Why do Gothic Churches look like they do?

Simulating arch pressure with Blender



Simulation is updated 2.2.2014. Works now with Blender 2.69.

With Blender's physics engine it is possible to build simple real-time simulations. I've made a small visualisation of arch pressure in Gothic Churches.

When an arch is made of for example of stone blocks over a wall, it generates a horizontal pressure towards walls. This makes it difficult to build high buildings with vaulted roofs. Higher wall means longer lever arm to the arch pressure. Therefore the thickness of the wall must be increased.

Here is a simple Blender/Bullet simulation showing this in practise. The two archers are similar but higher wall can not resist horizontal force produced by arch and structure collapses.

arch (vault) pressure


That can be solved by making wall thicker. But higher you go, more massive structures are needed.



Flying buttress

However, the aim of the Gothic architecture was to achieve light looking, vertical buildings. So they had to invent ways to handle vault pressure without heavy walls.

With flying buttress it is possible to keep inner walls thin because:

the flying buttress' design provides for an equal and opposite force to be imposed on the wall, thus keeping the wall in balance. This, firstly, enables the vaulted roof and, secondly, by externalising some of the structural elements of the wall, allows the wall so supported to be thinner, which in turn enables the development of large arched window sections to let in light and be filled by stained glass (source: wikipedia).

flying buttress

Here are different solutions side by side. Running simulation shows how they behave. Download and check it out!

pressure compare


Cross (groin) vault and barrel vault simulations

It is difficult to make large windows to the walls supporting barrel vaults. Therefore cross (groin) vaults are used in gothic churches. Cross vault needs support only on the corners of the vault so there is a lot of room for light to come in.


Arch pressure simulation: arch_pressure_simulation_2014.blend

Vault simulation: vaults.blend

Please note that because of the changes in Blender's physics engine, your results may vary between different Blender versions

How do I run these simulations?

  • First, install Blender from blender.org
  • Then launch Blender and open file File->Open.
  • Then make sure your cursor is over an 3D-view and press P on keyboard (Blender uses Unix-style method for focusing window).
  • Stop the simulation by pressing Esc.

Ok, this is fun! How can I edit these simulations?

You can select any vault brick by clicking with RIGHT mouse button over it. This brings up the 3D-transform manipulator:

Now you can move brick by dragging it from arrows by holding your LEFT mouse button. Then just run simulation again and see what happens. Enjoy your architectural studies!

NOTE: Don't see arrows? Press Ctrl + Space and select disable/enable

After you have played it for a while, you want to learn to use Blender :). There are lot of tutorials in the net and also this site has few (see the navigation on the left).