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<table><tr><td>Load ID (*DLOAD)</td><td>Abaqus/CAE Load/Interaction</td><td>Units</td><td>Description</td></tr><tr><td>BZNU</td><td>Body force</td><td> $FL^{-2}$ </td><td>Nonuniform body force in the axial direction with magnitude supplied via user subroutine DLOAD.</td></tr><tr><td>CENT</td><td>Not supported</td><td> $FL^{-3}$  $(ML^{-2}T^{-2})$ </td><td>Centrifugal load (magnitude is input as  $\rho\omega^{2}$ , where  $\rho$  is the mass density per unit area,  $\omega$  is the angular velocity). Since only axisymmetric deformation is allowed, the spin axis must be the z-axis.</td></tr><tr><td>CENTRIF</td><td>Rotational body force</td><td> $T^{-2}$ </td><td>Centrifugal load (magnitude is input as  $\omega^{2}$ , where  $\omega$  is the angular velocity). Since only axisymmetric deformation is allowed, the spin axis must be the z-axis.</td></tr><tr><td>GRAV</td><td>Gravity</td><td> $LT^{-2}$ </td><td>Gravity loading in a specified direction (magnitude input as acceleration).</td></tr><tr><td>HP</td><td>Not supported</td><td> $FL^{-2}$ </td><td>Hydrostatic pressure applied to the element reference surface and linear in global Z. The pressure is positive in the direction of the positive element normal.</td></tr><tr><td>P</td><td>Pressure</td><td> $FL^{-2}$ </td><td>Pressure applied to the element reference surface. The pressure is positive in the direction of the positive element normal.</td></tr><tr><td>PNU</td><td>Not supported</td><td> $FL^{-2}$ </td><td>Nonuniform pressure applied to the element reference surface with magnitude supplied via user subroutine DLOAD. The pressure is positive in the direction of the positive element normal.</td></tr><tr><td>TRSHR</td><td>Surface traction</td><td> $FL^{-2}$ </td><td>Shear traction on the element reference surface.</td></tr><tr><td> $TRSHRNU^{(S)}$ </td><td>Not supported</td><td> $FL^{-2}$ </td><td>Nonuniform shear traction on the element reference surface with</td></tr></table>

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<table><tr><td>Load ID(*DLOAD)</td><td>Abaqus/CAELoad/Interaction</td><td>Units</td><td>Description</td></tr><tr><td></td><td></td><td></td><td>magnitude and direction supplied via user subroutine UTRACLOAD.</td></tr><tr><td>TRVEC</td><td>Surface traction</td><td> $FL^{-2}$ </td><td>General traction on the element reference surface.</td></tr><tr><td> $TRVECNU^{(S)}$ </td><td>Not supported</td><td> $FL^{-2}$ </td><td>Nonuniform general traction on the element reference surface with magnitude and direction supplied via user subroutine UTRACLOAD.</td></tr></table>

# Foundations

Foundations are specified as described in “Element foundations,” Section 2.2.2.

<table><tr><td>Load ID(*FOUNDATION)</td><td>Abaqus/CAELoad/Interaction</td><td>Units</td><td>Description</td></tr><tr><td>F</td><td>Elasticfoundation</td><td> $FL^{-2}$ </td><td>Elastic foundation. For SFMGAX1 and SFMGAX2 elements the elastic foundations are applied to degrees of freedom  $u_{r}$  and  $u_{z}$  only.</td></tr></table>

# Surface-based loading

# Distributed loads

Surface-based distributed loads are specified as described in “Distributed loads,” Section 34.4.3.

<table><tr><td>Load ID(*DSLOAD)</td><td>Abaqus/CAELoad/Interaction</td><td>Units</td><td>Description</td></tr><tr><td>HP</td><td>Pressure</td><td> $FL^{-2}$ </td><td>Hydrostatic pressure applied to the element reference surface and linear in global Z. The pressure is positive in the direction opposite to the surface normal.</td></tr><tr><td>P</td><td>Pressure</td><td> $FL^{-2}$ </td><td>Pressure applied to the element reference surface. The pressure is positive in the direction opposite to the surface normal.</td></tr><tr><td>PNU</td><td>Pressure</td><td> $FL^{-2}$ </td><td>Nonuniform pressure applied to the element reference surface</td></tr></table>

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<table><tr><td>Load ID(*DSLOAD)</td><td>Abaqus/CAELoad/Interaction</td><td>Units</td><td>Description</td></tr><tr><td></td><td></td><td></td><td>with magnitude supplied via user subroutine DLOAD. The pressure is positive in the direction opposite to the surface normal.</td></tr><tr><td>TRSHR</td><td>Surface traction</td><td> $FL^{-2}$ </td><td>Shear traction on the element reference surface.</td></tr><tr><td> $TRSHRNU^{(S)}$ </td><td>Surface traction</td><td> $FL^{-2}$ </td><td>Nonuniform shear traction on the element reference surface with magnitude and direction supplied via user subroutine UTRACLOAD.</td></tr><tr><td>TRVEC</td><td>Surface traction</td><td> $FL^{-2}$ </td><td>General traction on the element reference surface.</td></tr><tr><td> $TRVECNU^{(S)}$ </td><td>Surface traction</td><td> $FL^{-2}$ </td><td>Nonuniform general traction on the element reference surface with magnitude and direction supplied via user subroutine UTRACLOAD.</td></tr></table>

# Incident wave loading

Surface-based incident wave loading is also available for these elements. See “Acoustic and shock loads,” Section 34.4.6.

# Element output

Output is currently available only when the surface element is used to carry rebar layers. See “Defining reinforcement,” Section 2.2.3, for details.

# Node ordering on elements

![](images/page-1003_600be562e1e31016d67960c7d3e7bc6d35abf98e07202fc638c1a337220c70b5.jpg)

<details>
<summary>natural_image</summary>

Simple line diagram with two labeled points (1 and 2) connected by a straight line (no additional text or symbols)
</details>

2 - node element

![](images/page-1003_fc816b7a2ce3132878bd872b4b7ed18ad03a2f2d05731f7ca37218380fb6a6ea.jpg)

<details>
<summary>text_image</summary>

1
2
3
</details>

3 - node element

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![](images/page-1004_2542c0882a1add27b365943146fa4d1b24609dff55792b9a82ea909b650bbd2c.jpg)

<details>
<summary>text_image</summary>

1
1
2
</details>

2 - node element

![](images/page-1004_07748dee7b10e92ba67d442029367ba3d8827adc2d319bf4dee7974d1f0f9162.jpg)

<details>
<summary>flowchart</summary>

```mermaid
graph TD
    1["1"] --> 2["2"]
    2 --> 3["3"]
    1 -->|×| 1
```
</details>

3 - node element

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# 32.8 Tube support elements

• “Tube support elements,” Section 32.8.1   
• “Tube support element library,” Section 32.8.2

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# 32.8.1 TUBE SUPPORT ELEMENTS

Product: Abaqus/Standard

# References

• “Tube support element library,” Section 32.8.2   
• \*ITS   
• \*DASHPOT   
• \*FRICTION   
• \*SPRING

# Overview

Tube support elements:

• are provided to model the interaction of a tube with a closely adjacent tube support, for cases where intermittent contact between the tube and the support may occur; and   
• are made up of a spring/friction link (to simulate direct contact between the tube and the support) and a parallel dashpot (to simulate the effect of the fluid in the annulus between the tube and the support), as shown in Figure 32.8.1–1.

Details of the element formulations can be found in “Tube support elements,” Section 3.9.4 of the Abaqus Theory Guide.

# Typical applications

An ITSCYL element can be used to model a drilled hole support (see Figure 32.8.1–2).

Several ITSUNI elements can be attached to the same node of the beam elements representing the tube to model the case of a tube support made up of a series of straight segments, as in an “egg-crate” design (see Figure 32.8.1–3).

# Choosing an appropriate element

Two types of tube support elements are provided.

# ITSUNI elements

ITSUNI is a “unidirectional” element, which always acts in a fixed direction in space. One node of the element must be located on the axis of the tube, which is modeled using beam elements; and the other node must be located equidistant between the two parallel support plates. The support plates are built into the ITSUNI element definition.

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![](images/page-1008_493a79042c9402fff97c9a837aad819d6918fa23d318438e7a9fdde9ea5f4c9d.jpg)

<details>
<summary>text_image</summary>

P₃
Q ←
2
Spring
(linear or nonlinear)
Dashpot
(linear or nonlinear)
Friction
1
Q
P₃
</details>

Figure 32.8.1–1 Tube support element behavior.

# ITSCYL elements

ITSCYL is a “cylindrical” element, which can be used to simulate the interaction between a circular tube and a circular hole. One node of the element must be located on the axis of the tube, which is modeled using beam elements, and the other node must be located at the center of the hole in the circular tube support plate. The circular hole is built into the ITSCYL element definition.

# Defining the behavior of ITS elements

You define the diameter of the tube and other geometric quantities that define the ITS element. You must associate these quantities with a set of ITS elements. In addition, you must define the behavior of the spring, friction link, and dashpot that make up a tube support element.

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![](images/page-1009_c43905d80e72e43f9c6e48f5301fb7ab8d9e14cae3be637fda989c9154d457dd.jpg)

<details>
<summary>text_image</summary>

Tube center
Tube
C of tube
Tube support plate
1
2
Center of hole
ITSCYL element
</details>

Figure 32.8.1–2 Use of an ITSCYL element for a drilled hole support.

The spring behavior of an ITS element is shown in Figure 32.8.1–4. Relative displacements in the element are measured from the position where the tube and the hole in the support plate are aligned exactly—when the nodes of the element are at the same location. As indicated in Figure 32.8.1–4, the spring behavior of an ITS element is modified from that of the assigned spring definition to account for any clearance between the tube and support when the nodes of the element are at the same location. When there is no contact between the tube and the support, no force is transmitted by the spring; when the tube is in contact with the support, the force increases as the tube wall is deformed. This force can be modeled as a linear or a nonlinear function of the relative displacement between the axis of the tube and the center of the hole in the support.

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![](images/page-1010_0918c9d73babf1d6ff2cf2c5a862912c54a8c2298f679c127cae5c284e75bb94.jpg)

<details>
<summary>text_image</summary>

ITSUNI elements
Tube
C of tube
n₂
1
2
n₁
Center of opening
in support plates
Parallel support
plates for element 2
Parallel support
plates for element 1
</details>

Figure 32.8.1–3 Use of ITSUNI elements for an “egg-crate” support.

Friction between the tube and support will generate a moment at the tube node if the tube diameter is greater than zero and a moment at the hole node if the hole size is greater than zero. At least one of the following should be true for any node of an ITS element that will have a moment acting on it:

• the node should be associated with a beam or other element that can carry a moment;   
• the nodal rotation should be set to zero with a boundary condition.

Input File Usage: Use the following options to define the behavior of ITS elements:

\*ITS, ELSET=name   
\*DASHPOT   
\*SPRING   
\*FRICTION
