Structural Repair Outline
While performing pre-construction services on a precast parking garage for a forensic engineer, a large crack was noticed at the mid-span of a double tee stem in a parking garage. The unique stressing of the precast parking garage required our project manager to develop a creative double tee stem repair solution. The engineer directed us to excavate into the stem to determine the cause of the crack, where we found that 6 of the pre-stressing strands had corroded and were no longer intact. The double tee had to be shored and would need to be repaired to re-establish its’ structural capacity. The work needed to be fast tracked and done while the garage remained operational.
Creative Double Tee Repair Solution
Restruction Corporation received a sketch from the engineer utilizing Grab-its, post tensioning devices, and pressure jackets to repair the DT stem. The design was not typical and he wanted to make sure the solution is a viable construction solution. We evaluated the design for him and helped determine the geometry and materials that would work. The design allowed us to execute the repair in a short time frame keeping the garage open for use.
The repair is executed in three stages.
- Excavate the stem enough to allow installation of both pressure jackets and Grab-its.
- The excavation had to be done with care to make sure the pre-stressing strands to remain were not damaged in any way.
- Install both pressure jackets and connect the broken pre-stressing strands with the Grab-its.
- Pre-stressing strands entering and exiting the pressure jackets was critical.
- Once the system was oriented and connected we then grouted the pressure jackets full with high strength non shrink grout.
- Install mild reinforcing for new DT section. The new section had to be larger to encapsulate the geometry required for the pressure jackets and Grab-it system.
- Form the new beam section leaving the Grab-its exposed for stressing after the new section had gained sufficient strength to transfer the stressing loads across the excavation without damaging the existing DT.
- Place the section with repair material and allow it to cure.
- Re-stress the pre-stressing strands with the Grab-its.
- Form and place the section left open for stressing.
- Allow material to cure.
- Remove shores.