鋼筋混凝土版之貫穿剪力強度評估

Abstract

各國規範對鋼筋混凝土版之貫穿剪力設計公式皆採用統計回歸的方式而求得，不但缺乏力學機制，且應用範圍也有一定的限制。本研究應用軟化壓拉桿理論，建立鋼筋混凝土版之貫穿剪力強度分析模型。文中收集147組鋼筋混凝土版試體，以軟化壓拉桿模型、英國BS-8110規範與美國ACI 318-99規範進行分析與比對。 本研究測試鋼筋混凝土版設計參數在軟化壓拉桿模型、英國BS-8110規範與美國ACI 318-99規範中的反應情形。研究結果顯示：軟化壓拉桿模型在混凝土抗壓強度低於20 MPa時，會有略偏保守的情況，而在其他情況皆可有效反應試體內各設計參數對貫穿剪力強度之貢獻，亦可對高強度鋼筋混凝土版作出保守且準確的預估；英國BS-8110規範之分析結果尚稱精準，但在混凝土抗壓強度甚低或拉力鋼筋比較高的情況下，會有略偏不保守的情況；美國ACI 318-99規範未考慮拉力鋼筋比之貢獻，且將柱斷面長寬比列入考慮，其分析結果過於保守，且當拉力鋼筋比越高、柱斷面長寬比越大或版有效深度越小時，會有越趨於保守的趨勢。此外，軟化壓拉桿模型亦可預測以碳纖維貼片補強鋼筋混凝土版之貫穿剪力強度。

Based on statistic regression, various design code expressions used to calculate punching shear strength of reinforced concrete slabs do not fully consider the force transferred mechanism, but also have some limitations in application. This study adopts the theory of Soften Strut-and-Tie (SST) model to establish an analytical model for predicting the punching shear strength of reinforced concrete slabs. The test results of 147 reinforced concrete slabs are collected to compare the predicted results calculated from SST model, British Standards (BS-8110), and American Concrete Institution Building Code (ACI 318-99). Effects of design parameters of reinforced concrete slabs on predictions calculated from SST model, BS-8110, and ACI 318-99 are studied. The results show that the SST model is effective to reflect the various design variables on the punching shear capacity, and the model can be used to predict slabs with high strength concrete also. However, the prediction of SST model is conservative for slabs having concrete strength lower than 20 MPa. BS-8110 can well predict the punching shear capacity, but it is un-conservative for slabs having lower concrete strength and higher tensile steel ratio. ACI code doesn’t consider the contribution of steel reinforcement even the effect of the aspect ratio of the column side lengths is included. Therefore, ACI code leads to a too conservative prediction, especially for the slabs with higher steel ratio, higher aspect ratio of the column side lengths, and lower effective slab depth. Moreover, the SST model can estimate well the punching shear capacity of reinforced concrete slabs strengthened with Carbon-Fiber-Reinforced-Plastic laminates.