JEC COMPOSITES MAGAZINE - Issue #69 - November/December 2011 - 16

building & construction
stiffness with steel unsuitable for such an application. to the public. Concretely, the structure was assembled rather quickly. The tubes were shipped from the Top Glass pultrusion factory in Italy with the help of their French distributor, Solutions Composites. The assembly required: 5 people working for one day for the ground assembly; a half-day to lift the structure and plant the stakes, 2 days with 5 people for the triangulation and another half-day to stretch the coated fabric made by Ferrari Textiles over the structure (see Fig.2).

Fig. 2: some of the main construction steps

Assembly
To start, a primary grid was made by laying the tubes flat in a regular square lattice on the ground and then raising it with the help of two cranes in order to bend it into shape and attach it to 150 anchor points (stakes planted in the ground). The structure was easily shaped due to a combination of two factors: the rotating connections provided by the cross clamps and the elasticity of the composite tubes. This technology thus made it possible to reduce the radii of curvature down to 3 metres. With the anchor points taking up most of the load, it was essential that the stakes be correctly planted in the ground. For security reasons, their number was largely oversized. Afterwards, another series of tubes in a third direction was added to the inside of the structure to ensure its rigidity. Due to this triangulation, the structure acts as a shell and its rigidity is multiplied by 20. Note that the shape of the structure is accurate to a centimetre. Finally, the structure was covered with a stretched PVC-coated fabric. In addition to the students and researchers, the Viry company (manufacturer of metal structures, at the request of the T.E.S.S. engineering consultants) was in charge of the assembly; French laws being particularly strict in regards to collapsible structures open

performed by a public laboratory in France). Finally in June 2011, after assembly, the project was crowned with success after welcoming the debates and a dance floor for three days as planned.

Technical know-how
It was mainly the Navier laboratories – thanks to the efforts of Ing. Lionel du Peloux (project manager), Prof. Jean-François Caron and Dr. Olivier Bavarel – who carried out the modelling and design calculations for the structure. Their experience – almost unique in France and quite rare in the world – in the joined fields of construction and composite materials was essential. This project is in fact a world first for a structure of this size in operation. Only two prototypes (the size of the larger one corresponded to the smallest span of the structure for Solidays) were built by Navier laboratory; proof of the expert mastery of the computer simulations. Numerous skills were implemented for: (1) finding

jec composites magazine / No69 November - December 2011
The tubes, pultruded from glass fibre (70% by weight) and polyester resin, were pushed to about 30% of their capacity, given the permanent load induced by the curvature. The UD fabric was naturally selected given the main stress on the tubes. This achievement is an example of matching between material and structure, since the flexibility of the GFRP is here to serve the structural rigidity. It leaves the frontal confrontation in terms of

the best shape-structure compromise by analysing the geometry in interaction with the structure (lattice and dynamic relaxation algorithm); (2) dimensioning (needed for the buckling and modal analysis as well as the wind resistance tests required for obtaining a building permit for areas open to the public, ); (3) the assembly simulation (rigging plan for lifting and shaping of the gridshell); (4) postprocessing (3D integral modelling for creating the production drawings).

Generosity and costs
All the players united together for a technical challenge and a good cause. Solidarité Sida was able to acquire this collapsible structure for the modest sum of about €45,000, or €150 per m2. This would not have been possible without the help of the Ecole des Ponts ParisTech, through tutoring and temporary work contracts, and by the generous prices offered by each of the manufacturers: Offered time of engineers or technicians, low material prices and even donations (Fabric from Ferrari, glass fibre from OCV and resin from DSM for example). In “reality”, the price would have been higher, while at the same time very low as compared to other technologies or materials; composite profiles being very cost-effective in relation to their characteristics. A large improvement margin is possible for rationalization and optimization. Here the Forum is a bespoke structure.

JEC COMPOSITES MAGAZINE - Issue #69 - November/December 2011

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #69 - November/December 2011