051207-MPLS-006Metrodome-crop  Metrodome_Typical_Yarn_Tear_WPM Metrodome_Fabric_Panel_104_MSFC

The Metrodome was built in 1980 in Minneapolis, Minnesota and is home to the Minnesota Vikings, United FC, and the Golden Gophers.[a] The building will be demolished this year.[a] Hubert H. Humphrey Metrodome has been no stranger to failures involving its inflatable roof structure. “In fact, the December 12, 2010 roof collapse marks the fifth time in the Metrodome’s history the domed roof has failed. Three of the four previous roof collapses, in 1981, 1982, and 1983, have been attributed to snow, while the fourth failure, in 1986, was due to strong winds.” [b] A severe winter storm moved into the Minneapolis region on Saturday, December 11. The storm dumped more than seventeen inches of snow in the Minneapolis area. [b] Anticipating the approaching storm, maintenance crews at the Metrodome took preventative measures by heating the internal temperature of the dome to around 80 degrees while pumping warm air into the cavity separating the inner and outer layers of the roof structure.[c]

At approximately 5:03 A.M. on Sunday December 12, 2010, a sliding mass of snow and ice broke free and slid down the roof, slicing a gaping hole in fabric panel number 104, seen in Figure 3. Although the internal pressurization system of the Metrodome was designed to compensate for minor tears, a hole of this magnitude resulted in the depressurization of the space and ultimately the collapse of the dome. Upon impact with roof equipment, the sliding mass caused tears in fabric panel numbers 43 and 44, directly over midfield.[b]

“On December 12th, a series of firms were contacted to assess the damage that had been done to the Metrodome roof structure.According to the Metropolitan Sports Facilities Commission, it was unanimously accepted that the deflation of the dome was caused by sliding snow and ice impacting the ring beam along the perimeter of the roof structure, rupturing the roof fabric at panel number 104. The tear in this panel caused the loss of internal building pressure resulting in the deflation of the air supported fabric.”[b] Birdair Inc., reported numerous minor tears and abrasions in the fabric. Their examination revealed the loss of the Polytetrafluoroethylene (PTFE) protective coating on the fabric membrane and the formation of cavities at the intersection of glass yarns within the inner fabric. If these depressions reached the depth of the inner woven glass yarns they would have been exposed to the elements, and the infiltration of moisture would ultimately weaken them. The ring beam and columns, and cables were inspected and deemed useable for future use. [b]