混凝土軟化模式對輕質骨材鋼筋混凝土深梁剪力強度之影響

Effect of Softened Model of Concrete on Shear Strength of Lightweight Concrete Deep Beems

本研究以不同之混凝土軟化組成律，利用軟化壓拉桿評估常重混凝土（NWC） 與輕質骨材混凝土 （LWC） 之深梁剪力強度，並且以混凝土之峰值應變與彈性模數為參數，討論其參數對不同混凝土軟化組成律造成剪力強度評估結果之差異性。研究結果顯示，無論是NWC 或LWC，以Zhang 和Hsu、Belarbi和Hsu、Vecchio 和Collins 之Model A、Ueda 等人、簡算法，所建議之軟化組成律可以有效掌握不同混凝土強度及跨深比對深梁之剪力強度行為，但評估LWC 時，上述軟化組成律之軟化係數需折減為NWC 之0.85 倍，否則會有些許安全之疑慮。利用上述五種軟化組成律，在混凝土峰值應變可能變化內（0.7 å0~1.3 å0），其評估剪力強度比之變異性，只有在3%以內；在彈性模數可能變化內 （0.8Ec~1.1Ec） 其評估剪力強度比之變異性，約在7%以內，且NWC 評估結果偏向安全側 （實驗值大於評估值），LWC 經過修正後 （軟化係數為NWC之0.85 倍） 評估結果亦偏向安全側，這顯示如果用上述之五種軟化組成律評估深梁之剪力強度，其混凝土峰值應變、彈性模數之變異性，對其評估之結果是可以接受的。

This paper presents the results of using a softened strut-and-tie modelwith different softened constitutive laws of concrete to predict the shearstrength of normal weight concrete (NWC) deep beams and light weightconcrete (LWC) deep beams. In addition, 2 parameters, the peak strainand the modulus of concrete, were reviewed because of their impact on theprediction of shear strength based on different softened constitutive laws ofconcrete. The results of the predictions show that the softened constitutelaws of concrete proposed by Zhang and Hsu, Belarbi and Hsu, Vecchio and Collins [Model A], Ueda et al. and the simplified method can wellpredict the shear strength of the LWC deep beams or NWC deep beamswith different concrete strengths and shear span ratios. However, thesoftening coefficient must be decreased to 0.85 while evaluating the LWC,otherwise there might be safety concerns. With the peak strain range fallingbetween 0.7 å0 and 1.3 å0, the predicted shear strength of deep beamsresulted in variations in ratio of the shear strength that are equal to ordiffering by less than 3%, calculated based on 5 different types of softenedconstitutive laws of concrete mentioned above. If the modulus ofconcrete ranges between 0.8 Ec and 1.1 Ec, the predicted shear strengths ofdeep beams will be equal to or vary less than 7%. Such prediction resultsindicate that it is safe to accept these numbers. If the softening coefficientis decreased to 0.85 while evaluating the LWC, the result of the predictionalso indicates that it is safe. These results indicate that by using the 5different types of softened constitutive laws of concrete mentioned aboveto evaluate the shear strength, the variation of the peak strain and themodulus of the concrete shows that the results of the predictions arereasonable.