低強度混凝土RC結構受反覆荷載之力學行為;Experimental Study on the Seimic Behavior of Reinforced Concrete Structures with Very Low Concrete Strength

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题名:	低強度混凝土RC結構受反覆荷載之力學行為;Experimental Study on the Seimic Behavior of Reinforced Concrete Structures with Very Low Concrete Strength
作者:	羅婉瑜;Lo, Wan-Yu
贡献者:	土木工程學系
关键词:	低強度混凝土;彈性模數;鋼筋混凝土梁;反覆荷載;等值應力塊;伸展長度;有效慣性矩;very low concrete strength;elastic modulus;reinforced concrete beams;cyclic loading;equivalent stress block;development length;effective moment of inertia
日期:	2019-01-29
上传时间:	2019-04-02 14:09:03 (UTC+8)
出版者:	國立中央大學
摘要:	本研究主要以混凝土抗壓試驗與鋼筋混凝土(簡稱RC)梁實驗，分別受單向與反覆荷載方式，來探討低混凝土強度與一般混凝土強度之RC結構耐震行為差異。在混凝土抗壓試驗結果方面，台灣混凝土彈性模數建議公式[16]，用於很低強度之混凝土會有不保守現象。再者，低強度混凝土彈性模數亦會受到反覆荷載影響，其中會再低至經驗公式值的0.67倍。至於，低強度混凝土受單壓與反覆荷載之應力應變曲線試驗結果相近，且可以用Popovics[5]所提出的混凝土應力應變理論模式來作保守的描述。文中第二部分，亦製作不同混凝土強度(設計強度f_c^′分別為21MPa與10MPa)之RC簡支梁試體，受三點載重之單向與反覆荷載，來探討低強度混凝土強度對RC結構影響。結果顯示，使用現行規範ACI 318-14[1]與Collins[3]之應力塊方法來評估一般與低強度混凝土之RC梁彎矩強度，其兩方法評估值相似，且均小於量測值；當中亦顯示，應力塊方法可用來評估低混凝土強度RC梁彎矩強度。然而，低強度RC梁最大彎矩發生於受壓頂部混凝土應變達0.006，與一般強度RC梁的應變達0.003，有明顯不同。對於實驗中量取一般與低強度RC梁之有效慣性矩(I_e)結果，在鋼筋降伏受力階段而言，不論受單向或反覆荷載，其I_e值約在0.2-0.3I_g(全斷面慣性矩)。從RC梁實驗也發現，以ACI 318-14規範伸展長度公式來評估低強度混凝土之RC結構握裹能力，會有不保守現象。 ;The purpose of the study is to observe the seismic behavior of reinforced concrete(RC) structures with normal and very low concrete strengths by means of the monotonic and cyclic loading tests on compressive concrete cylinders and RC simply supported beams. The results of the concrete compressive test showed that the empirical equation of the concrete elastic modulus suggested by the Taiwan’s researcher [16] is not conservative for the very low concrete strength. Meanwhile, the effect of the cyclic loading on the elastic modulus of the very low-strength concrete is much more obvious than the normal concrete, which decreases to 67% of the value calculated by the empirical equation. The stress-strain curves measured from the monotonic and the cyclic loading are repealed in a similar excursion. Also the stress-strain curve of the very low concrete strength can be conservatively described by the theoretical model proposed by Popovics [5]. In the second part of the study, four simply supported RC beams with different concrete strengths (f_c^′ respectively equals 21 MPa and 10 MPa), subjected to three-point monotonic and cyclic loading, were tested. The results showed that the stress block method proposed by ACI 318-14 [1] and Collins [3] could be used to evaluate the bending moment strength of RC beams with normal and very low concrete strength. The predicted values using these two methods are similar. These predicted values are smaller than the measured ones. That is, the stress block method can be used to evaluate the bending moment strength of RC beams with very low concrete strength. However, the maximum bending moment of the low-strength RC beam occurred at the concrete compressive strain of 0.006, which is significantly different from the strain of 0.003 measured from the normal RC beams. As for the effective moment of inertia (I_e), these values(I_e) measured from the tested beams at the yield loading stage are ranged between 0.2 to 0.3I_g, where I_gis the full sectional moment of inertia. These values represented as no different, regardless of the efficiency of monotonic or cyclic loading. It was also found that the development length equation specified in ACI 318-14 showed less conservative when the bond strength of the RC beams with very low-strength concrete was assessed.
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