Metrodome Roof CollapseDecember 12, 2010

Steven C. Maki, PE

Director of Facilities & Engineering

MSFC

Metrodome Roof Operation & Care

Monitoring 24/7 basis

Experienced staff

Annual inspection and repair

Periodic roof surveys as recommended by Birdair

Birdair Roof Surveys

Conducted in 2003, 2007, & 2010

2010 survey indicated fabric in good condition

Metrodome Snow/Wind Incidences

3 snow collapses early 1980s with one panel replacement

1 wind incident 1986

No collapse or panel replacement in 27 years

Snow Procedures

Preheat interior to 80-85 deg F air temperature

Hot air (150F) is directed between outer and inner to melt snow

Internal pressure increased by 50%

Manual snow removal if necessary

This procedure worked for 27 years

December 10, 2010

Winter storm warning with projected heavy snow

Typical snow procedure is begun

December 11, 2010

Overnight heavy snow/strong winds

Leo Pidde calls for manual snow removal 10:15am

Steve Maki on roof at 11am

Pressure is raised higher late morning

7 personnel on roof by 1pm

December 11, 2010continued

Significant snow accumulations on roof/strong winds

Inverted triangular panels (tips) North/West sides

Decreasing temperatures

Conditions deteriorate; manual snow removal not effective

December 11, 2010continued

Snow removal crew down at 5:30 pm unsafe conditions

Steve Maki/Leo Pidde pull drain plugs

All personnel off roof 6pm with plans to return next day 8am

Conference call made to postpone game

December 12, 2010

Roof collapse at 5:03am

(play video) This is precursor to FOX video

Staff arrives to begin mitigation

Conference call with MN Vikings/NFL to cancel game.

Initial Damage from Collapse

Panel 104 (triangle) ruptures from snow slide

Panels 43 & 44 (diamonds) rupture sequentially from snow loads as tons of snow and ice funnel to roof center

Panel 15 ruptures spontaneously about 5:30 pm on 12/15

Panel 35 ruptures after attempting to induce drainage 12/20

Other Collateral Damage

Frozen pipes and broken seats

Minor structural damage to wind girt system

Damaged roof vents, lightning rods, inner liner

Other misc damage

12/12/2010 HHH Metrodome

View towards panel 76

12/12/2010 Internal View of Ruptured Diamonds

Approx. 9am view from Section 136 area

12/12/2010 Panel No. 104

View from interior

12/12/2010 View of Roof from Panel No. 104

Roof Stabilization EffortsDecember 12-26, 2010

Significant snow loads/stresses on roof

Safety is no. 1 priority

Low outside temperatures hamper progress

Birdair, Geiger, WPM contacted and to site

Arrangements made with local firms to assist

Roof Stabilization Effortscontinued

Initial focus is on repair

Birdair determines panel 104 is severely damaged and can not be temporarily repaired 12/14

MN Vikings game on 12/20 is switched to U of MN TCF Bank Stadium

Roof Stabilization Effortscontinued

Ruptured panels are curtained or temporarily covered

Panel 15 ruptures suddenly 12/15

Work is stopped, work plan is reviewed for safety

Geiger designs roof restraint system using jersey barriers Birdair/Sowles installs system to ballast for wind loads

Roof Stabilization Effortscontinued

Inner temperatures rise after curtain/covering

Panel drain plugs are pulled

Laser survey is used by WPM to acertain loading/damage

Roof structure is stabilized by Christmas

Roof AssessmentDec. 26, 2010-Jan. 14,2011

Warm weather with rain

Photo survey of roof inner liner conducted; diamond panel liner removed (Geiger recommendation)

WPM recommends fabric samples to be tested

Strong winds New Years Eve tears panel 104 curtain

Sampling starts; cold/snow/winds slow efforts

Roof AssessmentDec. 26, 2010-Jan. 14,2011

Seating reduction curtain removed (Geiger recommendation)

Birdair notes panel no. 100 in bad condition

MSFC requests Birdair perform roof survey

Roof AssessmentJan. 15, 2011 +

Birdair roof inspectors arrive on site Jan. 18

Weather conditions hamper survey

Test results both bad and good

TT requests certain samples

Birdair reports roof panels in poor shape, tears/holes in triangles; survey completed 2/3

Summary of Results to Date

5 panels ruptured with significant damage to remaining roof and liner

Testing results are good and bad

Birdair survey indicates roof in poor condition

Sliding snow/ice have degraded fabric; wind/wicking are negative effects

Public Safety Concerns

No support for partial restoration of the roof

Significant concern if partial restoration, weakened fabric could fail during event causing panic

Conclusions/Recommendations

Replace external roof fabric (cables are ok)

Replace inner liner above seating area (triangles/rectangles)

Save liner cost on diamonds by replacing with acoustical batt + increase heat transfer for snow melting

Conclusions/Recommendationscontinued

New roof clamping required; remainder of roof system is good

Minor collateral damage cost wise

Remove seating reduction curtain

Syracuse experience provides positive results