One of the very first engineers working on form-finding is the Italian Pierluigi Nervi. He worked on this (without any FEM software!) because of the shortage of concrete and especially steel during fascism. What he engineered still amazes many engineers all over the world!
Other very famous “early form-finding engineers” are: Frei Otto, Buckminster Fuller, Sergio Musmeci, Antonio Gaudì and Felix Candela. So the idea is: what about using timber instead of steel/concrete?
3D Model (LOD 100)
It’s normal to start from a 3d model: LOD 100 or a concept design or even just some sketches/ideas from the designers. The preliminary analysis is super important because it aims to find the right shape where to start; it sets some boundaries/limits and gives some inputs for the development of the project. We call this stage of the project “the dancing shape” because it changes continuously and sometimes it looks like it’s dancing.
This innovative approach to the design has as a final result a fully customized 3d parametric model that can be easily adapted to the specific needs of the clients because it is based on an algorithm. In our case, we also implemented a link between Rh+Gh and Dlubal RFEM to run some FEM analysis and get the most out of both software.
The algorithm that creates the shape will be also used in the final stage to prepare the part list and the production drawings (LOD 400).
So the right workflow is “form-finding -> FEM analysis -> optimization” in a sort of an iterative process.
These images are taken from an analysis we performed for a client asking for a “waffle” big double-curved roof. The only way to cut the costs was to change its shape and develop some form-finding algorithms. Thanks to our experience in timber engineering and computational design we managed to reduce the size of the elements and the forces on the connections. The design of the elements is now driven mainly by the axial forces and not by the bending moments.
We used a form-finding engine to “relax” the structure which will change its shape according to the loads and the boundary conditions. The structure reaches its equilibrium once the simulation “converges”; then the simulation is stopped.
An important part of the form-finding method is to compare different solutions to each other to better understand the parameters driving the design. How different is the new shape from the old one? How many m²/m³ of materials can be saved? Can this difference be accepted by the client/designer? If the answer is yes, then it’s possible to move into the next step.
In a perfect world, the final FEM model has nothing but axial forces and this means that it is super-optimized. In the real world, there are still some bending moments because of the different load patterns/combinations. In our specific case, we proved that this special analysis allowed us to reduce the quantity of materials by 30% and to reduce the cost of the connections by more than 40%.
Why is form-finding so important for timber structures?
We collected a few reasons in the next list:
Obsidian Rain pavilion
Also on this project we used a form-finding approach to optimize the Pavilion structure and determine the real length of the ropes and prepare the part list. Click here for more information.