by HEIMO RAHTU, Director of Laboratory, State Institute for Technical Research, Helsinki, Finland
Work on the stadium started in 1934 with the construction of the arena comprising a 400 meter race track, jumping and throwing points and a football field measuring 45 x 65.5 meters. Of the reinforced concrete stands designed to enclose the oval, the grandstands and a part of the bleachers providing for a total of 25,000 spectators were made first. Later, when it was decided that the 1940 Olympic Games were to be held at Helsinki, temporary additional wooden stands were built raising the total seating capacity to 62,000 spectators. Owing to the war the Games could not be held and the wooden stands, intended as a temporary measure to be pulled down after the Games, remained in position for a decade and rotted badly.
Figure 1. Shows supporting concrete frames.
Figure 2. A general view of the south curve of the Stadium.
When it was decided to hold the 1952 Olympic Games at Helsinki these stands were dismantled and replaced by reinforced concrete constructions providing for 50,000 spectators. These permanent stands enclose the arena entirely, and for the purpose of the Games the bleachers were enlarged with wooden constructions so as to give seating capacity for an additional 20,000 spectators.
Since the soil in the area of the stadium varies considerably and is composed of every type ranging from gravel to mud, the supports had to be driven down to bedrock and their upper ends joined with tension bars. The concrete stands are supported by reinforced concrete frames to which the wooden constructions are attached (Figure 1). In making strength calculations, a live load of 300 kg. per sq.m. was taken for the stands of the seated audience and 450 kg. per sq.m. for the standing audience; in addition, some sections were testloaded with soldiers. Materials required for construction of the stadium amounted to: timber - 610 standards; Bufoplates - 90,000; spikes - 31.6 tons. Figure 2 shows the south curve of the stadium from the outside.
On dry days the wooden stands were sprayed with water before the Games started to avert danger of fire, and, in fact, they sustained no damage in the course of the Games. ho final decision has yet been taken to dismantle them.
Figure 3. Diagram of the Swedish HB beam.
Figure 4. Showing the depth of beam at the corner of the frame.
Figure 5. The frames seen in a vertical position.
About two years ago the students of the Institute of Technology started to build dwelling houses for their own use at Otaniemi near Helsinki, and it was decided that an earth-floored sports hall should also be built which might serve as a training centre throughout the year. In view of the training facilities needed for the Olympic Games, construction work was pushed ahead so that the hall-the first of its kind in Finland - could be put into use at the beginning of February 1952.
To keep down costs, the hall is small in area (47 x 89 meters) with only a 160 meter race track, jumping and throwing points, and a stand for 1,500 spectators. The framework consists of prefabricated nailed and glued board frames set 4 meters apart. The structure of these frames is that of the Swedish patented HB-beam (Fig. 3) consisting of the "web" E and flanges P. The former has two courses of 7.8 in. (2.2 cm.) planed boards, each set at 45 degrees to the axis of the beam, but in opposite directions. The flanges are composed of three planed boards glued together with special joints and nailed to the "web". The frames, which have a span of 47 cm. and a "free" depth of 12 cm. at the center, are joined to the concrete foundation. On these frames are 4 x 6 in. (10 x 15 cm.) joists (62 cm. center to center); 2.2 x 3.0 cm. ribs (5 cm. center to center); a 7.5 cm. thick glass wool mat (for thermal insulation); a 7/8 x 5 in. (2.2 x 13 cm.) diagonal sheathing as reinforcement against wind stresses; a 7.5 cm. high opening for ventilation; 7/8 in. (2.2 cm.) tongue and groove sheathing, and double bitumen felt for water insulation.
In order to support these great static stresses, the frame dimensions needed were considerable; the depth of beam at the corner of the frame is 3.36 m., the effective area of cross-section being equal to 1,150 sq. cm. (Fig. 4). The frames were made at three factories producing prefabricated houses, in different parts of Finland, and were transported to Helsinki. On arrival at the building site they were assembled in a horizontal position one by one and nailed with pneumatic hammers. They were then raised vertically (Fig. 5) and transported to their final position by truck along three rails parallel to the hall.
As early as February 1952 sportsmen were able to start training in the hall, and some weeks before the beginning of the Games the student quarters began to be filled with foreign athletes who used the hall and adjoining buildings for eating, training and recreational purposes.
