11 Working drawing, section through arch intersection, scale approx. i:io. Galvanized steel flats, rigidly connecting the incoming non-continuous ribs, pass through the continuous 6oo x 160 mm rib; 1300 x 150 x 10 mm flats top and bottom, 350 x 150 x 10 mm in the centre, with bolts and steel dowels to transfer the loads. The bolts are screwed in at two levels: into the steel flat within the timber itself and then with a washer at the surface of the timber member.

8, right | Working drawing, section through joint in connecting member, scale approx. i:io. Visible here is the angled position of the steel flats, bolts and steel dowels which needs to be taken into account.

approx. 1.20 m high, placed in front of the walls which are set back into the building. This avoids height limitations within the hall, despite the low springing of the arch. Daylight enters via the gable ends and, therefore, the roof is not interrupted by openings.

The entire construction utilizes glulam members. The basic pattern for the roof is formed by arches arranged at an angle of approx. 290 so that they intersect with each other to form the diamond-like pattern. As in cross-section the roof spans 40 m and forms an arc with a radius of 25 m and a rise of 10 m, the 600 x 160 mm arches take on an elliptical form and must span 45.65 m.The arches are straight on plan and stand vertically - not perpendicular to the plane of the arch like in "Zollbau". This leads to an actual increase in the size of the "diamonds" as they approach the supports, although they remain identical on plan - again, a deviation from "Zollbau". However, it leads to changes in cross-section over the length of the arch which ensue from the geometry and can only be sensibly solved by means of CAD. On the whole though, it follows the principle of "Zollbau" in that it is a membrane in which any load at any point causes stresses and deformations in every loadbearing member. This effect allows for savings in material even when regarding partial distributed loadings, such as snow or wind.

The problem of the arches intersecting in the same plane was solved by using two 1300 x 150 x 10 mm steel flats at each joint, one top, one bottom, which are fitted into slots across the non-continuous ribs and join these together by passing right through the continuous rib. In this way, the forces perpendicular to the members and the couple of forces resulting from the bending moment are accommodated. Every non-continuous rib is connected by means of one 14 mm diameter bolt and twelve 16 mm diameter steel dowels, and the continuous rib with one 14 mm diameter bolt and four 16 mm diameter steel dowels. In addition, a 350 x 150 x 10 mm flat is provided in the centre to transfer the relatively low shear force by means of bearing stresses. However, owing to the differing cross-sections of the arch members, this detail does require accurately positioned holes for the bolts and slots for the steel flats, as well as corresponding wedge-shaped washers. Nevertheless, this form of joint does make it easy to slide in the non-continuous ribs from the side during erection.

The continuous ribs are in each case rigidly jointed adjacent the ridge by means of vertical plates slotted into the members, and steel dowels. A joint at the ridge itself would have been too complicated because the arches already intersect at this point. The system of the directions of the joints was changed during fabrication, in contrast to the initial concept. Concern had been expressed regarding the, of course, unequal flexibility in the joints; it was felt that this might have an adverse effect on the overall stiffness of the structure. Therefore, the direction of the joints was varied evenly over the whole area of the "diamonds", thus cancelling out any unequal flexibility in the system. Erection was possible without the use of scaffolding. Starting at one gable arch, the continuous ribs were erected, held in place by guys and then the non-continuous ribs were erected bay by bay. The connections were assembled from elevating platforms.

The "Bramac-Domico" system was chosen for the roof construction. It consists of steel sheets top and bottom, intermediate components and a 120 mm layer of thermal insulation. This system is strong enough to cope with the largest span met with on this roof - 5.50 m - without additional support. However, this system cannot accommodate thrusts and hence cannot brace the entire building.Therefore, it was necessary to brace the diamond pattern by means of steel ties along the length of the hall at every second row of diamonds. The gable ends, as "half-diamonds", are already triangulated and are, therefore, stiff in themselves. All timber has been left untreated, thus clearly emphasizing the diamond pattern.

9 | Arch with projecting steel flat connectors at the intersections.

10 | A completed joint.

n | The hall during the topping-out ceremony in 1994.

12 | The roofing to the tennis hall employs the "Bramac-Domico" system.

1 | Ground floor plan, scale i:8oo. i Entrance hall. 2 Cubicles. 3 Cafe. 4 Therapy pools. 5 Swimming pool. 6 Outdoor pool.

1 | Ground floor plan, scale i:8oo. i Entrance hall. 2 Cubicles. 3 Cafe. 4 Therapy pools. 5 Swimming pool. 6 Outdoor pool.

2 | Section and elevations, scale 1:400.

3 [ View from sunbathing area. The three-legged rein forced concrete roof supports are clearly visible.
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