本文旨在探討預鑄輕質骨材混凝土梁在承受扭矩與彎矩組合載重作用下之變形與承力行為，另由試體表面應變之變化，來探討因組合載重比例變化對於試體破壞模式之影響。
試體部分共規劃8根在預鑄場製作之輕質骨材混凝土梁，試體斷面尺寸為350x500 mm，混凝土抗壓強度約為37～46 MPa，試體全長約為4500 mm，中央測試區長度為1700 mm，主要討論之變數為鋼筋量，扭矩與彎矩(T/M)之比值。
試驗結果顯示：(1)預鑄之輕質骨材混凝土梁試體施工性良好，但在澆注時，其坍度損失較快，可施加適當之強塑劑，來改善其施工品質。(2)輕質骨材混凝土梁在受到純彎矩與純扭矩作用下，均有良好的撓曲與扭矩韌性，實測強度值約為規範預測值之1.03～2.08倍，均達到規範之設計要求。(3)試體表面平均應變之變化主要是受到扭矩產生之剪應力與彎矩產生之拉壓應力所影響，隨著T/M比值的增加，試體頂面混凝土之橫向應變(εt)、縱向應變(εl)與主張應變(εr)均會隨之增大，試體底面之縱向應變與主張應變則會隨之減少。(4)試體之破壞模式會隨著扭矩-彎矩比值的不同而改變，當承力行為由彎矩主導時(T/M=0.5Tuo/Muo、2.5Tuo/Muo，為第一類破壞模式)，壓剪區位於試體頂面，頂面主壓應變值為三個面中最大的；當承力行為由扭矩主導時(T/M=4.5Tuo/Muo、6.43Tuo/Muo，為第二類的破壞模式)，壓剪區位於試體側面，側面主壓應變值為三個面中最大的。

The behavior of deformation and strength of precast lightweight concrete (LWA) beams subjected to combined torsion and bending are investigated. Eight sand-lightweight aggregate concrete beam specimens, 350X500 mm in cross section, made in precast plant, were tested. The main variables included the amount of reinforcement, ratio of torsion to bending (T/M). The concrete strength was approximately 42 MPa.
Test results showed that LWA beams exhibited satisfactory ductility of flexure and torsion. The test strength was greater than the code prediction. The average top surface strains measured in the transverse and longitudinal directions as well as the calculated principal tensile strains increased as T/M ratios increased. The average bottom surface strains in the longitudinal direction and the principal tension strain decreased as T/M ratios increased. Different failure modes were observed with respect to the variation of T/M ratios.

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