The International Concrete Repair Institute (ICRI) recently honored Structural Preservation Systems (SPS) for its contribution to the repair, protection
The International Concrete Repair Institute (ICRI) recently honored Structural Preservation Systems (SPS) for its contribution to the repair, protection and/or strengthening of seven structures, granting SPS four Awards of Excellence and three Awards of Merit.
For strengthening prestressed concrete beams that were structurally damaged due to an overload of snow at a Washington, D.C., government parking garage, SPS received an Award of Merit. The prestressed beam repair project was initiated following detection of concrete spall debris on the deck, prompting the observer to look up and discover cracked beams, plus exposed prestressing strands. To address the beam failure, SPS developed an in-place repair solution as an alternative to complete removal: damaged beams were enlarged using self-consolidating concrete (SCC) and post-tensioned with mild steel reinforcement to add strength. Thus, SPS satisfied the customer’s need for a sound, cost-efficient repair with minimal downtime.
Also receiving an Award of Merit was the full balcony removal and replacement for Le Chateau Condominiums, comprising two mid-rise buildings in South Palm Beach, Fla. The east building houses 64 units on eight floors; and, the 72-unit west building rises nine floors, while a four-story post-tensioned parking garage is centered between the two structures. Due to the corrosive effect of harsh coastal elements and lack of any formal restoration since the development’s 1973 opening, structural degeneration was evident, i.e., columns in the east building were deteriorated beyond 50 percent of their dimension.
Restoration included removal and replacement of balconies and railings, waterproofing, post-tensioned cable and column repairs, as well as a cathodic protection system on two columns. For the balcony removal, two different methods were used: a conventional method for the east building required two lower balconies to support the weight of shoring and new concrete; whereas, the west building saw demolition of all its balconies at one time. Shoring towers were installed from the ground up, and new concrete was placed in two pours. Implementing two methods for the balcony repair enabled SPS to increase production by 21 percent, leading to a six-week timetable reduction.
Additionally, an Award of Merit recognized concrete strengthening of the famous ring walls of Frank Lloyd Wright’s Solomon R. Guggenheim Museum, which opened in 1959 in Manhattan. After a comprehensive investigation was prompted in 2004 by signs of distress, structural strengthening and repair of the distinctive landmark were initiated, while preserving the appearance of the exterior texture by performing all repair strategies to wall interiors. Carbon fiber-reinforced polymer (CFRP) and FRP sheets were the final choice of the team.
SPS also garnered four Awards of Excellence for the following projects:
Structural concrete repairs were completed and a cathodic protection system installed at an 18-story apartment building near the campus of John Hopkins University in Baltimore. Built in 1968, the complex was designed to provide balcony access from all 271 units. While minor repairs had been performed since the building’s original construction, damaging environmental conditions Û including multiple freeze-thaw cycles and harsh winters with corrosive de-icing salts Û necessitated concrete spall and crack repairs in 2004 for both the balconies and parking garage.
The balconies were repaired in six phases, each consisting of multiple vertical tiers around the structure. A unique formwork design developed for the parking garage waffle slab repairs entailed wood forms and prefabricated fiberglass forms customized to match existing waffle pan and rib dimensions. Further, SPS installed a cathodic protection system, protective coatings, and new drains to prevent future corrosion.
Concrete repair and cathodic protection at Calvert Cliffs Nuclear Power Plant (CCNPP) in Lusby, Md., were completed to remedy eventual structural deficiencies. When CCNPP, built by Baltimore Gas & Electric in the 1970s, exhibited severe deterioration of reinforcing steel in the intake-floor, circular water pump bowels (CWB), and salt-water pits (SWP), SPS was enlisted to repair the concrete surfaces with a bonded concrete overlay that would help prevent corrosion and last for a period of approximately 20 years.
Encompassing the three main areas of intake floor, CWB and SWP, the $3.25 million project utilized an impressed current cathodic protection (ICCP) system to help prevent corrosion of new and existing reinforcing steel in the floor. On all horizontal surfaces, concrete was removed to an average depth of 6.5 inches to eliminate high-chloride material and replace severely corroded reinforcement, as well as install ICCP ribbon within one inch of the top mat of reinforcing steel, prior to placing the new overlay. In all vertical surfaces and areas where the concrete was sound, slots were cut in order to position the ICCP ribbon. Impressed current cathodic protection systems employ a small, direct current that passes from a permanent anode to the reinforcing steel; thus, an external power supply connects the anode and steel with appropriate polarity and voltage to prevent reinforcing steel from giving up electrons, repelling chloride ions away from reinforcement toward the installed anode.
Concrete repair on a 3,000-ft.-long dock in the Gulf of Mexico involved slab removal and replacement. After an investigation of the dock’s structural integrity revealed substantial erosion on the bottom side Û in particular, visibly damaged concrete support beams and rebar dangling in water Û SPS advised performing repairs from the dock. That approach eliminated the problem encountered with a barge-and-crane method, i.e., each time a ship approached the dock, the barge would have to be moved. Completing repairs from above, the dock was removed in small, manageable pieces, and the lack of interruptions allowed continual progress. Despite a significant amount of repair work done by hand, including removal of 2,500-lb. concrete chunks, crews working around the clock completed the project in just two-and-a-half weeks.
Structural strengthening of the State University of New York (SUNY) Health & Science Center parking garage employed carbon fiber technology similar to that used in the aerospace industry. The 360,000-sq.-ft., 933-space parking structure, featuring three below-grade and seven above-grade levels, was built in 1967 using a cast-in-place reinforced concrete moment frame. The floor design incorporated a one-way joist/slab supported by beams of equal depth; however, during construction, a dome pan was used, creating a waffle floor slab appearance.
Immediately following construction, a structural crack perpendicular to the one-way joists appeared on all supported levels. An investigation revealed that a major structural error had occurred, and a substantial amount of the negative-bending reinforcing steel was insufficiently developed past column supports. Upon discovery of the error, the garage was shored full height and a corrective solution was implemented. However, over time, the parking structure’s condition deteriorated due to corrosion damage from deicing salts. Much of the waterproofing system and expansion joints began to fail, and many beams and columns were spalled from corrosion damage. Further, the structural concrete topping had debonded in large areas. To continue repairing the concrete overlay was ill advised, since the original defect remained untreated.
Meeting such challenges, SPS used carbon fiber reinforced polymers for strengthening the structure. CFRP is similar to material used to build the stealth bomber as well as the next generation of Boeing and Airbus jumbo jets. The project arguably stands as one of the largest top-side FRP strengthening applications in the U.S. Besides proving to be a cost-effective repair method, CFRP increased the headroom in a low-clearance structure, as well as eliminating the risk of future repair costs on a chloride-filled concrete overlay. SPS managed the project in 11 phases, effecting removal of only 100 spaces at a time.