Pneumatic formworks for concrete and ice shells

International Conference on Textile Composites and Inflatable Structures
B. Kröplin and E. Oñate, (Eds)
 CIMNE, Barcelona, 2009
Institute for Structural Engineering
Vienna University of Technology
Karlsplatz 13, 1040 Vienna, Austria
e-mail: [email protected], web page:
e-mail: [email protected], web page:
Key words: Textile Composites, Inflatable Structures, Innovative Design.
Summary. This document presents a construction method for shell structures which is
currently under development at the Institute for Structural Engineering at Vienna University
of Technology. With this method concrete as well as ice shells can be created by transforming
a plane plate into a shell by means of a pneumatic formwork.
Shells are natural, logical and functional load carrying systems. If a space has to be
surrounded by a minimal area of surface, the shell is the logical optimum. Additionally, for
the load transfer of a uniformly distributed load, the shell structure is the perfect choice
because mainly normal forces appear in the cross section1.
Although shell structures possess this excellent load carrying system and make a great
visual impact, only few shells have been built in the last decades. The main problem is the
difficult, time-consuming and expensive production. Traditionally, shells are produced by
means of complex formwork. Creating such formwork increases the construction time and
affords additional material which cannot be reused after the shell has been completed.
In order to achieve a more economic production of shell structures many new production
methods have been developed. Beside the possibility of using formwork structures for more
than one concrete step2 or using precast concrete elements, pneumatic formworks can be used.
Frei Otto describes different applications of pneumatic formworks (air-houses) in his
work3. One possibility to build thin concrete shells is to spray-coat an inflated rubber-like
membrane with a layer of concrete. Another procedure consists in inflating a membrane
covered with freshly mixed concrete.
According another construction method4,5 it is possible to build a doubly curved shell from
a flat circular plate made of concrete and a soft styrofoam component between segments
which enables the plate to be deformed. A tendon is placed along the edge of the plate. The
erection becomes possible by stressing the tendon so that the circular plate slowly lifts up
with the help of a pneumatic formwork to give the needed vertical impulse and outweigh the
dead load. The photographs in Figure 1 demonstrate the shaping process of a reinforced
Sonja Dallinger, Johann Kollegger
concrete shell with a diameter of 13m which was built by the Institute for Structural
Engineering at Vienna University of Technology in June 2005.
Figure 1: Transforming a plate into a shell
This construction method is not only suitable for concrete shells but also for ice shells9. In
December 2005 the scientists of the Institute for Structural Engineering at Vienna University
of Technology constructed an ice dome with a diameter of 13m originating from one flat
Building ice shells by means of pneumatic formworks is also exercised by Tsutomu
Kokawa6, who created several ice shells in Japan. His method consists of building up a 3dimensional formwork by inflating a 2-dimensional membrane bag covered with ropes
anchored to the snow-ice foundation. Then this inflated membrane is covered with a snow-ice
sherbet layer.
At the Institute for Structural Engineering at Vienna University of Technology a new
construction method for building shells is under development. With this new method, a
doubly curved shell is built from a flat plate. The method consists of transforming a plate into
a shell by means of a pneumatic formwork.
One characteristic of doubly curved shells is that the surface is not developable which
means that the surface can not be flattened onto a plane without distortion. If one tries
flattening the hemispherical half of an orange peel into a plane surface, wedge-shaped gaps
will open (see Figure 2). This new construction method makes use of this very concept.
Therefore the shape of the plane plate, which is going to be transformed into a shell, has to be
chosen according to the final shape of the shell.
Figure 2: Shell structure inspired by nature
Sonja Dallinger, Johann Kollegger
Moreover, for this construction method the hemispherical shell is divided into matching
plane elements approaching the real shape of the shell. In the strict sense, the shell structure is
fragmented into a polyhedron (see Figure 2).
The shell consists of individual plane elements which are placed on a planar working
surface and are assembled by means of tendons. There are tendons in radial direction holding
the elements together as well as tendons in circumference direction which carry the hoop
forces after the removal of the pneumatic formwork.
In order to transform the plate into a shell a pneumatic formwork is used. While air is
inflating the pneumatic formwork, the plane plate is transformed into a shell. After the
transformation process the interfaces are filled with grouting material and post-tensioning can
be applied.
For the pneumatic formwork a membrane made of PVC is used. To obtain the desired
shape of the formwork parts of this PVC membrane have to be glued together with
appropriate PVC glue.
To demonstrate this new construction method, timber models were created in order to find
the most suitable process to accomplish the transformation process to achieve the
transformation operation of a flat plate into a shell successfully. Moreover, these timber
models were used for experiments with different shapes of the pneumatic formwork. The
shapes of formworks ranged form pneumatic formwork which only lifted up the centre of the
shell to membranes which were shaped identically to the final shape of the shell.
3.1 Ice as construction material
Ice is a fascinating and natural material. Most people associate ice with images of glaciers,
icebergs, frozen waterfalls or lakes, icicles or ice crystals.
As a construction material, ice is suitable for temporary structures, but the low mechanical
properties compared to other construction material have to be considered. Because of the low
mechanical properties and the strong creep behaviour, ice is normally used as a decorative
material on a supporting carrying structure or on constructions with small material stresses in
the serviceability limit state. One example for an application is the yearly rebuilt ice hotel in
Jukkasjärvi, Sweden, where blocks of ice are placed on curved profiled sheetings.
Figure 3: Ice shell with a height of 2m, winter 2008/09
Sonja Dallinger, Johann Kollegger
Using ice as a carrying construction material for the first time, cupolas are load bearing
systems which are especially suitable because only very small stresses appear in the structure.
Igloos and Japanese ice buildings for the storage of vegetables and sake can be given as
examples for cupolas made of ice.
3.2 Ice Shell Experiment
In December and January 2008/09 this construction method was tested on two ice shells in
Obergurgl, Tyrol. Initially 2 circular ice plates with a diameter of 6m, respectively 13m were
built, and were then cut in 96 individual elements, held together by means of tendons. Due to
the inflating of the pneumatic formwork, the ice plate with the diameter of
6m became a hemisphere with a diameter of 4m and a height of 2m (Figure 3). Figure 4
shows part of the shaping process of the ice shell with the original diameter of 13m.
Figure 4: Shaping process of an ice shell, winter 2008/09
Currently we are planning the construction of a concrete shell consisting of 96 precast
concrete elements with a thickness of 5cm and a diameter of the circular plate of 13m.
Therefore the dome will have a diameter of 8,3m and a height of 4,1m
[1] D.P. Billington, Thin Shell Concrete Structures, McGraw-Hill Book Company, 1965.
[2] E. Ramm and E. Schunck, editors, Heinz Isler: Schalen. vdf Hochschulverlag AG an der
ETH Zürich, 2002.
[3] F. Otto, Pneu and bone, Institute for Lightweight Structures, University of Stuttgart,
[4] S. Krispel and J. Kollegger, Bau einer Stahlbetonschale ohne Schalung. Beton – Zement
2006, 2:24-29.
[5] J. Kollegger, C. Preisinger and M. Kaulfus, Ice shells for temporary event architecture,
Structural Engineering International 2004, 14:274-276
[6] T. Kokawa, Field Study of a 30m Span Ice Dome, Journal of IASS Vol.43 (2002), 93-100