NTPC Gazebo Tensile Structure

On a site the size of a power station, a covered outdoor space earns its keep — a place for people to assemble at shift change, wait for buses, or get out of the sun during the working day. The brief for a structure like this is to shelter a sizeable group, stand up to an exposed site, and — usefully on an otherwise grey campus — give people an easy landmark to head for.

Ekra Decor’s scope covered the canopy end to end: survey, 3D form-finding and structural design, fabrication of the galvanised steel frame and the membrane, and installation and tensioning on site, over about 1,200 m² and roughly three months.

A sail canopy is an anticlastic, or saddle, surface: the membrane rises to high masts on two opposite corners and is pulled down to anchors on the other two, so it curves one way along one axis and the opposite way along the other. That double curvature is what makes a thin fabric roof rigid — it pre-stresses the membrane so it cannot flap, invert or balloon in the wind.

On an open field the wind is unobstructed from every direction, so the governing loads are large and come at the structure from all sides. Ekra Decor form-finds the geometry so the pre-stress stays balanced, designs the masts and edge cables to carry the peak forces, works the steel to IS 800, and takes wind and seismic actions to the applicable Indian codes. The mast foundations are sized for compression and overturning and the anchor foundations for uplift.

The bold red membrane is a deliberate choice — a coated architectural fabric holds its colour under years of UV, so the canopy stays a clear landmark rather than fading to grey.

The masts, edge assemblies and fittings are fabricated and hot-dip galvanised in the workshop, and the sail is cut to its computer-generated pattern, edge-reinforced and cabled, so it arrives as a finished piece. The foundations are cast on site.

Erection is a staged lift: the masts go up and are guyed plumb, the membrane is spread on the ground, then it is raised to the mast heads and tensioned corner by corner until the saddle shape pulls up true. On an open site with a longer programme, the sequence had room to be done carefully rather than rushed.

NTPC gained a large, weatherproof covered space that people can gather under and navigate to easily — a genuine piece of campus infrastructure with a distinctive shape. Once tensioned, a sail canopy is close to maintenance-free apart from cleaning and a periodic check of the cables and mast connections.

Ekra Decor builds gazebo and sail canopies and larger tensile roofs for industrial clients. See more finished work on the projects page.