Monday will mark 25 years since the infamous collapse of L’Ambiance Plaza. On April 23, 1987 the L’Ambiance Plaza building, in Bridgeport, Connecticut, collapsed without warning during construction operations. This collapse spurred a large scale, eight day, rescue attempt but ultimately left 28 workers dead and many more injured. The 16-story L’Ambiance consisted of 13 apartment stories over 3 parking levels and was being constructed using the lift-slab method. Lift-slab is a construction technology that consists of casting concrete (in this case post-tensioned) floor slabs, one on-top of another at ground level and then hydraulically lifting or jacking each level into place.
At approximately 1:30pm on April 23rd a loud bang was heard and within the next 2-10 seconds the entire building crashed to the ground. As a result of the collapse, several investigations were launched. In an effort to compensate the victims and their families, legal claims were quickly settled out of court ending all investigations and leaving the exact cause of the collapse unknown or at least untested in court. Although the exact cause of the collapse remains unknown, at least five major theories have been proposed in the years since the collapse by various investigators and consultants. Due to the L’Ambiance disaster, Lift Slab construction was halted in the United States for a considerable time period with very few new projects erected in the last 25 years.
For a detail account of the collapse and the various theories related to the failure see the L’Ambiance Plaza Case Study at Failures Wiki. The site includes additional photos, diagrams and a set of references for the case, including the topics below.
More Lift Slab Failures of Note
Although the collapse of L’Ambiance Plaza effectively ended the use of lift-slab construction in the US, a number of structures had been built prior to April 23, 1987. Many of these were successful and are still in service today. Others experienced problems such as column-wedge failures, global instability (sidesway failure mode) or related construction issues that resulted in collapse or remediation during construction. Fortunately there was no loss of life with these cases, however there were injuries and significant economic losses. Examples of several problem lift-slab buildings are noted below:
- On July 15, 1954, the Junipero Serra High School Roof in San Mateo, California collapsed due to sidesway instability. This 16 ft. tall one-story building was approximately 65 ft. x 70 ft. in plan and used 6 inch diameter steel pipe columns for support. Attempts by the contractor to stablilze the leaning structure with guy wires on one side of the frame backfired as the contractor apatently overcompensated and failed the building in sidesway in the direction opposite the original lean.
- A structure based on the Canadian wedge system (a system that relies on frictional resistance between the column and wedges) collapsed under construction in Marion, Indiana in 1962.
- Cleveland, Ohio experienced a near collapse on April 6, 1956 when the Pigeonhole Parking Garage (using the Youtz-Slick lifting system) nearly collapsed in winds of 35-65 miles per hour prior to the steel wedges being permanently welded. Fortunately the contractor was able to right the structure by pulling it back into plumb and finish the project without further incident even though the the building was leaning as far as 7 feet out of plumb (Zallen and Peraza 2003, pg 24-25; Delatte 2009 pg 121). An expanded account of the Pigeonhole Parking Garage case, including dramatic original photographs of the leaning structure, can be found on the Failures Case Studies websiteof the (NSF MatDL) created by Dr. Norbert Dellatte.
Vintage Lift Slab:
A photographs of one of the early post-tension lift slab structures constructed in the US, is shown below. Provided by former Professor Vincent L. Pass, P.E. of Penn State AE, the photograph is that of the Trinity University Library, San Antonio, Texas and was taken in April of 1951.