The mechanical strength of this natural Venturi effect wind extractor had to be reinforced during strong winds. Its aeraulic efficiency was validated in 2013 in real conditions.

In partnership with Ademe, the Eiffel Aerodynamic Laboratory (CSTB), LEU Réunion (Laboratoire d’écologie urbaine) and JG Conseil (headed by Jacques Gandemer) have developed a high-performance static extractor to ensure natural and hygienic ventilation of collective residences. The extractor is composed of a guyed metal tube and a metal weather vane at the top which culminates three meters above the ridge. The aeraulic efficiency of the process was validated in a real situation in 2013 with fifteen weather vanes deployed for the natural ventilation of about a hundred dwellings in a collective residence. However, following the passage of cyclone Bejisa in January 2014 on Reunion Island, a certain number of these weather vanes were damaged. " Assembled by small 3 mm thick folded and riveted aluminium angles, these weather vanes have progressively "unravelled" under the action of the strong wind to self-destruct by separating from the elements or components that make them up., says Jacques Gandemer. No damage appeared on the chimney columns or at the base."The proven aerodynamic design is not in question, but the windvane has been modified into a mechanically reinforced version, known as "cyclonic", with the participation of Jean-Marc Bouchut of the BET 12M steel structure in the studies. Following this LEU Réunion filed and obtained an Atex qualifying the high wind performance of the new model.

A conclusive reinforcement

The actions undertaken concern the following points: Reinforcement of various elements (bolting of the aluminium sheet assemblies, multi-point bolting and continuous folding at the tail angles, reinforcement of the lower and upper plates, stiffening of the leading edges with a stainless steel bar, reinforcement of the anti-tearing safety ring of the mobile part, reinforcement of the anchorage of the attachment eyelets for the shrouds, etc.); balancing by suspension; lowering of the centre of gravity of the mobile part; systematic elimination of water stagnation points; drainage of risk areas; reduction of the effects of lift and improvement of the operation in rotation; etc. After analysis and discussion with the team of technicians and experts and the tests, which, above 130 km/h, showed the flexibility of the windvane shaft, new improvements were adopted, including the sleeving of the hollow shaft with a solid steel tube, a lowering of the centre of gravity and the installation of handling rings to facilitate implementation.

François Ploye

Source : Les Cahiers Techniques du Bâtiment

Date de parution : Décembre 2018

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