Engineering an Identity — Henri de Dion
Henri de Dion wove engineering prowess into the tapestry of French identity by saving the iconic Bayeux Cathedral from certain destruction. De Dion possessed an exceptional grasp of the scientific principles needed to address the great variety of questions that an engineer of the time would have encountered. De Dion taught the principles of structural analysis at the Ecole Central des Arts et Manufactures, where Gustave Eiffel was one of his students, and he designed a number of notable structures during his career.
As a young engineer, De Dion came to the attention of the Eugene Flachat, an innovator in the then new field of design and construction of metallic structures. Flachat recruited de Dion to be his assistant and gave him the job of studying designs for a bridge at Langon. In 1855, Flachat assigned de Dion to direct the restoration of the Bayeux Cathedral, in effect saving the 11th-century cathedral from imminent collapse. De Dion was only 25 years old.
The Bayeux Cathedral was home to the medieval Bayeux tapestry that depicts the exploits of William the Conqueror, a national hero in France. The central tower of the cathedral had been added 400 years after construction of the original structure. The tower was supported on four pillars that were part of the original structure. The architects of the tower had reinforced the pillars. However, the underlying foundations, built on loose fill material, proved inadequate to take the additional weight.
By the middle of the 19th century, progressive failure of the building had reached an alarming state. When de Dion arrived to begin restoration work, the walls of the tower were cracking and the stonework of the pillars was visibly deteriorating day-by-day, almost hour-by-hour. The central tower was settling at the rate of one centimeter per day. Architects had given up and called for the tower to be torn down and rebuilt. But, Flachat assured them that modern engineering science could save the iconic cathedral from destruction.
De Dion’s solution employed the immediate construction of an immense structure of wooden scaffolding. He used jacks to lift the entire weight of the tower off the pillars, thus preventing their complete collapse. De Dion encircled the base of the tower with iron bands to hold the stonework together where it sat on the scaffolding. These bands were heated before being put in place, so that the base of the tower was compressed as the iron cooled. This succeeded in closing cracks that had formed in the tower walls. With the tower thus stabilized and supported, the old pillars were demolished and replaced with pillars on new foundations strong enough to support the tower.
For his success with the Bayeux Cathedral Henry de Dion was awarded the knight’s cross of the Legion of Honor. During the rest of his career, de Dion divided his time between teaching structural design, working as a structural engineer for railroads, and leading the development of the new profession of civil engineering. At the end of his career, de Dion created an innovative design for the exposition gallery at the 1878 world exposition in Paris. De Dion’s roof truss is capable of spanning large distances (35 meters in the case of the 1879 exhibition building) without the need for interior support.
Henri de Dion is one of the 72 engineers and scientists named on the Eiffel Tower.
Reference:
Molinos, L. and T. Seyrig, 1879. Overview of the work of Henri de Dion, class of 1851. Bulletin of the Association of Former Students of the Central School of Arts and manufactures, September 1879, p 217–228.
