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A steel-cable net and PTFE and ETFE membrane structure holds up under heavy wind and snow loads.
The Sun Island Resort is one of China’s favorite vacation spots. Because the city of Harbin (where Sun Island Resort is situated) is at a high latitude, it is cooler than the rest of the country in the summer and hence an ideal location for vacationers looking to escape the heat and humidity of southern China.
A sun motif is evident throughout the area, including at this eye-catching shade structure on a riverside plaza at the Sun Island Resort. Like a radiating sun, this symmetrical canopy is a cablenet structure with a combination PTFE and ETFE membrane cladding.
“To make the project aesthetically pleasing,” says Claire Fu, regional sales manager for Covertex Membranes (Shanghai) Co. Ltd., “the cables are laid out radially to match the original steel frame that the membrane cladding is attached to.” The gently curved dome is made with clear (ETFE) and translucent (PTFE) ringed sections.
Although there is much efficiency in a symmetrical plan, the challenge in constructing the structure comes as the radial cables converge to the center. “The distance between cables is reasonable at the outer edge of the roof,” Fu says, “but the cables are too close [to construct] around the center. Therefore, we divided the ETFE portions into three annular sections to allow a more reasonable arrangement.” Some cables that start at the outer ring stop at one of the inner rings, transferring their load laterally to some cables that reach all the way to the innermost ring, thereby maintaining a separation of space that is more easily constructed.
Supporting cables are attached to the underside of the ETFE with membrane cable pockets and tensioned with the shallow curvature. Fu says that great care was needed when welding the cable pockets to avoid having a pocket line up with a major seam of the membrane and risk higher stresses on joints.
Covertex designed the steel cable net and membrane sufficiently robust to hold up under heavy wind and snow loads. Covertex’s choice for both PTFE and ETFE are 250µm thick membranes from Asahi Glass Co. Ltd.
The resulting shade structure has proven durable, and is attractive to vacationers, providing clear sunlight through the ETFE roof as people gather under the roof to relax and enjoy the strong blue skies and warming sun of northern China.
Bruce N. Wright, AIA, is a Minneapolis-based writer, editor and educator.