WHAT HAPPENED TO SHELLS ?
By Milo S. Ketchum
Concrete shell structures were introduced to this country, in the early 1930's, by the Roberts and Schafer Company of Chicago, who imported the technology from Germany. Their development and promotion, was very successful, and a large number of industrial buildings were built during the war. The real impetus after the war, came from other sources rather than these proprietary methods. Most notable was the publicity given to the shells of Felix Candela, a Spanish architect and engineer living in Mexico. For a decade, starting from 1956, the architectural magazines were full of examples of structures built by many different designers. Then the construction seemed to stop and little was heard. The movement had run its course.
There is no single reason that accounts for the demise in the construction of shell structures, rather, it is a result of many factors. I will attempt to list and explain some of these and show their effect on the construction of shells.
At the present time, shells have a great many advantages going for them that they did not have in the past. Pumped concrete makes it easier to place at the heights required for roofs. With the computer, analysis has become much more precise, and construction estimating is less laborious. Preliminary estimates for the costs of shell structure are easy to estimate.
I do not accept that the reason was the exorbitant cost. For industrial and commercial structures, it is true that unfireproofed steel structures of short span are much less expensive, but as the span increases, shells become more and more competitive. If all the cost factors are considered, they may actually cost less. For monumental structures, the architectural solution is the dominate factor, not the structural material.
- The end of the shellbuilding era, it must be noted, coincided with the Vietnam War and all of the social disruption that occurred. Labor also was having different attitudes, and construction was affected by the removal of men from the labor market.
Most great movements center around strong and charismatic leaders, and the building of shells is no exception. In this case it was Felix Candela, whose achievements both in number and quality will never be duplicated. If you do not believe this then go to your library and find, if you can, "Candela, the Shell Builder" by Colin Faber. Candela was an architect, engineer, contractor, entrepreneur, and mathematician. As an engineer, he was not dependent on others for the architectural design, and as a contractor, he was not hedged in by a engineer or architect. Also, the building climate in Mexico City was favorable with low cost labor. Furthermore, he took great pains to publicize his work.
Architects were quick to get on the band wagon at the time, and many shells were designed, often to show the extreme forms available. In my opinion, however, not many architects really understood the possibilities and the proper function. Shells, to be effective, must use the interior beauty as an asset rather than depend on the external appearance.
Few engineers, of the period, really understood the structural design of shells and the possibilities, nor did the have the confidence in their knowledge of structures.
Coincident with the development of shell structures, was that of precast prestressed concrete. This was a factory product, readily available to the engineer, without excessive calculations. There was an eager staff of salesmen to push the product, with a national society to back them up. No such support was available to the designers of shell structures.
The Portland Cement Association put on a vigorous promotional campaign with sales engineers of a high caliber available to any engineer. When the financial situation in the country got tough in the cement industry during the 1960's, this support was withdrawn.
Some time in the future, the cost of structural steel will rise beyond reason, and some one will discover the utility and beauty of shell structures, will design them, find they are salable, publicize them, and will start the cycle of popularity again. Things are not built or done because they are economical, beautiful, or utilitarian. The are built or done because someone wants to build or do them, and in the process then become economical or beautiful or utilitarian.
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