SPACE FRAMES HISTORY
In 1880 August Föppl published his “Theory of space grid
systems” where – as well as in hisa following articles pulsipher in
1881 in “Eisenbahn” and “Schweizerische Bauzeitung journals” –
he defined the theoretical and practical foundations of space structures.
Certainly, at the time he could not imagine that many decades later, nowadays,
his a theoretical and practical intuitions would
have been appropriately acknowledged by those working in the
building trade. As a matter of fact, only today have technology and
science come together with market economy and profit.
This has happened thanks to the introduction of new processes
in the production of space systems, to the new techniques employed in the
production of truss joints, to the scientific systematization of new
calculus and test codes connected to the newly developed potentials
of computers. FÖpples’ “Das Fachwerk in Raume” dates back to
1891. It was written after a bridge in Birs, near Monchestein,
collapsed because of the instability of its space structure in space.
This text laid the scientific and technological foundations of steel space
structures. In 1892 FÖppl worked out a detailed description of a
rigid barrel vault that influenced the subsequent development of
three-dimensional systems. The original structure, rejected by the
German Patent Office in 1890, consisted of beam grids arranged
along the length of the barrel vault with the beams resting at their
extremes on pillars or walls. A few years later, Robert Le Ricolais,
a well-known French engineer, was the first to perceive the potential
of double-layer grids, proving that such shapes can be also
found in structures created by nature in such a way that the internal
forces always act in the direction of minimum stress. In this regard,
it is still captivating to observe the drawings of some marine animal
skeletons viewed through a microscope and drawn by Ernest
Heinrich Haeckel more than a-hundred years ago. Also the field of
biology offers very many examples of molecular structures based on
elementary space geometries.
It may be surprising to know that the “water” structure organizes the
7 combinations of oxygen and hydrogen atoms in space, but “this is
very important, because it is from it [the combination] that many of
its fundamental properties allowing life derive.” (Giovanni Parisi,
Biological Propaedeutics). The molecular structure of steel itself
shows a three-dimensional arrangement of iron and carbon atoms.
The years straddling the two centuries were an exciting time in terms
of inventions and technological innovations: the Universal Exhibition
in Paris had triggered a deep change. In this climate of modernity
and research Alexander Graham Bell was portrayed with hisa
pioneering prototypes of plane frames based on tetrahedron. He
introduced the first rod-node connection, even if he was far from
imagining that about a century later more than one-hundred patents
concerning space grids would have been issued. Starting from the
50’s, an important contribution to industrial prefabricated constructions
and in particular to three-dimensional structures was given by
Richard Buckmister Fuller, a man of great intelligence, who was
able to combine hisa simplifying research on the geodesic domes
he invented with universal scientific and philosophical practical and
theoretical concepts derived from hisa immense sensitivity.
In the last decades many of the most famous architects and scholars
have turned their attention to space structures. In the mid-sixties
Konrad Wachsmann carried out hisa studies at the University of
South California on new joint systems and their application in the
field of fundamental geometries. Max Mengeringhausen is the
creator of the Mero-Trigonal node, which is still one of the most merchandised
systems in the world. The realization of several structures
has been based on the Spherobat system, invented by Stephane
Du Chateau, a French scholar. For many years the Department of
Civil Engineering of the University of Surrey, directed by Z.S.
Makowsky, has been providing a valid and fundamental contribution:
since 1966 the Space Structure Research Center (UK) has
organized four International Conferences. The latest symposium
organized by IASS (International Association for Shell and Spacial
Structures) has taken place quite recently, in September 1995.
The advantages of a space grid system based on the assembly of
tetrahedral elements can be summed up as follows:
• defining a basic finished element through a simple model
(rod tetrahedron) to achieve an effective and essential representation of
material continuity in space;
• its structural lightness, together with an extremely appropriate
uniform distribution of stress (tension and compression) in the composing elements;
• considering the great constituent and assembly versatility, the possibility to realize
structural couplings and geometries that may exclude resonance phenomena in case
of earthquakes and/or vibrations;
• the convenient and quick assembly using not particularly skilled labour;
• the possibility to easily transform, reinforce and disassemble the
structure, and consequently recover the material employed.
What has been said before is also perfectly coherent with the properties structures
intended for seismic areas are required to have.
As far as this is concerned, it is enough to make an observation
about the intrinsic geometry of space grid structures. The tetrahedral element,
variously assembled in order to form more complex
vertical and horizontal structures, redesigns in space the basic finite element
of deformable continuity; structural simplicity as well as
the technology of space truss enable this kind of structures to provide a uniform
tensional response when loaded with variable horizontal and vertical forces.
Instead, this uniformity cannot be achieved when using structural elements
made of intrinsically orthotropous beam- and pillar-based frames and of horizontal slab floors.
The above listed properties also allow an isotropic response to
external stress; together with lightness, this puts the plane represented
by the three-dimensional system in a distribution of forces
anyway acting on the plane pillars through the simple space distribution
of nodal normal stress. These positive aspects related to the
geometry and structural conception of the system are reinforced by
merely economic and practical aspects. Unfortunately, especially
in recent years, profit has more and more prevailed over research
and quality and producers have been less and less interested in
investing in the experimentation necessary to increase knowledge
and develop new technologies. Nowadays, the market demands
more and more competitive products and this results in less creative
and more commercial products. This is also due to the lack of
proper tools and specific guidance and information that may help
designers choose the most appropriate and convenient geometry
or technology without hindering form and creativity. For example,
it is paradoxical that the different regional specification and price
lists do not include items or prices related to space grid systems
defining their structural and technological characteristics.