# 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:

**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.**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.**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.**Bolt Shear Strength -**Whether Shear Strength of the bolt is considered.

There are six possibilities considered, as illustrated in the figure below.

Possible bolt deformation modes [Windsor, 1996]

## 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:

**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**.**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**.

**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.

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