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Last modified by Casper Egholm Hougaard on 2024/03/13 14:41

This page is not up to date on PREFAB's capabilities. We're working on it. For correct guidance or information contact us via strusoft.com or get help from support here.

PREFAB is an extension to FEM-design that is developed to give a quick overview over the analysis results from FEM-Design 3D Structure, and at the same time be able to compile a report to the precast concrete supplier. By using the software a uniform structure and high level of quality of the results can be maintained for your precast concrete models.

The purpose of the program is to display the loads and the resulting forces on the structure storey by storey down to the foundation and present a documentation of stabilizing forces for the precast concrete supplier in a simple and standardized way in a smart PDF-document. The file format gives any supplier the possibility to see the results, even though they are not using FEM-Design.

PREFAB is a powerful tool that gives the user the possibility to create dynamic reports. By selecting the tooltip-option in the program PREFAB is able to show large amounts of data in a very limited space and still be very easy to read. Information about objects, loads, load combinations etc. can be found by simply clicking on given objects in the file, a tooltip window will show the information about the object. This will reduce the time for searching through long tables with information.

Release notes

Collection of release notes:

PDF Viewers

Hence the interactive features of the PDF, it's not compatible with all PDF viewers.:

ViewerInteractive supportPDF MergeRecommended
Bluebeam X(X)* 
PDF-XChange EditorXXX
Google Chrome-- 
Microsoft Edge-- 
Adobe AcrobatX(X)* 

*Inserting pdf's into the original PREFAB pdf will work. But multiple PREFAB pdf's can't be merged.

Modelling in FEM-Design

It is important to remember that PREFAB might need the FEM-model to be modelled in a certain way.

Read more in the Limitations and known issues-section.

Edge connections

It is of most importance to define edge connections towards connecting shell elements as they are used to track and display reactions and connection forces in the report.

One example of necessary connections is shown in Figure 1. The program will display an error message if a edge connection is missing since the equilibrium of all elements are checked.

Figure 1. Example of edge connections.

Edge connections.gif

Figure 2. Example of how to quickly setup and model a hinged wall

In the first release of PREFAB, the reactions from the wall will only be presented if it is placed at an edge connection. In practice it means that the FEM-model might have to be modelled in a different way. In the second release it is now possible to model T-junctions similar to Figure 3.


Figure 3. Solution for a T-junction where there are no edge connections.


Storeys are used in the program to define different levels of the building. If no storeys are defined in FEM-Design all results will be shown in the same picture in the printout. It is therefor recommended to always create storeys in FEM-Design to get a simpler and faster result document.

If the storeys are defined, then links will be created in the document enabling shortcuts to the different results for each storey.


Figure 4. Storeys in PREFAB


With the help of axis in FEM-Design, the user has possibilities to switch between different elevations to get a better overview of the model. These axis are used in PREFAB Print to enhance the readability of the printout. In the printout an elevation of each axis are shown and a bookmark is generated in the bookmark-list. By clicking on the mark in the list the user can seperate the results per axis.

Shell elements

The shell elementens (Plane Plate, Profiled Plate, Plane Wall and Profiled Wall) must be assigned a concrete material and the elements are not allowed to have variable thicknesses.

Truss member

All types of tensile anchors and connections should be modelled using truss members in FEM-design, see Figure 5. The material for the connections must be steel, and the user has the option to customize the properties of the steel similar to what the supplier of the connection presents for their connections, this can be managed by setting a plastic limit , see Figure 6. Note that the end of the truss should be placed within the borders of the shell element, on the edge do not count as being within the borders. In general these connectors do not transfer and compressive forces. In general a dowel of S355-steel is used, with a yield strength of fyk = 355 MPa, but dowels using reinforcement bars are commonly used (fyk = 500 MPa), this is shown in Figure 8.


Figure 5. Truss member in FEM-Design


Figure 6. Setting a plastic limit of a Truss member in FEM-Design


Figure 7. Definition of a new steel material, first select a steel material and then press New...


Figure 8. Definition of a new steel material. PREFAB automatically selects the lowest yield strength in the red selection box.


Point and line loads needs to be assigned to a shell element, while surface loads works fine with covers too. This is an important step in the FE-modelling in order for the program to decide where the load is being applied.

This can be done in two ways. Either by using the Assign load to structure, shown in Figure 9 (recommended solution). Or by placing the load in such a way that PREFAB can comfortably identify on that shell element it is being applied on. For example in Figure 10 the point load could be moved 1mm to the left or the right to only act on one structural element, same with the line load that could be moved up or down a few millimeters to not be acting on the joint. The second of these ways are more time consuming, and might be harder to find errors in. Assign load to structure is by far the most reliable command in order to reduce modelling time and cause less problems if a setting like Assign mesh to load position is being used.

Figure 9.  Assign load to structure

1587367276874-595.png 1587367281546-224.png
Figure 10.  Exemple of a point load and line load that is badly placed, i.e. not assigned to any structures, only edges or corners of more than one structure.

Design checks

1587367293590-856.png Design checks are only added if it is being activated withi the program. The option is found in the print out settings.


Figure 11.  Settings of the print out, highlighting the design checks.

Edge connections

It is possible to assign two load capacities for the edge connections for PREFAB, the program will choose the lowest in the design checks. The first one can be set in FEM-Design (using the plastic limit) and the second will be defined in PREFAB Print from the compression capacity of the materials.

Plastic limit

All plastic boundary conditions in the FEM-Design shell elements are checked at design of the edge connections. This is being performed independently of what calculation is being made in FEM-Design.

For example the plastic limit force for a 200mm thick wall using the settings in Figure 12 would be: 1587367321472-791.png. Note that for shear the limit value will be chosen as the smallest value in compression or tension, even if only one of them are defined for both edge connections for both elements.
1587367334918-964.png .

Figure 12. Definition of plastic limits for edge connections in FEM-Design, and how PREFAB Print will read the following limits: VRd = 45 kN/m, CRd = 4000 kN/m och TRd = 10 kN/m

General design check

The capacity of the concrete is defined in the program as 1587472848585-352.png where fcd is the design compression capacity, fck is the concrete characteristic compression strength (shown to the left in Figure 13) and γc is the partial factor for concrete according to the right window in Figure 13. If the user wants lower values it can be set as in the Plastic limit section.

1587367638836-895.png 1587367643438-851.png

Figure 13. Definitions of concrete properties in FEM-Design. Left: Characteristic strength of a concrete cylinder. Right: Red arrows show the partial factors of concrete γc in ultimate limit state (U) to the left and accidental and seismic loading to the right (Ua, Us). The partial coefficients of the dowels will be shown in the steel material properties as γs in ultimate limit state (U) to the left and accidental and seismic loading to the right (Ua, Us).

By defining the edge connections as Detach y’ tension, see Figure 14., the program will calculate the design shear capacity according to the formula: VRd CEd × µ. Where VRd is the design shear strength, CEd is the design compressive resultant in the shear area and µ is the friction factor.


Figure 14.  Exemple of a non-linear detachable edge connection in FEM-Design. Use Detach y’ tension to find the y-direction to only get shear in the areas where there is only compression in the joint.

Truss member

The program will use the smallest limit of elasticity, i.e. Yield strength, for all thicknesses in the model to check the tensile capacityof the dowels. The formula used is 1587387918081-235.png . Where TRd is the design tensile capacity of the dowels, As is the truss cross section, fyk is the characteristic strength of the steel and γs is the largest partial coefficient of the connected shell elements. If there is compression in the tension trusses/dowels, the program will use the design strength of 0,8×TRd. If the user doesn't want the dowel to take and compression it can be set as in Figure 6.

Export options

For a description about export options go to this page: Export 

Limitations and Known issues

  • This version is for 3D-building only.
  • Shell elements (Plane Plate, Profiled Plate, Plane Wall, Profiled Wall and Fictitious Shell) can be used as plates or walls, but only results for elements with a normal vector of zero in the global Z-direction will be printet. 
  • Edge connections needs to be straight lines, They can't take the shapes of circles or circle segments.
  • No design control will be performed for:
    • Beams
    • Columns
    • Fictious bars
  • It is recommended that shell elements aren't modelled too thin, when using the plastic solver. Due to the limit of fcd * t being reached so early the solver is "locked".