Forensic engineering often involves diving into the aftermath of structural failures to uncover the root causes. Like detectives at a crime scene, forensic engineers piece together clues from the rubble, using their expertise to identify the root cause(s) and ultimately help prevent similar potential disasters. In this article, we explore some notable high profile case studies in forensic engineering, showcasing the crucial lessons learned and how they can inform better construction practices moving forward.
The Kansas City Hyatt Regency Walkway Collapse
Background: On July 17, 1981, two walkways collapsed at the Hyatt Regency Hotel in Kansas City, Missouri, during a tea dance event. The disaster resulted in 114 deaths and over 200 injuries, making it one of the deadliest structural failures in U.S. history.
Investigation: The forensic investigation revealed that the original design called for rods to support both the upper and lower walkways, with both walkways being suspended from the roof (the second floor was not to hang from the fourth floor walkway). However, during construction, the fabricator proposed hanging the second floor from the fourth floor. The engineer of record approved this change, but assumed the fabricator would design the fourth-floor walkway connections for the approximately doubled loads. The fabricator did not redesign the connection, but assumed the engineer had already checked the connection, as the engineer approved the change. The National Bureau of Standards (now NIST) concluded that the structural capacity of the connections was insufficient, leading to catastrophic failure.
Lessons Learned:
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The Engineer of Record is ultimately Responsible for Proposed Changes: Fabricators may propose changes to improve efficiency and/or lower costs, but the Engineer of record should not assume the fabricator will redesign the structure for those changes. If the fabricator is to design those changes, that should be clearly communicated in writing.
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Need for conformance and “buy in” to internal quality control processes: The design engineering firm had an internal policy to check special connections on fabrication drawings. The fourth floor connections on the re-issued fabrication drawings were not checked by the engineer of record. This tragedy underscored the necessity that engineers “buy into” and strictly follow internal policies, especially those involving quality control. The Boston Molasses Disaster
Background: The Boston Molasses Disaster of 1919, also known as the Great Molasses Flood, saw a massive storage tank containing 2.3 million gallons of molasses burst, sending a wave through the streets of Boston, killing 21 people and injuring 150.
Investigation: Forensic engineers found that the tank was poorly constructed, with inadequate thickness, faulty riveting, and a chemical composition causing tank brittleness and making it prone to cracks. Moreover, the molasses had fermented, increasing internal pressure. The tank construction had also been rushed, insufficiently tested, and had not received an inspection. There were also reports of leaks that were merely painted over.
Lessons Learned:
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Construction of large structures requires regulation: This disaster led to great changes in the way the United States regulates industries, including that engineers must sign and seal plans, building inspectors must examine projects, and design professionals must show calculations justifying their work. Material Quality and Construction Standards: Ensuring the use of appropriate materials and adherence to construction standards is essential to prevent similar failures.
L’Ambiance Plaza Collapse
Background: In 1987, the partially completed L’Ambiance Plaza in Bridgeport, Connecticut, collapsed, killing 28 construction workers. The building was under construction using the lift-slab method, where floors are cast on the ground and then lifted into place.
Investigation: The forensic analysis was inconclusive, but it is likely that the failure was due to high concrete stresses on the floor slabs initiated by the placement process, which resulted in a punch-through failure. Twenty or more separate parties were found guilty of “widespread negligence, carelessness, sloppy practices, and complacency.”
Lessons Learned:
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Proper Care and Load Assessment During Construction: While buildings constructed by the lift-slab method are stable once completed, they can be dangerous if great care is not taken during construction. During construction, a considerably low factor of safety had been used on the L’Ambiance Plaza. Building regulations should be changed to require a high standard of safety during construction.
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The Engineer of Record is Ultimately Responsible: Design responsibility was fragmented among so many subcontractors, several deficiencies went undetected. If the engineer of record had taken overall responsibility for the building design, these defects probably would have been detected.
The I-35W Bridge Collapse
Background: On August 1, 2007, the I-35W Mississippi River bridge in Minneapolis collapsed during rush hour and ongoing construction, resulting in 13 deaths and 145 injuries. The bridge was a major thoroughfare, and its sudden failure was a stark reminder of infrastructure vulnerabilities.
Investigation: The National Transportation Safety Board (NTSB) identified a design flaw in the gusset plates, which were undersized and failed under the load. The plates had not been adequately inspected or maintained, and additional weight from construction equipment contributed to the collapse.
Lessons Learned:
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Regular Inspection and Maintenance of Infrastructure: Aging infrastructure requires regular, thorough inspections and maintenance to identify and address potential issues.
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Critical Evaluation of Design Specifications: Designs must be critically evaluated, especially in the context of changing loads and usage patterns over time.
The Role of Forensic Engineering in Future Practices
These case studies highlight the indispensable role of forensic engineers in understanding structural failures and preventing future incidents. Firms like MarcorSEN Engineering, led by experts such as Marcor Platt, specialize in forensic structural engineering, offering insights that shape safer construction practices.
Whether dealing with existing structures or planning new projects, it’s essential to engage qualified, licensed engineers to assess risk factors, ensure code compliance, and adequately assess structural integrity. MarcorSEN Engineering provides expert forensic engineering investigations to determine the cause of failure and provide potential repairs or retrofits to address the failure.
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