| Summary: | 博士 === 國立臺灣大學 === 土木工程學研究所 === 102 === The reinforced concrete (RC) Short columns in building structures are generally considered to be members with high stiffness. They usually sustain large forces during earthquake and are susceptible to brittle shear failure. In the mechanism of lateral load resistance, short columns are often the first member to fail. Therefore, lateral load deflection curves for short columns have significant influence on the seismic assessment. In this study, a trilinear load deflection curve, which includes the shear cracking, shear strength, and the loss of vertical load-carrying capacity points, is proposed to simulate the behavior of short columns subjected to lateral load. The comparison with the experimental results shows that the proposed curve is consistent with the stiffness change in shear cracking of concrete. The Softened Strut-and-Tie model which was developed to predict the crushing strength of concrete is also able to estimate both the shear strength and its corresponding deformation of cracked RC short columns. In addition, the failure mode of the proposed model conforms well to test observations, which is the crushing of concrete. The degradation of shear strength after shear failure was simulated reasonably using the negative gradient of the proposed curve.
Moreover, this study also verifies the proposed equations of shear strength and shear deformation prediction to the short columns using high-strength materials. The comparisons among the experimental results and the proposed model show that the force transfer mechanism in short columns should be modified to account for the use of a large amount of high strength steel. The modified model was able to capture the failure mode of short columns made of high strength materials, which is the concrete crushing at the ends of diagonal struts. The calculated shear strength and shear deformation using the proposed model also showed reasonable agreement with the test results. This study found that the characteristics of the RC short columns made of normal strength and high strength materials are similar. Finally, the proposed model, simple and easy to use for engineers, gives reasonable predictions of shear strength and deformation of RC short columns.
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