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Bolt Support Force

The bolt support force that is ultimately applied to a wedge and the orientation of the applied force (tension or shear) depend on the following factors:

  1. Bolt Deformation Mode - The mode in which a bolt intersects a wedge failure plane. The deformation mode depends on whether the failure plane is a shear (sliding) plane or a dilating (opening) plane, and also on the orientation of the bolt with respect to the plane and the sliding direction.
  2. There are six possibilities considered, as illustrated in the figure below.

    Bolt Deformation Mode

    Possible bolt deformation modes [Windsor, 1996]

  3. Bolt Tensile Capacity - The maximum Tensile Force which can be supplied by the bolt is determined from the Bolt Force Diagram and the point at which a wedge plane intersects the bolt along its length. The Bolt Force diagram is derived from the bolt properties (e.g. Tensile Capacity, Plate Capacity, Bond Strength) entered in the Bolt Properties dialog.
  4. Bolt Orientation Efficiency - If considered, Bolt Orientation Efficiency is only applied to the Tensile Force. Bolt efficiency can be toggled on or off, and there are three possible methods of computing the efficiency.
  5. Bolt Shear Strength - Whether Shear Strength of the bolt is considered.

Applied Bolt Support Force

The following table summarizes the possibilities of applied bolt support force, for all combinations of bolt deformation mode, bolt efficiency (on / off) and shear (on / off).

Bolt

Deformation

Mode

Bolt Efficiency: Off

Shear: Off

Bolt Efficiency: On

Shear: Off

Bolt Efficiency: On

Shear: On

Bolt Efficiency: Off

Shear: On

A

tensile

tensile * eff

tensile * eff

tensile

B

tensile

tensile * eff

tensile * eff

tensile

C

tensile

tensile * eff

tensile * eff

tensile

D

tensile

tensile * eff

shear

shear

E

tensile

zero force

shear

shear

F

tensile

zero force

shear

shear

Table 1: Summary of bolt support force.

NOTES:

  • tensile - the Tensile Failure capacity (without applying Bolt Efficiency), determined from the Bolt Force Diagram.
  • eff - The Bolt Orientation Efficiency factor
  • shear - The bolt Shear capacity, if the Shear Strength option is used.
  • Modes A, B, C - if a bolt is in mode A, B or C, only a tensile force will be applied, in the direction of the bolt. The tensile force will be multiplied by the Bolt Efficiency Factor if Bolt Efficiency is being used.
  • Mode D - if a bolt is in mode D, the bolt can use either tensile or shear force. If the Shear Strength option is ON, then the Shear Force will be used. Shear force is applied opposite to the sliding direction of the wedge. If the Shear Strength option is OFF, then the Tensile force will be used.
  • Modes E, F - if a bolt is in mode E or F, the bolt can use either tensile, zero, or shear force, depending on the selection of Bolt Efficiency and Shear.
  • If both Bolt Efficiency and Shear are turned OFF, then the full tensile force will be applied, in the direction of the bolt, regardless of how the bolt intersects the wedge (i.e. even if the bolt is in a shear deformation mode).

Direction of Bolt Support Force

There are TWO possibilities for the direction of the applied bolt support force. Referring to Table 1:

  1. Tensile - For all cases marked as tensile or tensile * eff, the direction of the applied bolt support force will be in the direction of the bolt.
  2. Note: The direction is not affected by the bolt efficiency factor. The direction is always exactly in the direction of the bolt, even if the efficiency factor is applied.

  3. Shear - For all cases marked as shear (Shear Strength option is toggled ON), the direction of the applied bolt support force will be opposite to the sliding direction of the wedge.

A bolt can never apply both Tensile and Shear support at the same time. The two cases are completely exclusive in the UnWedge implementation.

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