Two new reports on the fatal stage collapse reveal both structural and planning flaws that contributed to the tragedy. AP Photo/Darron Cummings
Two investigations into last summer’s fatal stage collapse at the Indiana State Fair reveal a structure with inadequate lateral load resistance and questionable decision making as a severe storm approached.
April 24, 2012—The stage that collapsed in strong winds at the Indiana State Fair on August 13, 2011, killing seven people and injuring 58, failed because the lateral load resisting system—guy lines, ratchet straps, aluminum fin plates, and concrete Jersey barriers—was “grossly inadequate,” according to a detailed investigative report titled Indiana State Fair Collapse Incident and released by the New York City-based engineering firm Thornton Tomasetti earlier this month. (See “Investigation.”)
The report, coupled with a report prepared by Witt Associates—a Washington, D.C.-based public safety and crisis management consulting firm—following an investigation into emergency management decision making at the fair, paints a tragic picture of miscommunication, muddled decision making, and a stage almost certain to collapse in the strong storm National Weather Service (NWS) forecasters began warning about nearly two hours earlier.
“I’m going to be frank. These reports are really hard for me to read,” Fair Commission Chairman Andre Lacy said at an April 12 press conference, releasing the reports to the public. “We’ve got a lot to learn and reflect on,” he added.
The 107 ft by 57 ft aluminum lattice stage assembled from multiple prefabricated trusses was the property of Mid-America Sound Corporation, erected on a reinforced-concrete slab. The structure weighed 25,300 lb, and was supporting about 44,300 lb of entertainment equipment at the time of the collapse.
The lateral load system comprised 14 3/8 in. diameter guy lines attached to 10 Jersey barriers, each weighing 4,100 to 4,300 lb, via synthetic webbing ratchet straps to induce prestress tension. Most of the guy lines were attached to the structure by 1in. thick aluminum fin plates on the columns. Those plates also housed the chain hoists used to raise and lower the superstructure.
“Calculations and in-situ physical testing determined the Jersey barrier ballast system had grossly inadequate capacity to resist both the minimum code-specified wind speed (68 miles per hour) and the actual wind speed that was present at the time of the failure (approximately 59 miles per hour),” the Thornton Tomasetti report states.
Thornton Tomasetti’s calculations indicate that the structure could resist winds of 25 mph from the north, 28 mph from the northwest, and 43 mph from the west. The gusts that collapsed the structure are estimated to have been 57 to 59 mph.
“Had the structure been designed by a competent professional, permitted as such, reviewed as such, it’s likely we would have had a different outcome,” said Scott Nacheman, M.Sc. Eng., AIA, a Thornton Tomasetti vice president based in the firm’s Chicago office, at a press conference announcing the findings.
Inadequate ballast and guy wires are a common problem for temporary structures designed without input from engineers, says William B. Gorlin, P.E., S.E., SECB, M.ASCE, the vice president of the Entertainment Division of the McLaren Engineering Group, in West Nyack, New York. Gorlin has engineered live performance stages for three Super Bowls and many nationally touring entertainers, including Lady Gaga and the Black Eyed Peas.
“The amount of ballast and the size of cables are misunderstood by people casually doing these things without engineering,” Gorlin says. “We have had situations where people have said, ‘Oh, I have a stage roof, and this is how we use it, this is the amount of ballast we use.’ And when you run the numbers, the ballast is often insufficient, or the cable tensions are greater than those folks typically would guess,” Gorlin says.
The failure sequence at the Indiana State Fair began when high winds buffeted the west side of the structure and one of the Jersey barriers moved and then failed. The three remaining barriers on the west side of the structure moved and failed, one after another, until the structure collapsed as a result of second order effects.
The Thornton Tomasetti investigation found that had the Jersey barriers not failed, the guy wires and ratchet straps were still inadequate to handle the lateral loads of the wind gusts. The investigation further found that had the Jersey barriers and the guy wires been sufficient, the fin plates attached to the columns were also inadequate to handle the lateral loads and would have failed.
“We do feel that there’s a need for some enhancement of design practices for these structures,” Nacheman said at the press conference. “Currently the vast majority of the industry standards within the entertainment industry for these types of structures really doesn’t conform to best practices of structural engineering.”
Indiana law excludes temporary structures from building codes, which contain a wind speed provision of 68 mph. That’s nearly identical to guidance in American National Standards Institute (ANSI) E1.21, developed by PLASA, an international membership group for the event, entertainment, and installation industries that establishes minimum design and performance standards for temporary, ground-supported overhead structures. According to Gorlin, a stage erected for less than six weeks and built to E1.21 standards “would need to be able to withstand 67.5 mph 3-second wind gusts.”
Gorlin says it is common for building codes to exclude temporary structures. “The rationale for that is the demands for a temporary structure are not as great as they are for a permanent structure. So to make them be designed the same as a permanent structure can be onerous,” Gorlin says.
“You can think of a spectrum. The example I like to make is a ladder you put up on the side of your house to clear your gutters. It’s sort of a temporary thing. Should you comply with building codes for that? Probably not. If the winds start kicking up, you’re going to use good wisdom and get down. Can you get down in five minutes? Sure,” Gorlin says. “Keep expanding that to a scaffold. At some point, there are requirements. Scaffolds are an example of something that does have strict requirements.”
The use of good judgment by a trained staff is a significant bonus for temporary structures, Gorlin explains. A trained staff can take actions on a temporary structure in advance of a severe storm to lessen the impacts. “You can’t really do that with a building.”
The decision making at the Indiana State Fair was investigated by Witt Associates. The report by the firm titled An Independent Assessment of the August 13, 2011, Indiana State Fair Collapse Incident states: “It was not clear who or what organization was responsible for public safety during the 2011 Indiana State Fair. As a result there was ambiguity of authority regarding who was in charge of public safety leading up to the collapse.”
Although fair officials had been warned by the NWS at 7 PM and again at 8 PM to expect a severe storm at the fairgrounds between 9 and 9:30 PM, public safety was not the focus of an 8 PM meeting between fair officials and performers. It was decided to begin the concert at 8:50 PM and to interrupt it in the event of a severe storm.
Captain Brad Weaver of the Indiana State Police expressed public safety concerns about the threat of severe weather to the fair’s executive director, Cindy Hoye, sometime after that meeting and the two discussed evacuation plans. At 8:39 PM the NWS issued a severe weather warning, but neither Weaver nor Hoye received that information.
At 8:45 PM Bob Richards, a local radio personality, announced that the concert would begin soon, mentioning the threat of a storm, and directing people to seek shelter in that event.
“This was not the message Captain Weaver expected, and he confronted Director Hoye. They headed up the stage to announce an immediate evacuation. The structure collapsed before they got the chance to make the announcement,” the Witt report states.
Gorlin says it is important to have a clear, written list of responsibilities for events using temporary structures. He recommends that his clients have a clear list of actions to take based on weather forecasts or observed wind conditions from an anemometer on the structure.
“You should demonstrate that you can actually accomplish the things you say you are going to be able to accomplish,” Gorlin says. “So if you were to say ‘we need to be able to dismantle this structure in five minutes’ but it’s something that’s going to take you three hours, that’s not practical.
“You should know who is responsible for what. Who makes the decision to clear the area? That should be defined ahead of time in writing. And it should be based on a qualified person. Someone who has adequate knowledge of the system to know what they are dealing with,” Gorlin says. “You should not be arguing who gets to make that decision when you feel the wind blowing.”