应力分析的神奇问题

finish /clear,start
/PREP7 et,1,solid45 mp,ex,1,1.6e8
mp,prxy,1,0.25

block,0,100,0,2,-20,20
block,44,46,-2,0,-20,20 block,54,56,-2,0,-20,20
block,42,45,2,5,-1,-9 block,42,45,2,5,-11,-19 block,55,58,2,5,-1,-9 block,55,58,2,5,-11,-19 block,42,45,2,5,1,9 block,42,45,2,5,11,19 block,55,58,2,5,1,9 block,55,58,2,5,11,19
block,45,55,2,2.5,4.25,4.75 block,45,55,2,2.5,14.25,14.75 block,45,55,2,2.5,-4.25,-4.75 block,45,55,2,2.5,-14.25,-14.75
nummrg,kp alls esize,1 mshape,0,3 mshkey,2 vmesh,all alls nummrg,kp
nsel,s,loc,x,44,46 nsel,r,loc,y,-2,0 nsel,r,loc,z,-20,20 d,all,all,0 alls
nsel,s,loc,x,54,56 nsel,r,loc,y,-2,0 nsel,r,loc,z,-20,20 d,all,all,0 alls

nsel,s,loc,x,30 nsel,r,loc,y,0 nsel,r,loc,z,5 f,all,fy,-2000
nsel,s,loc,x,70 nsel,r,loc,y,0 nsel,r,loc,z,5 f,all,fy,-2000 alls fini
/solu antype,static solve fini
/post1 PLNSOL,sx