On February 16, 2021, 3 buildings collapsed after snow accumulation caused by a storm reached 30 centimeters. In total 6 vacant or abandoned structures have failed amid February in Chicago. The structures were nearly 100 years old and have deteriorated over the years so they could not withstand the heavy snow accumulation loads and the freezing temperatures. The failures included mostly roof and wall collapses.
Some of the buildings had bowstring truss roofs, a design frequently used in old infrastructure that features an arched roof that is not supported by columns in its middle part. The span of a bowstring truss is usually large and that makes the structural part vulnerable to increased distributed loads such as that imposed by snow accumulation.
Fortunately, no one was injured since the buildings were not used. However, there has been subsequent damage in some cases. For example, falling debris from a building that collapsed on the 700 block of West 91st Street impacted two vehicles. In another case, the building failure sent rubble to local roads and traffic was halted. Finally, the collapse of a buildings' walls in the 200 block of Prairie Street impacted a local graphic design studio and a banquet hall facility.
According to Matt Beaudet, Chicago's Buildings Commissioner, the fact that the buildings were vacant also contributed to the collapse. Those buildings did not have heat and consequently, the roofs and other structural parts were not heated and the snow did not melt quickly.
Except for the sheer weight that the snow imposes on a structure, there is another mechanism that can lead to failure. As snow is deposited in temperatures below 0°C, it may freeze and expand, putting high stresses on the structural components of a building. Depending on the extent of this phenomenon, severe cracks or even total failures can be triggered.
Authorities warn that as bad weather persists, more failures may occur as many buildings present similar characteristics in Chicago. According to J ohn Tully, the Commissioner of the Department of Streets and Sanitation, more than 70 centimeters of snow have fallen in Chicago in less than 20 days. The initial snowfall has created a layer that densified over the following days and has created a "base" in which more snow layers accumulated.
Officials suggest that, by the time snow melts, building owners must have their roofs inspected and restored or replaced. Moreover, authorities warned people not to shover the roofs in fear of a potential failure that can lead to casualties.
The collapsed buildings will be probably demolished when the conditions are favorable.