Textile River Over Participants’ Street In Expo Zaragoza 2008

Performance, Seville, Spain

A 400m-long structure designed for the World Expo Zaragoza 2008 site (Saragossa, Spain) turned out to be a leading attraction at the event. It consisted of 13 pieces that twisted and turned at a height of 17m. The idea was based on water, to represent Zaragoza’s river, that flowed overhead and cast its shade onto the main street.

With the aim of providing shade for the participants’ street, a partial roof was built along the 500m of its length so no element would interfere with the views of the street from the pavilions or obstruct the route where activities would take place.

Several limitiations complicated the project. Anchorages could not be placed on the existing buildings or in the public walkways. The structural and architectural solutions had to be completely stable with respect to horizontal loads because only vertical reactions could be supported on the pavilions.

A modular design helped to solve all the problems and modules of 32m x 24m were proposed, with a central part of these comprised of 14m x 32m of textile. To prevent the repetition from being monotonous, they were mounted so they curved like a meandering river.

The main challenge was to achieve a support for the textile surfaces capable of functioning with vertical reactions exclusively. Tubular metallic arches would be stabilized by tendons on the upper part of the arches and by cables below them. An arch is considered to be stable when it cannot be opened by an outward horizontal thrust, and here the arch could not be expanded because of the lower cable. It was also prevented from closing inward because it could not be stretched, due to the upper tendon. The lower cable worked with pushing loads and the upper tendons worked when pulling loads were acting. A succession of 14 arches set at 32m intervals left 13 spaces in which modular roofs could be drawn taut. The covers were designed to be seen and used as a continuous canopy over the street. The tensile fabric structures used were surfaces of toric geometry (the inner part of a doughnut), 14m wide and 32m long, as mentioned above. The pieces used are limited by two vertical planes and two curves of circular projection.

To support the curved fabric borders, steel cable curved edges were placed at the exterior, which were the fundamentals of the entire structure. Between the self-stressed arches and the border cables, or “bolt ropes,” a highly resistant fabric was extended and it defined the overall design. Another series of cables and rods were fundamental for the functioning of the assembly, but are barely visible. On the right, the arches were connected to the roof of the pavilion buildings; on the left, they were connected to the top of 17m masts. These masts were of variable cross section and pinned at their base to easily absorb the twisting and bending movements typical of these types of supports for light structures. Masts and arches were rigidly connected, more to facilitate construction than to transmit bending loads, as these were only vertical. Horizontal stability of the masts was guaranteed by diagonal cables for the longitudinal direction, which prevented them from turning over, and with the arches in a transverse direction.