Sporting stars.

The astronomer Johann Kepler was born in Graz. The Kepler Grammar School named after him is one of the biggest in the city with about a thousand pupils, built at the turn of the century in the massive neo-Baroque manner typical of that time. It stands on Keplerstrasse, on the right bank of the river Mur and close to the centre, just north of the Schlossberg (see AR October 1995, pp4-7). This street is an important link to one of the few bridges, and with the growth in traffic it had become unsafe and unhealthy as the main entrance to the school, so there was pressure to recreate the approach in the courtyard behind. This court was very much a backyard, however, its potential having been curtailed by the addition of an ill-placed and inadequately sized sports hall. There was a further difficulty that the school had no adequate main auditorium or Festsaal for large communal events, so in a bid to solve these problems, a competition for replacing the sports hall was held in 1987, and won by Volker Giencke. The building was completed in 1992, though alterations of the old structure, also planned by Giencke, are still going on.

The main idea was to sink the new double sports hall about 10 m into the ground, recreating the outdoor space of the court on top of it at original ground level both as a cour d'honneur for the new approach and as an outdoor sports ground for summer use. With this strategy, Giencke succeeded in rendering a very large volume almost invisible, for only roof lights, service stack, and the wall and canopy of the entrance steps appear above the plane of the tarmac. The original competition scheme proposed a single large hall beneath, with tiers of spectator seating at both ends and changing spaces along one long side. This would have been divided into two sports halls for everyday use, but on ceremonial occasions it would have been usable advantageously as a single space. Fearing high costs and technical difficulties, the clients opted for the less ambitious version built, with two equal-sized halls divided by a central changing area, and spectator galleries still at the outer ends. This allows two rows of concrete columns marching across the centre of the building to carry a main roof structure spanning 18 m, as opposed to the 30 m minimum span needed if the space were clear.

The central tract has two levels, the changing rooms being sandwiched between two open galleries above, with equipment stores and technical rooms below. Entry is from either end. To the north, there is an underground connection to the central stair rising to the entrance hall of the old school building, while to the south the sports hall has its own external entry stair. In plan this follows the skewed alignment of the adjoining building, the only departure from the orthogonal in the whole complex. This produces a tapered vestibule at mid-level which indicates the direction of approach, expanding towards the way out and up. In the court above, an in-situ concrete flank wall defines the dropping stair's edge, and a flamboyant canopy in folded steel draws attention to its position.

The potential claustrophobia of being in an underground building is mitigated to a surprising degree by the generous roof lighting, for there are bands of horizontal glazing three metres wide on either side of each hall, daringly sunk into the plane of the tarmac. In the court above, you walk straight across them, and since not only pedestrians but even vans of up to two and a half tons must be able to traverse them, these roof lights involved advanced glass technology including non-slip treatment to the upper surface. The central changing areas are lit by two large oval roof lights which project up as truncated cones, marking the cross-axis of the complex. Sunlight bounces off the inside of these cones, giving an inspiring quality of light which is intentionally and necessarily different from that of the glazing bands to the sides. The risk of solar overheating from the various roof lights is greatly reduced by the huge thermal inertia of the buried structure, which also renders the winter heating requirements relatively modest. The major environmental servicing requirement was the provision of mechanical ventilation, since natural cross-draughts are not available.

The building depends on modern technology and must have involved a good deal of sophisticated technical work, not least in the provision of waterproof retaining walls whose presence in the finished building is hardly evident. For contextual and pragmatic reasons, the plan needed to be simply orthogonal, a far cry from the same architect's flamboyant botanical glass houses which were under construction nearby at the same time (AR October 1995, pp47-51). Nor is the section particularly telling, apart from its revelation of the roof lights. But there is none the less a sense of architectural drama provoked by the treatment of the roof structure which is also the floor of the court above. Remarkably thin for a 30 by 18l m span, this has an elegant and very three-dimensional structure in which the various layers are on display.

The plane of the floor is defined by a network of rolled steel joists a mere 250 mm deep welded end to end at the intersections. This divides each sports hall into three bays one way and four the other, the subsidiary rectangles being cross braced with the same depth of joist. Within the depth of this steelwork is cast the in-situ concrete deck, leaving only the bottom flanges of steel visible except where the whole member traverses a roof light. Insulation, waterproofing, and a surface for traffic are all added on top, the whole thickness being revealed at the roof lights. The steel structure so far described is only the top member of a great three-dimensional truss, for to its underside is applied a series of down-standing struts, one at each intersection, which project increasingly towards the centre of the span, allowing ties to be added in a bow-shaped arrangement. The ties are of circular section rod welded onto flat plates at the joints, which stack up on a single pin projecting from the bottom of each strut. Diagonal rods of smaller section are applied as a second layer over the main ties to provide bracing. This method of jointing allows 12 ties to intersect in an orderly way, still showing the structural hierarchy in the layering.

The drama of Giencke's structure was more powerful in the raw construction than it is in the finished building, now that both materials are painted white and much superstructure has been added. For the users this is quietly appropriate, for arguably buildings should not be too rhetorical outside their given purpose, and the roof structure is still impressive enough within its more polite dress. For the critic though, the spectacle of buildings in the raw can be more telling, for it reveals the architect's view of materials and the way they are applied in layers, not just pragmatically according to the building process, but conceptually. Particularly interesting in this case was the marriage of welded steel and concrete, the component assembled as opposed to the cast. One striking detail is a webbed steel plate transmitting the load from a column to its concrete slab. Usually the problem of punch-through in this position is avoided by giving the concrete a mushroom head: Giencke evidently wanted to keep it within the thickness of the slab by relying on the superior strength of the steel.

Another intriguing element which was much more evident in the raw construction is the surprisingly thin slab of concrete above the changing rooms, supported on the most minimal of steel posts, and seeming to float. It would have collided with the main concrete columns, but is cut neatly away in a semi-circle to avoid all contact. The use of such heavy material here is a surprise because it is not really a structural element, more a visual space-defining layer or a baffle for the light coming down the conical light-canons. Practically speaking, it could have been a flimsy piece of superstructure, yet it was made part of the primary construction, of the first layer, of the skeleton of the building. In this role, it repeats at smaller and more delicate scale the relationship between steel and cast concrete that occurs also in the primary structure, and so indicates a change of mood and scale, a switch to intimacy for smaller rooms within the large. This provocative element is a reminder that questions of building and construction are no mere technicalities to be disposed of in the most efficient technical way, but potential bearers of subliminal meaning.