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123456789_123456789_1123456789Parametric Buildings (Revit Add-ins FRBL)

Information model (Geometry)
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Geometry Model


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Trial Version




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Roof Truss Construction

Welcome to Roof Truss Construction (RTC) in addition to Parametric Building in Revit and LUSAS models.


RTC provides the following opportunities:


› Automation for unlimited number of Roof Truss Construction with precise geometry at intersection.

› The first RTC is at (0, 0). The next RTC is positioning by (MoveX, MoveY) from the previous,

  and where all detailed dimensions are given for each RTC.

› The RTC can be designed in many groups A, B, C with associated laths.

› Ready to Additive Manufacturing in Wood as the generic geometry has been programmed and where Revit can export

  IFC to 3D printing.  


This section shows a simple example of RTC designed in type T15 King Post. There are 18 RTC automated three groups A, B, C in longitudinal X-direction. The RTC have a breadth B=14m in group B but B=10m in the two groups A & C, as shown in the Floor Plan view below.

Figure: Revit Floor Plan and input MoveX, MoveY...(mm)




Figure: Revit Elevation Left and input H, B... (mm)

The Excel input below shows data for the 18 RTC and the three groups of laths. To type the same value in many cells, just select the cells, type a value and press Ctrl+Enter to write on all selected cells. Input at each RTC give many opportunities to optimize the type T15. By a few changes of the input, the user can obtain a geometry as shown in Elevation Left view above:


› B=10m and 14m breadth rtc, incl. 1m overhang on each side.

› The bottom of all bottom chords has the same height, even in different geometries.

The top chords are parallel for different spans as the slope H/B=3500/5000=4900/7000=7/10.



FigureExcel input of roof truss construction 1 to 18 and laths.



With the first estimated geometry the user can verify the capacity of the roof truss construction for a given load combination on it according to Eurocode 5. To keep the geometry as shown in Elevation Left one can reduce the center distance 1200mm (MoveX) between two RTC to increase the capacity, or to increase the overall thicknesses of 80mm currently. Note that the case the center vertical king post is located above a structural wall, the capacity is doubled for that RTC.  


Roof truss construction is a part of Parametric Building FRBL tool, but it can also be run solely. RTC uses the input sheet name ‘Generic’ in the Excel file for the parametric building, or just in a new Excel file named ‘INPUT FRBL EXCEL.xlsm’ having the input for the roof truss construction only.


Roof truss construction is under developing for the other types than T15.




Figure: Revit 3D View



In this section the roof Group A is considered in LUSAS FEM model as shown below.

Figure: LUSAS FEM model for Roof Group A.



FigureLusas supports P43, P60 and section eccentricity. 


Eccentricities & Supports

The element mesh in FEM model is where the results are calculated, as shown with the grey line and results 1, 2mm vertical displacement in figure to the left. The beam cross sections have been set eccentricities from the mesh to meet the geometry designed as in the Revit BIM. Here the top chord is located bt breath below the mesh, and the bottom chord is located bb breadth below the mesh.


To keep the FEM exactly as the Revit BIM model, there can be some extreme short beam elements between a two-points in the FEM model. ICDAS has performed a simple test with a short beam element of only 2.5% length of the neighbor beam, the LUSAS keep the same results as the beam is modelled in one long element.

For the support, Point P60 is assumed to be fixed in all translational directions and be 300mm from point P43 on top of the top chord. However, the 300mm end of the bottom chord is located on a structural wall, i.e. point P43 is also a support point (with released UY in horizontal direction for temperature motion). 

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Thus, by visualization thicknesses of elements the user can define support condition in details instead of working on the line mesh having point P43 supported only. In that case the sectional forces at the bottom chord is not correct at the 300mm end.



Figure: Lusas 3D deformation for vertical load 2.5kN/m2. See animation.


The most important in FEM work is the correct FEM model, regrading to all elements have been connected to each other. This correctness can be easily checked by deformation figure, already at the deadload earliest stage in the analysis. 


Above shown deformed shape where the roof carrying 2.5kN/m2 to give some deformed values large than 1mm. The deformed values itself are not important in this single loadcase but the ratio between them are useful to estimate the entire structure. The vertical displacement 1mm at center of the bottom chord where the strongest section 300x80mm are used. The displacement is bigger 2mm at the end of the top chord cantilever. The displacement is also 2mm at center of the lath having 1.2m span between two top chords, and a section of only 73x38mm.


In the animation one can clearly the outer frame deforms in X-direction (3mm) more than the inner frames (0mm). This 3rd dimension will not be see if the frame is modeled in 2D ZY-Plan.



As the model is deformed correct, the user can model other load cases and load combinations on the structure to verify the timber dimensions according to Eurocode 5.

Modify automated model from ICDAS *.cmd file


The beams model is automated when import the *.cmd file in LUSAS. The following additional manual works are needed for a beams model in LUSAS interface:

› Create User Sections (Tools > Section Property Calculator).

› Double click on a cross section automated in Geometric folder. The ‘Geometric Line’ dialog open, navigate to the 

  associated user-defined-section created from above. Set the eccentricity ez here and click ‘Apply’. The model will

  update all beams with that section.

› Rotate the laths with beta angle arctan(tan(H/B)) so they are perpendicular to the top chords (left side with angle b,

  right side with angle -b). In Geometric folder right-click on the section name ‘Laths Left’ > Select Assignments. When

  all the laths on the left side are selected > go to Mesh folder > right-click on ‘Elem 0.250m’ and press ‘Assign’ (again).

  The ‘Line Mesh Assignment’ dialog open, set beta angle = b and click OK. All laths on the left side will rotate with the

  angle b in once. Do the same for the laths on the right side.

Revit Robot Integration Options


In this option the roof construction is created in with Revit standard beam elements. The crossing of two top chords on top needed to modify so it looks like ICDAS generic model creation.


When integrate to Robot, the user need to check all elements have been connected to each other as they are in ICDAS Revit LUSAS Option.


Robot does not show the deformed shape in 3D cross section. Load combinations need to create in Robot manually and there is no smart combination in Robot (favour/disfavour).


Updated 13-04-2022



ICDAS  •  Hans Erik Nielsens Vej 3  •  DK-3650 Ølstykke  •   E-mail: th@icdas.dk  •  Tel.: +45 60 53 83 79  •  CVR no.: 34436169