模态分析前四阶为0

cad建了一个高耸塔架，然后导入ansys生成有限元模型，/PREP7
ET,1,BEAM188 !设置梁单元
SECTYPE,1,BEAM,RECT,JM,5
SECDATA,0.06,0.06
MP,EX,1,2.1e11
MP,NUXY,1,0.3 !设置材料常数
MP,DENS,1,7800 !设置材料的密度
LATT,1,1,1,,,,1
NUMMRG,all !针对所有对象进行合并
NUMCMP,all !压缩所有对象的编号
LSEL,all !选择所有的线
LESIZE,all,,,10 !设置单元的划分段数为10
LMESH,all !进行线型单元的划分
N,3000,1222.5,1598.6,0 $N,3001,1221.5,1599.6,0 $N,3002,1221.5,1598.6,-1
N,3003,1222.5,1582.8,0 $N,3004,1221.5,1581.8,0 $N,3005,1221.5,1582.8,-1
N,3006,1206.5,1582.8,0 $N,3007,1207.5,1581.8,0 $N,3008,1207.5,1582.8,-1
N,3009,1206.5,1598.6,0 $N,3010,1207.5,1599.6,0 $N,3011,1207.5,1598.6,-1
ET,2,COMBIN14 !设置弹簧单元
R,2,4e13
TYPE,2
REAL,2
E,12,3000 $E,22,3003 $E,105,3006 $E,94,3009
E,12,3001 $E,22,3004 $E,105,3007 $E,94,3010
E,12,3002 $E,22,3005 $E,105,3008 $E,94,3011
FINISH
/SOLU
D,12,ROTX,,,,,ROTY,ROTZ $D,22,ROTX,,,,,ROTY,ROTZ
D,105,ROTX,,,,,ROTY,ROTZ $D,94,ROTX,,,,,ROTY,ROTZ
D,3000,all $D,3001,all $D,3002,all
D,3003,all $D,3004,all $D,3005,all
D,3006,all $D,3007,all $D,3008,all
D,3009,all $D,3010,all $D,3011,all
进行模态分析的结果是前四阶为0，其余的也很小。于是将弹簧单元去掉，直接在四个角点上采用完全约束，可是，还是前四阶模态为0，而且得出的结果和去掉弹簧单元之前的结果一样。
这是哪里出错了呀？呜呜呜~~~求指导！