Post Tensioning Repair Robinson Parking Garage

The Robinson Center Parking Garage, located in downtown Little Rock, is a post-tensioned (PT) concrete structure with a paper wrapped, button-head wire PT tendon system. The below-grade garage had signs of capacity loss with large deflection cracks present within the slabs and beams. Concrete had begun to spall and was at risk of falling on cars and pedestrians.

The owner needed a team to perform an investigation and associated testing to determine the root cause of the capacity loss and formulate a solution that would extend the life of the structure. The Investigate-Design-Build (IDB) team of STRUCTURAL (a licensee of STRUCTURAL TECHNOLOGIES) and Walker Restoration, with support from STRUCTURAL TECHNOLOGIES were selected to provide turnkey services to inspect the garage, provide design and engineering services to address the issues, and implement the best repair option.

The IDB team performed a comprehensive condition assessment on all of the structural elements and in order to properly determine the existing capacity of the structure. Destructive testing was utilized to evaluate the existing PT system, confirm accuracy of as-built drawings, map the corrosion levels present, and estimate the life expectancy of the structure. As a result of the investigation, the number of broken tendons more than doubled versus what was originally projected, creating both a financial and schedule conflict for the client. The IDB team worked with the owner to evaluate the project scope and identify areas where money could be reallocated in order to complete the necessary structural repairs and as a result, the additional tendons were repaired with limited cost impact to the project.

The use of button-head PT systems is uncommon and result in a lack of industry standard for repairing and are typically replaced when service life is exceeded. Working with Walker during the design phase, STRUCTURAL TECHNOLOGIES designed and manufactured a unique splice block enabling the repair of the button-head tendons which eliminated the need for a full replacement. This provided substantial financial savings to the client along with a reduction in schedule.

STRUCTURAL crews performed button-head tendon splice repairs to repair structural capacity within the slabs. Corroded supplemental steel was removed and new steel was reinstalled. Steel supports were installed along the perimeter columns to increase shear capacity of the beams. Epoxy injection was used for slab and beam cracks and a new traffic bearing waterproofing membrane was installed over the concrete repairs.

Through extensive pre-planning and the development of both a site-specific safety plan and quality assurance program, the repairs were completed under the highest level of quality and maintaining the safety of the community and crews.