FEM-Design 14 and trapezoidal steel sheet (TRP-plåt)

There are a few features that are not so commonly known, one of which is the Profiled panels and the usage of trapezoidal steel sheet. In the following guide we will explain the usage of profiled panels to enhance the design of lightweight roofs.

 The feature of profiled panels is located in the Structure-tab in 3D Structure.

This example shows a simple structure and how to add the trapezoidal steel sheet as a roof.

First we need to add the profile to the section library. Do this by the Section Editor-module, it can be found under Tools > Section Editor.

 Draw the contours or use an external reference to add the background lines, then use Draw Section to generate the profile. The following two links show one CAD-drawing and one is a Section Editor generated profile of a steel sheeting profile.

Next step is to calculate the profile, and add it to the Section library.

The section library needs to have access/authority to write so be sure to close any instances where FEM-Design (3D Structure, Plate etc) have the library open (properties-windows or similar)

After adding the section, return to 3D Structure.


Start the Profiled panels-command, and select Defaul settings. There are a few settings that needs to be explained:

General tab:

Physical model: Selection of cast in-situ or prefabricated elements. Prefabricated elements enable possibility to set panel edge connection properties.

Panel type identifier: For the program internal numbering of  elements. Recommendation: Leave at default.

Gap between panels: This is not an actual gap. It is more like a filler-space to get the panels to have a width that is better divided with an even number. Concrete hollowcore elements are usually 1197mm and a 3mm gap makes the objects in FEM-Design 1200mm. It basically gives the physical space in the panels in the real world a stiffnes so that the 1197mm panels aren't stacked exactly next to eachother. As for this steel sheet (width = 735mm) I have added another 15mm to make the FEM-Design-object 750mm and to make it evenly distributable over a 6m wide area (8 elements instead of 8.163265...). It will be possible to work with divided elements aswell, so if I had a width of 6500mm I still could use 735+15 and get 8 elements and one cut element that is one third of a real element (250mm in this case).

Analytical model: Used for prefabricated physical model to select a continuous plate or panel-by-panel type (same as pre-version 14).

Transverse flexural stiffness factor: Different stiffness-parameters in different directions. E1 is the actual stiffness of the material in the main direction, while E2 is the stiffness in the weak direction. If E2/E1 is 0.1 then the structure will only have one tenth of the stiffness in the weak direction and thus transfer 10% of the load in that direction while about 90% will go in the stiff E1-direction. Basically the same as Orthotropy for plates but this is only in flexural direction (displacement out of plane).

Alignment: This setting will not affect the calculations, only the presentation. See the first picture of this page for reference.

Eccentricity: This option will change the stiffnes by adding the eccentricity*area-term to the original stiffness-value if the setting for 'Consider eccentricity in calculation' is ticked.

Border tab:

These are the boundary conditions of the whole slab towards the surrounding objects (beams, walls, etc).

Panels tab:

The settings in this tab are the boundary conditions between each of the panels. If they are not connected in the vertical direction to eachother, but want them to transfer forces in the horizontal plane, then set Kz' to zero. This would simulate a hollowcore floor without grouting, or a thin steel sheeting without a rivet-connection. In the finished structure a connection between these objects are usually common practice so in that case, use the Hinged-button to connect the panels internally with a hinge-connection.

When all settings of the slab has been set, press OK to return to the model. Now we need to define the direction of the slabs, this is done by choosing two points in the direction of the slab. This step is quite important that it will be completely straight. If it is not then the program might create very thin slabs due to the direction of the slab is not the same as the direction of the slab-edge.
 

Note the text in the bottom left corner that says that this will be the stiff direction.

Next step is to define the borders of the slab, usually a polygon-shape is needed, but a rectangle would work for many occasions.

When the polygon is closed or the area has been drawn then next step happens. The choosing of an achor point. The anchor point is a point where the panels will be split from, or if it chosen in a corner then the panels will be evenly distributed:

Finished geometry:

A few things to take note of with profiled panels:


Loads:

When applying a load as 'Pick exsisting region', each panel is a region. To add a load over the whole slab, use 'Polygon'- or 'Rectangle'-tools.

Finite elements:
The setting of the mesh with 'Region by region'/'Consider all regions together' might create very different meshes and thus have very different calculation times. The result should not be affected that much though. If Cast in-situ or Prefabricated/continuous options are selected the slab will be modelled as similar as a normal plate, but with stiffnesses like the section selected.

 

(consider all regions together)

 

(Region by region)

This difference is important to know since connecting slabs might cause meshing problems in the line between the regions. If the regions are not thoughtfully considered then these meshing-issues might spead over to walls.

Note that a building of this size might need secondary beams aswell, those have not been modelled here for clarity.