Fabric Art Sails at 731 Lexington Ave in Manhattan.

Fabric Art Sails at 731 Lexington Ave



The ‘Fabric Art Sails’ is a design study that would occupy the existing courtyard of the Bloomberg Building on 731 Lexington Avenue in New York City. The artistic composition of four double-curved ‘sails’ is pre-stressed and anchored to stainless steel brackets at the curtain wall side surrounding the elliptical courtyard of the building, forming ‘dancing couples’ in the sky that will be lit at night and can also serve as advertisement surfaces.

The sails are made of a synthetic, translucent membrane of polytetrafluoroethylene (PTFE), a synthetic fabric (brand names Teflon/Tenara) that is fiber-reinforced, does not creep and can be pre-stressed, while maintaining water-tightness and durability over time.

Thornton Tomasetti was the specialty skin fabric engineer of the design study, helping to determine the best sail shapes based on architectural sketches and models during various iteration loops, so that the existing support brackets are not overstressed due to anchoring cable forces and adjacent sails do not touch each other during strong wind loading. To make the project possible, two thin counterbalancing cables were introduced to reduce weak axis bending of the support brackets. All max/min cable forces and membrane warp/fill stresses were determined, based on a 10-year design life for the project, as well as first natural sail frequencies and their exact membrane areas. Slope lines were determined to avoid ponding due to rain water.

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The use of lightweight membrane structures can enhance design, budget and building performance – but only if their attributes are considered early in the design process. With the ability to span great distances, these systems are used in dynamic and sculptural forms and can be quickly modified to meet changing weather-related or programmatic needs by adjusting shading, thermal and aesthetic characteristics. Our façade engineering consultants are experts in the application of ETFE, fabric and tensioned membranes, from concept evaluation to integration of these lightweight systems into building skin designs.