CONCEPTION AND CONSTRUCTION OF BUILDINGS FROM THE ARCHITECT’S POINT OF VIEW
Congress of the International Prestressed Federation in Stockholm in 1982. Published in the Proceedings of the Ninth Congress of the Fédération Internationale de la Précontrainte. STOCKHOLMG 10 June 1982. Volume 1 . Seminar Papers. Fédération Internationale de la Précontrainte.
In the first place I would like to thank the General Secretary of the International Prestressed Concrete Federation, the invitation that they have given me to present a paper in the Congres of the F.IP. in 1980, on the “Conception and Construction of Buildings from the Architect´s Point of View”.
In other eras of History, it was the structural necesseities of architecture that demanded technical inventions. As is the case of cross vaulting—In order to cover those large cathedral spaces—in gothic architecture
Today engineering problems are the largest bridges, the ones that have most demanded new technical solutions of which Prensile Concrete is, without doubt, of the highest interest.
One must recognize that the appearance of this new technique hasn’t given architecture more than a few sporadic applications—like technical solutions brought to concrete instances—by specialists, and without affecting the profound structural and aesthetic problems of today’s architecture.
In certain ways, the road that this new technique is following is analogous to that of laminated steel, that if indeed it achieves important results in the architecture of Fairs and Expositions at the end of the last century and beginning of this one, it doesn’t acquire its authentic architectonic expressivity—with Mies van der Rohe—until more than a half-century later, after being used daily.
In spite of this evident indifference by architects towards prestressed concrete, there are several essential reasons to believe that prestressed concrete is the first material and the first technique that satisfactorily resolves the ancient duality: “durable-flexible”.
After the solutions of primitive man to defend himself from hostile nature, in caverns and cracks in the rocks, and also to construct almost instinctively conical huts; like the birds do in their nests, man begins the construction of habitable spaces that end up being what we call architecture
Within these spaces, man by himself or in groups more or less numerous, must not live inactive and sedentary, but rather he must carry out tasks of very diverse nature and characteristics, both static and dynamic. Superior animals posess a certain sense or territoriality; of possession of a space, above all in certain brids. There also exists a space that surrounds man, which doesn´t end where his skin begins, but forms, in the words of Edward T. Hall a “bubble”.
This bubble, which varies in dimensions according to different cultural, climatic, and idiosyncratic factors (etc.), becomes the generator of architectural space when man carries out different functions within it.
The result of the motion of such generator volume of the human “bubble” is in all cases a limited space on both top and bottom by two parallel planes with a lintel. The lintel contains, however, a flexed member where some areas are submitted both to compression and to tensile forces.
This double property of bending and tensing makes it necessary for the material forming the frame to have a very peculiar molecular structure. This is met by wood, but not by store material.
Wooden materials are good, but they rot. Stone materials are lasting, but do not bear tensile forces well. The history of architectural structures is that of the evolution of technology, looking to solve the duality: “durability-tensile aptitude”.
In some cases, as in monumental archaic Greek architecture, the problem is stated and solved correctly in its tensile aspect, though wood rots.
A transfer from wooden solutions to stone or marble makes the whole expression of classical architecture misleading: Greeks, Romans and Renaissance people all solved the durability dimension, but neglected the requirement of tensile strength.
The replacement of a correct anthropomorphic architectural space with the right structural space, starts a whole series of lasting architectural achievements (such as vaults and domes which are still built today as concrete diaphragms), generated often but not always by ganged surfaces, even in simple and double suspended roofs, making it possible for the stone or the concrete to work only through compression on the whole member.
Reinforced concrete, where the concrete mainly supports compression forces and steel reinforcement tensile forces, has nearly solved the historical duality “durability-tensile aptitude”. Nevertheless, even if steel supports tensile forces, concrete in tensile areas is also subjected to tensile forces and cracking, even if only in microscopic cracks, because reinforcement does not allow larger cracks.
It might seem a “joke” to make a previous compression in concrete by means of steel wires or tendons, stressing and making it with concrete by means of bond or anchorage, so that when the member is put to work and is subjected to tensile forces, these can be balanced by the previous compression forces, while still maintaining some initial compression force, which is called ‘prestressed concrete’. We must admit that this is the first material discovered by man that correctly solves the architectural duality “durability-tensile aptitude” .
But there is another duality in architecture which may also be solved by means of prestressed concrete.
In my opinion, architecture is a “piece of air made human”. The chief problem in architecture is the creation of spaces for man, places where he may be able to develop some particular functions previously planned, and where the most forbidding features of nature have been corrected: cold, heat, rain, etc.
This problem is solved by demarcating a portion of free space with some limiting and insularing surfaces.
Such limiting surfaces, however—roof, floor and walls—must stand. This is the moment when man must face the problem of the structure as a bearing system where these limiting materials of the architectural space are gathered.
If we could find a material that could be both a structure and cladding, we would have solved the architectural problem, once and for all, and no division between a structural (bearing) part, and the transparent mass cladding born by the structure, would be needed any more.
Prestressed concrete solutions—using hollow members, as a rule—may be the best way to settle, in a uniform pattern, this structural and architectural problem. Hollow forms are neither new nor typically architectural. In engineering solutions, such as girder boxes—which I suppose come from the blending of two double T beams—similar structural solutions have also been successful.
But if—as in my own works—hollow prestressed concrete members are made with a structural and architectural purpose, the result is very similar to the bone structures of vertebrate animals. This is the reason why I have called, with a touch of humour, such prestressed and postensioned members: bones.
With objectivity we can assure that architecture has, so far, discovered a material and a technology that is best suited for the double purpose: structural-architectural / durability-tensile aptitude,.
But there is another problem, typically plastic, since we must not forget that architecture belongs to the fine arts.
A material that contains properties in such a new form, must aesthetically have its own power of expression, absolutely different from that of other building materials.
In the same way that other materials have had their own expression in the history of Architecture: wood, stone, rolled steel, etc., the new reinforced concrete technology, and that of prestressed concrete, should have its own expression, abandoning all imitations which have been giving us solutions in wood, stone or steel up to this point.
Concrete is the only material which is applied in a work in a different state as its final one (paste). This paste condition should be remembered in its final state, as a genetic print of a material that was first soft, being later cast in a mold which gave it its final shape a texture.
Secondly, its “durability-tensile aptitude” quality must be developed as much as possible to achieve anthropomorphically correct architectural spaces, to the measure and the convenience of man and human society.
Finally, all the financial and plastic possibilities of such a structural-architectural blend must be also developed. I have been contemplating all these possibilities during 25 years of creative preoccupation. The following pages show some modest achievements.