Partial Depth Bridge Deck Replacement
Partial Depth Bridge Deck Replacement
(OP)
Hello all,
Looking at rehabbing an old bridge deck by means of a partial depth deck replacement on the entire bridge. Existing deck and overlay would be hydrodemolished off to free the existing top mat of black steel. The top mat would be removed and replaced with new stainless steel reinforcement as per the Client's wishes. Deck would be recast to original thickness and asphalt overlay added. Doing some research,I haven't been able to find much regarding complete replacement of the top mat of reinforcement... most things I find involve limited areas of removal in which the top mat is maintained in the rehab.
Anyone have any experience conducting something similar? Comments/concerns with procedure?? My concern right now is the significant depth of removal results in a pretty thin deck that needs to support the hydrodemo equipment. Haven't crunched any numbers yet but not feeling too comfortable about that. Another thing I've thought about is that the existing bottom deck layer and the new top deck layer would really have no mechanical connection between the two. Composite action would rely on the interface shear bond. With such a large plan area, maybe this is a non-issue. Curious to hear thoughts on this rehab approach.
Thanks
Looking at rehabbing an old bridge deck by means of a partial depth deck replacement on the entire bridge. Existing deck and overlay would be hydrodemolished off to free the existing top mat of black steel. The top mat would be removed and replaced with new stainless steel reinforcement as per the Client's wishes. Deck would be recast to original thickness and asphalt overlay added. Doing some research,I haven't been able to find much regarding complete replacement of the top mat of reinforcement... most things I find involve limited areas of removal in which the top mat is maintained in the rehab.
Anyone have any experience conducting something similar? Comments/concerns with procedure?? My concern right now is the significant depth of removal results in a pretty thin deck that needs to support the hydrodemo equipment. Haven't crunched any numbers yet but not feeling too comfortable about that. Another thing I've thought about is that the existing bottom deck layer and the new top deck layer would really have no mechanical connection between the two. Composite action would rely on the interface shear bond. With such a large plan area, maybe this is a non-issue. Curious to hear thoughts on this rehab approach.
Thanks






RE: Partial Depth Bridge Deck Replacement
With no experience in this approach....
Seems like you are opening Pandora's box in terms of repair and retrofit. Even if you have good moment positive moment capacity from reduced concrete section (very reduced!) How will you deal with areas of negative bending moment? I would expect cracking over beams and supports. It seems like the client will be chasing repairs in the remaining deck section as well
Jeff
Pipe Stress Analysis Engineer
www.xceed-eng.com
RE: Partial Depth Bridge Deck Replacement
Crunch the numbers. I'm not talking about a sophisticated computer model. Just take a preliminary simplified approach. Consider the remaining span depth (after top mat removal), the self weight of that span, the length of the span, and a reasonable construction live load and see what "should" happen with those assumptions.
As a former bridge Contractor, I've rehabilitated a fair number of bridges... but none in that (IMHO, risky) way.
Can the span be supported with falsework during the rehab?
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Partial Depth Bridge Deck Replacement
RE: Partial Depth Bridge Deck Replacement
Strongly suggest that you put an assumed construction load of 50 PSF on the slab (with upper mat / concrete removed) and find out what will happen. If the span collapses... then the detail repair design is irrelevant.
www.SlideRuleEra.net
www.VacuumTubeEra.net
RE: Partial Depth Bridge Deck Replacement
RE: Partial Depth Bridge Deck Replacement
The key thing with a bonded overlay is surface preparation. Depending on the material, finishing and curing is also important. In NY we use mircosilica concrete - works very well - but it's not very forgiving.
RE: Partial Depth Bridge Deck Replacement
Bridgebuster - we would be using a high-performance concrete overlay. We've locally completed entire bridge decks all at once but the top layer is usually maintained... concerns regarding structural integrity are almost non-existant. In order to avoid the many many splices, etc., doing this in stages in not an option (we are already doing the bridge in two stages to be able to maintain traffic). There will be a closure pour required down the middle of the deck.
RE: Partial Depth Bridge Deck Replacement
As far as a new steel mat is concerned, typically the replacement mat is based upon a structural design as a new slab, with consideration of what is being left behind ... all the pieces of the puzzle need to fit together. The new should meet current code.
Bonding new to old should not be difficult as long as the proper procedures are followed. No mechanical connection required on any of my projects. You should be able to develop a bond strength of over 1.5 MPa, generally in excess of the tensile strength of the 1950's parent concrete. Keep in mind that the hydrodemo equipment produces an excellent surface to bond to as long as it is kept clean and the replacement concrete is placed in a reasonably short time frame after demo. Some form of bonding agent is necessary, a good quality one can help your bond strengths. Have bond testing done at least several days after the pour.
RE: Partial Depth Bridge Deck Replacement
Indeed, the new top mat will be designed with several concerns in mind including the fact that we are incorporating new (large) deck overhangs and higher crash level traffic barriers as well as the fact that the deck is currently overstressed and under-reinforced for negative moment over the piers. Design of the new top mat will be relatively straight forward.
I'll look into your recommendation for a bonding agent and will see what we have done on other partial depth repairs. As you mention, I haven't ever seen a mechanical connection provided between the layers so the bond must be sufficient for the two concrete layers to act as a single unit.
There has been some history with repairs/rehabs and engineering work on this project so I just want to cross all my t's and dot my i's on this one.
Thanks