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Title: Breaking Ground on the Roof

Author(s): Hutton

Publication: Web Session



Appears on pages(s):



Date: 10/17/2021

Renelle is an 18-story residential building located along Wabash Avenue in Chicago Illinois. It is 150,000 square feet and features 50 condominium units. The building features an amenity floor at level 18, and a vegetated roof. The building was constructed on top of an existing 4 story garage which was built in 1976. The garage was designed to support additional future floors however, the number of future floors was unknown, and no provisions were provided for future elevators, stairs or a structural lateral system. In addition, the garage had to remain open and in service throughout construction, with minimum disruption to the occupants who individually own specific parking spaces. Practically no new columns or walls were allowed within the existing garage. Given these constraints numerous architectural, engineering, construction and logistical challenges had to be overcome to bring this project to fruition. Extensive in situ investigation of the existing structure was performed to validate the data provided in the existing drawings and to determine the maximum capacity of the existing structure. Both destructive and non-destructive testing of the caissons, slabs and columns was performed. Based on an evaluation of the original caisson installation records the foundation design capacities were increased by up to 20%. The columns were cored and evaluated per ACI 214.4 R10 which resulted in an average of 10% increase in existing column design capacity. Multiple structural framing systems were evaluated to determine the structure that would maximize the number of floors while minimizing the modifications of the existing garage. A post-tensioned flat slab, concrete moment frame, utilizing lightweight concrete on the upper floors was selected as the optimum structural system.