本研究旨在探討矩形斷面鋼筋混凝土梁受到彎矩、剪力與扭力組合載重作用下之分析與設計，包括試體破壞強度與空間桁架模式理論驗證及探討破壞模式的分界點、ACI318和AASHTO-LRFD設計規範的印證和比較，及混凝土軟化效應之影響。
本研究試體分為8根承受彎矩和扭力之鋼筋混凝土矩形梁(TM試體)和13根承受剪力和扭力之鋼筋混凝土矩形梁(TV試體)，TV試體中又分為實心試體6根與空心試體7根。TM試體主要變數為承受扭力和彎矩的比值(T/M)；TV試體主要變數為承受扭力和剪力的比值(T/V)，及實心斷面與空心斷面差異。
主要研究結果如下：(1)Elfgren互制式之預測較為保守。承受TM與TV的試體，實驗值和理論值的比值平均分別為1.27與1.29倍；但以Elfgren互制式推估TM中第三類破壞模式的強度可能太過於保守。(2)對破壞模式的分界點，以本研究TM試體為例，在 處，與實驗結果相符。(3)將規範設計之橫向和縱向鋼筋量轉換為總鋼筋體積比形式，結果顯示AASHTO-LRFD規範之設計值較接近實際用量。(4)TM試體中第三類破壞模式試體的軟化係數隨T/M比值增加而降低；以軟化後的極限主壓應變和實際破壞主壓應變比較，兩者下降趨勢接近，顯示混凝土確實受到軟化效應影響而提早產生壓碎破壞。

This thesis presents analysis and design of reinforced concrete beams subjected to combined bending (M), shear (V), and torsion (T).Comparison of experimental failure load with prediction of Elfgren’s interaction equation, the requirements of reinforcement according to AASHTO-LRFD (2010) and ACI 318-08 Code, and the softened effects of concrete under various combined loads are studied.
Two series of beam specimens were tested. One is TM series including 8 beams under various T/M ratios, and the other is TV series including 13 beams with solid and hollow sections under various T/V ratios. Both have 350×500mm cross section.
Results indicated that conservative estimate of failure load were found from Elfgren’s interaction equation. The ratios of test to prediction of failure loads for TM and TV series are 1.27 and 1.29, respectively. In TM series, failure modes changed at M=0.59Mo. The volumetric ratio of reinforcement requirements based on AASHTO-LRFD is closer to actual design than ACI 318 Code. As T/M ratio increased, the softening coefficient of TM series beams decreased. The softening effect of concrete is also evidenced from the measured of softened compressive strains at failure stage.

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