Fundamental Soil Mechanics - Mathematics and Statistics for the Environment - page 318

Poor maintenance, use, and inspection also play an important role in structural failures.
Obviously, exposures to various conditions during their use changes structures. Improper main-
tenance can affect a structure's useful life. Improper use can have the same affect. Inspection is
important to ensure that maintenance and use are providing effective care and to guard against
unexpected failure.
Case Study 12.1. The Hyatt Regency Hotel Disaster *
On July 17, 1981, at 7:05 pm, the Kansas City, Missouri, Hyatt Regency Hotel Atrium held over
1600 people. At that moment, two suspended structurally connected skywalks connecting two
towers on the second and fourth floor levels failed and fell, crushing the heavily occupied res-
taurant bar beneath them.
The death toll for this structural failure (the worst in U.S. history) was 114. Over 200 more
people were injured, many permanently disabled. Plaintiff's claims amounted to over $3 billion.
The hotel owner, Donald Hall, with an admirable sense of duty and decency, settled more than
90% of the claims.
Immediate theories on what caused this structural failure ranged from continued resonance
to faulty materials to poor workmanship. A National Bureau of Standards investigation finally
discovered the most probable cause—and their findings laid the blame squarely at the feet of
the structural engineers. The cause? A design change submitted by the contractor and approved
by the design engineers and architect. In the original designs, both skywalks were supported
by nuts at both the second- and fourth-floor levels that were threaded onto single continuous
hanger rods and spaced at regular intervals. Because of the single-rod design, while the roof
trusses held the load of both, the welded box beams that supported the load of each skywalk
were independent of the other.
The change? The contractor's design change shortened the hanger rods, added an extra hole
to the fourth floor beams, and hung the second floor walkway by an independent second set of
hanger rods from those box beam connections, thus putting the entire load of both walkways
on the fourth floor walkway. This was not the only factor involved, however. In determining
the dead load of the structure, the investigators discovered an 8% higher load than originally
computed, because of changes and additions to decking and flooring materials. The live load,
however, was well within the limits. The obviously weak element in the design was the fourth-
floor box beams, so the investigators tested both new duplicates and undamaged beams and
hanger rods from the Hyatt Regency Atrium.
The National Bureau of Standards report stated that the skywalks were underdesigned and
that the design lacked redundancy. Six important points summarize the report:
• The collapse occurred under loads substantially less than those speciied by the Kansas
City Building Code.
• All the fourth-loor box beam-hanger connections were candidates for the initiation
of walkway collapse.
• The box beam-hanger rod connections, the fourth-loor to ceiling hanger rods, and the
third-floor-walkway hanger rods did not satisfy the design provisions of the Kansas
City Building Code.
• The box beam-hanger to rod connections under the original hanger rod detail (con-
tinuous rod) would not have satisfied the Kansas City Building Code.
• Neither the quality of the workmanship nor the materials used in the walkway system
played a significant role in initiating the collapse.
* Based on Levy, M. and Salvador, M., Why Buildings Fall Down: How Structures Fail . W.W. Norton, New York, 2002.