When this option is cleared, the bolt's length at zero stress state
L0 is determined based on the
length of bolt at the start of analysis Lst, which corresponds to the undeformed geometry
state of the components attached through the bolt connector. The
bolt's length at zero stress state is calculated from:
L0 = Lst / (1+(P/A*E))
As the nonlinear analysis progresses, the bolt's length Lstep at each analysis step adapts
itself to the deformed geometry of the attached components as
they deform due to the applied loads. The bolt's final stress at
the end of the nonlinear analysis differs from the user-defined
pre-load stress. The bolt's axial load at each analysis step is
calculated from:
Pstep = A* E* (Lstep -
L0) / L0
When this option is checked, the program first runs an analysis with the
user defined pre-load P as initial condition without any
external loads. The deformation of the parts connected through
the bolt is calculated and is used to determine the bolt's
length at zero stress state L0.
Let’s define Lf as the deformed
length of bolt that corresponds to the settlement of the
connecting parts due to prestress. The bolt’s length at zero
stress is then calculated from:
L0= Lf / (1+(P/A*E))
For the second step of the analysis, all applied loads are included. The
bolt's axial load at each analysis step is calculated from:
Pstep = A* E* (Lstep -
L0) / L0
During the analysis, if (a) Lstep
<= L0 then the bolt is loose, and if (b)
Lstep > L0, the bolt is under
tension and keeping parts together.
Notation:
- P: User-defined axial pre-load
- Pstep: Axial load of bolt at
current analysis step
- A: Bolt section area
- E: Bolt material modulus of
elasticity
- L0: Original length of bolt
at zero stress state
- Lst: Length of bolt at start
of analysis (corresponds to the un-deformed geometry
state of the components attached through the bolt)
- Lf: Deformed length of bolt after
settlement of connecting parts due to prestress (Keep
bolt-prestress selected)
- Lstep: Deformed length of
bolt at current analysis step
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