Located in Arlington, one of Virginia's most popular and fastest growing cities, a new high-rise building is staged to become an integral part of the neighborhood. However, during construction, the project faced challenges that required prompt remedial actions. After construction began, it was determined that the eight-inch-deep concrete drop panels in part of the garage-level structural slab were constructed four inches shallower than designed.

With scheduled turnovers at hand for certain portions of the building, it was critical that repairs be achieved in a timely manner. Also essential to the project's overall success was that repairs be made to restore the structural capacity of the building for the intended use. To meet these needs, the concrete contractor brought in Structural Preservation Systems (SPS) to provide a strengthening solution to resolve the deficiency in the structural slab.

The scope of the project included strengthening a total of 31 under-built drop panels through a combination of techniques, including concrete enlargement and installation of carbon fiber sheets and carbon fiber rods. Concrete enlargements were used wherever possible because the concrete contractor could self-perform most of the work, minimizing the associated repair costs. SPS developed a unique relationship with the concrete contractor, overseeing the work performed by the crews to ensure that the job was completed according to SPS' repair drawings and specifications. The enlargements were a success, and the existing slab and new enlargement that were poured at different times were able to act as one monolithic structural element. By utilizing adequate surface preparation, proper design of steel dowels, self-consolidating concrete and pressurized concrete placement techniques, it was possible for the newly placed concrete enlargement to act as a composite with the existing slab.

One of the major challenges of the enlargement included coordinating the logistics for the concrete pour in a garage two stories below grade on a very busy jobsite. Access was limited for the concrete pump and ready-mix trucks, and a number of other trades were working in the area, further complicating the pumping operation. SPS set up a pump truck and ready-mix trucks near one of the ramps leading to the garage, then cut holes through an existing wall and garage floor in order to run the pump line down to the desired level. Close coordination with the concrete contractor and the general contractor was important to the success of the concrete pours. SPS worked diligently to keep all parties involved aware of the project plans, and this communication was critical in order to prevent any surprises on the days of concrete pours.

A second strengthening solution included externally bonded carbon fiber reinforced polymer (CFRP) sheets, which provided an unintrusive solution in tight spaces. These sheets were used in locations where existing pipes, conduits or other mechanical fixtures prevented the use of concrete enlargements. The small footprint of the carbon fiber sheets made these an ideal solution in areas where it was necessary to work over and around existing mechanical fixtures.

Using carbon fiber rods, also know as near-surface mounted (NSM) rods, provided an innovative solution where additional reinforcement was needed on the top side of the slab. In certain sections of the slab, the top side provided the only access, as existing conduits and mechanical lines limited access to the underside of the slab. The top side of the slab was the floor of a parking garage, and the surface-embedded carbon rods provided a more durable solution in this high-traffic area. To install the rods, SPS cut long grooves in the concrete, placed the rods and epoxy injected the grooves.

Despite the deficiencies in the structural slab, the project remained on schedule due to the innovative solutions and detailed planning by SPS' project team. The completed structure will perform as originally designed, and the community will benefit from the building's convenient access to transportation, stores, restaurants and nightspots.