# 9. Bolt

Warning

The Bolt section is known to have limited functionality in implicit analyses.

    BEGIN BOLT SECTION <string>section_name
      ATTACHMENT RADIUS = <real>radius
      SURFACE 1 = <string>surf1
      SURFACE 2 = <string>surf2
      NORMAL DISPLACEMENT FUNCTION = <string>normFunc
      SHEAR DISPLACEMENT FUNCTION = <string>shearFunc
    END

The `BOLT` command block is used to define a two node beam or set of beams representing individual bolts or other fasteners. This capability is similar to the `SPOT WELD` capability. The beam elements should be meshed such that one beam end node is roughly on surface 1 and the other beam end node is roughly on surface 2. The beam element does not need to be meshed contiguous with the surface nodes.

The beam element is attached to all nodes and faces within a specified radius of the beam end nodes given by the `ATTACHMENT RADIUS` command. To be valid the bolt must find at least one face and three nodes within this radius on each surface.

The `NORMAL DISPLACEMENT FUNCTION` and `SHEAR DISPLACEMENT FUNCTION` define normal and shear force displacement functions for the bolt. The normal displacement function defines tensile response in positive x and compressive response in negative x. The shear displacement function is radially symmetric and only the positive x portion of the function will be used. The last point on the shear displacement function and the first and last points on the normal displacement function implicitly define the bolt failure criteria. Once a bolt fails the strength will ramp down over 10 steps and the bolt will provide zero force thereafter.

The bolt uses the same combined shear/normal mode failure as does the spot weld as defined in (9.1). \(u_n\) is the bolt normal extension. The maximum value given for \(u_n\) in the normal displacement curve is \(u_{n_{crit}}\), but is different for positive and negative displacements. \(u_t\) is the bolt shear deformation. The maximum value given for \(u_t\) in the normal displacement curve is \(u_{t_{crit}}\). The value \(p\) is a exponent that controls the shape of the failure surface, currently this exponent is defaulted to 2.

(9.1)\[\left(\frac{u_n}{u_{n_{crit}}}\right)^p + \left(\frac{u_t}{u_{t_{crit}}}\right)^p < 1.0.\]

The original direction defining normal and shear displacement is defined by the bolt element orientation. This normal will rotate based on the rotation of attached faces, not rotation of the bolt element itself.

Table 9.1 describes the output variables available on the bolt elements.

Table 9.1 Bolt Element Output Variables
Name | Description
--- | ---
`displacement_normal` | Current normal displacement in bolt
`displacement_shear` | Current shear displacement in bolt
`force_normal` | Current normal force in bolt
`force_shear` | Current shear force in bolt
`bolt_death_status` | One for alive, zero for dead, some value between zero and one when fading out immediately after hitting the death criteria.