When we won the competition "LRT Station Rathaus Süd, Bochum" in 1995 we only had a faint idea of how long the integration of two LRT stations into a grown urban structure would actually take. In retrospect, the underground works appear like intensive in-vivo surgery with comprehensive function-preserving measures.
The client brief for the works comprised
- the underground LRT Station Rathaus Süd (Line U21) including distributing levels, with connection to an existing Metro Line (U35) and several department stores. - the LRT Station Rathaus (Line 306) at the Town Hall (Rathaus) side on a slope, including tunnel entrance and crossing the head space of Station Rathaus Süd by means of an underground bridge. -restructuring of the road spaces and re-development of Rathausplatz (Willy-Brandt-Platz), the plaza in front of the historic Town Hall from the 1920s. - development of a leitmotif for the future boulevard from Westring to the Main Station, predominantly above the Metro route.
In 1995, the situation in Bochum’s city centre was similar to that in many Ruhrgebiet cities. Wide, desolate traffic-debased road spaces, fragmentary inner-city pedestrian areas with 1970s charms, a visible withdrawal of qualified retailers and 'Centro Oberhausen' as a horror image in close pursuit.
In addition, a commenced underground LRT routing without an integrated operating concept. Presently, Bochum’s LRT trains travel to Herne, Gelsenkirchen, the Ruhr University and form a clocked system with DB AG (German Rail plc) stations, albeit with different track gauges and access heights.
The planning brief for the Rathausplatz area provided for a complex underground hub with giant-sized distributing levels, underground accesses to three Metro stations, department stores, shop-floor spaces and platforms with differing height for the variety of rolling stock. An instrument with colossal proportions. This situation was not in line with our ideas, hence, we exchanged – contrary to the client brief – falling gradients, demolished distributing levels and relocated one station (Line 306) to the Town Hall side, above-ground and as an ordinary tram stop.
This move came as a surprise to the competition initiator and resulted in a dramatic simplification of traffic relations. Thus, free spaces for design and construction were created from which especially the Station Rathaus Süd (U21) benefited and which permitted adoption of a uniform design principle to surfaces (of the future boulevard).
Station Rathaus Süd (U21), a folded ceiling and daylight
The disentanglement of complex underground interrelations created some latitude, in particular for the station space volume. While the tunnel sections were built with mining techniques, an open construction was envisaged for the stations, with considerable interferences into urban spaces.
A cover-type method of construction was suggested in order to reduce impairments as much as possible, i.e. initially the station ceiling was installed on lateral bored piles and subsequently the station’s underground lining is completed – independent from above-ground uses.
Rather than backfilling the volume above the cover of the station, we used the space for ceiling design and construction. The outcome is a large-volume, support-less station space that is borne by an R.C. folded-plate ceiling. The innovative approach: Daylight and glass
Moreover, 13 prismatic glass bodies penetrate both ceiling and road space and thus permit conveying daylight into the Metro station. While the prismatic glass bodies make the location of the station visually experienceable at the surface in urban space.
The effectiveness of the daylight apertures was verified in advance in Lichtlabor Bartenbach, Innsbruck, and in the heliostat of Messrs. ERCO, Lüdenscheid, in 1995.
The glass bodies in the road space are made of pre-crashed glass which allows for a crystalline imagery and natural light scattering. The elements have also a vandalism-retarding effect since they visually appear already destroyed.
In 1998, we installed crashed glass prototypes as ventilation structures in the pedestrian area in order to test their effects. The three-layered glass elements had a symmetrical configuration and the centre pane was pre-crashed. The 13 prisms above the station were made with a similar technology.
Subjective sensations, visual reference to daylight, changes due to time of day, position of the sun, clouding over – all this is tangible beside the spaciousness of the column-less space and provides for a new well-being.
Two more structures penetrate the station space: A glazed sloping elevator from train to road level and a glazed bridge of Line 306 that crosses the head space.
The train level (ca. 14 m below road elevation) is characterised by the station’s longitudinal walls with a length of ca. 110 m. The rough-faced concrete walls illustrate the installation process of the cover-type construction, i.e. the initially cast folded-plate ceiling and subsequently cast-concrete tunnel walls. Concreting apertures were provided in the top formwork sections to permit seamless concrete placing. The circular, steel concrete placing funnels have remained visible as structural design elements, likewise the anchor crowns of the rear anchorage.
At the eyelevel of waiting passengers, the longitudinal wall is made of backlit, coursed glass. Some rear sides of the coursed glass plates of float glass, white glass und parsol-green glass were pre-crashed. The crash patterns can be seen through the glass on the front side. The glass wall also serves sound absorption, in particular of deeper frequencies through slots between the glass packages and cavities at the rear. Together with the bed of broken stones it reduces the reverberation times in the large-volume space. The target was not creation of an anechoic space but a reverberation time clearly below that in a church space. The station’s quality features are continued to the surface.
The surface, road spaces at Rathausplatz
The above-ground structures are made of steel and glass. The steel constructions are assembled from sharp-edged steel sheets, uniformly coated with iron glimmer. Fixtures and fittings are of stainless steel and contrast with dark, large-sized stone paving that provide the basis for the future boulevard. Embedded is the historic Rathausplatz of bright and heavy 1 x 1m granite slabs. We have almost doubled the surface area of this plaza. Rathausplatz is a political square and shall be largely free from urban furniture and commercial activities and provide the historic Town Hall an adequate appearance again. Also the 30-metre wide boulevard is classically and clearly zoned: wide strolling areas along shops on either side, rows of brought-forward plane trees with illumination, at the centre integrated areas for temporary market stalls, a centre lane for deliveries and bus lines. The above-ground, surface design is an offer, a working overlay in a gruff cityscape with numerous ruptures and isolated qualities that should be manifestly further developed by the residents and business community.