弯矩图如下图所示 MBA=+3Fp//56 3F 56 FPL/4 9Fp56 C B MBC=-3FP/56 MCB=+9Fp/56 A弯矩图如下图所示: 3FP l/56 9FP F l/56 P l /4 MBA= +3FP l/56 MBC= - 3FP l/56 MCB= +9FP l/56