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    Categories: Concrete ReinforcementMethodsParking Garages

Creative Double Tee Stem Repair

 

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.

Execution

The repair is executed in three stages.

Stage 1

    • 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.

 

Stage 2

  • 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.

Stage 3

  • 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.

The owner was satisfied with the timely completion, cost effective construction proposal and finished product of this creative repair solution.

Steed Lopez :