Infrastructure Technology Institute
In late 2008, construction began on a new high-rise condominium building in the fast-growing South Loop area of Chicago. The site of this planned 53-story reinforced concrete tower is a prime example of the infrastructure congestion typically found in urban centers: the embankment of the East Roosevelt Road bridge is a mere six feet north of the site, and South Indiana Avenue, an abandoned water tunnel, and several underground public utilities lie immediately west of the tower. The City of Chicago’s Board of Underground laid out strict monitoring guidelines to ensure the safety of these nearby critical facilities.
ITI researcher Professor Richard Finno and his team have deployed a network of over 70 vibrating wire strain gages to monitor the loading of the different sections of each basement slab during the innovative “top-down” construction process in which the concrete slabs of the basement levels are constructed as the excavation progresses rather than after excavation is complete. Just before each slab of concrete is poured, engineers attach these gages to the reinforcing steel and immediately begin to take readings. When the slab is poured, the sensors become a permanent part of the structure and provide critical information about how the slabs bear load as the soil beneath them is excavated.
In December 2009, the Chicago Department of Transportation and owners of the largely completed building requested that ITI continue its investigation into the effects of the construction method on surrounding infrastructure with the goal of developing design recommendations for future use of this innovative construction technique. Keeping the sensing system in place for a longer period of time makes more data available to engineers about the long-term performance of “top-down” construction as it relates to the surrounding soil and infrastructure.
Though the building’s basement levels were part of an active construction site at the time of the installation of the equipment, these levels will become the garage where the building’s new occupants will park their cars. As with any long-term structural health monitoring system, especially those that exist in an area to which the public has access, great care must be taken by engineers to protect the equipment from accidental damage and to inconvenience the building’s occupants as little as possible. The efforts of the ITI engineering team to leave the building’s residents with a functional yet inconspicuous monitoring system not only ensure the safety and continued successful operation of the equipment, but also provide a stage on which to showcase the advancements in structural and geotechnical health monitoring pioneered by ITI.