Cold bent Arches of laminated Glass

Ulrich Breuninger, Martin Stumpf

The bow and arrow are known to us all as sports equipment and medieval weapons. The principle of such a bow consists of a strut which, by nsertion of a shortened string between its ends, is subject to compression and bending and is itself considerably deformed through bending. The overall system of the bow, consisting of the bow strut and the bow string, is in a prestressed status because of this.
This principle can also be transferred to two-dimensional elements, for example of glass. Through the support of a rectangular, flat glass pane on the two shorter, opposite edges and two-dimensional loading, a bending of the pane is forced. If the two support sides of the pane in this status are
connected through at least two straight round steel bars, then these round steel bars form chords to
the arches of the pane. After removal of the external load from the pane, the round steel bars are subjected to tensile stress and the pane to compression and bending. A prestressed glass element results.

The advantages of this glass element can be summarized in the following points:
- High load-bearing capacity of the glass in arched shape, with two-dimensionally distributed loads (dead weight, snow and wind), since the stresses are taken up, for the major part, through normal forces and not through bending.
- With a given span width, the thickness of the glass pane can be reduced and thus the costs.
- Favourable and cost-reduced manufacture of the glass elements, since flat panes are employed as planned, which are forced into the shape of an arch in cold condition.
- Simple installation of the glass elements, since the elements are bent in the works and are equipped with the round steel bars. On the construction site, they can simply be placed
without further expenditure.
- The unlimited array of elements in arched longitudinal and arched perpendicular direction is possible.
These prestressed glass elements were developed by Glasbau Maier a glass construction company in Heidenheim and ourselves. In the present article, the development of the glass elements is
represented for application as overhead glazing. A decisive use of this development was in the loggia in Aalen-Wasseralfingen and the central bus station in Heidenheim. Approval on an individual basis was required for both projects.

Loggia in Aalen-Wasseralfingen, Germany
The loggia in Wasseralfingen was
constructed in the course of the
restructuring of the area centre. It is
located in Stefansplatz, parallel to
the parish church of St. Stefanus and
diagonally opposite the city hall.
The city park is located behind the
loggia. The square was recessed
from the street space by steps. A
free-standing pavilion was desired,
which, on the one hand defines a
recreation space for versatile use,
on the other hand, by means of
maximum transparency, should
restrict the view of the church as
little as possible (Fig. 1).

7 Arched glasses with a span of
5.4 m and a width of 2 m were installed. Their curved pitch is 30
cm. Both fully prestressed panes
have a thickness of 12 mm and a PVB intermediate layer with 1.9 mm thickness. Every glass element is forced into the arched shape with two stainless round steel bars of diameter 14 mm.

Central Bus Station in Heidenheim, Germany

The new central bus station in Heidenheim is located perpendicular to the street and has three parallel bus
lanes (Fig. 2). All three bus lanes and three adjacent buildings are provided with a roof of 7 m height. The
roof has 61.5 m length and 29 m width corresponding to the bus lanes.

31 arched glass elements, with 3.9 m span and 2 m width, were installed in the 3 glazed fields. Their curved pitch is 22 cm. Both fully prestressed panes have a thickness of 10 mm and a PVB intermediate layer with 1.9 mm thickness. Every glass element is
forced into the arched shape with two stainless round steel bars of diameter 12 mm.

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The Authors