KẾT CẤU MỚI ON FREI OTTO''S PHILOSOPHY OF WIDESPAN LIGHTWEIGHT STRUCTURES

19
ON FREI OTTO'S PHILOSOPHY OF WIDESPAN
LIGHTWEIGHT STRUCTURES
Michael Dickson
This is a text prepared in collaboration with Professor
Frei Otto and based on a presentation given on his behalf
at the inaugural session of the Bath University
Symposium on Widespan Enclosures in April 2000.
Frei Otto's long career in lightweight structures includes
the development of stressed tensile sails for the Lausanne
EXP064, the distinguished German Pavilion membrane
and pre-stressed cable nets for EXP067 in Montreal, the
Munich Olympic Roofs in 1972, and the Gridshell at
Mannheim in 1975. The conceptual design studies for
these and many other projects were carried out at the
Institut fur LeichteFlachentragwerke (I.L.) which Frei
founded at the University of Stuttgart. Between 1967
and 1995 he worked often with Ted Happold, a friend
and fellow spirit, on such projects as the 120m x 90m
cable net structure for Jeddah University and the
Diplomatic Club, Riyadh, (Aga Khan prize for
architecture 1998). Professor Otto's current work
includes consultancy on the Venezuelan and Japanese
pavilions for the EXPO at Hannover 2000, and
conceptual design for the new railway station for
Stuttgart 21. He is one of the leading innovators in the
development of lightweight structures and has recently
received the following international prizes:
• Honda prize for
ecological
technology 1990, Tokyo

•
77ie*
principle prize of the German
Institution
of
0 Architects and Engineers in Berlin, 1996
• The Wolf
Prize
for Arts, Jerusalem, 1997
He is an Honorary Fellow of the Institution of Structural
Engineers and of the Royal Institute of British Architects,
and Dr of Science honoris causa at the University of
Bath.
INTRODUCTION
In both the developed and the developing world,
widespan enclosures are increasingly required to house
and facilitate many of the collective activities of society.
Such enclosures need to do this without drawing down
excessive quantities of scarce construction material or
drawing upon unnecessary quantities of energy in their
operation. To ensure such aims requires an efficacy of
construction, a delight in their occupation and
appropriateness to their location. Beauty of architecture,
efficiency of structural form and appropriateness of
material usage are the fundamentals in securing this aim.
Yet in the solution of this theme the use of large spans is
not just a game to make the Guinness Book of Records
but a search for real solutions for mankind. To know
about large spans also opens opportunities for advances
for shorter spans. In the absence of scale factors on short

spans it is possible to use material less effectively.
Conversely for the larger spans, it is necessary to seek
out fundamental 'absolutes' of performance and to
recognise the significance of 'scale' and the problems of
enclosure.
Part of this search is the recognition of optimal
performance and benefits of different structural forms in
ascending order of opportunity - so this paper tackles the
fundamentals of performance of successive structural
types - bending structures for smaller spans, lattice
structures, gridshells and compression vaults, tension
structures and finally the opportunities for pneumatic
structures. These structural systems are discussed and
illustrated principally through a wide variety of projects.
BENDING AND LATTICE STRUCTURES
The scaffolding lattice system for roofs was devised to
avoid the volume of material that would have been
required of a 'bending' structure. Small diameter
compression or tension tubes in a three dimensional
lattice transfer the roof loads back to a few columns for
the 102m x 52m membrane covered Interbau Buildings
Berlin 1961. This was a 'first' for Mero and in a way the
precursor to the many lattice space frame structures by
Kenzo Tange at Osaka 1970 (fig 1).
Fig 1
20
Prefabricated standardised galvanised Delta units and
'bolted' cross nodes made up the 42 cm deep
intermediate viewing platforms for the German Pavilion
at Montreal (1967). Engineered by Leonhardt and Andra

the cruciform head units positioned diagonally across the
grid concentrate loading from the floor grid onto the
column top, each element as in the human body prepared
for its particular duty (fig 2).
Fig 2
In the 24m high Bell Tower for Berlin (fig 3), the
architectural form of the virendeel truss is retained while
the plate thickness is aggregated from 10mm at the top to
50mm at the bottom in order to restrain the drift of the
Tower to 16mm under the ringing action of the 3 bells -
function following form:
Fig 3
DIRECT FORCE STRUCTURES
Inescapably, the most efficient way to transfer load back
to foundations is by a 'direct' way - an inclined straight
spar. Early investigations with the mushroom support
'spars'
to the 'humped' tent at Koln 1957 led to studies
for radiating 'fan' systems for the Transrapide Maglev
viaduct system (figure 4a). It should be noted in passing
that the alternate form to the nose of the model capsule
21
on the bridge is itself a holistic proposal to reduce wind
resistance at speed, hence the required magnet power and
therefore also the weight to be supported by the bridge
itself.
The purpose of the viaduct design for the Maglev was to
reduce the impact of the linear induction Transrapide
support system on the countryside of Northern Germany
from Hamburg to Berlin. The Transrapide Maglev is a

light multicar system capable of travelling at up to 450
km/hr using the technology of aircraft systems. Breaking
loads from emergency deceleration are more critical to
the support structures than vertical loading. Structural
continuity and close accuracy of construction, allowing
also for thermal distortions, is essential for ride comfort
- hence the structural concept of a minimal triangulated
tubular network casting little shade on the ground below
and supporting loads onto simple foundations.
Fig 4b
A further development of these thoughts has led to the
fan pedestrian bridge system for Gelsenkirchen 1999 (fig
4b).
In line with earlier studies of bamboo structures at
the I.L., the various spans of this radiating system are to
be made from kit form of solid 70mm galvanised bars
and 4-bolt cup-clamp systems. Individual buckling
lengths are to be reduced by an internal criss cross of
stabilising bars - also 70mm 0. The 1960 study at Yale
for a thin roof did so by dividing the individual spars to
form a "triangulated" network of stable compression
elements (fig 5). For the Council of Ministers project in
Riyadh (1978) the loading from the 3'D' hexagonal grid
shell for the seating bowl is gathered by irregular
triangulated configurations of tubes of successively
increasing diameter. These match the buckling length
restrictions to the requirements of increasing load back
onto a single composite column of 3 individual braced
tubes (fig 6).
Fig 6

But the aesthetic of a design in its surrounding is also of
great importance - the tree fountain on its well in
Warmbronn drips its water carefully into the well (fig 7).
Sometimes a symbol will be sufficient. For the one day
meeting of the Evangelic Church at the Berlin Olympic
Stadium (1961), only a single 40m high guyed cross
structure was needed to express the enclosure (fig 8).
Fig 7
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Fig 8
22
FUNDAMENTALS OF MATERIAL AND
FORM
In terms of the 'absolutes' of measurement, illustrations
on a logarithmic scale relate the basic forms of stability
of everything from mountains to grasses and hairs - aim
high grass has a H/D of 100 or more (fig 9). Of
consideration too, for all enclosure tension studies, are
the fundamental rupture lengths of different materials
under their self-weight - wood is the leader.
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Fig 9
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Other studies have also shed light on fundamentals of

performance:
• What stable forms does sand create when allowed to
run away? (fig 13).
• What are the laws of form for spine structures (fig 10)
and for hanging vaults? (fig 11).
Fig 13
• Based on the historic shells from Harran (fig 12) what
crucial forms from local brickwork can resist the
lateral forces of an earthquake? - as measured on the
tipping table, the cone of make 0.3g (30°).
Fig 11 Fig 14
23
The proposals for the naturally light and ventilated forms
for Islamic University at Uzbekistan, constructed solely
of bricks is the outcome of such studies (fig 14). To
optimise bridging, theoretical studies show that you can
bridge 10 miles so probably at least 1/10 of that can be
achieved in reality. How do vaults really work? In the
vousoir model, it is to be noted that the zig-zag string
transmits the 'shear' for stability (fig 15).
Indeed the study of arch forms led directly to the form of
the openings in the supporting walls of the Diplomatic
Club,
Riyadh [now CasaTuwaiq] (fig 18).
Fig 15
On the tipping table, lower arch forms are more stable
than high forms. Even arches can be curved in plan,
(figures 16 & 17).
Fig 16
Fig 18

SHELLS, GRID-SHELLS AND VAULTS
In 1958, with the help of students at Washington
University, a rubber membrane weighted with nails was
used to investigate forms "without bending". Such forms
were then stiffened with plaster and inverted into a shell
form.
There followed the single layer timber gridshells for
Essen (1962) (fig 19) and that by students at Berkeley
(1962) constructed out of steel rods and washers from the
hardware store (fig 20).
Fig 20
24
The bending free grid-shell form is really a low cost
construction method for creating complex forms for
public space. An early example is the auditorium of the
German Pavilion, Montreal (1967) prefabricated in
Germany and drawn out into its final form on site (fig
21).
This was a forerunner to the minimal energy house
designed for Ted Happold. Here oak lath gridshell, turf
covering, south facing glass wall, pv cells and wind
generation are all part of a holistic approach to design
(fig 22).
Fig 22
With the help of the computer, there are now forms
which are difficult/impossible to model physically - the
naturally light and ventilated workshop in Dorset for
John Makepeace of roundwood spruce trees formed by
green bending the tapered green debarked trees is one
(fig 23). Another, the Japanese Pavilion at Hannover

with Shigeru Ban is in reality only "findable" on the
computer even though here physical modelling gets
close to the final form (fig 24). An originally flat grid of
12cm diameter paper tubes banded together in a 1 metre
grid is pushed up to form a bended amphora form
subsequently stiffened by the cable - undertied timber
ladders and diagonally braced cable formed honeycomb
end walls. In turn these were used to attach the paper
membrane. All components including the "sand box"
foundations were designed to be easily recyclable and so
give an enclosure which specifically "touches both the
'planet' and ground lightly" (fig 25).
Fig 25
The double layer gridshells for the Bundesgartenschau,
Mannheim designed by Frei with Mutschler, Langer,
Happold and Liddell were most courageous enclosures
and extremely inexpensive (fig 26). So inexpensive that
Kikutake followed them with a much larger 'shell' for
the Japanese Silk Road Exhibition in 1988 (fig 27).
Fig 26
'Inversion' of the tension eye for Montreal and the I.L.
(fig 28) led to the development of the compression forms
for the new below-ground naturally light station beneath
the Schlossgarten, Stuttgart with Ingenhoven and Buro
Happold/LAP (fig 29). The inverted forms modelled in
plaster span a grid of 60m x 30m using only a concrete
vault 35cm thick at the crown thickened to 65 cms
around the eye. Indeed each pier supports of the order of
35,OOOkN of loading from the landforms above.
Recent form models for Stuttgart 21 envisage

inexpensive construction techniques using propped
timber grid shell forms (remember the bending free
forms of Mannheim) to create the free vaulted form from
the plasticity of wet reinforced concrete.
Fig 27
26
HANGING STRUCTURES AND DEAD
WEIGHT FORMS
Simple hanging forms are able to exploit the
effectiveness of the long rupture lengths of tension fibres
- especially if they can be stabilised against disturbing
loads by self weight, damping or enclosure. Early
studies for a pagoda roof 1983 previewed the prototype
house at Hooke Park with Richard Burton. The hanging
roundwood spruce thinnings curved down under dead
weight are opposed by A frame compression spans (fig
30).
The elegant Wilkhahn factory with Gestering
architects and Speik und Hinkes engineers for timber
products in its agricultural landscape uses a similar
philosophy but employs square sawn timber (fig 31).
Really this was a focussed study in the use of minimum
embodied energy and of minimum operational energy in
the industrial context - built in the countryside.
Fig 31
Both are predated by the aluminium covered, heavily
insulated auditorium for Mecca with
Gutbrod/Arup/Happold. The 22mm 0 spiral cables
hanging from the central steel portal are cross connected
by double angles that support and distribute the loads of

the insulation and cladding and contain the enclosed air
volume (1968) (fig 32).
Fig 32
More daringly, the wind tunnel at Teddington was used
to investigate the stability of the proposed hanging roof
for covering the Berlin Olympic Stadium. Solid steel
rods supported on tension cables add sufficient weight to
the plexiglass forms (1973) (fig 33).
Fig 33
PRESTRESSED TENSIONED ROOFS
At the heart any discussion of prestressed tensile roofs
are the many studies that contrast tents with a central
support point and radial cutting patterns to those with
double curved saddle and sail surfaces into which eyes,
rings or mushroom supports are introduced. The Riyadh
Heart tent (1986) with its radial spider net of stainless
steel cables supporting painted glass panels onto a central
mast (fig 34) is diametrically different to the 40 x 30m
Berlin humped tent of deformed cotton canvas tied down
at the edges but supported on a series of mushroom
supports (1957) (fig 35). The 55m radial patterned
squares of the Hadj tents by Fasler Khan of S.O.M.
supported on central cable-hung rings of ptfe glass fabric
by Chemfab/Birdair are forerunners to the triple layer
central supported tensile enclosure for Storek Furniture
in Leonberg (2000) (fig 36).
Fig 34
Fig 37
The 36m 0 wave tent for Dance Stage at Koln 1957 is
now also a protected structure for its six exceptionally

slim supporting batten masts, each externally guyed to
separate foundations (fig 38). To save on foundations,
the high points of the waveform for the Biennale at
Venice (1996) use A-frame masts to transfer loads to
foundations shared with the tie down (fig 39).
Fig 35
Fig 38
Fig 36
The first wave form system had 3 parallel spans of 15m
and was patterned by overlapping cotton canvas to create
the enclosure (fig 37) for a flying priest, Pater Schulte.
Multipurpose, it doubled by day as a translucent place of
worship and at night as a covering to his small aircraft!
Fig 39
28
Tension structures offer a huge opportunity for very
longspan lightweight structures. The recently restored
building of the Institut fur LeichteFlachentragwerke (IL)
is now also a listed building (fig 40). Originally this was
the prototype eye structure for the many masted free-
form translucent white pvc enclosure for the German
Pavilion at Montreal (1967). The patterned membrane
was hung underneath the cable net of 12mm galvanised
cables at 500mm centre on springy bretzels (fig 41).
This remarkable cable net construction brought the skills
of Gutbrod architect, Fritz Leonhardt engineer, and Peter
Stromeyer, tent maker and manufacturer together with
Otto to create a longspan building that brought with it a
paradigm shift in cable net technology. This technology
was then transferred to the 120m x 90m double

membrane cable net enclosure on eight masts for the
Sports Centre, King Abdul Aziz University, Jeddah
(1978) (fig 42). Clamped anchorages and chizel point
masts and 'teller'plate membrane supports were
introduced here.
Fig 41
The plan of the multimasted Voliere at Munich (1980) is
reminiscent of Montreal but the doubly-curved snow
supporting stainless steel woven mesh gets its form from
the earlier humped tents at Berlin and Dyce (Aberdeen)
1975 (fig 43). Here computer visualisation enabled
development of the zigzag eye form required to support
Fig 42
the mesh over an existing ash tree. The particular form
for this Voliere was devised to facilitate flight and resting
patterns for the ornithological occupants within a natural
landscape. The architect for Miinchen Tierpark was Jorg
Gribl.
Fig 43
Another protected structure is the Olympic Roof at
Munich (1972), by Behnisch, Otto and Leonhardt.
These structures with their first use of the flying mast laid
the corner stone to the wide-ranging research (SFB64) on
long span structures directed by Leonhardt, Otto and
others in many departments of the University of Stuttgart
(1975-1985) (fig 44)
Fig 44
29
Fig 45
Along the way, the entrance arch tent originally of

polyurethane covered glass fabric stabilising a single
150mm diameter tubular arch was a preview of the
Otto/Tange/Arup proposal for arch supported cable net
forms for the Kuwait Sports City. The design proposed
only a 1.0m diameter steel pipe stabilised by a cable net
roof for the 250m long main Olympic Stadium (fig 45)
The 1961 proposal with Leonhardt for a 1800m x 550m
covering to Bremen Harbour employed high masts and
primary cables supporting a cable net under which was
hung a thin membrane skin (as subsequently executed at
Montreal in 1967). This is probably the alternative
technique for spanning spaces as large as that of the
Dome at Greenwich (1999).
In a way, the 80m x 40m study for a pvc covering at
Sullom Voe, Shetland Islands (1981) which is supported
from a number of masts by arrays of single cables is a
scaled down version of the design for Bremen (fig 46).
DEMOUNTABLE STRUCTURES
Historical studies at the IL on Roman Vela and Islamic
Toldo's resulted in the design and execution of a number
of demountable or semi demountable enclosures. Early
projects at Cannes and Paris led to the demountable
covering over the ruined church at Bad Herschfeld
(1968).
A central mast supports radial primary cables
down which crawler tractors deploy the unfurling pvc
membrane. A large scale study for deployment over the
swimming pool at Regensburg (1972) demonstrates the
importance of obtaining a construction geometry that is
capable of delivering a well resolved geometry -

especially under the extreme load of wind, snow and
snow ponding (fig 47). At Regensburg this was made
possible by having a mast which was sufficiently high.
Fig 47
PNEUMATICS
Fig 46
Studies and calculations in 1958 indicated that a factory
of 3 pneumatic bubbles, made out of aluminium sheet
might be able to enclose spans up to 800m (fig 48).
Many fundamental pneumatic forms were originally
investigated during research using flexible rubber
membranes whose forms were "captured" by plaster
casts (1960) (fig 49).
Fig 48
30
Fig 49
The creation of stable pneumatic enclosures is concerned
with the differences of pressure between the internal and
external medium - air, water, helium etc. At one level,
air supported structures enable economic and safe
enclosure of very large public spaces - City in the Arctic
(1971) (fig 50) - or the project for "58° North". At the
smaller scale for the Academieschiff, Berlin, positive
internal pressures generate the stable screen for
projection of images onto the largely cylindrical internal
surfaces (fig 51) while on an earlier project negative
pressure produces a concave spherical surface for
external projection (fig 52).
Fig 50
Fig 52

The ultimate pneumatic structures are those of man
himself - Bone is made as a liquid filled tension structure
- a baby, a composite pneumatic structure, is gestated
within a protective water sack.
As a concluding thought such illustrations show that if
we are to break open the discussions between architect,
engineer, user and constructor, we need to attend to some
of the 'absolutes of performance'. Reference to the
underlying form of the many natural structures around us
will help address the problem of achieving similar
efficiences - or at least coming closer.
Fig 51