2D Members - basic types

Definition, application

One of basic elements for modeling structures in SEN.

Where to find it

In basic tree - in group "Structure".

Overview

2D member	Basic description
Plate	A standard plate is a planar 2D member with an arbitrary number of edges that may be straight or curved.
"Definition of a composite deck"	A deck (composite deck or metal deck) is essentially a plate in SCIA Engineer. It may be input as any 2D member that accepts ribs. That includes plates and straight walls. To define a composite deck, the user would usually define a standard plate, or a ribbed plate in the case that he would like to assign the ribs in the very same modelling operation. A composite deck is created from a standard plate via the property Element type. This property defines whether the 2D member is a standard plate, a composite deck, or a metal deck.
Metal deck
Ribbed Slab	2D slab member with possibility to define ribs from Cross section library.
Prefab slab
Wall	A wall is a vertical 2D member whose base is either straight or curved
Masonry Wall	A wall is a vertical 2D member whose base is either straight or curved from material "Masonry" and orthotropic behaviour.
Shell	Shells are defined by border lines (i.e. border curves). The shape of the shell can be defined by four, three or two curves / straight lines. Some shapes require certain "mathematical imagination" when they are created. Therefore, the basic shapes has been pre-created in the form of templates and can be easily input through user blocks.
Shell - surface of revolution
Shell - swept surface

Slab parameters

Name

Defines the name of the slab.

Element type

Standard = standard finite element plate

Metal deck = special type intended for decks made of a profiled steel sheeting

Composite deck = special type intended for decks made of a profiled steel sheeting with a concrete topping

Load panel = allows to switch the 2D member to a load panel

Masonry orthotropic = it is used for masonry walls and automatically define orthotropic behaviour of wall.

The options Metal deck and Composite deck are available only when both concrete and steel materials are enabled in the project settings; see details in the chapter Composite Analysis Model

The option Load panel is available only in the post-processing environment v17; when switching to Load panel type, a number of additional settings are available, related to the load panel functionality

Element behaviour

Standard FEM = standard finite element plate in the analysis model

Flexible diaphragm = only axial in-plane stiffness, no bending stiffness; load transfer ensured by built-in load panel functionality

Semi-rigid diaphragm = in-plane stiffness identical to Standard FEM, no bending stiffness; load transfer ensured by built-in load panel functionality

Rigid diaphragm = infinite in-plane stiffness, no bending stiffness; load transfer ensured by built-in load panel functionality

Diaphragm behaviours are available only for Metal decks and Composite decks; see details in the chapter Composite Analysis Model and also more information about 2D Member Element Types & Behaviours

Type

Specifies the type of the slab. The user may select from types: (i) plate, (ii) wall, and (iii) shell.

This type plays role e.g. in code checks. The check procedure applied depends on this parameter. Therefore, pay attention to the selection of proper type.

Material

Defines the material of the slab.

FEM model

Isotropic = A normal isotropic slab with identical properties in all directions is used.

Orthotropic = An orthotropic slab with different properties in two orthogonal directions is used.

Membrane = Special membrane elements are used for the analysis of the slab.

Press only = Special elements capable of resisting only compression stress are used for the analysis of the slab.

Thickness type

It is possible to input a slab of constant or variable thickness.

See also paragraph Variable thickness later in this chapter.

Thickness

For constant thickness, just one thickness value must be defined.

For variable thickness, two thickness values must be defined. Input of slabs with variable thickness is described in a separate paragraph below. Also the relevant parameters are described in that section.

Orthotropy (for orthotropic FEM model only)

This item specifies the orthotropy type of the slab. It also enables the user to open the Orthotropy manager and define a new orthotropy type.

Member system-plane at (not for membrane FEM model)

The input-plane (system-plane) of the input slab may be in the mid-surface of the slab, at the top surface or bottom surface of the slab.

Eccentricity z

If required, eccentricity of the slab may be input.

LCS type

Defines the type of the local coordinate system of the slab.

See also paragraph LCS types later in this chapter.

Swap orientation

The orientation of the local Z axis of the slab may be easily turned around. This check box does it. See paragraph The effect of the Swap orientation parameter later in this chapter.

LCS angle

The direction of the local X-axis may be input here.

Layer

Selects the layer of the slab. It also enables the user to open the Manager of layers and define a new one.

Geometry parameters for walls

Height

Defines the height of the wall.

Insertion point

Specifies whether the bottom base or the top base of the wall is input.

 

Variable thickness

The variable thickness of a slab can be input in the property table of a slab. There are several options to choose from.

Direction X

The thickness varies in the global X-direction.

For this option the user can select two points in which the thickness is specified. Then the user can input the two thickness values for the two points.

Note: Attention must be paid to the selection of the two points. If two points located on a line parallel e.g. to the global Y axis, nothing happens - the variable thickness in the global X-direction cannot be calculated for such input.

Direction Y

The thickness varies in the global Y-direction.

For this option the user can select two points in which the thickness is specified. Then the user can input the two thickness values for the two points.

Read also the for the Direction X above.

Direction Z

The thickness varies in the global Z-direction

For this option the user can select two points in which the thickness is specified. Then the user can input the two thickness values for the two points..

Local X

The thickness varies in the direction of the local x-axis of the slab.

For this option the user can select two points in which the thickness is specified. Then the user can input the two thickness values for the two points.

The local x-axis is normally defined by the first two input vertices of the slab.

This option is not available for slabs input as shells (i.e. using function 2D member > Shell)!

Local Y

The thickness varies in the direction of the local y-axis of the slab.

For this option the user can select two points in which the thickness is specified. Then the user can input the two thickness values for the two points.

This option is not available for slabs input as shells (i.e. using function 2D member > Shell)!

Variable in two directions

The user selects three points (slab vertices) in which the thickness will be specified. Then the user can input the three thickness values for the three points.

This option is not available for slabs input as shells (i.e. using function 2D member > Shell)!

Variable in 4 points

This option is available only for slabs with four vertices.

The user selects four points (slab vertices) in which the thickness will be specified. Then the user can input the four thickness values for the four points.

Radial

This option is available only for circular slabs.

The user defines the thickness in the centre of the slab and on its edge.

It is advisable to input the points in place where the thickness change starts and ends. Otherwise it may happen that due to the extrapolation of thickness, the final thickness value becomes negative, which would result in an error message during the calculation of the project.

The definition of a slab of variable thickness is a two-step procedure. First, a slab of a constant thickness must be input. This slab may be then modified and changed into a slab of variable thickness. The reason is that the "property" of variable thickness is bound to the particular nodes of the slab that are not yet known in the phase of slab input. In other words, variable thickness is similar to a haunch on a 1D member – it is an additional property of a slab, not the basic, fundamental parameter.

Local coordination system for 2D member and mesh elements

The results of a Finite Element analysis are primary computed with respect to a Local Coordinate System (LCS) of mesh elements inside the 2D member. As a consequence, these results - among others like a generated load or designed reinforcement - depend on the way the local axes for mesh elements (and 2D member respectively) are defined.

Warning: Be aware, the LCS of mesh elements and 2D member itself may vary depending on the selected method for LCS definition. Such discrepancy is important to notice mainly in Results service, because both systems (LCS - 2D member / LCS mesh element) can be used as referenced for the presentation of the results.

A wrong definition / selection of local axes system can lead to very misleading results so it's always recommended to check the orientation of the considered local axes system graphically. To visualize local axes of mesh elements or 2D member you can use the View parameters settings (for the mesh local axes, first the mesh itself must be generated).

The change of LCS system of the 2D member can be done using the following properties:

Property	Description
LCS type	Adapts the local x and y axes of mesh elements according to a selected method. Standard Only method, where the local axes of mesh elements and 2D member itself are linked together. The direction of local axes is derived from the global coordination system (GCS). Perpendicular to vector The selected local x(y) axis is perpendicular to the vector in the plane of the mesh element (the vector can be defined by its coordinates or graphically using [...]) Congruent with line The selected local x(y) axis is oriented from the centre of the element towards the intersection between the plane of the mesh element and a line defined by its start and end point (points can be defined by their coordinates or graphically by using [...]) Smallest angle with vector The selected local x(y) axis is oriented such it makes the smallest angle with the defined vector projected into the plane of the mesh element (the vector can be defined by its coordinates or graphical using [...]) Tilt of vector defined by point The selected local x(y) axis is oriented in the direction of a vector defined by the given point and the centre of the element tilted into the plane of the element (the point can be defined by its coordinates or graphically by using [...]) Tilt of vector normal to line The selected local x(y) axis is oriented in the direction of a vector perpendicular to a defined line titled into the plane of the element
Swap orientation	Controls possibility to quickly turned around the direction of local z axis of 2D member and its mesh elements as default automatically defined by the program. Be aware, such change may influence the direction of a load (when it's defined by using LCS of 2D member) or identification of the upper / lower surface of the 2D member for a proper reinforcement definition there. No= normal orientation Yes = swapped orientation
LCS angle	Rotates the direction of local x axis of the 2D member by inputting user defined angle (by value or by selecting two points on screen using [...]). Be aware, the mesh elements are rotated as well only when LCS type = Standard because only in such case the LCS of 2D member and its mesh elements are linked together.