When this option is cleared, the bolt's length at zero stress state
L_{0} is determined based on the
length of bolt at the start of analysis L_{st}, 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:
L_{0} = L_{st} / (1+(P/A*E))
As the nonlinear analysis progresses, the bolt's length L_{step} 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 userdefined
preload stress. The bolt's axial load at each analysis step is
calculated from:
P_{step} = A* E* (L_{step} 
L_{0}) / L_{0}
When this option is checked, the program first runs an analysis with the
user defined preload 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 L_{0}.
Let’s define L_{f} 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:
L_{0}= L_{f} / (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:
P_{step} = A* E* (L_{step} 
L_{0}) / L_{0}
During the analysis, if (a) L_{step}
<= L_{0} then the bolt is loose, and if (b)
L_{step} > L_{0}, the bolt is under
tension and keeping parts together.
Notation:
 P: Userdefined axial preload
 P_{step}: Axial load of bolt at
current analysis step
 A: Bolt section area
 E: Bolt material modulus of
elasticity
 L_{0}: Original length of bolt
at zero stress state
 L_{st}: Length of bolt at start
of analysis (corresponds to the undeformed geometry
state of the components attached through the bolt)
 L_{f}: Deformed length of bolt after
settlement of connecting parts due to prestress (Keep
boltprestress selected)
 L_{step}: Deformed length of
bolt at current analysis step
