Cited as an Example of Total Progressive Collapse
The total collapse of a building under construction in Bridgeport, Connecticut has been cited as an example total progressive collapse. On April 23, 1987, a planned sixteen-story building about halfway through its construction, collapsed due to deficient temporary temporary connections. The collapse killed 28 workers. 1
|This diagram shows the state of the building's construction at the time of the collapse. (Figure by Rachel Martin)|
The building, which consisted of two adjacent towers, employed the lift-slab method of construction, patented by Youtz and Slick in 1948. This method consists of fabricating all of the floor slabs as a stack at ground level, then elevating the slabs up into their final positions using a hydraulic lifting apparatus. 2
The L'Ambiance Plaza building had steel columns and poured concrete slab floors. Each column had a hydraulic jack at its top connected to a pair of lifting rods extending down to collars in the floor slabs. The floors were permanently attached to the columns once they were lifted into place.
Sheer walls were required to stabilize the building against lateral loads. The plans called for the installation of the sheer walls within three floors of the elevated stack of slabs. However, at the time of the collapse the sheer walls had been built up to only about five levels below the stack.
The report by Rachel Martin notes that prompt legal settlement preempted all investigation leaving the cause of the collapse unknown. It ennumerates five differerent collapse theories, most of them blaming construction procedures.
|This photograph of the rubble of the L'Ambiance Plaza disaster shows a stack or broken yet substantially intact floor slabs in the center of the foreground. (Photo credit: National Institute for Standards and Technology)|
Comparisons to the World Trade Center Collapses
Any comparisons of the L'Ambiance Plaza collapse to the collapses of WTC 1, 2, and 7 should note the following differences.
- The L'Ambiance Plaza building was under construction, whereas WTC 1, 2, and 7 were finished buildings that had stood for many years. Buildings under construction rely on temporary structures and do not employ the reserve strength ratios required for finished construction.
- Procedures in the construction of the L'Ambiance Plaza appear to have violated design specifications.
- The rubble of the L'Ambiance Plaza building contained clearly recognizable stacks of floor slabs, contrasting with the striking absence of a single photograph showing a piece of floor slab or even steel truss at Ground Zero.
- Photographs of the L'Ambiance Plaza rubble show none of the fine dust that was one of the most striking features of Ground Zero.
- Unlike the L'Ambiance Plaza building, the World Trade Center skyscrapers had robust core structures with indepdent flooring systems.
- Witness recollections of the L'Ambiance Plaza, unlike accounts of the Twin Towers' collapses do not include perceptions of explosions or controlled demolition.
2. L'Ambiance Plaza Collapse, [cached]