Rosemont+Horizon+Arena

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Wiki team 13: Steve Gaddis, George Hayward, Shayna Huertas, Eric Vanistendael =Introduction= The Rosemont Horizon Arena collapsed during construction on August 13th, 1979. Located directly under a flight path to Chicago's O'Hare Airport, the arena's design employed a wood roof to dampen the resultant noise pollution. The roof was comprised of sixteen glue laminated arches spanning 288 feet, split into three trusses, joined by metal and braced laterally by wooden purlins. The arches were poorly aligned and varied as much as twelve inches laterally across a single span. This alignment issue prevented the purlins from being adequately connected to the arches; "Over 53 percent of the required connection bolts were missing from the building's roof" (Nazario). The general instability of the incomplete wooden roof frame combined with a gust of wind brought the construction to the ground, resulting in the deaths of five laborers and the injury of sixteen others. The arena was swiftly rebuilt using a different contractor and adhering to the connection requirements as originally specified by the architect and engineer. The Horizon Arena (now the Allstate Arena) has served the greater Chicago area for nearly 30 years, proving that it was construction techniques, not design failure, that brought the original structure to the ground.


 * Keywords**: timber roof, construction oversights, wind, Rosemont Horizon Arena

= = =Structure= The Horizon Arena was constructed with a timber roof comprised of sixteen 288' glue-laminated arches, laterally braced by wood purlins. These large arches were 6' deep by 1' wide and were made up of three separate pieces and erected in three different stages. Connecting the arches laterally to each other were smaller wooden girders, spanning approximately 20'. The roof was supported and buttressed by concrete columns situated at the ends of the arches. As construction workers moved along, they didn't place all the nuts and bolts in position, because they wanted to let the natural deflection of the wood set in before doing so. By making this decision, each new arch became progressively off center, and in combination with being ill-supported, the first arch fell and caused a domino effect that accordingly brought the other arches down as well.

= = =Collapse= A westward gust of wind perpendicular to the arches was responsible for starting the collapse. The workers had begun work on the sixteenth and final arch, which was not tied laterally to the previous fifteen. As the wind brought the first arch down, a domino effect ensued, and within seconds the roof structure was on the ground (figure 2).

=Causes of Failure=

Construction Oversight
The timber roof was dependent on the fasteners, as wood tends to rotate, bend, and warp with time. In fact, in the initial stages of construction, workers noted that the void between the arches varied as much as twelve inches across a single span. This presented additional difficulty in attaching the lateral purlins, which were all cut to a uniform size. Many improvised connection methods were used to make up for this shortcoming; the use of drift pins in place of the specified bolts, cutting new holes for the connections with torches, and even omitting bolts where exceptional difficulty was noted. Although too late now, any on site decisions should have been checked by at least an engineer and perhaps the designer as well.

Fasteners
The difficulties of alignment had a direct effect on how the structure was assembled. The supervising contractor made the decision to omit fasteners to allow the wood structure to deflect downward as much as possible before adding the final connections (see unfamiliarity subsection for rationale). Of the 966 specified bolts, over 54% were missing. Out of the 444 bolts that were installed, 338 did not have nuts (Carper). This leaves a total of 106 properly assembled fasteners, only 11% of the intended amount.

Unfamiliarity
The contractors hired for the Horizon Arena were from the Chicago area. Builders in this region are accustomed to working with steel structures. It was common practice to leave out some of the bolts during construction of steel structures to account for the stretching and bending of the steel as loads are placed on it. The contractor's unfamiliarity with the demands of a wood structure played a key role in the collapse, however, it is no excuse. The contractor should have at the very least discussed this with a structural engineer and/or done research into it as well.

Additional Causes
A twenty mile per hour westward gust of wind caused the final arch to fall. The arch fell to the west, causing the other fifteen arches to collapse with it. Following the incident, an OSHA investigation led to the discovery of another factor in the failure; the additional weight of construction materials improperly stockpiled on the top of the incomplete roof. There has also been speculation that perhaps the rapid and continued plane flights overhead may have in some way have affected the building.

=Consequences= The roof collapse resulted in five deaths and sixteen injuries. Financially, the collapse added $3 million dollars to the total cost of the arena, which was initially projected at $8 million dollars. OSHA levied fines on the contractor for improper construction practices and the architect and subcontractors for irregularities in the building as it was built and the building as it was designed and approved. Additionally, the engineering firm that was hired to investigate the collapse was fined for exposing their employees to the hazards found on the building site (Nazario).

=Lessons Learned= Communication is of utmost important on large projects such as this one. As was shown by the new contractors after the collapse, the original //design// was fine and structurally sound. However, it was the original construction crew that failed to build the roof as it was planned. Had the architect(s) and construction workers perhaps collaborated better, and checked each others work as they progressed, the original roof could have been a success.

= = =Conclusion= Immediately following the collapse, the decision was made to rebuild the Horizon Arena. The architect and client hired a new contractor to displace the previous one, and the arena was constructed as per the original designs. Consideration of the special needs of timber, as well as a steadfast adherence to the numerous connections in the roof design resulted in success. Today, the Rosemont Horizon Arena (now known as the Allstate Arena) still stands, having served the Chicago area, sports teams, and traveling musicians and their fans for nearly thirty years.

=**Bibliography**=

The supervising engineer approved the omission of bolts, hoping the arches would deflect under the imposed loads and allow the installation of the remaining bolts. These omissions, combined with inadequate bracing and the storage of construction materials on the roof, resulted in the collapse of the structure.
 * 1. Carper, Kenneth L., and Jacob Feld. //Construction Failure, 2nd Edition//. 2 ed. New York: Wiley-Interscience, 1996.**

This article contains many facts and figures on the collapse, from the number of missing bolts to how many were out of place. It also mentions that the total cost of damage done was $3 million, and that the roof was later built to specification by a different contractor and it was successful.
 * 2. "DePaul's Allstate Arena." //Sports Stadiums//. Web. 06 May 2010. .**

An architect with the firm that designed the arena called the claim that a low-flying aircraft, which passed over the structure moments before its collapse, "wild and premature." A design consultant for the roof's construction did not rule out the possible effects of wind on the structure, asserting that the unfinished roof could have acted as a sail.
 * 3. "Designers assess reason for collapse of arena roof that killed 5 workmen." //Eugene Register-Guard// 14 Aug. 1979: 5A.**

Sixteen glue laminated arches spanning 288 feet were installed, in three pieces each, and were raised on precast concrete buttresses. The metal plates connecting the wood to the concrete did not have the proper amount of nuts and bolts installed.
 * 4. Feld, Jacob, and Kenneth L. Carper. //Construction Failure//. New York, N.Y.: J. Wiley and Sons, 1997. Print.**

Investigation shows that during construction the sixteen wood arches were not properly braced. Many bolts were missing and as more information was revealed, it became clear that the construction job was nothing less than faulty. This allowed a wind load to cause a collapse.
 * 5. Gorman, John. "Why Rosemont Arena Collapsed: Construction Was Lax, U.S. Says." //Chicago Tribune// 2 Sept. 1979: 15-16. Print.**

Having been written only two days after the collapse, this article first points out that engineers were still investigating. It then begins to question the source of the problem. Although not yet known, Gorman notes that speculators think the high frequency of planes in the area could of had an effect. He also describes in detail the long arches that traversed the stadium.
 * 6. Gorman, John. "Wooden Truss Beams Focus of Probe into Cave-in of Rosemont Arena Roof." //Chicago Tribune// 15 Aug. 1979. Print.**

The contracting firm, being from Chicago and therefore more accustomed to steel construction, did not feel it was necessary to utilize all the bolts in the connection between arches and purlins. In steel construction, it is generally accepted to omit some of the connecting bolts due to the inherent complexity of the structures. However, in a wooden construction, all connections are of an absolutely critical nature because the wooden arches needed the lateral support offered by the purlins.
 * 7. Modern Marvels Engineering Disasters 9. History Channel, A & E Home Video, 2004.**

In approving the omission of 2 out of 3 bolts on the purlin/arch connections, the construction supervisor hoped to allow the wooden structure to deflect as much as possible before attaching the final connections. However, he failed to account for wind loads and the weight and flexibility of the wooden structure, which resulted in failure.
 * 8. Nazario, Carlos. "Rosemont Horizon Arena Timber Roof Collapse." //NSDL Materials Digital Library Pathway - Fez//. N.p., 31 Oct. 2008. Web. 11 Feb. 2010. <[]>.**