Abstract:

This study investigates the lateral resistance of multi-storey steel frames with sparse Chevron bracing. The mechanical behaviour of structures with insufficiently strengthened horizontal beams was numerically and theoretically investigated. The series-parallel theoretical model for dual lateral force-resisting systems was first validated through nonlinear pushover analysis. The variation patterns of bracing internal forces with inter-story drift angles were presented. After the buckling of compressed braces, the stiffness and strength of horizontal beams were shown to have a significant effect on the development of axial forces in tensile braces. As a secondary lateral force-resisting system, the steel frame helps compensate for the loss of load-bearing capacity after buckling of compressed bracing. The composite effect of concrete slabs and steel beams enhances the flexural stiffness of horizontal beams, thereby facilitating the development of axial forces in the tensile braces and reducing the degradation of load-bearing capacity. In rigidly connected frames with Chevron bracing and insufficiently strengthened horizontal beams, plastic hinges first form at the beam end near the compressed brace side, then at the mid-span of the horizontal beam. Based on this failure mechanism, accurate formulas for calculating axial tensile forces in braces and unbalanced forces in horizontal beams are derived. The study shows that even if horizontal beams do not meet strengthening requirements in the Code for Seismic Design of Buildings, the overall structural capacity remains intact if the frame’s lateral resistance is sufficiently strong. This ensures compliance with seismic performance requirements in regions with a seismic intensity of 7 degrees (0.1g). The proposed calculation method for unbalanced forces offers a new approach to optimizing Chevron-braced frame designs, addressing the issue of excessive beam height in traditional designs, and providing valuable theoretical and practical insights for structural engineering.

Key words: chevron bracing, dual lateral force–resisting systems, flexural stiffness of the beam, effective breadth of the slab, axial force in bracing