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RE: Debonding of precast plank topping[Subject Prev][Subject Next][Thread Prev][Thread Next]
- To: <seaint(--nospam--at)seaint.org>
- Subject: RE: Debonding of precast plank topping
- From: Harold Sprague <spraguehope(--nospam--at)hotmail.com>
- Date: Thu, 3 Jan 2008 17:23:58 +0000
Apparently there was little of no provision to provide a mechanical bond to augment the adhesion. I have used a similar application in the past and have required both a raked surface and a truss embedded into the precast to provide a positive bond to the topping specifically to mitigate the problem you have identified. |
Investigate the possibility of creep, shrinkage and strand bond relaxation. If the bond in the precast strand is adequate, the precast concrete is sound, and topping concrete is sound then it appears that it a repair may be possible. You can calculate the anticipated precast deflection assuming zero bond on the precast. This should verify your hypothesis. It is a bit of a guess because you will have to assume an initial elevation.
1. Calculate the horizontal shear between the topping and precast assuming zero bond. Design new shear connectors in lieu of bond.
2. Jack and shore the slabs into place with allowance for DL deflection of the composite section.
3. Drill holes through the topping and through the precast at a workable uniform spacing (locate using NDT and avoid the strands).
4. Using a plate with a welded headed stud in the hole, place a repair concrete in the hole to establish the required bond between the precast and topping. Calculate the required hole size assuming no contribution from the headed stud and all shear is resisted by the concrete. (This is very conservative, but may be warranted). The headed stud can be wired in place from the top and the plate on bottom will serve as a form to hold the repair concrete in place. If you use rectangular plates and cut rectangular holes, you may be able to do all of the repair from the top. (Exception: Obviously the shoring will require access from the bottom.)
5. Cure the concrete, remove the shoring, measure the final deflections to verify the adequacy of the repair.
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