a3 ∑MA=0 ByPI1P22P33 a1 十F By P11P242P343 (↑)(a) B PI P2021P303 FA(FP1b, +F +E P2u2P303 F->3A B (个)(b) FE 2、∑MC=0 B Bx P32103 Bx b2)|/f By2P3(23 3、>F=0 Fp1 FR BxAX 0 F A F B H Ay1、∑MA=0 FByl–FP1a1 –FP2a2 –FP3a3 =0 FBy=(FP1a1+FP2a2+FP3a3 )/l (↑) (a) ∑MB=0 FAyl– FP1b1 –FP2b2FP3b3=0 FAy=(FP1b1+FP2b2+FP3b3 )/l (↑) (b) ２、∑MC=0 FByl 2 –FBxf –FP3(l2 –b3 )=0 FBx=[FByl 2 –FP3(l2 –b3 )]/f (←) （c) ３、∑Fx=0 FBx–FAx=0 FAx=FBx=FH (d)