Bearing Fixity

This section defines bearing fixity conditions at each support location, specifying translational and rotational constraints.

Navigation: Superstructure > Boundary Conditions > Bearing Fixity

Steps

Step 1: Navigate to Bearing Fixity

Navigate to Superstructure > Boundary Conditions > Bearing Fixity in the tree view.

Bearing Fixity navigation

Step 2: Select Insertion Points

Click the first cell in the Insertion Point column and use the Pick button to select insertion points that define the bearing locations.

Pick Insertion Points

Step 3: Define Fixity Values

Set the translational (Tx, Ty, Tz) and rotational (Rx, Ry, Rz) fixity values for each bearing:

Parameter	Description
Tx	Axial direction - Only IP1 and IP2 have assigned values (axial forces accommodated at these supports)
Ty, Tz	Transverse and vertical directions - Remain constant for all bearings
Rx	Torsional stability - Set to 10 for all supports to maintain stability during construction
Ry, Rz	Rotational constraints - Set as needed

Fixity Values 1

Fixity Values 2

Fixity Values 3

Quick Tip: Rx Parameter for Torsional Stability

Setting a non-zero Rx value is necessary to address torsional stability when constructing a beam without transverse components like diaphragms or decks. In this example, all supports are assigned Rx = 10.

Step 4: Configure Force Transfer

Set Transfer Force to Substructure to Yes for all bearing locations.

Transfer Force

Quick Tip: Transfer Force to Substructure

Setting	Behavior
Yes	Creates a two-node spring between pier cap and girder (use when substructure is modeled)
No	Creates a one-node spring at the bottom of the girder (use for abutment locations without substructure model)

Verification

The completed bearing fixity configuration is shown below.

Completed Bearing Fixity