ABC7's Eric Horng spoke with Chicago-area engineering experts Monday who weighed in on the issue.
Typically, the bigger the act, the bigger the stage, and engineers say therein lies the problem: wind force on a structure can multiply the taller it is. Even so, some experts question whether a 70 mph gust should have brought the stage down.
Sixty-to-70 mph winds brought down the scaffolding that supported the stage. Officials maintain that the high winds hit suddenly, surprising everyone. They say that they were in contact with the National Weather Service, but that the straight-line winds, gusting to near hurricane strength, were unseen on radar.
Fair officials said disaster struck as they were about to call off the concert. The collapse happened minutes after lead musical group Sugarland's scheduled performance time.
Sugarland reportedly had reservations about playing given the conditions. Monday night, the band's manager said a decision was made to wait despite assurances that the stage was safe, a move which may have saved singer Jennifer Nettles, partner Kristian Bush, and others.
Dozens of people in the crowd were less fortunate.
"I can't even imagine - in the front row of the 'sugar pit', there were so many little children," said Holly Iscon, whose daughter was injured.
As the fair reopened Monday, the dead and injured were honored in a ceremony.
"We come today with hearts that are broken, but also hearts that are full," said Indiana Governor Mitch Daniels.
Among the five people who were killed was Christina Santiago of Chicago. Her partner, Alisha Brennon, is still recovering from her injuries.
"Alisha is a very, very, very strong woman, she's very outgoing, she's very energetic," said Brennon's friend Leticia Medrano.
Indiana State Police inspectors are looking at the rigging. The stage builder has a long track record with the Indiana State Fair and is promising an investigation of his own.
A timeline released by Indiana State Police shows that the fair staff contacted the National Weather Service four times that night. Nearly an hour before the collapse, the weather service said a storm with 40 mph winds was expected to sweep across the fairgrounds at about 9:15 p.m. The stage collapsed just before 9 p.m.
"My worry would be regarding structural connections, bolted joints, welded joints," said UIC Professor Farhad Ansari, Civil and Materials Engineering,.
Ansari has been studying video of Saturday's stage collapse.
Though it is too early to know exactly what went wrong, Ansari says the investigation will likely center on several factors, including metal fatigue and whether the structure was assembled properly.
"In general, these canopies are designed that at a certain level of wind, excessive winds, they would fall off. If the wind direction changes, there is no guarantee that they fall off," said Ansari.
"In the Midwest, the general wind speed that you design for is 90 mph," said structural engineer W. Gene Corley, an expert in structure collapses who led the structural investigations following the 9/11 World Trade Center attack and the Oklahoma City bombing. "Something like that should never have happened. The stage should have been designed for winds that are normally expected in the area."
In Illinois there is no state agency responsible for inspecting outdoor rigging, but the City of Chicago says all outdoor stage setups undergo a permit and inspection process. Those structures, officials say, must be built to withstand at least 30 mph winds, and at higher speeds, there must be a plan in place for stage medications and even evacuations.
Indiana contractor Jay Kempton has assembled structures for more than 1,000 events and says canopies can and should be lowered when bad weather rolls in.
"The higher you go, winds are stronger, you got these high things in the air, and of course the wind is going to win in the long run," said Kempton.
In fact, on the night of the Indiana State Fair collapse, Kempton was working another concert near Chicago and chose to cancel the show because of high winds. He said he would have demanded that the canopy in Indiana be lowered if he had been working the event.
"It's just not worth it," Kempton said.
Officials at the Illinois State Fair in Springfield say bad weather prompted them to lower the canopy of its grandstand on Saturday. They say they lower it every night after the fair ends and inspect it every morning when it's raised. Officials in Illinois would not comment on whether Indiana officials should have also lowered their canopy.
The investigation into the Indiana collapse will likely focus, not just on assembly, but also inspection procedures.