posted on September 10, 2013 |
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Buildings come down for a variety of reasons. Sometimes it’s planned. Sometimes it’s an accident. Planned demolition is often due to the push for new development. Accidental collapse, such as happened with the Ranza Plaza Building, can be caused by poor engineering. The Harmon Tower in Las Vegas is a case study in both.
The $275 million Harmon Tower was planned to be a luxury hotel in the heart of Las Vegas Strip. Construction toward that goal came to an end in 2008. Now the plan is to tear it down. Why the change of heart?
As described by the New York Times, Clark County building inspectors found a critical error in the design of the rebar reinforcement in the structure. The rebar was either misplaced or missing entirely in places. Engineers warned that the Harmon Tower could collapse in the event of an earthquake or under other serious stress.
This emphasizes the importance of inspection and oversight, even in developed nations where engineering measures are commonly more stringent. The errors mean that remediation to the construction is required. According to MGM, one of the building’s principal owners, the only remediation is to tear it down. They want the contractor, Tutor Perini Building Corporation, to pay for the mistake, including dismantling the building. The cost? A jackpot-worthy $400 million.
You can imagine there is plenty of blame going around. MGM says the contractor hasn’t delivered. The contractor says the design firm gave them faulty specifications. No matter where the breakdown occurred, without reinforcement the concrete will be subject to catastrophic failure. If it begins to give way, it could fail rapidly and with little to no warning.
Modern engineered concrete structures are usually composite materials. The concrete excels at carry compressive loads. These forces arise from the building’s own weight and any additional people, equipment, furnishing, etc.
Concrete does not handle tension well at all. This can arise during bending or any deviation from purely compressive loading. Steel rebar is added to give the concrete better tensile characteristics. It can also add compressive “pre-stress” to avoid ever entering the tensile regime. If the concrete should begin to fail, the steel holds it together long enough to allow timely response.
When large structures like the Harmon Tower are built, there is little room for error. A sufficient factor of safety must be included to account for unforeseen events. Originally slated to be 49 stories tall, the magnitude of the imminent danger in such a densely populated area is certainly cause for concern. Fortunately, as long as there are good engineers paying attention, the only imminent danger visitors to Las Vegas should fear is the collapse of their savings account.
Image courtesy of: http://woofclan.blogspot.com/2011/08/demolishing-vegas-hotel-before-its.html