The Ashford Perimeter Parking Garage supplies approximately 1,000 parking spaces for a commercial office on four levels. The lowest level is on-grade with three above in a terraced configuration. No internal structural ramps exist as each level is accessed on-grade. The deck is 8-inch thick, 2-way, post-tensioned, flat slab.
The column-strip post-tensioning in the east-west direction was inadequate. A repair was developed using a heavily-reinforced Gunite beam added to the underside of the slab column strip. Soon after, delaminations between some beams and the slab were noticed. A non-destructive testing (NDT) investigation (pulse velocity test) demonstrated that approximately 30 percent of the area might have more than 40 percent delamination.
An engineering firm recommended more NDT inspections utilizing impact echo. Of the 133 beams tested, 105 showed some delamination, and 19 had 33 percent or more delamination.
The first phase of the repair included an in-depth in-situ load testing of the existing slab under various conditions - including as strengthened with FRP sheets.
A load testing procedure was proposed to provide a non-destructive demonstration of the performance of structural components. The procedure utilizes hydraulic jacks to induce forces equivalent to those resulting from distributed loads
Test results indicated that the beams in the east-west direction with a minimum of 70 percent bond performed well. A span with no beam demonstrated poor performance. Results also showed that carbon fiber reinforced polymer (CFRP) strengthened slabs (after removing the Gunite beams) were satisfactory. Accordingly, at 19 locations the east-west beams would be removed and the slab would be strengthened with CFRP sheet. Typical spans in the north-south direction were found to be acceptable without additional upgrade.
Large overstress in the east-west end spans and excessive deflection to the second level cantilever required another strengthening approach. External steel-framing was installed to reduce the clear span, and additional steel supports were installed under the cantilever slabs. At steel support points, "pancake" jacks were permanently installed to engage the steel frame.