Research on Optimization of Large Span and Large Cantilever Steel Frame Structures

Abstract

This paper takes the design optimization of a large cantilevered steel frame and a large-span steel frame structure at a school in Jinan as an engineering case, and conducts an in-depth comparison of the significant differences in structural systems, member cross-sections, and steel consumption before and after optimization. Due to the lack of steel structure design experience among the designers, concrete design thinking was improperly applied to the design of large cantilevered and large-span steel structures, resulting in seriously unreasonable structural layout. Although the reinforced concrete frame and steel frame structural systems have similarities in simplified member modeling and force transmission paths, there are significant differences in aspects including beam-slab interaction, joint connection methods, torsional resistance, and seismic performance. For large-span steel frame structures, taking the steel structure roof of a 20-meter-span school auditorium as an example, this study compares and analyzes two schemes: arranging secondary beams along the large-span direction and arranging secondary beams perpendicular to the large-span direction, and draws the conclusion that the scheme with secondary beams arranged perpendicular to the large-span direction can reduce steel consumption by more than 50%. For large cantilevered steel frame structures, taking the 3-meter cantilevered external corridor of the school as an example, through comparative analysis of two schemes: the joint cantilevering of primary and secondary beams and the cantilevering of only primary beams, it is found that the scheme with only primary beams cantilevering can save approximately 30% of steel consumption. The biggest problem of the original scheme lies in its failure to fully leverage the core advantage of low self-weight of steel structures. This case clearly demonstrates that in the design of large cantilevered and large-span steel structures, structural layout scheme is the key factor determining structural efficiency and economic performance. Adhering to the design concept of "light roof, high-performance members" is the fundamental approach to achieve an integrated structural solution that is safe, economical, and reasonable.