*CLOAD should be applied to the reference node of the pre-tension section. Maybe there’s an issue with the way those beam elements are attached to the solid model. CalculiX documentation suggests distributing coupling and equation constraints for that. There’s a simple example that you can try first:
**
** Structure: bolt-like structure.
** Test objective: pre-tension force with beam element.
**
*NODE, NSET=Nall
1,0.000000000000e+00,0.000000000000e+00,0.000000000000e+00
2,0.000000000000e+00,1.000000000000e+00,0.000000000000e+00
3,2.000000000000e-01,1.000000000000e+00,0.000000000000e+00
4,2.000000000000e-01,0.000000000000e+00,0.000000000000e+00
5,1.414213562373e-01,0.000000000000e+00,-1.414213562373e-01
6,1.414213562373e-01,1.000000000000e+00,-1.414213562373e-01
7,1.000000000000e+00,1.000000000000e+00,0.000000000000e+00
8,1.000000000000e+00,0.000000000000e+00,0.000000000000e+00
9,7.071067811865e-01,0.000000000000e+00,-7.071067811865e-01
10,7.071067811865e-01,1.000000000000e+00,-7.071067811865e-01
11,2.000000000000e-01,5.000000000000e-01,0.000000000000e+00
12,1.847759065023e-01,0.000000000000e+00,-7.653668647302e-02
13,1.414213562373e-01,5.000000000000e-01,-1.414213562373e-01
14,1.847759065023e-01,1.000000000000e+00,-7.653668647302e-02
15,6.000000000000e-01,1.000000000000e+00,0.000000000000e+00
16,6.000000000000e-01,0.000000000000e+00,0.000000000000e+00
17,4.242640687119e-01,0.000000000000e+00,-4.242640687119e-01
18,4.242640687119e-01,1.000000000000e+00,-4.242640687119e-01
19,1.000000000000e+00,5.000000000000e-01,0.000000000000e+00
20,9.238795325113e-01,0.000000000000e+00,-3.826834323651e-01
21,7.071067811865e-01,5.000000000000e-01,-7.071067811865e-01
22,9.238795325113e-01,1.000000000000e+00,-3.826834323651e-01
23,2.775557561563e-17,0.000000000000e+00,-2.000000000000e-01
24,2.775557561563e-17,1.000000000000e+00,-2.000000000000e-01
25,2.220446049250e-16,0.000000000000e+00,-1.000000000000e+00
26,2.220446049250e-16,1.000000000000e+00,-1.000000000000e+00
27,7.653668647302e-02,0.000000000000e+00,-1.847759065023e-01
28,2.775557561563e-17,5.000000000000e-01,-2.000000000000e-01
29,7.653668647302e-02,1.000000000000e+00,-1.847759065023e-01
30,1.249000902703e-16,0.000000000000e+00,-6.000000000000e-01
31,1.249000902703e-16,1.000000000000e+00,-6.000000000000e-01
32,3.826834323651e-01,0.000000000000e+00,-9.238795325113e-01
33,2.220446049250e-16,5.000000000000e-01,-1.000000000000e+00
34,3.826834323651e-01,1.000000000000e+00,-9.238795325113e-01
35,-1.414213562373e-01,0.000000000000e+00,-1.414213562373e-01
36,-1.414213562373e-01,1.000000000000e+00,-1.414213562373e-01
37,-7.071067811865e-01,0.000000000000e+00,-7.071067811865e-01
38,-7.071067811865e-01,1.000000000000e+00,-7.071067811865e-01
39,-7.653668647302e-02,0.000000000000e+00,-1.847759065023e-01
40,-1.414213562373e-01,5.000000000000e-01,-1.414213562373e-01
41,-7.653668647302e-02,1.000000000000e+00,-1.847759065023e-01
42,-4.242640687119e-01,0.000000000000e+00,-4.242640687119e-01
43,-4.242640687119e-01,1.000000000000e+00,-4.242640687119e-01
44,-3.826834323651e-01,0.000000000000e+00,-9.238795325113e-01
45,-7.071067811865e-01,5.000000000000e-01,-7.071067811865e-01
46,-3.826834323651e-01,1.000000000000e+00,-9.238795325113e-01
47,-2.000000000000e-01,0.000000000000e+00,-8.326672684689e-17
48,-2.000000000000e-01,1.000000000000e+00,-8.326672684689e-17
49,-1.000000000000e+00,0.000000000000e+00,-2.775557561563e-16
50,-1.000000000000e+00,1.000000000000e+00,-2.775557561563e-16
51,-1.847759065023e-01,0.000000000000e+00,-7.653668647302e-02
52,-2.000000000000e-01,5.000000000000e-01,-8.326672684689e-17
53,-1.847759065023e-01,1.000000000000e+00,-7.653668647302e-02
54,-6.000000000000e-01,0.000000000000e+00,-1.804112415016e-16
55,-6.000000000000e-01,1.000000000000e+00,-1.804112415016e-16
56,-9.238795325113e-01,0.000000000000e+00,-3.826834323651e-01
57,-1.000000000000e+00,5.000000000000e-01,-2.775557561563e-16
58,-9.238795325113e-01,1.000000000000e+00,-3.826834323651e-01
59,-1.414213562373e-01,0.000000000000e+00,1.414213562373e-01
60,-1.414213562373e-01,1.000000000000e+00,1.414213562373e-01
61,-7.071067811865e-01,0.000000000000e+00,7.071067811865e-01
62,-7.071067811865e-01,1.000000000000e+00,7.071067811865e-01
63,-1.847759065023e-01,0.000000000000e+00,7.653668647302e-02
64,-1.414213562373e-01,5.000000000000e-01,1.414213562373e-01
65,-1.847759065023e-01,1.000000000000e+00,7.653668647302e-02
66,-4.242640687119e-01,0.000000000000e+00,4.242640687119e-01
67,-4.242640687119e-01,1.000000000000e+00,4.242640687119e-01
68,-9.238795325113e-01,0.000000000000e+00,3.826834323651e-01
69,-7.071067811865e-01,5.000000000000e-01,7.071067811865e-01
70,-9.238795325113e-01,1.000000000000e+00,3.826834323651e-01
71,-1.110223024625e-16,0.000000000000e+00,2.000000000000e-01
72,-1.110223024625e-16,1.000000000000e+00,2.000000000000e-01
73,-4.440892098501e-16,0.000000000000e+00,1.000000000000e+00
74,-4.440892098501e-16,1.000000000000e+00,1.000000000000e+00
75,-7.653668647302e-02,0.000000000000e+00,1.847759065023e-01
76,-1.110223024625e-16,5.000000000000e-01,2.000000000000e-01
77,-7.653668647302e-02,1.000000000000e+00,1.847759065023e-01
78,-2.775557561563e-16,0.000000000000e+00,6.000000000000e-01
79,-2.775557561563e-16,1.000000000000e+00,6.000000000000e-01
80,-3.826834323651e-01,0.000000000000e+00,9.238795325113e-01
81,-4.440892098501e-16,5.000000000000e-01,1.000000000000e+00
82,-3.826834323651e-01,1.000000000000e+00,9.238795325113e-01
83,1.414213562373e-01,0.000000000000e+00,1.414213562373e-01
84,1.414213562373e-01,1.000000000000e+00,1.414213562373e-01
85,7.071067811865e-01,0.000000000000e+00,7.071067811865e-01
86,7.071067811865e-01,1.000000000000e+00,7.071067811865e-01
87,7.653668647302e-02,0.000000000000e+00,1.847759065023e-01
88,1.414213562373e-01,5.000000000000e-01,1.414213562373e-01
89,7.653668647302e-02,1.000000000000e+00,1.847759065023e-01
90,4.242640687119e-01,0.000000000000e+00,4.242640687119e-01
91,4.242640687119e-01,1.000000000000e+00,4.242640687119e-01
92,3.826834323651e-01,0.000000000000e+00,9.238795325113e-01
93,7.071067811865e-01,5.000000000000e-01,7.071067811865e-01
94,3.826834323651e-01,1.000000000000e+00,9.238795325113e-01
95,1.847759065023e-01,0.000000000000e+00,7.653668647302e-02
96,1.847759065023e-01,1.000000000000e+00,7.653668647302e-02
97,9.238795325113e-01,0.000000000000e+00,3.826834323651e-01
98,9.238795325113e-01,1.000000000000e+00,3.826834323651e-01
99,0.,0.,0.
100,0.,0.,0.
101,0.,0.,0.
*ELEMENT, TYPE=B31, ELSET=Ebeam
1, 1, 2
*ELEMENT, TYPE=C3D20R, ELSET=Evol
2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12,
13, 14, 19, 20, 21, 22, 15, 16, 17, 18
3, 6, 5, 23, 24, 10, 9, 25, 26, 13, 27,
28, 29, 21, 32, 33, 34, 18, 17, 30, 31
4, 24, 23, 35, 36, 26, 25, 37, 38, 28, 39,
40, 41, 33, 44, 45, 46, 31, 30, 42, 43
5, 36, 35, 47, 48, 38, 37, 49, 50, 40, 51,
52, 53, 45, 56, 57, 58, 43, 42, 54, 55
6, 48, 47, 59, 60, 50, 49, 61, 62, 52, 63,
64, 65, 57, 68, 69, 70, 55, 54, 66, 67
7, 60, 59, 71, 72, 62, 61, 73, 74, 64, 75,
76, 77, 69, 80, 81, 82, 67, 66, 78, 79
8, 72, 71, 83, 84, 74, 73, 85, 86, 76, 87,
88, 89, 81, 92, 93, 94, 79, 78, 90, 91
9, 84, 83, 4, 3, 86, 85, 8, 7, 88, 95,
11, 96, 93, 97, 19, 98, 91, 90, 16, 15
*ELEMENT,TYPE=DCOUP3D,ELSET=Ecoup1
10,100
*ELEMENT,TYPE=DCOUP3D,ELSET=Ecoup2
11,101
*MATERIAL,NAME=EL
*ELASTIC
210000.,.3
*SOLID SECTION,ELSET=Evol,MATERIAL=EL
*BEAM SECTION,ELSET=Ebeam,MATERIAL=EL,SECTION=RECT
0.001,0.001
0.,0.,1.
*PRE-TENSION SECTION,ELEMENT=1,NODE=99
0.,1.,0.
*NSET,NSET=FIX
49,68,61,80,73,92,85,97,8,20,9,32,25,44,37,56
*NSET,NSET=Ncoup1
5,12,4,95,83,87,71,75,59,63,47,51,35,39,23,27
*NSET,NSET=Ncoup2
6,14,3,96,84,89,72,77,60,65,48,53,36,41,24,29
*BOUNDARY
FIX,1,3
*DISTRIBUTING COUPLING,ELSET=Ecoup1
Ncoup1,1.
*DISTRIBUTING COUPLING,ELSET=Ecoup2
Ncoup2,1.
*EQUATION
2
100,1,1.,1,1,-1.
2
100,2,1.,1,2,-1.
2
100,3,1.,1,3,-1.
*EQUATION
2
101,1,1.,2,1,-1.
2
101,2,1.,2,2,-1.
2
101,3,1.,2,3,-1.
*STEP
*STATIC
*CLOAD
99,1,1.
*NODE PRINT,NSET=Nall
U
*NODE PRINT,NSET=Ncoup1,TOTALS=YES
RF
*NODE PRINT,NSET=Ncoup2,TOTALS=YES
RF
*END STEP