Nonlinear Dynamic Evaluation of a Hospital Stair Tower with SSI and Pounding Effects

A six-story hospital stair tower with a single level of basement, integrated within an existing two-story administration services structure, provides emergency egress and access between two acute care wings of a hospital. The tower is located at the corner of an L-shaped plan. The tower and adjacent hospital wings are separated from one another by a two to three inch gap. A peer reviewed nonlinear analysis of the structure identified the possibility of global instability due to pounding between buildings, potentially leading to collapse of the stair/elevator tower. In order to accurately model realistic behavior, we explicitly modeled pounding in our analysis. Additionally, we modeled the effect of rocking behavior and sliding foundations. ASCE 41-06’s Nonlinear Dynamic Procedure permitted a minimal retrofit for tower, significantly reducing projected construction cost and schedule relative to our previous design based on linear analyses, while still satisfying SPC2 requirements.