To prepare a new mixed-use development for a restaurant tenant move-in, numerous core holes were cut in the floor slab to accommodate a large number of mechanical, electrical and plumbing systems to support restaurant functions.  More than 80 holes were cut in the two-way reinforced concrete floor slab and reinforcing bars were cut at many of these penetrations, reducing the load bearing capacity of the floor slab. The number, layout and depth of severed bars varied at each location, making it harder to come up with standard repairs for these locations. This occurs often when a mixed-use building is being laid out and the tenants are not finalized prior to or during initial building construction. 

The general contractor brought in Structural Preservation Systems (SPS) to work with the engineer of record to develop a supplemental, externally bonded, high strength carbon-based fiber reinforcement polymer (CFRP) solution. CFRP is ideal for this type of repair and is able to restore the loss of strength created by the cutting of existing reinforcing bars.

The owner desired an unintrusive reinforcing system that would remain unnoticeable and would not affect the new restaurant's specified flooring systems. In addition, the owner needed a system that could be installed without delaying construction for the rest of the building's fitout. To meet these goals, a CFRP solution was developed that considered the global effects of all the holes on the floor slab.  External CFRP strips were designed to augment the existing strength in all middle and column strips of the slab. To achieve this, SPS installed carbon fiber to both the top and soffit sides of the slab. The top of the slab presented perhaps the most significant scheduling challenge because other construction activities, such as the flooring installation and interior wall framing, couldn't continue until the carbon fiber reinforcement was completed.

One of the primary challenges was the number of holes in the concrete slab. The large number of penetrations and their proximity to one another made it difficult to lay out the carbon fiber so that the proper amount of reinforcement could be installed in the slab area adjacent to the core holes. To address this challenge, SPS performed a thorough field survey of all the newly created holes to determine their precise layout.  Next, the survey was translated to drawings and used to determine the optimal reinforcement layout. Design and detailing of the new reinforcement system had to also account for all new slab holes required to attach finishes.  Thorough preplanning and detailed mapping of existing conditions were critical elements in producing a seamless schedule of construction events. By investing time to produce detailed drawings before work began, the carbon-fiber installation process was speedy and greatly simplified.

Another major challenge was the soffit obstructions: electrical conduit, pipes and other mechanical fixtures. Once again, a thorough survey of as-built conditions and careful coordination were necessary to work around the obstructions. Coordination was also vitally important when working on the underside of the slab because of its position over an active parking garage. To minimize disruption in the garage, work was completed in phases and during night shifts.

Carbon-fiber reinforcing is an innovative solution, especially advantageous in this project because of its ability to fit in small spaces with numerous obstructions. In addition, the relatively thin carbon fiber reinforcement (1/32" to 1/16") minimized impact on the floor surface so the restaurant's wood, tile and epoxy floor surfaces could be installed with the CFRP remaining undetectable.

Despite numerous challenges and tight scheduling requirements, SPS completed its contract on schedule. The reinforcing system was installed as proposed and with minimal impact to the overall project's finished schedule. An experienced and highly motivated field crew, with a keen eye for detail, was key to the overall success of this project