FEA Bearing [SIG]

In this section, bearings can be defined for Finite Element Analysis.

Articulation

Insertion Point: Used for specifying the bearing location and can be selected by using the three dots and the options ‘Pick...’ and ‘Select...’.

Tx[Fixed/Free/Stiffness]:When the bearing rotation is 0 degrees, Tx represents the stiffness in the longitudinal direction. It is typical for a continuous girder to have at least one fixed bearing (or to use a real stiffness value) in the Tx direction.

Ty[Fixed/Free/Stiffness]: Ty represents the stiffness in the transverse direction when the bearing rotation is 0 degrees.

Tz[Fixed/Free/Stiffness]: Tz represents the stiffness in the vertical direction. It is common to use a high stiffness value, such as 1000 kip/in, or to fix the bearing.

Rx[Fixed/Free/Stiffness]: To address stability concerns, a small Rx stiffness can be used in the torsional direction (Rx) under certain conditions. If the constructed girders are not connected with bracings to other girders at any stage, it can result in stability issues. Therefore, a small Rx stiffness is recommended to overcome this problem.

Ry[Fixed/Free/Stiffness]: Typically, bearings are free to rotate in the Ry direction.

Rz[Fixed/Free/Stiffness]: Typically, bearings are free to rotate in the Rz direction.

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FEA Bearing Representation: Tx = Free, Ty = Fixed, Tz = Fixed, Rx = Free, Ry =Free, Rz = Free

Bearing Rotation: Curved decks can be guided either radially from a fixed point or tangentially to the radius of curvature. When the deck is guided radially, precise geometry is crucial for the bearings that are farthest from the fixed point. For structures with constant curvature, it is recommended to align the bearings tangentially to effectively guide the deck around the curve as it expands and contracts.

To achieve tangential alignment, as shown in the figure below, on a curved bridge, the user should set the bearing rotation to 0.

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Tangential alignment on a curved bridge

In order to achieve radial alignment, as shown in the figure below, the user needs to input non-zero bearing rotation values. Although inputting a non-zero value will not change the global behavior if the bearing is fixed (or has the same stiffness) in the x-y direction, the spring forces reported in the local axis will be different. Therefore, it is crucial to input rotation values accurately.

Transfer Forces to Substructure[Yes/No]: If the user chooses to connect to the substructure, a two-node spring is generated between the pier cap and the girder. On the other hand, if the transfer to the substructure is selected as no, a single node spring with specified fixities is generated instead. In general, selecting "no" for transferring forces to the substructure and using a single-node spring aids the user in comprehending the behavior and designing the superstructure without modeling the substructure.

Bearing Bottom Elevation (readonly): The bottom location of the bearings in 3D, with respect to the Z-axis of the Global Coordinate System, is displayed to the user in this column, regardless of the alignment's vertical definition.

Graphical Settings

The geometry of the FEA bearing can be adjusted using the parameters under the Graphical Settings tab.

Width: The width of the bearing in the transverse direction can be adjusted by this parameter.

Length: The length of the bearing in the longitudinal direction can be adjusted by this parameter.

Depth: The depth of the bearing in the vertical direction can be adjusted by this parameter.

Capacity

Bearing Capacity: The bearing capacity can be adjusted using this parameter.