This is an in-class activity where students physically model a flying buttress in order to understand the flow of forces and their importance in gothic cathedrals.
After this activity, students should be able to:
- Understand that horizontal thrust develops in pointed arches
- Explain the role of flying buttresses in diverting the horizontal forces to the ground
- Outline the main structural characteristics of gothic cathedrals
- Recognize the importance of gothic cathedrals in civil engineering
- Appreciate the link between gothic cathedrals and modern "tall buildings"
Gothic cathedrals were the first tall buildings of the New Age. These masonry structures soared to new heights and pushed the limits of gravity-dominated structures. The three main structural characteristics of gothic cathedrals are: pointed arches, flying buttresses, and ribbed vault ceilings. The ribs of the ceiling/pointed arches would come down at an angle and rest on vertical pillars. The horizontal thrust from the arches had no way to resolve and would cause, in some cases, catastrophic collapses. The development of flying buttresses was necessary to transfer the horizontal thrust to the ground and prevent unwanted tension in the arches.
It is unknown who invented the flying buttress, but once architects and engineers started using them, they could use more glass in the walls and cathedrals became lighter and appeared more "airy".
Students are first show clips from the NOVA documentary ‘Building the Great Cathedrals’ that explain the above principles of gothic cathedral construction.
In this kinesthetic activity, two students form an arch while another student hangs as a weight from the “arch”. Students can feel the difference in the forces between an arch without a buttress, and a buttressed arch. Through this activity, students can experience and understand the importance of flying buttresses in cathedral construction.
- 5 students (2 as buttresses, 2 to make the pointed arch, and 1 to act as a weight) and one metal rod
Two students stand facing each other and hold a rod between them with straight, raised arms. They represent the pointed arch. A third student will stand between the two and grasp the rod. This student will act as the weight of the roof load on the structure. Two additional students stand with their arms straight and supporting the shoulders of the arch students.
Have the students try the example where there is no flying buttress to support them. They will most likely not be able to support the weight of the student in the middle, or will find it difficult to do so. Then, make the students try again with the added flying buttress students. They should be able to feel a significant difference in the ease with which they can hold the student up. Have the students switch roles so they can all experience the difference in supporting the load with and without a flying buttress.
Finally, have the students summarize what they learnt from this activity with a question or discussion about the general conclusions. The responses to this question can be used to assess the learning objectives of this activity.
From the lecture: The Gothic Cathedral and the Skyscraper