"a3y3" - 1 õppematerjal

Kesk- ja peainertsmomendid

Kujundi staatilise momendi Sx abil leian koordinaadi yc ­ yc = Sx0/A y1 = 2/3 * a = 2/3 * 7 = 4,67 (cm) y2 = 1,5 * a = 10,5 (cm) y3 = 3 * a = 21 (cm) Liitkujundi staatiline moment: Sx0 = Sx1+Sx2+Sx3 = A1y1 + A2y2 + A3y3 = a*2a*4,67 + a*b*10,5 + (ba)/2*21 = 7*14*4,67 + 7*9*10,5 + (9*7)/2*21 = 1780,66 (cm 3) ristlõikepindala ­ A = A1 + A2 + A3 = 98+63+31,5 = 192,5 (cm3) Pinnakeskme koordinaat ­ yc = Sx/A = 1780,66/192,5 = 9,25 (cm) Ristlõike keskpeainertsimomendid ­ Iy = Iy1 + Iy2 + Iy3 = (2a*a3)/12 + (a*b3)/12 + (ab3)/48 = (14*343)/12 + (7*729)/12 + (7*729)/48 = 400.167 + 425,25 + 106,3125 = 931,73 (cm 4) Ix = (Ixi + Aiyci2) = =