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How to fix geometry problems

Mistakes in the geometry can cause

  • problems in the mesh generation/ calculation, resulting in a variety of errors.
  • deviations in the mesh, leading to poor quality results

This article lists common geometry mistakes and their solutions.

  • You’ll notice that the finding the problem and solving it, is usually not ‘plug & play’. So regurarly save a copy of your model!
  • A demo model containing all the mistakes listed below, can be downloaded at the end of this article.

 

Mistakes usually leading to an error

Mistake 1. Small imperfections in the point coordinates

Small imperfections in the point coordinates can lead to:

  • plates with a weird orientation.
    For example: the orientantion of the local coordinate system (can be defined here) is the same for all plates. Yet, there are 2 two plates acting weird.
  • small plate strips.
    The small plate strips in the floorplan and the small strip near the door will have a bad influence on the mesh.
  • surfaces/ walls with a small slope.
    • Take a Top View and a Wireframe representation.
    • Make the entire model visible (click on, turn on all Types , turn on all Levels).
    • Disable the Level Manager .
      In Diamonds 2019r03 (or older), it is not possible disable the Level manager. In that case, take a 2D view.
    • Set the size of Fonts and Symbols to zero.
    • Optionally, for larger models, set the grid invisible.
    • Zoom in and out. If there some lines become thicker then others, they are not perfectly aligned above each other. The wall definition between those lines might be corrept. 
  • double plates, lines or points.
    • When zooming in and out in a transparent  3D view, you see ‘a shadow’ on the plate. This indicates there’re two plates above each other. Showing the surface numbers in the Configuration settings , confirms this.
    • Requesting the line numbers, reveals there’re multiple lines above or very close to each other.
    • Requesting the point numbers reveals there’re multiple points very close to each other.

Solution

Fix using Projection function (recommended) 

  • Read the workflow here.

Fix using Data table 

  • Go to Options > Units and decimals. Set the units of Length to ‘mm’ and ask 6 decimals.
    Especially, if the walls of the building don’t run parallel with either the global X- or Z-direction, the coordinates may seem equal, but when showing the coordinates with a high precision, there’re not equal.
  • Select the points for which you want to adjust the coordinates.
    Tip: start with walls for which don’t run parallel with either the global X- or Z-direction
  • Click on.
  • Copy-paste the coordinates.

‘Fix’ using Structure verification (not recommended because not so effective) 

The procedure on how to use the Structure verifcation can be found here. BUT ‘Fix’ is in parentheses because this function isn’t so effective in solving the core issue.

  • The Structure verification checks the consistency of the surfaces.
    Assume that point X is a little bit out of the plane of wall Y. Then the Structure Verification will be able to see there’s a problem with the circumference of wall Y in point X, but it doesn’t not have the intelligence to adjust the coordinates of point X in such a way that point X becomes perfectly in the plane of wall Y.
  • The Structure verification can merge points that are within a specified radius of each other.
    Assume that point X is a little bit out of the plane of wall Y and point Z is in the plane of wall Y. The distance between point X en Z is 5mm. Points X and Z should actually be merged.
    The Structure Verification (with a geometric tolerance > 5mm) is able to see those two point are too close to each other, but it doesn’t understand which point should be merged with the other in order to solve the problems. It will either merge point X with point Z or point Z with point X. If point Z is merged with point X, the circumference of wall Y is no longer coplanar. The function made the situation worse.
Mistake 2. Wong modelling of a thicker part in the foundation slab

A thickening in the foundation slab shouldn’t be modelled using the footings icon, because it creates two plate above each other. You can see this in the ‘shadow’ that appears above the thickenings when you zoom in and out.

They should be modelled as a plate .

Solution

  • Take a Top view and set only the foundation slab visible.
  • Select all footings (menu Select > Footing) and hit DEL.
  • Draw the perimeter of one thickening next to the structure. Include the centerpoint.
  • Use the copy-functionto copy the pertimeter around each column.
  • Select all thickenings and adjust the plate section.
  • Make the necessary adjustments to eliminate internal plates! See next topic.
Mistake 3. Internal plates
 Diamonds has a hard time processing nested surfaces, also called ‘internal plates’.

The inner plate (or hole) (= plate 2) is completely surrounded by the outer plate (= plate 1). In other words: there is only one plate adjacent in to the inner plate, which is the outer plate. We call the inner plate an ‘internal plate’. The inner plate (or hole) (= plate 2) is not completely surrounded by one the outer plate. There are two outer plates (plate 1 and 3). There are no internal plates in this model.

More info here.
The demo model contains 4 internal plates in the foundation.

Solution

  • Draw additional lines to divide the outer plate in more smaller plate.
    Draw the lines in steps connecting the points, rather than drawing the line in one step. When you draw in step, you’re ensured the juction is correctly made. If you draw ine one step, you’re depending on Diamonds to make the junction. Which he will only do, if the lines meets certain criteria. 
Mistake 4. Nearly intersecting lines

A floorplan can contain lines in order to define line loads. When lines nearly intersect, the mesh must pass in the space between them. That creates difficulties. It is better to make the wall 10cm longer so that the plate is cut in two plates.

Solution

  • Use the translation-fucntion  to move the point so it creates an intesection.

Mistakes usually not leading to an error, but lead to poor quality results

Mistake: Points and lines with no purpose

The model contains points, lines and/or subdivisions that have no purpose. Their presence will affect the mesh a in bad way. 

Solution

  • Select the points and hit DEL.
    If Diamonds doens’t remove the points, it means that the lines are not inline. Double click the line and set the length to zero.
  • Merge plates.
Mistake: The floorplan is too detailed
Don’t overdetail the floorplan. Especially in larger models ( = building with multiple floors, like an appartement building). Too many details cause and irregular mesh and increase the calcation time. In addition, they are hard to remove if they cause trouble.

Solution

  • Start with a simple floorplan. If that calculates, add relevant details.
    A floor/wall is modelled in Diamonds using a surface. The thickness of a floor/wall is not modelled in Diamonds. It is taken into account by means of the stiffness matrix (moment of intertia), but the thickness is not meshed. Then why should you add details smaller than the plate thickness for Diamonds to mesh? Ask yourself if the details you’re adding, will really make the difference in the calculations.
  • Replace non-bearing walls with an equivalent surface load on the entire floor (see EN1991-1-1 §6.3.1.2 (8)).
  • Openings with dimensions up to ± 400x400mm² hardly influence the force distribution. Don’t model them in Diamonds.
    (Source: Constructieleer, Gewapend beton 2, page 281, ISBN 978-94-6104-006-0)

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