| Summary: | 碩士 === 國立交通大學 === 土木工程系所 === 106 === Conventional steel brace dissipates energy by its tension yielding and compression buckling. Most of the inelastic deformation of a buckling brace concentrates in the mid-length. This region dissipates most energy in a brace under cyclic loading, but it is also vulnerable to failure modes associated with low-cycle fatigue. In this research, we proposed a strategy to improve the cyclic behavior of the conventional steel braces by a spliced mid-segment with more suitable sectional properties and materials. By doing so, we can prevent the local section from concentration of large plastic deformation caused by cyclic tension and compression.
We use ANSYS to conduct the finite element analyses of braces under cyclic loading. The primary variables to be investigated include the cross-sectional shape, material and length of the mid-segment. Numerical speciments include wide-flange and hollow square braces with various compactness ratios. The mid-segments of all the specimens are all made up of wide-flange sections with compactness ratios comforming to the current design code. Based on the numerical simulations we compare the distributions of von Mises stress and equivalent plastic strain (PEEQ) which are used as indices of fatigue life in this study. The analytical results show that it is ineffective to replace the mid-segment with the same section but higher-strength material; the PEEQ is only reduced by 4% to 15% which is less than the other series of specimens. Contrarily, the braces with more compact mid-segment show more favorable distributions of von Mises stress and lower PEEQ; the PEEQ is reduced by 10% to 40%. For the braces with slender original section, when the mid-segments are replaced with more compact sections, the PEEQ is reduced by 40% to 55% and von Mises stresses are also reduced. To reduce PEEQ most effectively, the analytical results suggest that the mid-segment should be replaced with a more compact section and length greater than 55% of the original length. If the parameters are properly designed, the ductility, energy dissipation capacity, and fatigue-life of conventional buckling braces can be enhanced obviously by splicing a mid-segment.
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