Metrodome Roof Fails … Once Again

In the 28 year  history of the Minneapolis Metrodome, it has collapsed or significantly failed five times.  The most recent collapse occurred at around 5:00 AM this morning.  News reports and video of the event reveal that the collapse initiated form tears in the Teflon fabric roof opening up as a result of a heavy accumulation of snow that recently occurred in the Minneapolis area.

According to Dr. Jeff Masters’ WunderBlog about 17 inches of snow fell on December 12 in Minneapolis with a water equivalent of 1.75 inches.  That puts the ground snow load for the 24 hour period at just over 9 psf.  

If you had to shovel 17 inches of snow at that weight it would feel pretty significant but as a roof snow load in Minneapolis the total isn’t all that significant.  Informal reports coming in from industry representatives indicate that wind may have scoured snow from one side of the dome and deposited it on the other.  This type of unbalanced load is expected on structures of this type and ASCE 7 outlines design loading conditions of this nature. 

Investigations are just beginning and the main effort at this time is safety, stabilization and getting the structure back in use.  UPI reports that a four man team was dispatched from Birdair Structures of Buffalo, NY, the original designers of the roof.  In addition, forensic engineers from at least one other major US firm have been contacted to review the condition of the roof.

No formal announcements of the exact cause of the failure have been announced but it is likely that investigators will be looking at a variety of issues or even a combination of factors including drifting, problems with the fabric, improper response to the change in weather (changes in air pressure and heat between the double layered fabric roof are part of the snow resisting system), wind or any number of other possible contributing factors.

Multiple Failures

This is the 5th time the roof has deflated in the history of the facility.  The first happened in 1981, even before the facility was officially opened.  That roof collapse  / deflation was due to snow.  Similar failures also occurred in 1982 and 1983 due to tears from snow events.  The forth roof failure was due to wind in April of 1986.  During today’s event, stadium workers attempted to remove snow from the roof for a period of time but efforts were halted over safety concerns.

Not the Only One

The Metrodome is not the only inflatible fabric roof known to have failed over the years.   BC Place stadium in Vancouver failed and deflated in 2007 due in what was reported to be over-inflation due to human error in conjunction with a defective section of fabric.  As a young engineer working for HLM in Iowa in 1975, I recall watching news video of a roof failure at the University of Northern Iowa  UNI-Dome as a result of high winds tearing one of the fabric panels.  The roof deflated into a concave position and began to fill with water from heavy rains.  I’ll never foget the image as repreentatives used shotguns to blow holes in the roof for drainage to make sure the roof cables did not become overstressed.

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