鋼筋混凝土短柱受剪破壞之側力位移曲線研究

Lateral Load Deflection Curves for Reinforced Concrete Short Columns Failed in Shear

李翼安(Yi-An Li)

指導教授 ： 黃世建

國立臺灣大學/工學院/土木工程學研究所/博士(2013年)

https://doi.org/10.6342/NTU.2013.00136

摘要

鋼筋混凝土短柱桿件在一般建築結構中，是屬於勁度高、韌性較低且為脆性剪力破壞控制之結構桿件，故在結構抵抗側力機制中，短柱通常都是早期產生破壞的結構桿件。因此，短柱之側力位移曲線對於結構之耐震評估有極大之影響且有著極重要之角色。由於目前既有建築物的耐震評估方法，對於短柱桿件耐震行為之預測不盡理想。所以，本研究將建議一套剪力主控之短柱側力位移預測曲線，來模擬短柱桿件於剪力破壞控制下之耐震行為。建議曲線以三線性關係來模擬短柱之側向載重位移曲線，即短柱耐震行為之轉折係以剪力開裂點、剪力強度點與垂直承載能力喪失點來定義。經過與現有短柱實驗結果比對，建議曲線符合短柱因混凝土剪力開裂之勁度轉折。開裂鋼筋混凝土之短柱剪力強度與其位移，採軟化壓拉桿模型作分析，其符合實驗觀察之混凝土擠碎破壞模式，並在側向位移預測中包含剪力變形計算。在強度點後的側力衰減以負勁度斜直線模擬，與短柱實驗之強度衰減相符。故建議曲線有合理之預測結果。
此外，本研究將建議曲線中之剪力強度與其對應位移評估方法，即軟化壓拉桿模型，應用在高強度鋼筋混凝土短柱。經實驗結果與分析模型顯示，其傳力機制因配置高箍筋量且使用高強度鋼筋，應可對傳力機制作出修正。修正後之建議分析結果較佳，但其破壞模式仍為混凝土壓桿之擠碎。本研究發現，普通強度與高強度鋼筋混凝土短柱皆具有類似之特性，並可使用本研究建議之模型作合理地預測其側力位移行為。本研究建議方法簡單有效，可使用手算方式，其有助於工程設計之應用。

關鍵字

鋼筋混凝土 ； 短柱 ； 剪力破壞 ； 軟化壓拉桿模型 ； 高強度 ； 剪力變形 ； 側力位移曲線

並列摘要

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.

並列關鍵字

high strength ； load-deflection curve ； reinforced concrete ； shear deformation ； shear failure ； short column ； Softened Strut-and-Tie

參考文獻

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