Modeling bolted connections

Video: Create a bolt connection with a nut

Video: Create a bolt connection with a tapped hole

Use the Bolt Connection command to model the following types of bolted connections with finite elements:

• A bolt that is held in place with a nut.

• A bolt in a tapped (threaded) hole.

• A bolt-type connection that is represented by only a spider element at the junction plane between two mating bodies.

Bolted connections are solver specific

With Bolt Connection, how the software models the bolt depends on your specified solver environment. Typically, 1D elements are used to model the bolt's shank. To connect those 1D elements to the nodes in the surrounding mesh, the software creates a spider-type connection.

• In Nastran models, the software uses rigid or constraint elements to create the connection. Each connection has a single central node with multiple leg nodes that branch out from the central node in a spider-like pattern. For more information, see Understanding spider elements in bolted connections.

• In Abaqus and ANSYS models, the software uses specific types of constraint boundary conditions to create the connection.

Solver	Bolt shank	Spider-type connection
Nastran	1D elements, such as CBAR or CBEAM elements*	RBE2 or RBE3 elements
Abaqus	1D elements, such as B31 or B21 elements*	*KINEMATIC COUPLING constraint
ANSYS	1D elements, such as BEAM44 or BEAM188 elements*	CERIG,CP constraint equations
Simcenter Samcef	1D elements, such as rod, beam, rigid body, or mean elements	rigid body or mean elements
*You can also choose to model the bolt with a 1D spring element, rather than with a 1D beam element. See Modeling the bolt's shank with a spring element for more information.

The following graphic shows an assembly in the Nastran environment that is connected together by bolts in several tapped bolt holes.

• (A) shows the model with meshes created on the individual components.

• (B) shows the model with the bolt connections generated in the bolt holes. Here, RBE3 elements connect the CBAR elements along the bolt's shank to the CTETRA elements in the components' meshes.

• (C) shows only the bolt connection including the beam cross section shape defined for the PBARL physical property table assigned to the CBAR element. For more information on rendering beam elements as solid elements, see Displaying beam cross sections.

Defining the characteristics of a bolt

You use the Bolt Connection dialog box to specify all the information necessary to create a bolted connection. This information includes the type of bolt, key bolt dimensions, and attributes for the beam and connection elements that the software creates to model the bolt. The following graphic shows the key dimensions for the two main types of bolts.

• (A) is the diameter of the bolt's head. In the Bolt Connection dialog box, you can select either the edge of a hole or the center point of the hole to define the location of the bolt's head.

• (B) is the length of the bolt. If you create a bolt in a tapped hole, you must specify the bolt's length in the Bolt Connection dialog box.

• (C) is the diameter of the bolt's nut. In the Bolt Connection dialog box, you can select either the edge of a hole or the center point of the hole to define the location of the bolt's head.

• (D) is the diameter of the bolt's shank. You control the diameter of the bolt through the beam cross section you associate with the 1D element that represents the beam's shank. For more information on beam cross sections, see Creating beam cross sections.

• (E) is the effective thread length for a bolt. For a bolt in a tapped hole, you must specify the effective thread length in the Bolt Connection dialog box.Note: The specified Effective Thread Length must be less than the specified Bolt Length.

Bolt with a nut	Threaded bolt for a tapped hole

Defining a pre-load on a bolted connection

After you use the Bolt Connection command to model bolts, you can use the Bolt Pre-Load command to define a pre-load on the bolt. For more information, see Bolt pre-load.

Updating bolted connections

For bolts that you create with the Bolt Connection command, the software preserves the bolt connection recipe when the underlying CAD geometry or the associated polygon geometry is modified or deleted. For example, an update to a CAD part may delete the head, nut, or tap geometry in a bolt. When this occurs, you can now edit the bolt connection recipe to modify the geometry or to add new or updated geometry to the bolt.

Note:

To delete a Bolt Connection recipe that is no longer valid, right-click the recipe in the Simulation Navigator and select Delete.

Where do I find it?

Application	Pre/Post
Prerequisite	A FEM file as the work part and displayed part
Command Finder	Bolt Connection

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Command reference

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Modeling bolted connections, Simcenter 3D 2021.1 Series

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