例1求图示截面对z轴的惯性矩 丌(2R R 264 R IR 2) 3+命y 8 a (3) C元 a 316(316例1 求图示截面对z轴的惯性矩。 R (1) z R (2) z a a z (3) z a a (4) 64 8 (2 ) 2 1 4 4 R R I z   =  = 2 8 16 1 4 4 R R I z   =  = 2 4 2 4 3 1 12 2 a a a a Iz   =      = + 4 4 4 3 16 1 3 16 a a a I z       = − = −  