自充填混凝土梁撓曲行為之探討

Abstract

本研究以試驗的方式，探討自充填混凝土梁之最大彎曲強度與韌性，並與一般混凝土梁作比較。藉由27支自充填混凝土梁與5支一般混凝土梁試體，針對混凝土種類、軸向鋼筋量、箍筋間距、箍筋強度以及剪跨比等各項試驗變數，於梁承受單向靜態載重作用時，探討其對鋼筋混凝土梁撓曲行為的影響。 根據試驗觀察，自充填混凝土梁的裂縫發展及破壞過程與一般混凝土梁相當近似。自充填混凝土梁與一般混凝土梁最大彎矩強度試驗值均較ACI計算值為高，同時兩系列梁之最大彎矩強度試驗值並無明顯差異，所以ACI計算方法亦可適用於SCC梁。 試驗結果顯示，提高拉力筋量會提高混凝土梁的彎曲強度，但是梁韌性卻反而下降。提高壓力筋量會稍微提高梁的彎曲強度，同時提高了梁韌性。縮小箍筋間距對於提升梁的延展性是相當有助益的。剪跨比=3.443的梁，在梁韌性表現比剪跨比=4.426的梁佳。在相同條件下，自充填混凝土梁的延展性較一般混凝土梁略佳。 試驗中觀察梁之裂縫發展，發現採用高拉力箍筋（ ）之梁試體，其裂縫寬度仍然滿足ACI依據Gergely-Lutz計算公式對裂縫寬度的限制（0.33mm）。同時觀察到自充填混凝土梁的裂縫控制優於一般混凝土梁。箍筋間距愈小，撓曲裂縫將會愈多、愈密，而使裂縫控制較佳。

An experimental program was conducted to investigate the maximum moment strength and ductility of the self-compacted concrete (SCC) beams and compared with those of ordinary property cement (OPC) beams. Twenty-seven SCC beams and five OPC beams were fabricated and tested with vertical monotonic load to investigate the flexure behavior of reinforced concrete beams. The parameters considered were type and strength of concrete, amount of longitudinal steel, space of stirrup, yield strength of stirrup and shear span-to-depth. Observation during the tests indicated that the pattern of crack initiation and propagation for SCC and OPC beams were similar to each other. The values of experimentally obtained maximum moment strength of SCC and OPC beams were higher than the values calculated by ACI code. The SCC beams and OPC beams had similar maximum moment strength. The results demonstrated the suitability of ACI equations for SCC beams. Experimental results showed that an increase of tension reinforcements would increase the maximum moment strength but decrease the ductility of the beams. The increase of the compression reinforcements would increase the maximum moment strength slightly and more on the ductility of the beams. Decreasing the space of stirrup would increase the ductility of the beams. The ductility of the beam with a/d = 3.443 was better than the beam with a/d = 4.426. With all the other parameters same, SCC beams performed somewhat better than OPC beams on the ductility. Based on the observation during the tests, we found that the crack width of the beams with stirrups of higher yield strength ( ) still satisfied the crack width limitation of ACI code in accordance with the Gergely-Lutz equation. SCC beams had better crack control than OPC beams. Decreasing the space of stirrup would make more closely spaced flexure cracks and thus better crack control.