Parametric design can be described as a set of rules (a parametric script) that is fed to a computer. The computer then uses these rules to produce a digital model. A quite simple example of such a rule can be to place lighting posts every twenty meters along the centreline of the road. The advantages of modelling using a parametric design compared to modelling manually are many.
If, for example, the centerline of the road is moved, the computer will automatically move the lighting posts with it, eliminating the human labour needed to update the position of all the lighting posts. If the desired distance between the lighting posts is revised in the script, the computer revises the design in seconds. The same principles can be used for more complex modelling like reinforcement or post-tensioning.
When using enough of these rules, most of a structure can be described by parametric design. This leaves a very flexible design that can be revised quickly and without human errors. The parametric scripts can also easily be reused in future projects. For the Randselva bridge project, more than 60% of the structure is modelled using a parametric design. All the tendons and over half of the reinforcement and concrete form have been created this way.
Revising the road alignment late in a drawing-based project would normally mean months of rework. With the parametric design, we can adapt to new road lines in days. The same applies to revisions on reinforcement, tendons and form. In the case of Randselva, the process involves over 200 unique tendons, 200,000 rebars, and more than 200 concrete pour phases.
Grasshopper is a visual programming language and environment that runs within the Rhinoceros 3D software. Visual programming lets humans describe processes using illustrations or graphics. This type of programming is based on the idea of "boxes and arrows." Boxes or other screen objects are treated as entities, connected by arrows, lines or arcs, which represent relations.
What is essential with Grasshopper-Tekla live link is the fact that it creates and manipulates native Tekla objects. This functionality was crucial to the great success of this connection. Together with geometry, all types of reinforcement can be created through Grasshopper. All data that defines reinforcement in Tekla can be manipulated from the Grasshopper level. Including creating reinforcement in tapered or curved form.
Figure Workflow Rhino/Grasshopper with Tekla
Not just creating advanced geometry and reinforcement was the key to success here. Grasshopper can query for all Tekla model information. BIM data, attributes and object placements can be changed in real-time. It is possible to extract all UDA (user-defined attributes) from Tekla to Grasshopper and another way around.
Figure Filling out User-defined attributes directly to Tekla reinforcement