Structure: Dallas Cowboys Practice Facility
Location: Irving, Texas
Year of Construction: 2003
Year of Failure: 2009
Type of Failure: Structural
Structural Engineer: Enrique Tabak
Construction Firm: Summit Structures LLC
The Dallas Cowboys indoor practice facility collapsed on May 9, 2009 during a severe thunderstorm. The facility, designed and constructed in 2003, was a fabric-covered tubular steel frame structure. In 2008, it was upgraded with additional purlins, new roof covering, and reinforcements for a few members. About 70 people were in the practice facility upon collapse and 12 of them were injured.
To better understand the collapse, it was estimated that at the time of collapse the wind speed were 55 to 65 mph predominantly in the westerly direction. The wind speed was well below the specified 90 mph design wind speed by ASCE Standards for the time and location of collapse. But the wind loads used for the design were different from the calculated wind loads based on the provisions of ASCE Standards, “producing significantly lower design demands by a factor of up to 3.9” [a]. Another factor contributing to the collapse was that the frame member capacities in the design were larger than calculated capacities based on AISC specifications “by a factor of up to 3.0” [a].
The remaining two factors discovered were not miscalculations of construction standards, but just details that were not considered in the design. The joints at the knees of the frames produced large bending moments and shear forces in the chords of the frame. These were not considered in the design, “increasing demand-capacity ratios by a factor of up to 2.3” [a]. Also, the upgrades in 2008 only affected the “compressive capacity of selected members; the most critical members were not reinforced” [a].
The design assumed that the tension exterior fabric was going to provide lateral bracing for the frame. But what happens when the fabric is ripped by flying debris during a storm? The design also assumed that the building was “enclosed” for the sake of calculating internal wind pressure. But the door openings around the building and vents would classify the structure as “partially enclosed”. A rip in the fabric from debris could also result in a higher internal pressure. [a]
Likely Collapse Sequence: [a]
- Buckling of inner chord in straight section of roof resulting in formation of a kink in the frame
- Failures at the east and west knees allowed frame to sway eastward
- Compressive failure of east keystone web led to tensile fracture of the inner and outer keystone chords at the ridge
- Spread of individual frame failures in similar patterns, through load redistribution and loss of lateral bracing, resulted in total collapse of facility
Recommendations by NIST: [a]
- Concern for the use of fabric covering to provide lateral bracing for structural frames
- Determination of the appropriate enclosure classification in the calculation of internal pressures for design wind loads
- The ability of the structural system, including bracing, to maintain overall structural integrity