Petritor Bridge, Braunschweig

The brief of this competition was to design a four lane bridge in such a way that it could at some time in the future be expanded by tracks for a tram line. In addition, the new structure should proclaim the approach to the city over the River Oker, which previously was hardly perceptible.
Our design envisaged the expansion, not in terms of a direct widening of the bridge, but instead separated pedestrians and vehicles on three distinct bridges with the option of using the intermediate space to add two traffic lanes, which would then reduce this intermediate space to just an interstice to admit light. The pedestrian bridges as simple cable-guyed bridges, are subject to tension forces; announce the entry into the city, whereas the motorized traffic bridge, as a reversal of the pedestrian bridges, is subject to compression forces and best reveals its construction when viewed from underneath.
The quality of the design results from the clar-ity of the complementary bridge constructions and from the quality of the clear space below the bridge. It means that a path along the Oker obstructed by the former arched bridge can now be extended. The experience of crossing the river is also heightened as a result of dividing the bridge into three parts.

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Expo, canopies, communal areas

The requirement was for a canopy roof employed as a basic additive form with a striking appearance that, by means of repetition and its strong colouring and in conjunction with the modular service containers, would give the main axes of the EXPO grounds both continuity and identity. The form is determined by the performance required for the short period during which the canopy is used. All the connections in this light minimised structure are bolted. All parts are prefabricated in the works and, along with the foundations, could be taken down after the EXPO without causing any damage and used again elsewhere. The mem-
branes, made of environmentally friendly cotton, are intended to last for just one summer.The principle of the structure is convincingly simple: 4 double curved membrane surfaces on a square plan are spanned between steel sections that are stabilised against wind pressure and suction by means of tension and compression rods. Each canopy covers an area of 7.50 metres x 7.50 metres. The membrane surfaces are fixed linearly to edge beams and are post-tensioned by the process of fixing to the main beam. These beams also serve as gutters to lead rainwater runoff into a down pipe placed within the three-dimensional column.Each canopy can be coupled with further elements by means of bolted metal plates to create either linear or spreading forms. Makrolon coverings that extend beyond the edge beams
ensure that rain cannot enter through the connecting sections.

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Expo canopies North, Hannover

The canopies at the north entrance date back to a design for a bus station in Oldenburg from 1996 that was never implemented. Whereas
the canopies in the 1996 design were connected and thus stabilised each other, the competition for the temporary EXPO shelters called for freestanding roofs measuring 15 x 5 metres. Our freestanding canopies, which are convincingly protected against being lifted by the wind by tension rods and double curved membranes, won first prize in the competition and it was recommended that they
be carried out. However, in integrating them into the urban planning concept of the EXPO, they turned out to be too large. Freestanding canopies covering only one quarter of the area seemed more suitable for the avenues leading to the national pavilions. A second competition therefore followed, which we also won. However, the large canopies were still viewed as a solution to the question of how to accentuate and enhance the north entrance to the EXPO. In contrast to the smaller EXPO canopies, these ones were to be permanently retained as an entrance to the trade fair. This required a structural design that takes snow loads into account, as well as the use of a durable PTFE membrane. As we wanted to retain the existing grid of the forecourt, which is structured in large squares, we adapted the dimensions to this grid and reduced the size of the canopies to 11.30 x 11.30 metres. The canopies were used here both as freestanding elements and linked to provided larger sheltered areas. The clear accentuation of the individual module, even where several canopies are connected, was achieved by changing from a translucent to a transparent surface at the edge profiles, which take the form of horizontal lattice beams.

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