铰接，出错

求助各位大虾，小弟做一个计算题时，要铰接两个地方，但是铰接之后就不能在梁上加载集中荷载了，也不能solve。。。这根梁两端是铰接的。希望各位帮帮忙~~~~感激不尽
命令流如下：
/PREP7
ET,1,BEAM3
KEYOPT,1,6,1
KEYOPT,1,9,0
R,1,3.14*0.01,4.91e-6,0.2,
MPTEMP,1,0
MPDATA,EX,1,,2.1e+11
MPDATA,PRXY,1,,0.3
MPTEMP,,,,,,,,
MPTEMP,1,0
MPDATA,DENS,1,,7850

K,1,0,0,0,
K,2,0.5*1.732,0.5,0,
K,3,0.5*1.732,-0.5,0,
K,4,0.5*1.732,0.5,0,
K,5,0.5*1.732,-0.5,0,
K,6,0.5*1.732,0,0
LSTR, 1, 2
LSTR, 1, 3
LSTR, 4, 5

lesize,all,,,40
lmesh,all

nsel,s,loc,x,0.5*1.732
nsel,r,loc,y,0.5
cp,1,ux,all
cp,2,uy,all

nsel,s,loc,x,0.5*1.732
nsel,r,loc,y,-0.5
cp,3,ux,all
cp,4,uy,all

*set,q,-0.1e-1*(7850*3.14159)*9.8,
*do,i,1,40,
a=q*abs(nx(i)-nx(i+1))/2,
f,i,fy,a,
f,i+1,fy,a,
*end do
*set,q,-0.1e-1*(7850*3.14159)*9.8,
*do,i,40,80,
a=q*abs(nx(i)-nx(i+1))/2,
f,i,fy,a,
f,i+1,fy,a,
*end do

F,6,FY,-9.8*(3.14159*(7850*2)*0.1e-1)

SOLVE