Analysis of Stability of L'Ambiance Plaza Lift-Slab Towers

Nonlinear analysis of the construction collapse of the L'Ambiance Plaza lift-slab structures is presented. During construction, the temporary connection between the columns and slabs is distinctly nonlinear. Due to that nonlinear response, overall structural behavior changes rapidly with horizontal displacement, leading to reduced lateral stiffness and stability of the structure as a whole and large changes in load path with relatively small lateral movements. It is hypothesized that jacking operations intended to plumb the towers provided lateral displacement that altered the stability and load path sufficiently to trigger collapse. It is concluded that failure was the result of one or several specific deficiencies in the design and construction identified by various investigators, and not any inherent shortcoming of the lift-slab method. Implications of the collapse on issues of professional responsibility, safety assurance during construction, and continued use of lift-slab construction are discussed.