# Analysis elements
# Element types
The table below may aid decisions on which kinds of elements should be used in a model.
# 1D element types
| Element type | No of Nodes | Description | Limitations | See also |
|---|---|---|---|---|
| Bar | 2 | Models a bar or beam with axial, stiffness only – no bending stiffness. | Releases are not relevant | Strut element, Tie element |
| Beam | 2 | Models a beam with axial, bending, shear and torsional stiffness: Releases allow the ends of beam elements to be pinned in any of the local three rotation axes. | Warping degrees of freedom are not considered, so lateral torsional buckling modes cannot be considered in the way that Euler strut buckling modes are. | Bar element, Strut element, Tie element |
| Strut | 2 | Compression-only element. Stiffness depends on section area, Young’s modulus and length. | No moment stiffness. Analysis cases involving models containing these elements cannot be combined, because they are non-linear. Treated as bar element for modal analysis | Beam element, Bar element |
| Tie | 2 | Tension-only element. Stiffness depends on section area, Young’s modulus and length. | No moment stiffness. Analysis cases involving models containing these elements cannot be combined, because they are non-linear. Treated as bar element for modal analysis | Beam element, Bar element |
| Spring | 2 | A spring can have stiffness in one, or three directions specified by one, two or three stiffness parameters depending on the type selected: for example: only one parameter is relevant for an axial spring, whereas three stiffness parameters are required for a general spring. Springs may be translational or rotational. | Releases not allowed. | Nodal stiffness |
| Damper | 2 | Damping elements work as dashpots. These are only considered in explicit time-history analysis. | Releases not allowed. | Nodal damping |
| Link | 2 | Use links instead of very stiff elements. They simulate elements with infinite stiffness without causing numerical solver problems. Various types are possible, that are stiff/free in different axes and directions of movement. | Every link has a constrained node | Rigid constraint |
| Cable | 2 | Tension only elements. Connect individual cable elements together into a cable by giving them the same property number. | Tie element, Spacer element | |
| Spacer | 2 | Spacers don’t affect the stiffness of a model: they only control where the nodes end up on the form-found surface. Connect individual spacer elements together into a cable by giving them the same property number. | Only for use with Soap-film form-finding with GsRelax solver. | Cable element |
# 2D element types
| Element type | No of Nodes | Description | Limitations | See also |
|---|---|---|---|---|
| Quad4 | 4 | Linear shape functions. | 2-D element property types | |
| Quad8 | 8 | Quadratic shape functions | 2-D element property types | |
| Tri3 | 3 | Linear shape functions | Cannot calculate shear strains accurately due to insufficient degrees of freedom. | 2-D element property types |
| Tri6 | 6 | Quadratic shape functions | 2-D element property types |
# 3D element types
| Element Type | No of Nodes | Description | Limitations | See also |
|---|---|---|---|---|
| Brick8 | 8 | Linear shape functions, two types of Brick8 elements available, one is with finite size and one is for modelling infinite boundary | ||
| Wedge6 | 6 | Linear shape functions | ||
| Pyramid5 | 5 | Linear shape functions | ||
| Tetra4 | 4 | Linear shape functions |
# 2D element property types
This table shows the available material models for 2-D elements.
| Type | Stiff degrees of freedom per node | Limitations | Comments |
|---|---|---|---|
| Plane stress | 2: In-plane translation only. (x,y) | Assumes zero stress normal to element | |
| Plane strain | 2: In-plane translation only. (x,y) | Only allowed in Plane strain structures. | Assumes zero strain normal to element |
| Axisymmetric | 2: In-plane translation only. (x,y) | Only allowed in Axisymmetric structures. | Strain normal to elements is hoop strain (proportional to radial movement and distance from centre) |
| Fabric | 2: In-plane translation only. (x,y) | Disregards all moments and out of plane forces. | Warp and weft stiffness as well as in-plane Poisson’s ratio can be specified. Normally tension only (non-linear). A non-linear solver (such as GsRelax) is needed to get “out of plane” stiffness effects due to fabric displacement. |
| Flat plate | 3: Out-of-plane translation and rotations only. (z,xx,yy) | Similar to a shell element but excluding in-plane effects | |
| Flat shell | 6: All (x,y,z,xx,yy,zz) for Allman-Cook forumation 5: All except rotation about local z axis. (x,y,z,xx,yy) | Most commonly used 2D element for modelling slabs and walls. | |
| Curved shell | 6: All (x,y,z,xx,yy,zz) | Not currently supported by GSA, but available for export. | Element can be curved out of plane. |
| Load panel | none | Linear elements only | For application of load to adjacent beam elements |