OK, now for the big reveal for the architectural travel quiz from our last post. There are many structural concerns with this roof structure entirely constructed of glass- including all horizontal surfaces and even the beams- but the one we were looking at particularly was the phenomenon of structural deflection. All horizontal spanning structural systems deflect- it is not possible to have zero deflection. In this case deflection at the mid-span of the assembly from melting snow and ice (remember this is Montreal, and glass has an R-value of roughly R-1) would set in place a cascading negative feedback loop: melting snow and ice follows gravity accumulating at the low point at mid span, adding additional loading, leading to more deflection, causing additional melting snow and ice to accumulate at mid span, adding additional loading,…etc. and on and on until the system reaches allowable stress capacity and then potential failure. Not pretty. The solution: pre-camber the system with a slight positive crown providing a concave upper surface that would shed water to the sides. Now you know!…