a building that sets things on fire -- 10/13/21
Today's selection -- from Humble Pi by Matt Parker. In 2013, the building at 20 Fenchurch Street in London slightly melted a parked car:
"A building doesn't have to fall down to count as an engineering mistake. The building at 20 Fenchurch Street in London was nearing completion in 2013 when a major design flaw became apparent. It was nothing to do with the structural integrity of the building; it was completed in 2014 and is perfectly functioning building to this day, and was sold in 2017 for a record-breaking 1.3 billion pounds. By all measures, it's a successful building. Except, during the summer of 2013, it started setting things on fire.
"The exterior of the building was designed by architect Rafael Viñoly to have a sweeping curve, but this meant that all the reflective glass windows accidentally became a massive concave mirror -- a kind of giant lens in the sky able to focus sunlight on a tiny area. It's not often sunny in London, but when a sun-filled day in summer 2013 lined up with the recently completed windows, a death heat-ray swept across London.
|20 Fenchurch Street|
"Okay, it wasn't that bad. But it was producing temperatures of around 90 degrees C, which was enough to scorch the doormat at a nearby barber's shop. A parked car was a bit melted and someone claimed it burned their lemon (that's not cockney rhyming slang; it was an actual lemon). A local reporter with a flair for the dramatic took the opportunity to fry some eggs by placing a pan in the hotspot.
"There was an easy enough fix, though: a sunshade was attached to the building to block the sun's rays before they could focus on anyone else's lemon. And it's not as if this freak alignment of reflective surfaces could have been predicted in advance. It had never happened to a building before. At least, not since the same thing happened at the Vdara Hotel in Las Vegas in 2010. The curved glass front of the hotel focused sunlight and burned the skin of hotel guests lounging by the pool.
"But can we reasonably expect the architect of 20 Fenchurch Street to have known about a hotel out in Las Vegas? Well, the Vdara hotel was also designed by Rafael Viñoly, so we could probably expect some information flow between the two projects. But, for the record: there are always more factors at play. For all we know, Viñoly was hired specifically because the developers wanted a curved, shiny building.
"Even without a previous building having set something on fire, however, the mathematics of focusing light is very well understood. The shape of a parabola -- that ubiquitous curve from whenever you had to graph any variation on y=x2 at school -- will focus all directly incoming parallel light on to a single focal point. Satellite dishes are parabola-shaped for this exact reason; or rather they are paraboloids -- a kind of 3D parabola.
"If the light is a bit misaligned, a sufficiently parabolic shape can still direct enough of it into a small enough region for it to be noticeable. There is a sculpture in Nottingham, the Sky Mirror, which is a shiny, paraboloid-like shape, and local legend has it that it has been known to set passing pigeons on fire. (Spoiler: it probably hasn't.)"