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例4.4c已知:P1=4kN,P2=10kN,尺寸如图。 求:BC杆受力及铰链A受力。 解:取AB梁,画受力图。 ∑F=0 F-F,cos30°=0 ∑Fn=0F-P-+Fsin30°=0 (1① 30 ΣM,=0 Fsin30°.6-4P-3P=0 解得F,=17.33kNF=5.33N 比较: ∑F.=0 F-Ecos30°=0 ∑M=0 {Fsin30°.6-4P,-3P=0(2) ∑MB=0 -6F+3P+2P=0 比较: ∑M4=0 F,sin30°.6-4P-3P=0 三组 ∑MB=0 -6F+3P+2P=0 (3) 结果相同 ∑Mc=0 F·AC-3P-4P=0 入 例4.4c 已知:P1=4kN,P2=10kN,尺寸如图。 求:BC杆受力及铰链A受力。 解: 取AB 梁,画受力图。 解得 0 0 0 ix iy A F F M ∑ =  ∑ =  ∑ = 1 2 2 1 cos30 0 sin 30 0 (1) sin 30 6 4 3 0 Ax T Ay T T F F F PPF F PP  − =   −−+ =   ⋅− − =    F F T =17.33kN 5.33kN Ay = 比较: 比较: 0 0 0 ix A B F M M ∑ =  ∑ =  ∑ = 2 1 1 2 cos30 0 sin 30 6 4 3 0 (2) 6 32 0 Ax T T Ay F F F PP F PP  − =   ⋅− − = − ++ =    0 0 0 A B C M M M ∑ =  ∑ =  ∑ = 2 1 1 2 1 2 sin 30 6 4 3 0 6 3 2 0 (3) 34 0 T Ay Ax F PP F PP F AC P P  ⋅− − =  − ++ =   ⋅ −− =  三组 结果相同!
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