Mechanisms in two-story X-braced frames

High strength steel in chevron concentrically braced frames designed according to Eurocode 8

“…Indeed, the vertical deflection of those beams imposes larger ductility demand for braces in compression, thus deteriorating the story strength and stiffness and concentrating the damage at those stories. These results are also in line with recent studies carried out by Shen et al [44,45]. These Authors showed that brace-intercepted beams designed with the minimum required strength permitted by the current US design provisions could undergo significant vertical inelastic deformations which considerably increase ductility demands on both braces and beam-to-column connections.…”

“…The second feature is induced by the low flexural strength and stiffness of the brace-intercepted beams, which correspond to large compression demand in the braces, as early shown by [35,[44][45][46][47][48][49][50]. In the most of examined cases, the beam deflection caused by the unbalanced force is large enough to prevent tensile yielding of the brace in tension and to increase the damage in the compression diagonal at SD limit state.…”

Concentrically Braced Frames: European vs. North American Seismic Design Provisions

“…It should be noted that the braced-intercepted beams of chevron CBFs are characterized by large displacement demand at brace intersection [23,24] and in the most of cases, it is not possible to achieve the yielding of the braces in tension, while severe ductility demand is imposed to braces under compression. With this regard, it is necessary to underline that all codified design rules and requirements focus the attention on the strength of the beam intercepting the bracing members, disregarding the role played by its flexural stiffness.…”

Seismic Collapse Analysis of Concentrically-Braced Frames by the Ida Method

“…Regardless of the fact that numerous experimental and theoretical studies have been carried out for CBFs, the CBF system still suffers from various degrees of damage due to its poor ductility [3][4][5][6][7][8]. Thus, the CBFs constructed based on poor design guides in earlier days still attract the attention of researchers [9][10][11][12][13][14][15][16][17][18] CBFs in moderate seismic regions (MSRs) are typically designed using a response modification coefficient R equal to 3, which allows the seismic resistance detailing of a structure to be ignored, e.g., in the United States [19]. Although current codes and rules are obeyed strictly in the CBF design, past numerical simulations showed that the collapse of CBFs is sometimes unavoidable in moderate seismic regions [20].…”