2 Powerful Analysis Objects in Advance Design for FEM Analysis

30 May 2023Advance Design, BIM, Graitec, Structural designEngineering, finite element analysis, Structural, Tips and Tricks

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The biggest challenge in the design of building structures when using finite element method (FEM) software is the representation of the object’s actual function.

The designer’s task is more difficult because they have to select the finite element analysis (FEA) mesh in a way that the results are not underestimated or overestimated. Peaks at critical points in the structure are also dangerous (e.g. above the supports in the column – slab superstructures).

Another challenge is mapping the connections at the intersections of the components, as well as determining the appropriate elasticity of such a connection. Often this issue is underestimated; however, in some cases it can cause disturbances in the cross-sectional forces.

In this article, I demonstrate how such problems can be solved using GRAITEC Advance Design software. In fact, it is very easy with this FEM structural analysis solution dedicated to structural engineers operating in a BIM environment.

  1.  Creating a Link at Node

Imagine a situation where we have a simple structure consisting of several primary and secondary beams. These are continuous elements.

green and blue structural beams in hatch pattern

In FEA software, we can only specify the release of linear elements at their ends.

red and blue lines on computer screen with menu on right

How then can we account for the hinged support on the central primary beam? How do we represent the actual working of the structure, where the secondary beam will not transmit a bending moment into the torsion of the primary beam?

The user could divide the secondary beams into two elements and add releases at their ends. However, this is not a good approach, as the static scheme will change. The beams will then operate as single-span beams.

blue and redlines forming a series of squares numbered 5 through 10
computer rendering of beams showing colored bands of linear analysis

We are interested in making the beams work as continuous, two-span beams.

Advance Design has a dedicated function for such cases: Create a link at node.

Advance Design menu ribbon with tabs for Home, Objects, Utilities, Analysis, and Results

Once the function has been selected, the user must indicate where the node link will be created. This can be done by inputting a point or by selecting primary and secondary elements.

command line saying Press p to input a point or press x to select elements > >

After inputting the node link, the user sees a ‘point’ at the intersection of the elements and then has to set relations to it.

computer drawing showing coordinate system for setting a node link

An asymmetrical load is included in the structure shown to better illustrate the problem.

computer drawing of an asymmetrical load in building design

Now the “My bending moment” on the secondary beams looks like this:

computer rendering of bending moment on secondary beams

Where the Node link has been imposed, the graph is ‘smooth’. Where it is not, there is a bending moment dodge.

Node links are also often used in roof trusses.

 

2.  Column – Slab Structure

FEM software for civil engineering is characterized by the fact that the elements have no dimension. We imagine the cross-section of a linear element as follows:

computer drawing of cross sections of various columns in shades of blue

In FEA, by contrast, such elements are treated as a single line (‘pin’). Therefore, they do not have a dimension.

side by side computer drawings of columns showing blue elevations on the left and single line pins on right

If such a linear element is connected to a planar element, this will only occur at one node and not in relation to the entire column dimension.

computer drawing of linear column topped by planar element converting to a series of nodes in grid pattern

This will result in a concentration of forces at one node and the occurrence of a characteristic peak at that node.

Advance Design has a solution to this problem. This is the DOF – Constraint function, which allows the column’s dimensions to be mapped and the peak to be eliminated.

computer menu ribbon with tabs for Objects, Utilities, Analysis, and Results with DOF Constraint highlighted

Once this function has been selected, the user must indicate the primary node (the connection between the column and the slab), as well as the secondary nodes (the outline of the column’s dimension). It is a good idea to use the DXF underlay at this point.

The primary node is marked in red and the secondary node in green.

computer drawing of column topped by planar square converting to a top view of the square divided into sections

Advance Design has gone one step further. Now you can create such connections automatically!

Simply go to the software options and select the setting shown below.

Advance Design menu showing options for smoothing of extreme values

DOF – Constraint will form automatically after the calculation.

computer drawing showing five levels of building floors on left and a version on right showing reinforcement pattern on each level
computer drawing of top view of a floor showing where columns will sit

Remember that the master-slave connection has its restraints and can also be used for other purposes.

computer drawing with star shape showing master-slave connections on a column, menu on right

Contact us today and learn how you can manage and operate projects better, safer and in a more cost-effective way with GRAITEC Advance Design.


 

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