Creating FE surfaces

FE surfaces are defined by their boundary members. These boundary members are created using standard MasterFrame line elements. The first stage of creating an FE surface, then, is to create the shape of the boundary. To form an FE surface, the boundary members must form a planar region. Openings within any FE surface are also defined by using line elements to form the boundary of the opening. The boundary of both the edge of an FE surface and an opening must form a closed boundary.

The section used to form the boundary of a section size is not significant unless it is also to represent an "attached" beam, that is, a beam which is to act compositely with the FE surface. If a boundary member is not set as an attached beam within the FE menus, then the software will ignore it's section properties and will define the members as Dummy FE Members. This will be done by the software so it is not necessary to specify a Dummy Member when creating the boundaries of any FE surface.

A line element can be used to form the boundary of a number of FE surfaces. For example, a slab need not necessarily be modelled as a single FE surface and can be subdivided into multiple regions. In this case, at the interface between two FE surface there will be members which are included in the boundary of both regions.

When creating multiple FE surfaces, care should be taken to avoid any regions overlapping. The software cannot detect overlapping regions of FE surface, but this leads to double meshing in the overlap which will be incorrect.

Adding an FE surface.

To define an FE surface in a model, go to Create>Add Slab, Wall, Ramp (FE surface). This will open the FE surfaces pane on the right hand side.

A new FE surface will added to the list and the Main Border tab will be active. This means the software will be ready for the input of the boundary members forming the main boundary of the FE surface. The boundary members are selected graphically - to select members, click on the  icon. Next, select the members which form the boundary of the FE surface to be created by hovering the cursor over each member in turn and selecting by clicking the left mouse button. When selected, the members will highlight in red in the graphics view. The order members are selected in is not important. To assist in selecting the correct members, the masterframe viewing tools can be used to zoom into particular parts of the model.

As members are selected, the FE surface boundary is indicated in the right hand pane. The layout of the screen while selecting boundary members is shown below.

It is also possible to select the boundary members by using the mouse to window around the structure or part of the structure. Checking the "Auto Select Main Border Members" option ensures that only the main border members are selected.

Until a closed boundary is formed, the right hand panel will not the Status of the FE surface as "Status: Invalid FE surface". Some additional information is given which denotes why the FE surface is not valid.

Once the complete boundary has been selected, the right hand pane will note the status as "Status: Valid FE surface". The FE surface will be highlighted in Blue. The layout of the screen with a valid FE surface is shown below.

The FE surface boundary indicator also denotes the origin for the local surface coordinates. This is important when looking at the results, since the FE results as displayed in relation to the local surface coordinates. Each FE surface is located in the local x-y plane, with the z-axis representing the normal direction to the FE surface. This z indicates the direction relative to the section depth, with the positive z direction indicating the "top" of the FE surface. The section depth is measured relative to the centreline of the surface, so the bottom of the FE surface is in the negative z direction. The local axis direction can be indicated graphically on a selected surface by clicking on the  icon.

It may be desirable to swap the local axes of an FE surface, for instance, to match the axes of adjoining surfaces, to lead to simplified interpretation of the FE results. The software provides two option for doing this. Ticking the "Swap local z direction" reverses the direction of the z-axis. This also requires the reorientation of the y-axis to preserve the local coordinate system - the local axis comply to the Right-hand rule for coordinate systems.

The orientation of the x-axis can be controlled by aligning it with nodes on the boundary of the FE surface. This is done by inputting the node numbers to align the local x-axis with into the text input boxes. The direction of the x-axis is "from" Node 1 "to" Node 2. Nodes need not be adjacent, but they must be located on the boundary of the FE surface. Further control can be obtained by specifying a rotation relative to the line defined by Node 1 and Node 2. When the x-axis is reoriented, the key plan in the right hand pane will also reorient to reflect the change.

Adding further FE surfaces.

To add further FE surfaces, it is not necessary to exit the FE area or to go back to the Create Menu. From within the FE menu area, selecting the  icon adds a new FE surface to the list and allows the new surface boundary to be defined by following the above steps.