Giant triangular panels overlap to surround this American football stadium in Atlanta by architecture firm HOK, which has a roof that "opens and closes like a camera aperture".

The Mercedes-Benz Stadium, which opened in August 2017, provides a large-scale entertainment venue for the city and a new home for the Atlanta Falcons.
It replaces the Georgia Dome, located on a site beside, where the National Football League (NFL) team played for 25 years before the building was demolished in November 2017.

A key feature of the new stadium is its mechanised roof, which allows the pitch to be opened to the elements for passive cooling, or closed to create a watertight seal in poor weather.
"Inspired by the oculus in the ancient Roman Pantheon, the stadium's retractable roof is the centrepiece," said a statement from HOK.
Eight triangular "petals" ? formed from inflated pillows of ethylene tetrafluoroethylene (ETFE) plastic ? move backward and forward to narrow or widen the opening.
Due to their arrangement, the petals appear to rotate as they retract in unison. But in fact each moves in a straight line, on powered rollers along a set of tracks. "The tracks allow the roof to open and close like a camera aperture," HOK said.

ETFE also covers sections of the faceted external steel structure, which fold over one another to form an enclosure around seating for 71,000 spectators. The huge panels are shaped to look like wings, as a reference to th...