The idea is to be as lazy as possible so that you don't do twice the same operation.
1- The beam model : It consists of a sketch , fully parametric , with formula to represent the pattern of Beams used to create ALL the braces in the tower. This equivalent of a Beam is much lighter and more robust than if it was made with a solid Beam. In CATIA I created it using Sketcher , the two Red dots represents the two anchor points.They represent the only two geometries without constraints.
2- The Brace Group model : It consists of several beam Models, all centered . It is not yet instantiated in the Tower Context. The model is purely empiric. the focus is on the associativity of the geometry and not on their result ( how they look) . I have here two Instances of the Beam Models to design the Diagonal Left and Right braces. I also started to put a geometry to represent the Gusset at the intersection . Later they will evolve into a STAR Gusset or a simple ROUND Gusset . At this stage, the shape of the Gusset is not important, what matters is the topology.
3- The Section Template Model
For the first time I needed to use my reference Model .The Section Template Model represents the unit of construction of the Tower. Only the 4 curves of the Ref Model , and 2 planes are used to fully define the Geometry of each faces (8 total).
Those faces will later be the support for the Braces. There is a strong symmetry of plane in the design , the symmetry comes from the Curves. This symmetry was wanted by Eiffel to convey properly the stress from the top of the tower to the Foundation without the risk of Buckling.
Here the Model for Entretoises 24/25 ( Section included between Plane 24 and 25)
By changing the Two planes positions , I get a new Geometry of the Faces.
Here the Model for Entretoises 10/9 ( Section included between Plane 10 and 9) , Notice the angle is wider and the distance from the Axis tower ( yellow vertical line) is greater. The model is perfectly stable for any combination of Planes.
Now I can Instantiated the Brace Template Model on one Face . I have added also the Corner Gussets ( yellow contours) .Notice the dashed- intersection lines with the Faces on my Model. The model is iso-constraint. It is very important, all along the design to keep the Model iso-constraint at ALL COST.
I can Now repeat by copy paste the sketch on each Face , this is taking 2 minutes.
4- The Section Template Structure Model
I can now use SDD to Create the Plates with Thickness and the Beams . Here is the model for Entretoises 4/5 , this is close to the bottom of the Tower.
5- Instantiation
The Instantiation is the Operation of Population the Design by creating new Sections. Each Section is obtained by a new combination of Planes (Entretoises) and Parameters ( Arbaletriers, Brace Width, etc...) .each Instantiation takes 2 to 3 minutes. There is 28 Instances corresponding to the 28 sections of each leg of the Tower.
You can see below that Sections Below First Floor are very straight , while Sections above are quite curved. Each was obtained from the SAME TEMPLATE Model.
The strength of CATIA to handle complex parametric is demonstrated here.