Investigation of the Collapse of L'Ambiance Plaza

Results from an investigation of the collapse of the L'Ambiance Plaza building on April 23, 1987, are presented. The building was being constructed using the lift‐slab method; collapse occurred during construction. The investigation included examination of debris at the site of the collapse, review of eyewitness accounts of the collapse, review of project documentation, laboratory and field tests, and analyses of the structure. Several potential failure mechanisms are investigated. The most probable cause of the collapse is determined to be loss of support at a lifting jack in the west tower during placement of a group of three floor slabs. The loss of support was likely due to excessive deformation of a shearhead lifting angle, which caused a lifting nut to slip off its lifting angle. This failure mechanism was duplicated in laboratory experiments. As loads were redistributed after the initial failure, the remaining jack rod lifting nuts along column line E supporting the package of floor slabs slipped off their lifting angles and the slabs failed in flexure and shear. These slabs fell causing the slabs below them to fail.