Post-Tensioned Slab Opening for New Staircase
- 900ft2 post-tensioned slab opening
- De-tensioning and modification of post-tensioned reinforcement
- Installation of V-Wrap™ FRP Strengthening System
- Location: Southwest United States
- Engineer of Record: KPFF Consulting Engineers
- Specialty Contractor: STRUCTURAL
- Material Supplier: STRUCTURAL TECHNOLOGIES
A new tenant in an office building in the Southwest United States wanted to connect the two floors they were leasing with a new stairway. The four-story mixed-use office building was constructed using post-tensioned concrete, which required a team with experience to design and implement a solution.
The team designed a detailed project plan that was engineered to ensure the safety of the structure, so the occupied areas of the building would not be negatively affected during the construction process.
Construction activities began with radiography (x-ray) to identify precise tendon locations and depth. Following the confirmation of tendon locations, a structural steel support system was installed around the perimeter of the future opening, and CFRP system were installed within the area of deficient negative moment reinforcing. Additionally, shoring frames and a support platform were installed below the slab opening.
The design team developed a phased program to ensure that no more than 35% of the strands in each direction were de-tensioned and re-tensioned in each phase. This approach ensured that the slabs were not overloaded and maintained adequate prestressing force in the adjacent slab bays. Each phase included a similar process that included de-tensioning tendons, re-profiling tendons, and the installation of new anchorage systems and reinforcement.
Once the final tendons were stressed, the shoring frames below on the third floor were removed to highlight a new stairway opening. Overall, the project was completed in just six weeks, and all budgetary, safety and quality goals were met successfully.