2D Element Properties
2D element properties are used to describe two different classes of 2D elements:
- Finite elements - The basic type of 2D elements used for structural applications included in in-plane and/or out-of-plane behaviour. For more information, see the entry: Theory on 2D finite element formulation.
- Load panel elements - Non-structural elements used to apply load to beam elements. They have no stiffness, so do not need material or thickness parameters. For more information see the entry: 2D Loads on Load Panels.
Property Definition
General Properties
Analytical type
This specifies if the 2D element property immediately following will be used to define a finite element or load panel element.
Name
The name is only used as a convenient way of identifying a 2D element property.
Color
Define the color of the elements that use this property when element coloring by property on graphic view
Axis
Users may assign an axis to be used to define the orientation of 2D elements. If the axis is set to “Topological” the orientation of the element will be determined by the first two nodes of the elements and the orientation angle. If an axis (global or user defined) is assigned here then that axis will be projected on to the element plane to determine its orientation.
Material
The material definition breaks into three parts. The first part is the material type. it is one of:
- Steel
- Concrete - if it is concrete, then concrete slab property can be set for RC slab design
- FRP
- Aluminium
- Timber
- Glass
- Fabric
- <undefined> – not associated with any grade
The second part is the material grade index that this 2D property refers to. The material grade, which contains parameters including material stiffness and design properties, is defined in the material grade table.
The third part is the analysis material. This can be specified in analytical properties for finite elements. If material type is assigned and material grade is defined, analysis can use the analysis material based on the grade when from Grade is used in the Analysis column.
Concrete Slab Property
The Concrete slab property is used in concrete slab reinforcement area calculations
Profile/Thickness
In the simplest case this defines the thickness of the 2D elements. No thickness definition is needed if material type is fabric, and a unit thickness is assumed for plane strain and axisymmetric structure types. For a shell element there are four options for defining the property
- Solid – just the thickness
- Decking slab – a composite concrete slab based on steel decking and is defined on the next page of the dialog
- Hollow – a hollow core concrete slab and is defined on the next page of the dialog
- Layered composite – a layered shell that needs to be exported to LS DYNA for analysis and is defined on the next page of the dialog
Analytical properties for finite elements
Element Type
The types of 2D properties available will depend on the structure type. For the 2D structure types (plane stress, plane strain and axisymmetric) only the type corresponding to the structure type is available. Likewise for non 2D structure types the plane strain and axisymmetric types are not available, although the plane stress option is. The types are:
- Plane Stress – in plane effects only (no out of plane stress)
- Plane Strain – plane effects only (no out of plane strain), it is only active/used when the structure type is plane strain
- Axisymmetric – in plane effects only (the out of plane direction is the hoop direction), it is only active/used when the structure type is axisymmetric
- Fabric – in plane effects only (no thickness associated with fabrics)
- Flat Plate – out of plane effects only
- Shell – in-plane and out-of-plane effects
- Curved Shell – a general shell element which may be curved out of plane. Curved shell cannot be used in GSA analysis at present, it can be used to build a GSA model and exported to other software to run the analysis
Analysis Material This is the analysis material that will be used to determine the stiffness and mass of a finite element. The analysis material property can be defined in the Analysis material table. If analysis material is set to from Grade, then the material properties defined by the material grade will be used in the analysis.
Reference Surface
The reference surface is a virtual plane that the in-plane forces are assumed to act in a 2D element. If the reference surface is the top or bottom surface, in-plane loads will also generate a bending moment. The reference surface setting is only used by shell elements. There are two parameters to define the reference surface, "Surface" defines top, middle or bottom of the 2D elements as the reference surface, "Offset" defines an extra offset from the selected top, middle or bottom surface. If offset is zero, then the selected top, middle or bottom surface will be the final reference surface.
Property Modifiers
There are four factors, three for stiffness modifications and one for volume modification. The three stiffness modifiers are for in-plane stiffness, bending stiffness and through thickness shear stiffness, the volume modifier is for modifying the volume that is used to calculate the mass and self-weight of the elements. By using the property modifiers, the 2D element properties can be different from those calculated by the given thickness which may be useful to deal with situations such as cracked concrete slabs (reduced bending stiffness due to cracking) or hollow slabs where the stiffness of the slab in bending and in-plane will be less than that for a solid slab.
The modifiers can be an absolute values or a percentage of the calculated values from the given thickness. For Plane Strain, Axisymmetric or Fabric elements, these modifications are not relevant so they are not enabled.
The stresses in 2D elements are calculated using unmodified thickness.
Additional Mass
Normally the gravity loads on a 2D element are calculated from the density and thickness or modified volume. Fabric elements have no thickness but it may still be desirable to assign a mass, or where a slab is modelled which has a non-structural screed that adds mass. Both of these situations are provided for by the additional mass per unit area. This mass is in addition to the mass implied by the thickness and density.
Analysis properties for load panels
Load Distribution Type
The load distribution type defines how the load will be distributed from the 2D surface to its surronding 1D elements. The options are as follows:
- Two-way - two-way load panel elements distribute load to the nearest edge.
- One-way - one-way load panel elements distribute load to the nearest edge in the direction of its local x axis. To change the span direction, change the load panel element's orientation angle and/or the 2D property's axis system.
- Legacy - legacy load panel properties can only be used for load panel elements that are defined by either 3 or 4 nodes. It is defined by a support pattern as well as the reference edge.
Support pattern and reference edge for legacy load panels only
The support pattern and reference edge are applicable only to legacy load panel elements. The support pattern defines the number of edges to which the load is transferred and the reference edge sets the selection of the free/loaded edges. For more information see 2D Loads on Load Panels.
The support pattern defines the number of edges to which the load is transferred and the reference edge sets the selection of the free/loaded edges.
- All edges supported - the load is distributed to the edges in proportion to the contributing areas.
- Three edges supported - the load is distributed to the supporting edges so that equilibrium is maintained as far as possible. The edge opposite the reference edge does not take any load.
- Two edges supported - the load spans from the sides adjacent to the reference edge.
- Two adjacent edges supported - the load is taken on the reference edge and the next edge on the element.
- One edge supported - the load is all attributed to the reference edge. The moment due to the offset of the load is ignored.
- Cantilever support - the forces are distributed as for one edge supported but the moment is applied to the edge so that equilibrium is achieved.
