桩非线性分析？

做了一个水泥土组合桩，芯桩是钢筋混凝土，被压成了这样，请问是什么原因，下面是命令流。

FINISH            

/CLEAR

/prep7

ET,1,solid65              !定义混泥土单元类型

ET,2,solid45              !定义水泥土单元类型

ET,3,link8                !定义钢筋单元类型

keyopt,1,1,1              !不考虑形函数的附加项

keyopt,1,3,2              !无筋单元的压碎后行为

keyopt,1,7,1              !考虑开裂后的应力释放 

fck=40e6                 !C40混凝土抗压强度标准值 

ftk=4e6                  !C40混凝土抗拉强度标准值  

!====================================

!混凝土本构模型定义

mp,ex,1,fck*0.19/0.0002   !定义混凝土单元材料抗压弹性模量

mp,prxy,1,0.2             !定义混凝土单元材料泊松比

mp,dens,1,2500            !定义混凝土单元材料密度 

tb,concr,1

tbdata,,0.5,0.95,ftk,-1

tb,miso,1,,11

tbpt,,0.0002,fck*0.19

tbpt,,0.0004,fck*0.36

tbpt,,0.0006,fck*0.51

tbpt,,0.0008,fck*0.64

tbpt,,0.001,fck*0.75

tbpt,,0.0012,fck*0.84

tbpt,,0.0014,fck*0.91

tbpt,,0.0016,fck*0.96

tbpt,,0.0018,fck*0.99

tbpt,,0.002,fck

tbpt,,0.0033,fck

!=================================

!土定义

MP,EX,2,2.6e8            !定义土体单元材料抗压弹性模量            

MP,PRXY,2,0.42            !定义土体单元材料泊松比 

MP,DENS,2,1900           !定义土体单元材料密度                                

!钢筋本构模型定义

mp,ex,3,2.1e11

mp,prxy,3,0.3

tb,biso,3

tbdata,,360,0

!65单元实常数定义

r,1

pi=acos(-1)

r,2,0.025*0.025*pi/4

!桩模型建立

cyl4,,,0.8,,,90,21

cyl4,,,0.8,,1.1,90,21

circle,6,0.73,,,90,9

ldele,22,30,1

circle,1,0.73,,,90,9

ldele,22,30,1

L,15,25

L,16,26

L,17,27

L,18,28

L,19,29

L,20,30

L,21,31

L,22,32

L,23,33

L,24,34

vglue,all

nummrg,all

csys,1

lsel,s,loc,x,0.73

latt,3,2,3

lesize,all,0.3

lmesh,all

allsel

vsel,s,volume,,1

vatt,1,,1

vsel,s,volume,,3

vatt,2,,2

!=================

!划分单元

allsel,all

esize,0.3

vmesh,all

/solu

asel,s,loc,x,1.1

da,all,all

csys,0

asel,s,loc,z,0

da,all,all

asel,s,loc,x,0

da,all,symm

asel,s,loc,y,0

da,all,symm

asel,s,loc,z,21

sfa,all,,pres,4.5e5

allsel,all

antype,static

acel,,,9.8

time,1

nsubst,100

cnvtol,u,,0.05

cnvtol,f,,0.05

outres,all,all

solve