Physics for Architects

Photoelastic Models

The following photograph of a Photoelastic Model appears on page 179 of Scientific American November 1984 Volume 252 Number 5. The article by Robert Mark and William Clark is on Gothic Structural Experimentation and shows the effects of wind and dead load stresses on the original nave of the Cathedral of Notre Dame as built in Paris around 1180 AD. The flying buttresses were rebuilt half a century later, in the 1220’s, probably because of the stresses that show up here as colored interference patterns. Each color corresponds to a different level of stress. Where colored lines are closely spaced, the stresses become critical.

Professor Mark's group at Princeton formed this model out of transparent plastic and then heated it to 150 C. Weights were then added to simulate wind and dead weight stresses. After cooling, the model is shown here as viewed between cross polarizing filters.    

The following photographs appear on pages 91 to 96  of Scientific American November 1972 Volume 227 Number 5.  There, Professor Mark actually had the cover story for that month's Scientific American.                                                                                                       

The Bourges Model

And the Chartes Model

Then there is a view showing a model of Amiens while being weighted to simulate the wind loading.

Robert Mark

Robert Mark is a Professor of Civil Engineering and Architecture, Emeritus at Princeton University. He is the author of several books.

Experiments in Gothic Structure

Light, Wind, and Structure: The Mystery of the Master Builders