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 un-deformed 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 which corresponds to the settlement of the connecting parts due to pre-stress. 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 aplied 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 pre-stress (Keep bolt-prestress selected)
- Lstep: Deformed length of bolt at current analysis step
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