Königstein Fortress stands on the cliff of the same name, 240 metres above the River Elbe and the town of Königstein, in Saxon Switzerland. The fortress area is a protected historic monument. There was a need for a lift from the present-day car parking level to the case-mate and the level of the battlements. By minimising all the building elements, the design treats the fortress monument with the greatest possible respect, without yielding any of its independence. On the contrary, the special construction is new and was a challenge in
terms of both design and execution. The technology is for the most part left visible, so that the visitor can see how the lift functions. The ‘hoistway’ consists of only 2 supporting tubes
that, along the entire height, serve to hold the guiding tracks for the lift cabin and the counter-weight as well as the pulley in the ‘shaft head’.
The tubes, set 5 metres in front of the fortress wall, are fixed by means of compression and tension rods anchored in the rock and connecting bridges at the stops. The utmost performance in terms of steel construction lies in the minimal vertical tolerances of up to 10 mm. From the glassed-in lift cabin, visitors have a view of the cliffs at the side and the landscape.
Reflection-free glass and the minimized structure increase the degree of transparency. A roofed entrance area offers protection against the weather and small-scale erosion of the fortress cliff. The first station is at the level of the emplacements, where the technology of an historic transport lift can still be seen today. An opening in the fortress wall is reactivated as an access point for the new lift. The existing historic technology is integrated into the design of the museum laid out in the interior. The upper station of the lift serves the fortress plateau at the level of the battlements.
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.
Even after the end of the world‘s fair, the openair theatre has continued to be a focal point on the plaza. The diagonal positioning of the performing area asked for a round form that contrasts with the dominant angular forms on the plaza and also exploits the existing slope in the site. During the EXPO, performances by music and theatre groups from all around the world were held here daily. The 1900-square-metre roof offered audiences and performers protection from sun and rain. The spaces for performing artists (dressing rooms and toilets) are provided underneath the stage in containers inserted there.
The stage can be used in two directions: diagonal towards the open central area of the plaza, or in the opposite direction towards the roofed, stepped area used for seating. While the membrane between the inner and outer rings diffuses the light, the stage is emphasised through the greater amount of light entering through inclined glazing that slopes to the north. For performances that require artificial lighting effects, the glass area can be blacked out by means of aluminium louvres. A ventilation joint between both roof areas extracts the heat produced by the lighting system or the entry of sunlight by means of natural thermal forces. The roof membrane stretches between a compression ring with a diameter of 49 metres that is inclined from north to south, and a 16-metrediameter tension ring that slopes towards the north and rests above the performance area. Tensioning the membrane (PTFE) creates a form that provides good acoustic conditions. The sheet steel gutter at the lower end of the membrane is separated from the compression tube by brackets that also carry cable conduits and the outer stage lighting. The trusses that carry the lighting and sound equipment above the stage consist entirely of standard, commercially available elements used in stage construction.
This commission resulted from the competition for the EXPO and trade fair railway station, which also included the Skywalk as the connection to the EXPO grounds. In our competition entry the Skywalk was, as called for in the competition, directly connected to the upper level of the railway station.The 340-metre-long Skywalk, a pedestrian bridge with spans of up to 28 metres elevated over an existing road and its approach roads, was intended to provide a symbol at the entrance to the EXPO. The competition called for a structure that was naturally ventilated and lit, made economical use of resources, and could be erected at a low cost in just five winter months between trade fair dates. In addition, the structure and façades were not to restrict or impede the view. Working from these requirements, we developed a concept that contrasted with tubular pedestrian bridges in which only the level at which pedestrians walk is used structurally and the tubular shell has to span the entire width of the bridge. Our concept is instead a double tube in which diagonal rods enable the pedestrian level as the lower chord to function together with the roof structure as the upper chord in a full-height structure. This concept meant that the façade is only spanned between these two levels and the thickness of the curved steel sections could be kept to just 40 mm. This allows a view through the structure that, even from the perspective of the pedestrian, is hardly obstructed at all. The glazed, weather-protected space has air intake openings at the foot of the façade and outlet openings in the roof that ensure natural ventilation without build-up of heat. The space is not heated, but the walking level is protected against frost. The building is divided into three fire compartments with two fire escape staircases located between the sections. 2
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.
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.
The design of a new service centre was intended to bring with it an improvement to the heterogeneous and rather disordered industrial and commercial district. An existing elongated DATEV building that dominates the immediate surroundings became the starting point of the organisational concept: four long blocks and a tower building that not only form an ordered structure of buildings but also create a public urban space. In functional terms, all these slabs are connected with each other on three levels (basement, ground floor, and first floor). The connections consist of corridors, vertical cores, and bridges, forming a continuous network. The construction costs for the multi-storey blocks were kept low by using an economical precast concrete building system, while for the single-storey buildings a light and flexible composite steel system was employed. A filigree sun protection and maintenance envelope provides the formal connection between the different types of construction as well as helping to reduce heat loads and glare in the workspaces. Omitting suspended ceilings made it possible to exploit the thermal storage capacity of the building, thus reducing both construction costs and operation costs. During the day the concrete structure absorbs heat loads, while at night this heat is removed by cooling through ventilation. In the second construction phase this concept was further refined.
The important north–south axis on the EXPO grounds crosses the EXPO Plaza and needed a terminating feature at its northern end. At the same time, this location forms a virtual junction with the avenue running east-west in the western part of the EXPO grounds and therefore demanded a widely visible accent. The only planned function was a building for a café, and even here there were lengthy difficulties in finding someone to take on this venture. As a consequence, at the beginningof 2000, shortly before the opening of the EXPO, the implementation of the Plaza Café was still a matter of doubt. As a result of this situation, the design was shaped by the requirements of the time framework and the location: a building visible from afar that, if the decision to go ahead with it was made, could be erected in the shortest of periods and at a low cost. By placing the main areas on three terraced levels, a building height was achieved that, in urban planning terms, closes the space of the Plaza. The concept for the construction was developed by using the distance between the trees forming the two avenues as a construction grid. Originally, so that the building would terminate the axis and the square even more effectively, a hovering balloon the size of the crown of a tree was to be fixed above each column. This idea was later abandoned in favour of a tall stele that is illuminated at night. The café is entirely a steel structure and was erected in just 75 days. As the contracts with the people who run the business were only signed shortly after the start of building, the café had to be adapted during the construction
period to meet the new requirements of a restaurant with a full kitchen and three separate dining spaces. The restaurant, along with the terraces, can seat up to 400 people. The terraces are protected from rain by a glass roof.
The intention was that, after the world‘s fair,this EXPO pavilion would be disassembled, transported, and reerected as a church and community centre in Liepaja, Latvia. This led to the development of a modular timber system with a jointing technique that simplifies and facilitates the processes of erecting and disassembling the building. On the EXPO site, the main entrance to the pavilion is oriented towards the circulation axis of the national pavilions. The entrance is emphasised by the verticality of a bell tower that does not stand alone but was integrated in the rectangular plan of the pavilion. The pavilion, designed as a kit of parts, combines all functions in a flexible way under a single roof. The exhibition space encloses a calm courtyard with a form intended to recall the cloisters of old monasteries. On one side, it rises in steps to create a sacred space that formed the top attraction of the exhibition. This sacred space, later to become the church in Liepaja, reaches the same height as the bell tower and with it forms the main façade looking towards the EXPO grounds. The courtyard and cloister areas offers an area of calm and reflection in contrast to the bustling surroundings of the world fair. The intentionwas that on special occasions the courtyard would be opened up along the entire side facing towards the EXPO, that is, towards the axis leading to the national pavilions. On such occasions, the large screens made of wooden louvres could be swung upward to form a kind of roof canopy. The entire building is made up of 3.60-metrelong elements; larger spans are handled using inclined supports and trusses, giving the large exhibition hall a certain sense of scale and a sacred character. Glass elements alternating with closed panels, both measuring 120 x 360 centimetres,were intended to form a lively façade suited to the particular concept of the exhibition as well as the subsequent function in Liepaja.
To find an innovative concept and appealing appearance for the new antenna reception mast in Leipzig that is over 50 metres high, an invited entry competition was set up, from which our design emerged as the winner. The tower, which has three platforms at heights of 39, 45, and 50 metres, serves to position and operate wave control and surveillance antennas. It supports the largest platform at a height of 39 metres, on a three-chord mast in a Vierendeel form. One of the three chords continues as the main chord to the tip of the mast and supports the two other platforms. This creates the structurally clear tapering silhouette of the tower. From bottom to top, the distance between the struts connecting the three chords
of the mast increases, in response to their loading, from 1.25 to 5.0 metres. Seen in perspective from below, this creates an optical illusion, making the tower seem lower than it actually is. The entire structure is designed in such a way that all parts are dimensioned for the standard galvanising baths and fortransport by road. The chords are welded together with their struts in the works and then bolted together on site to form the sections of the Vierendeel structure, which are then hoisted in into the final position by crane. As the final part of this procedure, a prefabricated 5-metre-high telescoping antenna is placed on the highest platform, which increases the overall height of the mast and the effect it makes.