Design and construction of an independent stack extension

As a result of a new six-story addition, Backus Hospital in Norwich, Connecticut, USA, needed to increase the height of an existing tapered brick stack or replace it without any significant interruptions in use. A simple extension of the existing stack alone was not appropriate because the height increase would produce additional forces and moments that required extensive strengthening of the existing stack and foundation. The solution described in this paper has several unique aspects. Primary among these is the structural system used. The new structure is essentially independent of the existing one.