INTRODUCTION
LINK ELEMENTS are a new finite element type released in ADINA 2024. These spring-type elements can be used with nonlinear materials, in static and dynamic analyses, to represent the plastic and hysteretic behaviour of steel, reinforced concrete and other material types.
Link elements can be used to model moment or shear plastic hinges when they are created with zero-length. They can also represent the behaviour of structural elements such as buckling-restrained bracings or shear links, to mention a few, when given a length greater than zero. In both cases, their behaviour can be defined using Force-Deformation or Moment-Rotation curves in addition to the usual Stress-Strain relationships.
These element types are used to model concentrated plasticity events as well as the ductility and energy dissipation happening in full members which form part of structures subject to pushover analyses, cyclic dynamic events such as earthquakes, blast and so on. These structural materials than can be represented include steel, reinforced concrete, masonry and others.
In addition to the traditional plastic, thermo-plastic, cyclic and viscoelastic materials, Link Elements can now also be used with two new materials in ADINA: Takeda and Degrading-Plasticity. These two new materials include superior capabilities to represent the behaviour of reinforced concrete structures, including nonlinear cyclic hysteresis response, bounded by a user-defined backbone curve, peak-oriented, pinching or bilinear type of uniaxial response.
Link elements can be used in models:
- Created within ADINA User Interface
- Exported from STAAD.Pro, RAM Structural System or SACS Offshore to ADINA.
Link Element Sub-Types
Depending on the structural behaviour to be modeled, a link element sub-type must be selected.
There are four link element subtypes available in ADINA:
|
Link Element Sub-Type |
Link Element Type |
Degrees of Freedom |
|
General |
Finite-length |
6 (3 Translations, 3 Rotations) |
|
Standard |
Finite-length |
3 (3 Translations) (1) |
|
Moment Hinge |
Zero-length |
3 (3 Rotations, Translations are constrained) (2) |
|
Shear Hinge |
Zero-length |
3 (3 Translations, Rotations are constrained) (3) |
(1) The Standard link element behaves as “pinned” at its ends (similar to a truss element).
(2) By default, Moment Hinges have their translational DOFs rigidly constrained; this setting can be changed.
(3) By default, Shear Hinges have their rotational DOFs rigidly constrained; this setting can be changed.
General Note: At the moment, all DOF on each link element subtype are independent from each other (i.e., no coupling between axial and rotation).
Some examples of possible applications are shown below. The list is not exhaustive.
|
Link Element Sub-Type |
Application Examples (not exhaustive) |
|
General |
Structural members or links with restrained ends and plastic or cyclic behaviour. |
|
Standard |
Structural members or links with pinned ends and plastic or cyclic behaviour. |
|
Moment Hinge |
Concentrated moment-rotation plastic hinges at sections of expected plasticity (high moment) |
|
Shear Hinge |
Concentrated force-deformation plastic hinges at sections of expected plasticity (high shear) |
The link element sub-type can be selected from the Link element group definition dialog.
Figure 1: Link Element Group definition dialog (Element Subtype selection)
link element Material models
Link element material properties can be specified using either:
- Link Property Sets
- Material Property Sets
Figure 2: Link Element Group definition dialog (Link Property vs Material Property)
- Link Property Sets
These are purposely created material properties for Link Elements.
They are defined by Force-Deformation or Moment-Rotation sets of values.
The following Link element material models are currently available in ADINA:
- Elastic Isotropic
- Nonlinear Elastic
- Plastic Bilinear
- Plastic Multilinear
- Plastic Cyclic
- Degrading-Plasticity
- Takeda
Figure 3: Link Element Property (available models)
Figure 4: Link Element Property example (defined as Force-Deformation or Moment-Rotation law)
- Material Property Sets
Amongst the general material models in ADINA, some can be applied to Link elements.
When the Link Element material is selected using this method, Stress-Strain inputs are required.
Figure 4: Available material models for Link Elements (highlighted)
APPLYING link elementS IN A MODEL
After having defined the required Link Element Group, Sub-Type and Property (Material), this can be applied to the model.
This is done in two steps:
- Define the element topology (i.e. between nodes A and B)
- Define the element orientation
To define the element topology, we navigate to Meshing > Elements > Element Nodes and we populate the table for each existing Link Element Group. The Link Element number can be freely chosen. Node 1 and Node 2 fields represent the two nodes to connect via a Link Element.
For each zero-length Link Elements (i.e. Shear and Moment-Hinges), Node 1 and Node 2 will be coincident (will have the same coordinates).
Figure 5: Link Element topology definition (Element Nodes)
To define the element orientation (and other optional settings), we navigate to Meshing > Elements > Element Data and we populate the table for each existing Link Element Group. Here we explain some of these entries:
- Apply Constraint – The following settings apply by Default:
- General: No constraints are applied (None)
- Standard: Rotational degrees of freedom are constrained (Rotational)
- Shear Hinge: Rotational degrees of freedom are constrained (Rotational)
- Moment Hinge: Translational degrees of freedom are constrained (Translational)
- X-Vector, Y-Vector, Z-Vector: Direction of local ‘r’ axis for link element ‘i’. This is required for zero-length Link Elements (i.e. Moment Hinge and Shear Hinge). For a finite-length Link Element connecting nodes 1 and 2, the local ‘r’ axis is aligned with the line connecting nodes 1 and 2. Hence this entry is ignored.
- XO, YO, ZO: Together with the Link Element's 'r' local axis, it forms a plane containing the local ‘s’ axis which is also orthogonal to the local 't' axis. This entry is required for all Link Element sub-types.
- Alpha: Link element reference location position. It is defined within the range of 0.0 and 1.0. The values 0.0 and 1.0 correspond to the locations at element node 1 and 2, respectively. The default is the element centre location (0.5).
Figure 6: Link Element orientation (Element Data)
See Also: