The Tieback bolt model in Phase2 allows the user to model grouted tieback support. Bolts may be pre-tensioned and grouted with a user-defined bonded length.
In terms of its implementation in the Phase2 analysis engine, a tieback is essentially an End Anchored bolt connected in series with a Swellex/Split Set bolt. For a tieback with a bonded length less than 100%:
the unbonded length of the tieback behaves like an End Anchored bolt.
the bonded length of the tieback behaves like a Swellex/Split Set bolt.
For more information on these bolt models and failure mechanisms, see the End Anchored bolt topic and the Swellex/Split Set bolt topic. NOTE:
if the Bond Length = 0, then the tieback will behave like a simple End Anchored bolt.
if the Bond Length = 100% then the tieback will behave like a Swellex/Split Set bolt.
For more information regarding the bolt models and their numerical implementation in Phase2, see the Bolt Formulation document in the Theory section.
The following properties define a Tieback bolt in Phase2.
Bolt Diameter
The diameter of the tieback bolt.
Bolt Modulus
The Young’s Modulus of the bolt steel.
Tensile Capacity
The peak tensile capacity of the bolt steel.
Residual Tensile Capacity
The residual tensile capacity of the bolt steel.
Out-of-Plane Spacing
The spacing between bolts in the out-of-plane direction (i.e. normal to the analysis plane).
Bond Strength
This is the maximum shear force capacity along the Bond Length of the tieback. This should be the lesser of the bolt/grout interface strength or the grout/(rock or soil) interface strength. The Bond Strength is expressed as a Force per unit Bond Length. Note: Bond Strength can be determined from empirical methods such as pull-out tests.
Bond Shear Stiffness
This is the shear stiffness of the bolt/(rock or soil) interface. Note that the units of Shear Stiffness are FORCE / LENGTH / LENGTH. The Shear Stiffness can be thought of as follows:
On a shear force vs. shear displacement graph, the Shear Stiffness is equal to the slope of the Elastic portion of the graph. Remember shear force is expressed as a FORCE / LENGTH therefore the units of the Shear Stiffness are FORCE / LENGTH / LENGTH.
Bond Length
The bonded (grouted) length of the tieback, measured from the embedded end of the tieback. The Bond Length can be defined as:
a percentage of the total tieback length
an actual length
by selecting one of the two options in the dialog and entering a value.
Pre-Tensioning Force
See the Pre-Tensioning topic for information.