如何求解压杆的临界力，考虑杆的自重？

有预应力的屈曲分析，举一个正方体的屈曲分析的例子和另外一个例子
/NOPR ! Suppress printing of UNDO process
/PMACRO ! Echo following commands to log
FINISH ! Make sure we are at BEGIN level
/CLEAR,NOSTART ! Clear model since no SAVE found
/prep7
*SET,h,0.05
*SET,b,0.02
*SET,l,1
*SET,p,1
et,1,95
mp,ex,1,2.1e11
mp,prxy,1,0.3
blc4,,,b,h,l
lsel,s,loc,z,0.1,0.9
lesize,all,,,90
allsel
lsel,u,loc,z,0.1,0.9
lesize,all,0.005
vmesh,all
asel,s,loc,z,0
da,all,all
nsel,s,loc,z,l
*get,ke,node,,count
f,all,fy,-p/ke
allsel
FINISH
/SOL
pstres,on
solve
finish
/solu
antype,1
bucopt,lanb,1
solve
FINISH
/POST1
pldisp,1
!有预应力的结构屈曲分析
finish
/clear
/prep7
*SET,l,4
*SET,a,0.1
*SET,d,50/1000
*SET,fai,5/1000
*SET,p1,39742
*SET,pi,acos(-1)
*SET,e0,2.2e11
*SET,e1,1.95e11
*SET,a0,pi*d*d/4
*SET,io,pi*d**4/64
*SET,a1,pi*fai*fai/4
*SET,ps,15000
*SET,ista,ps/a1/e1
et,1,3
et,2,10
mp,ex,1,e0
mp,prxy,1,0.3
mp,ex,2,e1
mp,prxy,2,0.3
r,1,a0,i0,d
r,2,1e4*a0,1e4*io,d
r,3,a1,ista*1.049
k,1
k,2,,l
k,3,-a,l/2
k,4,,l/2
k,5,a,l/2
l,1,4
l,4,2
l,3,4
l,4,5
l,1,3
l,1,5
l,3,2
l,5,2
lsel,s,loc,y,l/2
latt,1,2,1
lesize,all,,,3
lsel,s,loc,x,0
latt,1,1,1
lesize,all,,,10
lsel,inve
lsel,u,loc,y,l/2
latt,2,3,2
lesize,all,,,1
dk,1,ux,,,,,uy,uz
dk,2,ux,,,,,uz
fk,2,fy,-p*1.2266
allsel,all
lmesh,all
finish
/solu
antype,0
nsubst,10
pstres,on
solve
finish
/solu
antype,1
bucopt,lanb,1
solve
FINISH
/POST1
set,list