Parapet upstand/stringcourse/edge beam

[RME1]

Hi,

I am doing a parapet replacement job in the UK, which involves breaking out the existing edge cantilever and recasting it with more rebar to increase the capacity. On the deck this is not a problem as the new rebar can just be lapped onto the existing bars to tie it into the rest of the structure. However, the parapet continues onto mass concrete wing walls.
My problem is this - As I have no reinforcement in the wingwall to lap the new bars onto, how much of the wingwall do I have to reconstruct as reinforced concrete?

 

[parapetguy]

This is a rather difficult question. It sounds like there is not an expansion joint between the bridge and the wingwall. Is this correct?

If that is the case, you might want to consider stopping at the existing mass concrete wingwalls and not extending the rebar into them. As long as the existing wingwall is adequate to serve the purpose of containing traffic and the new parapet you are building does not depend on the wingwall for strength you shouldn't have to do anything to it. The new condition should be no less than the existing.

 

[LittleWheels]

There would be a joint between bridge and wingwall but the parapets are being replaced with a stronger type, transferring more impact loading into the deck and wingwall. It is unlikely that the wingwall has had to deal with any impact loading previously but it should be able to resist it. Now it won't.

I've had to deal with this problem previously (when working in the UK) and didn't find any answer that I was completely happy with.

 

[RME1]

Dave, you're right there is a movement joint between the deck and the wingwall.
The solution we have eventually come up with invovles determining the point on the wingwall where the tensile stress in the mass concrete is <1N/mm2. This was done using a combination of pucher charts and 45 degrees distribtion with depth. We then propose to reconstruct the wingwall above this point with reinforced concrete and resin anchor some starter bars into the existing concrete to tie the new and the old together.
If anyone wants to comment on this solution, then I'm interested to hear other views.

 

[1983923]

Hi,

I am working on a job exactly the same as the one you had. Could you share your experience and how you deal with the problem in the end?

Thanks.

 

[RME1]

Well I wanted to avoid reconstructing the whole wingwall if possible, so we tried a few different methods to try to get a favourable result. This might not sound like the correct way to go about things, but it was a case of knowing that this huge lump of concrete wasn't going to go anywhere, but not being able to prove it with a conventional approach which is quite conservative. In the end we distributed the post loads down the wall at 45 degrees and calculated the tensile stress in the mass concrete. The wall gets thicker with depth so the stresses at the extreme fibres get lower the further down you go. We found a point where the stresses according to this method were less than 1N/mm2. At this point we assumed the wall was fixed and modelled the wall above this point using a pucher chart for a cantilever slab. This gave us a depth of about 1-2m that still failed. This area is to be reconstructed with reinforced concrete and tied into the rest of the wall with resin fixed bars.
A grillage model of the same wall produced worse results as the load didn't distribute very welll

 

[valleyboy]

Hi RME1

I think in principle your approach seems OK, but wondered how you arrived at the value of 1N/mm2 for tensile resistance of concrete ?

It is suggested within clause 4.2.3.4.1 of BS 8002 that the allowable stresses on mass concrete should be limited to 0.28N/mm2 and 0.55N/mm2 in tension and shear respectively.

VB