Date of Award
Master of Science
Civil, Construction, and Environmental Engineering
Civil Engineering (Structural Engineering)
This thesis focuses on a certain type of concentrically braced frames (CBFs) - two-story X-braced frames (TSXBFs) and provides solutions to existing problems.AISC 341-16 predicted the optimal first-mode mechanism to happen in multi-story concentrically CBFs under seismic loads, and existing TSXBFs were designed following the first-mode mechanism. However, Shen et al. (2015) proved that this first-mode mechanism was a rare event by simulating TSXBF and applying anticipated seismic force. The actual mechanism of the existing TSXBF is not consistent with the prediction of AISC 341-16. Furthermore, the actual mechanism causes existing TSXBFs with light brace-intersected beams to undergo significant inelastic deformation in the fracture-prone components and eventually causes malfunction. This thesis uses a series of simulation to test a solution. First, the thesis applies a channel-encasing technique from Seker et al. (2019) on the TSXBFs incorporating square hollow-structural-shaped (HSS) braces to limit them from buckling. The channel encasing is two C-shaped channels welded together by two wide T (WT) sections to encase the square HSS braces. Second, this thesis applied the finite element modeling and verified that the behavior of the simulated TSXBFs matched that of the real tested experiments. This verification included both the component and frame levels. Third, the thesis included a proven fact from Shen et al. (2017) that, when buckling was controlled, the seismic performance of CBFs would actually improve. This thesis also extended to investigate the hysteretic behaviors of TSXBFs with or without the channel-encasing in terms of base shear versus story drift ratio and single brace axial force versus story drift ratio. In addition, this study analyzes the buckling eigenvalues of the structural stiffness matrix to test if channel-encasing improves TSXBF performance under force and displacement. Also, by comparing the hysteretic behaviors of three different sections with the encasement, it could show the proposed channel-encasing system's capacities and limits. The results showed that the channel-encasing system would prevent the buckling of braces. The actual behaviors met the anticipated first mode mechanism in AISC 341-16, and the fracture-prone components in TSXBFs remained functional. Furthermore, the channel-encasing system allowed for reduction of beam size in TSXBFs and reduced steel weight and costs.
Liao, ShihKao, "Channel-encasing technique for two-story X-braced frames incorporating square HSS" (2021). Graduate Theses and Dissertations. 18538.