Indianapolis Fatal Stage Collapse

Many music festivals and other large venues are held outside, in expansive, relatively flat, areas where huge crowds can be more easily accommodated. The mobile stages used in today’s music industry are larger than those ever used before. The increased size of the stages allows for the high placement and use of elaborate lighting systems with visual displays, and can support large speaker arrays so that crowds can better hear and see performances.

While there are many different sizes of mobile stages, the load capacity of the trussing of the larger stages is approaching the 200,000 pound range. Most of the lighting and speaker equipment is held relatively high in the trussing, making the stage structures top-heavy with a high center of gravity. Many of these stages also utilize sun/wind screens to make the performers more comfortable. The use of sun/wind screens can significantly increase the surface area of the stage structure at the upper levels, elevating the stresses on the stage during high winds.

The recent catastrophic collapse of the mobile stage at the Indiana State Fair on August 13, 2011 in Indianapolis, Indiana, was a terrible disaster. While there is still much information to gather with regards to this accident, it appears that wind loading of the stage, in combination with a lack of lateral bracing, was the primary cause of the stage’s collapse. As can be seen from event photos, the blue colored roof tarp on the right top side of the stage experienced uplift and eventually was pulled from the structure immediately before the collapse. The wind forces on the windward side of the stage, along with the uplift wind forces exerted on the stage from the tarps, provided enough force to initiate the collapse.

It is noteworthy that the typical maximum wind rating for stages with wind/sun screens is on the order of 50 miles per hour, and stages without wind/sun screens is on the order of 75 miles per hour. It is not yet known what magnitude the wind gusts were during the Indianapolis stage collapse.

The degree of truss loading from the lighting and speaker arrays is another important factor to consider. It’s possible that the trussing may have been loaded near or beyond what the stage was designed for in the upper level of the structure, resulting in a very high center of gravity. The entire structural roof system appears to have remained intact and toppled over away from the wind, indicating a lack of lateral bracing for a high center of gravity structure. A detailed forensic investigation is required to determine the specific mode of failure and the contributory factors to the failure, including if any components of the temporary structure were improperly constructed and to determine if any building code requirements were not followed.

The Indianapolis stage collapse will likely trigger design modifications made to mobile stages in the future, in addition to the recommendations already made above, where more elaborate bracing systems or the use of guy lines to add to the structural integrity of the stages are utilized or incorporated.

Moreover, there was certainly a degree of human decision/action with regards to weather forecasts and crowd control prior to the accident occurring. It’s still too soon to comment on the timing of the weather forecasting, and the ability of the event staff to control or mobilize the crowd away from the mobile stage structure.

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