The building had been cited for cracks in concrete by municipal authorities a decade ago.
The collapse of a parking garage in lower Manhattan has thrown a spotlight on the structural integrity of older reinforced concrete buildings and bridges in the U.S.. The site is left with unstable partial walls and multiple damaged vehicles which represent an environmental hazard due to fuel, lubricants and coolants. Although the collapse occured with little warning, a forensic engineering study should reveal the the cause in due time. But the building had been cited for cracks in concrete by municipal authorities a decade ago.
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Episode Transcript:
On April 18th, 2023, a tragic incident occurred in lower Manhattan when a four-story reinforced concrete parking garage structure collapsed, resulting in one fatality and five injuries.
The immediate investigation into the cause of the collapse has been challenging due to debris and multiple vehicles obstructing access, as well as the instability of the remaining structure, which poses a risk of further collapse. In response, the New York City Fire Department has employed the use of drones to assess the site and help recover the body of the known fatality.
The exact number of vehicles inside the structure at the time of collapse is unknown, but it is estimated that around 50 cars were parked on the upper deck. The presence of fuel, lubricants and coolants in these vehicles has turned the site into a hazardous materials site, necessitating careful removal of intact vehicles and isolation of crushed autos to prevent environmental contamination.
As investigations into the cause of this tragedy continue, there are several known factors that are generally identified as potential contributors to the collapse of reinforced concrete structures like the parking garage:
1. Design errors during the engineering phase, although this is unlikely in the case of a well-understood structure like the reinforced concrete parking garage, which was reconstructed from an earlier building in 1957 using conventional materials, structural design and construction methodologies.
2. Environmental factors that were unforeseen during the design approval process, such as earthquakes, hurricanes or changes in subsoil or rock strata under the building foundation. Weather or seismic events have not been suggested as factors in this collapse.
3. Deviations in construction from the approved building design, such as the use of unspecified concrete grades, inferior reinforcing materials, inadequate rebar quantity or placement, poor concrete pouring practices, damage to precast beams or columns during assembly, or the use of substandard fasteners or unapproved assembly techniques.
4. Modifications to the structure after completion, which have not been properly studied and approved by competent engineering teams and local regulatory authorities.
5. Overloading of the structure beyond its load limits, though this is unlikely in a parking garage designed for passenger cars and light trucks.
6. Lack of maintenance, which in reinforced concrete structures can lead to corrosion-induced failure of rebar and concrete spalling due to water ingress into columns and beams.
Although it is still too early to definitively determine the root cause of this disaster, the fact that the structure had been in continuous use for 65 years and is located in an area with well-characterized geology capable of supporting tall skyscrapers makes foundation issues unlikely.
However, in reinforced concrete structures, especially in the Northeast, water infiltration, corrosion of rebar, spalling, and cracking of beams and columns will be a focus of forensic engineering investigation.
According to a report by ABC7 news from New York City, the owners of the structure had received several violation notices from the New York City building department, with four issues still open at the time of the collapse. One violation, related to missing concrete and steel beams on the first floor and exposed cracks, had been filed as far back as 2003 and was still listed as open at the time of the collapse. Ironically, last year New York City strengthened codes regarding parking garage inspections.
It is crucial to note that no definitive cause for this tragedy has been identified by any forensic engineering team yet, and even preliminary investigations will have to wait until the partially collapsed structure is stabilized.
