7
Bolt Pretension
Compressed Gasket
The pretension feature of ANSYS is useful for creating, managing, and loading structures
having multiple pretensioned bolts. This feature was introduced in version 5.6 but has been
upgraded to enhance bolt pretension modeling. In the example below 3 bolts are used to
attach a stiff plate to a gasket. The bolts are then sequentially tightened to 10,000 pounds
each, compressing the gasket. The problem starts by loading a database file which contains
an idealized 2D model of the bolt/gasket sequence shown below. In the file the bolts, plate,
and gasket have been modeled and meshed with beam, solid, and contact elements included.
Material properties and boundary constraints are already defined.
Bolt 1
Bolt 2
Bolt 3
Stiff Plate
Soft Gasket
Brief Instructions
1. Start ANSYS 5.7 with the default jobname (file).
2. Resume the database file
“Pretension.db1”
3. Create Pretension sections at each of
the bolts.
4. Apply 10,000-pound pretension loads
to the 3 bolts. Use 0.1% of force for
behavior before loading. After an
initial untensioned load step, load and
lock in sequence: Bolt 1 first (load in
step 2, lock in step 3), Bolt2 2nd, Bolt
3 last.
5. A solution/postprocessing script has been prepared to set up and solve the 5 load steps.
Click Read input from… “PT_util.dat”.
ANSYS 5.7 New Features Workshop Supplement
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Detailed Instructions
1. Start ANSYS 5.7 with the default jobname
(file).
2. Resume the database file “Pretension.db1”
Click on:
- Utility Menu > File > Resume from...
Pretension.db1
[OK]
3.
Create pretension sections at each of the bolts.
Click on:
-
Main Menu > Preprocessor >
Sections > Pretensn Mesh >
Picked Elements
 Select two elements at the
center of the vertical beam,
“elements to be separated”
(shown right).
[APPLY]
 Pick node on separation plane (node between two
chosen elements).
[OK]
 SECID = 1
 NAME = bolt1
 KDIR = Y-axis, then
[APPLY]
Repeat above for bolt2
 SECID = 2
 NAME = bolt2
 KDIR = Y-axis, then
[APPLY]
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ANSYS 5.7 New Features Workshop Supplement
Select two
elements at
central node
Repeat same procedure for bolt3
 SECID = 3
 NAME = bolt3
 KDIR = Y-axis, then
[OK]
When completed, the plot in ANSYS graphics window should look like:
Note stars at central nodes
4. Apply 10,000-pound pretension loads to the 3 bolts. To prevent sectioned bolts from behaving
as unconstrained free bodies, use 0.1% of force for behavior before load.
Click on:
- Main Menu > Preprocessor
> Loads > Apply >
Sections > 1 Pretensn
Sectn…
 Select “1 bolt1”
[OK]




KINIT = 0.1% of force
FDVALUE = 10000
LSLOAD = 2
LSLOCK = 3
[APPLY]
Repeat above for bolt2
 Select “2 bolt2”
[OK]
 KINIT = 0.1% of
force
 FDVALUE = 10000
 LSLOAD = 3
 LSLOCK = 4
[APPLY]
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Repeat same procedure for bolt3
 Select “3 bolt3”
[OK]




KINIT = 0.1% of force
FDVALUE = 10000
LSLOAD = 4
LSLOCK = 5
[OK]
5. Read input file to solve model
Click on:
- Utility Menu > File > Read input from…
PT_util.dat
[OK]
This input file is set up to solve 5 load steps. (The first load step is run prior to pretensioning any bolts,
to capture the initial configuration for display animation purposes.) The input file then animates the
results (Animate > Over Results).
Note that the bolt pretension forces and locking displacements are not specified in this input file -- the
program automatically applies these effects in the correct load step, in accordance with your earlier
SLOAD input.
A listing of file PT_util.dat follows:
/SOLU
ANTYPE,0
NLGEOM,1
! large displacement effects in plate & gasket
NCNV,2,0,0,0,0
RESCONTRL,DEFINE,ALL,LAST,5
/com,step 1 - establish contact
outres,all,last
nsub,1,1,1
solve
/com,step 2 - tighten bolt 1
outres,all,none
outres,all,-4
nsub,4,10,4
solve
/com,step 3 - lock bolt 1, tighten bolt 2
solve
/com,step 4 - lock bolt 2, tighten bolt 3
solve
/com,step 5 - lock bolt 3
nsub,1,1,1
solve
FINISH
/post1
set,last
FLST,5,52,1,ORDE,8
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FITEM,5,1
FITEM,5,-9
FITEM,5,82
FITEM,5,-98
FITEM,5,235
FITEM,5,-251
FITEM,5,388
FITEM,5,-396
NSEL,U, , ,P51X
/PSF,DEFA, ,1,0,1
/PBF,DEFA, ,1
/PIC,DEFA, ,1
/PSYMB,CS,0
/PSYMB,NDIR,0
/PSYMB,ESYS,0
/PSYMB,LDIV,-1
/PSYMB,LDIR,0
/PSYMB,ADIR,0
/PSYMB,ECON,0
/PSYMB,XNODE,0
/PSYMB,DOT,1
/PSYMB,PCONV,
/PSYMB,LAYR,0
/PSYMB,FBCS,0
/PBC,NFOR, ,0,,,,
/PBC,NMOM, ,0,,,,
/PBC,RFOR, ,2,,,,
/PBC,RMOM, ,0,,,,
/PBC,PATH, ,0,,,,
/triad,lbot
/RGB,INDEX,100,100,100, 0
/RGB,INDEX, 80, 80, 80,13
/RGB,INDEX, 60, 60, 60,14
/RGB,INDEX, 0, 0, 0,15
PLDISP,2
/user
ANDATA,0.5, ,2,1,14,1,0,1
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