Parking Garage Repair -- A Case Study
With more than 24,000 parking garages in the United States, there is no denying the important role they play in society. However, as some of the structures begin to age, experience an increase in loads, and suffer the effects of chemical and de-icing salt usage, garages are often left in need of repair and retrofit. This has led many owners to seek cost-effective and efficient repair and strengthening programs -- all while trying to manage the challenge of keeping their customers happy with an adequate temporary solution for their parking needs. Innovative structural repair professionals have responded to these needs on a design-build approach by developing inventive solutions for meeting these challenges.
One example of this scenario is a parking structure that is adjacent to a 1 million-square-foot mixed-use facility in New York. Despite being subject to an environment that experiences severe freeze-thaw conditions and consistent exposure to de-icing salts, the parking structure was not regularly maintained during its life, which led to a failure at the second supported level. It provided parking for hundreds of New York state employees, so maintaining the integrity of the structure was crucial.
Anatomy of the Structure
Constructed about 35 years ago, the free-standing structure can accommodate about 700 vehicles, with a gross area of about 200,000 square feet. It consists of three supported levels and one additional on-grade level. Originally built using cast-in-place and precast-prestress concrete components, each floor was constructed with precast single-T beams supported by precast columns founded on cast-in-place concrete piers and spread footings. The 6-inch cast-in-place floors were constructed with eight wire button-head post-tensioned reinforced concrete and mild steel reinforcement in the temperature direction. Precast concrete spandrel panels constituted the north and south facade, while post-tensioned concrete spandrel beams made up the east and west elevations. Vehicular access is direct from the street level, and pedestrians enter the structure via two stair towers that are connected to the building.
Planning a Repair Strategy
Wanting to ensure a cost-effective and efficient process, the owner opted to use a design-build team for the project. Design-build encompasses architecture, engineering and construction services within a single contract. The process allows for early collaboration and exchange of ideas, as well as the opportunity to maximize team knowledge of systems and products. Such early collaboration furthermore serves to solidify the relationship-building and trust needed to take the project to completion. By utilizing the design-build delivery method, the owner ensured that the project was free of unnecessary change orders and disputes, which saved both cost and time.
The design-build team began the repair process with a full condition survey of the parking structure, which included chloride ion testing, petrographic analysis testing, post-tension probes and chain-drag/hammer sounding. The results of the survey indicated that, overall, the cast-in-place concrete slab was in fair to poor condition.
Design Challenges Revealed
The most critical design challenges were repairing the failed second supported level and all the cantilevered expansion joints. The structural integrity of the second support slab level was fully compromised by the failure of slab button-headed tendons. Conventional repair methods would require full removal and replacement of the slab. As an alternative to this invasive procedure, Structural Preservation Systems (SPS) -- a leading provider of structural repair and protection services with locations throughout the United States -- developed an innovative repair strategy that included replacing the existing wire system with a fully encapsulated monostrand post-tensioning system. The construction and tensioning sequence of this repair omitted the need for additional shoring. Each of these elements in the design strategy reduced time and cost, while prolonging the useful life of the structure.
The existing cantilevered expansion joints were removed full depth, redesigned and replaced with a highly reinforced short-span support cantilevered section. New traffic bearing glands were installed, as well as Teflon slide-bearing plates at the bearing seat. Placement of the new expansion joint concrete headers ensured that water would run off in a direction that was opposite the expansion joint. Through the use of new post-tensioning technology, monostrands were used to mend the broken button-headed tendons that were found throughout the deck. Further, spalls on the deck were repaired with 5,000 psi ready-mixed concrete. Cracked T-stems were injected with epoxy resin. Overhead spalls on beams and slabs were fixed using a polymer-modified repair mortar applied with an overhead trowel. Then, the entire deck surface was shot-blasted and sandblasted clean for the application of the saline sealer.
Ensuring Safety of Building Occupants
Because of the poor condition of the garage, the design-build team and the owner decided to close the garage for the repair project, which allowed multi-tasking to occur. This strategy shaved four months off the initial proposed phasing schedule. To accommodate the displaced cars, an outside parking lot was built on an adjacent vacant property. The work schedule ensured that the project would be complete in one season to avoid outside lot maintenance during winter weather.
Since the garage was attached to the building, full-height wooden enclosures were built to keep patrons out of the work area. Further, compressors were located at the far end of the garage and hard-lined to the work area to help reduce noise entering the building. Negative air units also were used to minimize airborne dust.
Beyond the structural repair, several other areas of the garage were updated. The old lighting systems were replaced with a new fluorescent system, and the garage was repainted, which helped the reflection of the new lighting system. Below standard perimeter rail protection was replaced with new rail to meet the existing code requirements. The entire parking deck was restriped, which included ADA upgrades. Further, signage and directional arrows were installed to help vehicle flow within the garage.
Success Created Through Teamwork
By employing the design-build delivery method for this project, the owner benefited from a streamlined approach with minimal disruption to clientele. In this delivery system, the teamwork between the owner, engineer and contractor begins at the onset of a project and includes the condition survey, quantity assessment, design, budgeting and scheduling. This strategy encourages cooperation and avoids the challenges that can occur in other project delivery methods.
Owners should strongly consider engineer-contractor teams when determining who is going to perform the work for their next project. Experience, financial stability, safety records and project staffing are all essential aspects that need to be considered. When the team is responsible for design, budget, quality, communication and safety for the project, everyone wins. With a proven performance in the parking garage arena, the design-build method demonstrates that it can save owners time and money on their next repair project.
Bob Pirro is Branch Manager for the New York/New Jersey office of Structural Preservation Systems, a unit of Structural Group. He can be reached at (973) 636-2700 or via e-mail at firstname.lastname@example.org