本文旨在探討配置不同縱向鋼筋量之鋼筋混凝土梁在受到扭矩與彎矩的組合載重作用下之軟化特性。
　　本研究共使用11根方形斷面之高強度鋼筋混凝土梁(fc’=69MPa)，斷面尺寸為420 × 420 mm，主要考慮之變數為扭矩與彎矩組合載重比例值(T/M)和縱向鋼筋量等(Al)。
　　研究結果顯示：(1) 在相同配筋條件下，試體受不同T/M比例值作用，在試體頂面及底面之主應變角(θp)會隨著T/M比例值之增加而變大；試體增加縱向鋼筋量，在承受相同T/M比例值，頂面、側面及底面會隨著ρl/ρt比例值之增加而變小；(2) 在極限強度階段，試體頂面混凝土之平均主張應變(εr)會隨著T/M比例值的增加而增大，頂面混凝土之平均主壓應變(εd)將會減少；增加縱向鋼筋量，試體頂面混凝土之平均主張應變與平均主壓應變均會減少；(3) 以Lessig所提出之斜彎矩理論與本研究中建構模擬斜彎矩理論模式計算試體第一破壞模式下頂面之壓力區厚度，鋼筋混凝土試體受相同T/M比例值作用下，在極限強度階段時，試體頂面的壓力區厚度會隨著T/M比值的增加而減少。此外，當達極限強度階段時，試體頂面壓力區厚度會隨試體配置之縱向鋼筋量的增加而增大；(4) 採用Lessig之斜彎矩理論、Collins之斜彎矩理論及建構模擬斜彎矩理論模式依分析結果可以發現，Tu(test)/Tu(cal.)約介於0.89～1.21之間；上述之三種方法所預測之結果均非常接近，由此可知，混凝土之軟化現象確實存在於試體承受組合載重之中；(5) 由Hsu、McMullen 與 Ewida與本研究所建議之軟化係數計算公式，當試體在相同配筋條件下承受不同之T/M比例值作用時，試體在頂面之軟化現象會隨著T/M比例值的增加而變得越嚴重；在承受相同T/M比例值但增加縱向鋼筋量時，則會使試體的軟化現象較不嚴重。

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