In its final report on the collapse of the Dallas Cowboy’s practice facility, the National Institute of Standards and Technology recommends owners of other fabric-covered, tubular-steel-framed structures have their buildings evaluated. Some universities already have; of these, at least two have found the structures fail to meet established codes.
NIST concluded the Cowboy’s building designed and built by Summit Structures of Allentown, Pa., failed to withstand wind loads that were substantially less than required by design standards. The report indicates Summit designed the Cowboy’s facility as a fully enclosed structure, but the NIST team calculated internal wind pressure due to vents and multiple doors and found it consistent with a partially enclosed structure. NIST also did not rely on the fabric to provide lateral bracing, which was part of the original design documents. The federal agency included the effects of localized bending, while Summit had not. The “Final Report on the Collapse of the Dallas Cowboys Indoor Practice Facility, May 2, 2009” is available online. http://www.bfrl.nist.gov/investigations/pubs/
NISTIR7661_January%202010.pdf. Summit says the Cowboys practice facility was a one-of-a-kind structure. The firm is currently conducting research to evaluate the facility to determine what happened and why. “The important thing in our view is to understand precisely what caused the damage to the training facility,” says Nathan Stobbe, Summit president and CEO. “We will not be commenting further due to pending litigation,” he adds. Twelve people were injured when the structure collapsed.
Currently, the team is practicing outdoors on existing fields and at the Cowboys stadium. The team has not rebuilt the structure but is looking at its options, says Rich Dalrymple, a Cowboys spokesman.
The Cowboys facility was designed as a series of identical, tubular-steel frames with a tensioned fabric covering, says NIST. Assumptions and approaches used in the design of the building resulted in significant differences between the original calculated wind-load and structural demands and those derived by NIST.
Computer models of the building done by the Gaithersburg, Md.-based NIST recreated various wind conditions. NIST also worked with the National Oceanic and Atmospheric Administration National Severe Storms Laboratory to estimate winds at the time of the Cowboys’ training facility collapse. They determined wind speeds ranged from 55 mph to 65 mph, well below the national standard of 90 mph. NIST is aiding industry groups to revise standards and building codes based on its findings.
Meanwhile, NIST recommends owners of other fabric-covered, steel-framed structures, most with barrel-vault roofs, have their buildings evaluated. The assessments should look for whether or not the fabric provides lateral bracing, whether the structure is partially or totally enclosed and whether failure of one or a few frame members may lead to a partial or total collapse of the structure.
Summit has built multiple athletic facilities, including ones at Texas A&M University in College Station and the University of Texas at Austin. UT Austin had its Summit building inspected soon after construction in June 2009. CI Engineering and S2 Specialty Structures, divisions of JCI Holding, Las Vegas, conducted a visual observation and verified the structure was constructed according to the approved drawings and calculations.
HaynesWhaley Associates, Houston, completed a third-party evaluation of Texas A&M’s football practice and track-and-field facilities. Jason Cook, chief communications officer for the university, said the McFerrin Athletic Center had been inspected and found it could withstand 65-mph winds, not the campus standard of 90-mph winds.
The university is reinforcing the structure. A smaller section now meets code. The school is awaiting results of a wind-tunnel test on a larger portion of the building before making any adjustments. Texas A&M also has instituted a safety protocol: It does not use the facility during severe weather.
Chavez-Grieves Consulting Engineers, Albuquerque, which completed a report for the University of New Mexico, Albuquerque, about its Summit indoor practice facility, found that wind pressure could enter the steel-and-fabric building through openings in the structure and not escape, overstressing the training facility. In addition, several members and connections do not meet minimum strength requirements of the 2003 edition of the model International Building Code, published by the International Code Council.
According to the Chavez-Grieves report, Summit designed an enclosed building. The independent engineer says louvers, roll-up doors and other openings created a partially enclosed building. Currently, the university only uses the facility when the louvers and doors are closed and the winds stay below 60 mph.
The Chavez-Grieves report indicates 57% overstressing at the University of New Mexico facility. This is not as severe as the 500% overstressing NIST found in the Cowboys’ structure. Also, the university’s design does not rely on the fabric roof to provide bracing, as did the Dallas building.
Scott Heatly, a partner with Chavez-Grieves, suggests the University of New Mexico could make simple modifications to the existing structure to help ensure it behaves as an enclosed building. These changes would include permanently closing doors and changing louvers so they do not allow air inside. The firm recommends the university consult with Summit, which is the engineer-of-record, on specific changes.
In a written statement, Stobbe said, “Summit Structures has worked in the past and continues to work closely with University of New Mexico to ensure that they have a safe structure.”
John Quinn Pate, vice president, architecture, with Molzen-Corbin & Associates, the local architect for the facility, in a written statement released by the school, said, “Summit Structures has fully cooperated with the investigation” and will perform needed minor modifications “as soon as is practical.”
