STUDY ON THE BEHAVIOR OF QUASI-X BRACING (QXB) STRUCTURE SYSTEMS IN RESISTING LATERAL LOADS
In earthquake-resistant steel structures, bracing elements are incorporated to enhance stiffness and strength. However, conventional bracing, such as CBF, suffers from ductility deficiencies due to buckling in compressive bracing. The QXB structural system offers an alternative with elliptical braci...
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| Format: | Theses |
| Language: | Indonesia |
| Online Access: | https://digilib.itb.ac.id/gdl/view/84581 |
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| Institution: | Institut Teknologi Bandung |
| Language: | Indonesia |
| Summary: | In earthquake-resistant steel structures, bracing elements are incorporated to enhance stiffness and strength. However, conventional bracing, such as CBF, suffers from ductility deficiencies due to buckling in compressive bracing. The QXB structural system offers an alternative with elliptical bracing geometry, combining axial and flexural mechanisms to prevent sudden failure. This study examines the behavior of the QXB system in resisting lateral loads through a case study of a two-dimensional QXB frame with a height of three meters, a length of five meters, and perfectly elliptical bracing.
The structure's behavior was investigated using elastic analysis with centralized lateral loads and pushover analysis (both monotonic and cyclic). For comparison, SMF and CBF systems were also analyzed, with equalized cross-sections serving as control variables. The results indicate that the QXB structure, with clamped bracing and beam-column relationships, resembles the SMF system more closely than the CBF system in terms of internal force distribution, yield sequence, stiffness, strength, and energy dissipation. However, the elliptical bracing did not fully optimize the structural characteristics of the QXB system. While the strength and stiffness increased by 30% and 25%, respectively, energy dissipation by the bracing elements was still inferior to that of the beams and columns. The ductility of the QXB portal was comparable to that of the SMF system.
A parametric study of QXB element design was conducted with the beam serving as the fuse, mirroring SMF behavior. Column elements were determined using the strong-column weak-beam principle based on the plastic moment capacity ratio (????????????/???????????? ? 1.2). Bracing elements were designed using linear regression equations derived from 31 bracing-beam cross-section pair data. The results demonstrate that bracing elements can be designed based on the relationship between the moment of inertia and the plastic modulus of the strong axis of the beam cross-section, with the regression equation dependent on the height of the beam section.
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