum deflection under ultimate and serviceability load conditions, respectively, in accordance with Eurocode 3 by taking into account manufacturing and end-use design constrains. Population-based Big Bang–Big Crunch Optimisation method is employed to obtain optimum design solutions for twelve different CFS cross-sectional prototypes. To verify the flexural strength and stiffness of the optimum beam sections, detailed nonlinear finite element (FE) models are developed using ABAQUS by considering both material nonlinearity and initial geometrical imperfections. It is shown that the optimised sections based on serviceability limit state (SLS) and ultimate limit state (ULS) can provide, respectively, up to 44% higher effective stiffness and 58% higher bending moment capacity compared to a standard lipped channel beam section with the same plate width and thickness. Using plain channel and folded-flange sections generally leads to the best design solutions for SLS and ULS conditions, respectively. Finally, the results of detailed FE models are used to evaluate the adequacy of EC3 proposed procedures to estimate CFS beam capacity and deflection at ULS and SLS, respectively.
Introduction
Cold-formed steel (CFS) load-bearing members and structural systems are increasingly used in modern construction, for example in modular buildings, stud wall systems, purlins, trusses, side rails and cladding. Although CFS elements are susceptible to local/distortional buckling, they can be more economical and efficient compared to similar hot-rolled sections, due to their inherent advantages such as high strength-to weight ratio, speed and efficiency of construction, and especially higher flexibility in manufacturing various profiles and sizes through cold-rolling or press-braking process at ambient temperature. The flexibility in CFS cross-sectional shapes provides an excellent opportunity to achieve higher load carrying capacities by using more efficient design solutions. However, this can be a challenging task due to typical manufacturing and end-use design constraints and complex behaviour of CFS elements controlled by combinations of local, global and distortional buckling modes. In general, optimisation of CFS members may aim to obtain an optimal cross-sectional shape without considering any restriction on the general shape of the sections (i.e. selfshape optimisation) (e.g. [1–7]), or determine optimum relative dimensions of a predefined cross-section (i.e. size optimisation) (e.g. [8–23]).