Cable Structures on Advance Design

Cable structures are distinguished by their remarkable capacity to withstand significant tensile stresses. This advantage allows architects and engineers to design structures that are not only resilient but also lightweight, cost-effective, and visually striking. Additionally, owing to their lightweight, assemblage of cable elements is simple and effortless. Structures involving cables have a rich history, spanning various types. Notable examples include suspension bridges, cable-stayed bridges, and footbridges as well as mast structures, suspension roof systems, cable-net structures, and Tensegrity Structures.

Cable structural elements are geometrically non-linear and hence we need a non-linear solver in order to analyse this kind of structures. Advance Design, the structural simulation software by Graitec, implements non-linear solver that enables engineers to easily incorporate cables into their projects.

 

Figure 1: Trois-Soeurs footbridge Québec city, Canada
[Taken by Réal Filion:  Passerelle des Trois-Soeurs | Le monde en images (ccdmd.qc.ca)

Figure 2: The Lawn Tennis Association’s National Tennis Centre (Source: Hopkins Architects),

In this article, we will see together how to model a cable structure on Advance Design including analysis and theoretical.

1-    Example of cable structure

Our working example is inspired from the structure showed in the following figure which is a cantilever car parking shade.

 

 

Figure 3: Cantilever Car Parking Shade Structures
( source: Fabric Cantilever Car Parking Shade Structures – Single Bay – Tension Design (bdir.com)

2-    Modelling in Advance Design

To simplify the study, we will consider only one frame including one column fixed at the bottom end, one major cantilever beam, one small cantilever beam and three cables. The structure is modelled in Advance Design. Illustration of the structure, dimensions and cross-sections are shown in the following figure. We can notice that we used variable cross section W beams, and this choice is made to minimize the self-weight of beams at both ends and make the project more aesthetic.

Figure 4: Example of frame of cantilever car parking shade structure

After modelling the structure, we can apply different loads, but for this example we will consider only the self-weight and a uniform linear dead load of 0.5 kN/m applied on the major beam (See figure 5). This load is an estimation of the roof dead load.

Figure 5: Linear load applied on the cantilever beam

Once we apply the load, we can generate load combination following a specific code. For this example, the Canadian CNB 2015 code is selected (See figure 6)

Figure 6: Creating combinations

As mentioned in the introduction, cables are non-linear structures and hence we need to activate non-linear analysis in Advance Design. To do so, we need to right click on settings and click on nonlinear static.

Figure 7: Activate nonlinear analysis

For more details about geometrical non-linear analysis in Advance Design please consult this blog: Geometrical Non-linear Analysis In Advance Design | GRAITEC CANADA.

Next, we click on NL that we created. First, we enable large displacement and then we click on the icon pointed with the arrow in the next figure.

Figure 8: Setting nonlinear parameters

Then we need to select a load or a combination load by clicking on Add/Remove analysis in the bottom left of the window. In this example, we selected the combination 1.4 D1+1.4D2.

Figure 9: Add combination for nonlinear analysis

Once done, we can keep the following parameters by default and run the FE analysis.

Figure 10: Nonlinear analysis parameters

3-    Analysis and results

After launching the analysis, we can dispose several results for example the displacement of the structure subject to the applied load (figure 11).

Figure 11: Displacement of the analysed structure

What is important to verify is also the axial force of the structure. In Advance design, the normal force Fx is positive in case of tension and negative in case of compression, regardless of the orientation of local x. As it is shown above (figure 13), all three cables are subject to tensional forces, the maximum tensional force is Fx=15.8 kN and occurs for the bottom cable linking the foot of the column with the small beam.

Figure 13: Display of axial forces

Conclusion:

In summary, cable structures offer remarkable tensile strength, enabling architects and engineers to create lightweight, cost-effective, and visually appealing structural projects. Graitec’s Advance Design, with its non-linear solver, is a perfect software for analysing cable structures. Using a simple example, we covered the modelling process, load application, and non-linear analysis activation. The results highlighted the crucial role of cables in supporting the structure owing to their high tensile strength.

Written by Achraf Ben Afia, Solutions technical expert / achraf.benafia@graitec.com