Addendum 2003:
Structural and architectural refinement of Eduardo Torroja's Zarzuela Grandstand, Madrid.

Because of space limitations in the published book, Figure 17.2 was included without an explanation of the logic behind it. This internet version makes it possible to restore the draft text. The following sketches are based on those which appeared in Torroja (1958b).

The sketch above shows the basic functional requirements adopted by Torroja, though decisions have already been made on how the required spaces, surfaces, and sight-lines could be arranged and the load-bearing structure interwoven. The structure is envisaged as a frame which will be repeated at regular intervals along the length of the grandstand.

Torroja decided to resist the anticlockwise overturning moment of the canopy by means of a slender tie. The weight of the canopy, plus the force in the tie, would be transmitted to the foundation by the central column DCB which would therefore need to be fairly massive. The tie would exert an upward force on the roof of the betting hall. This would make it easier to cantilever the betting hall roof from the central support and make the right-hand wall of the betting hall (looking onto the paddock) non-load-bearing. The wall of the low-level gallery (below A) looking out to the race course could also be made non-load-bearing by cantilevering the stands above it. The need for load-bearing vertical members beneath the staff access gangway could be eliminated by cantilevering the gangway from the relatively massive central column.

This logic resulted in a stiff triangular structure ACB which would experience significant stress due to shrinkage and thermal movement. Tapering the central support towards its base would reduce stiffness at that point, reducing such movement stresses. The presence of the tie meant there was no need to have a strong moment-resisting junction at D, where the canopy met the central support, so the support could be tapered towards point D. Torroja's last refinement was to add an architectural flourish by giving the canopy an upward curve and making the ceilings beneath the tribune and above the betting hall in the form of cylindrical shells. These presumably span longitudinally from frame to frame.

Torroja decided to use shells for the canopy, and the determination of their form provides another interesting case-study in design. For a complete explanation, please refer to Torroja (1958b).

Return to Chapter 17, The art in structural design, text.

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