Many facilities that were originally constructed for a specific use now are being renovated or upgraded for a different application that may require higher load-carrying capacity. One example is an old industrial facility in Irvington, a suburb of New York City. The developer planned to convert the building into high-end loft condominiums with retail, office and restaurants on the ground level. Originally, the plan involved demolishing a 100-foot chimney because of the high cost associated with rehabilitation. However, the developer realized the location offered cell carriers superior strategic access and additional coverage to the densely populated area of Rockland and Westchester County. In working with the telecommunications company, it was determined the carrier would be responsible for stabilizing and strengthening the chimney. In return, they would be able to install multiple antennas on the chimney.
The scope of work for Structural Preservation Systems (SPS) included supplying all labor, equipment and materials to remove and replace all the deteriorated mortar joints (inside and out) and strengthening the chimney to accommodate the new loads created by the cell antennas. After a century of natural deterioration, the chimney was in very poor condition, with existing joints badly deteriorated - in some cases, completely through the wall. Extensive repointing of interior and exterior joints was carried out to stabilize and restore the integrity of the chimney, with the bricks at the top 4 feet so degraded they required replacement. The challenge in doing this was not only rebuilding the unique architectural shape for historic purposes, but also finding a source for the same type and color of brick. An extensive search of the United States found only one manufacturer who still had the materials available.
Structural analysis of the chimney revealed new wind loading created by the installation of the cell phone antennas would create overturning load. Not only would the chimney have to be strengthened for these forces, but the foundation would also have to be evaluated, since the external forces needed to be properly transferred down into it for stability. A structurally efficient, easy-to-install, and cost-effective strengthening option was achieved by using an externally bonded carbon-based FRP strengthening system that would increase the shear and flexural capacity of structural elements. The thin carbon FRP plates were bonded to the inside face of the chimney, serving as vertical tension reinforcement. The continuous FRP laminate plates were installed in single, 30.5-m (100-ft) long pieces extending the chimney's full height. Since carbon FRP is only a quarter the weight of steel, the plates were easily handled by workers inside a small diameter work area (only two workers could fit in the structure) and added only minimal weight to the structure. As such, no upgrade was necessary for the existing foundation.