Structural Design of Restrictor Wall inside of Existing Reinforced Concrete Pipe

[oengineer]

I have been assigned to design a restrictor wall inside an existing RCP.

Here is an example image of the task I have been given:

I am seeking some guidance about how to tackle this assignment. I have never preformed structural designs for brick.

I imagine that I need to design the brick to resist the hydro static loads acting on it when water is flowing through the pipe. Are there any design examples to for this situation?

Suggestions/comments are appreciated.

 

[oengineer]

As long as you don't reinforce it smile

For non-reinforced CMU blocks, as shown in my original sketch, how would you ensure that the block wall is attached to the existing RCP?

Since it is non-reinforced, I would think it would not be doweled in ti the existing RCP. But If it's not doweled, how does one make sure it stays in place?

 

[BridgeSmith]

I think you've hit on a major problem with using block or brick for this wall, oengineer. Also, if you need internal reinforcement, it will be very difficult to incorporate with either one. I think concrete is a much better option, whether poured through a hole in the top of the RCP, pumped in under pressure, or sprayed on.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[oengineer]

I think you've hit on a major problem with using block or brick for this wall, oengineer. Also, if you need internal reinforcement, it will be very difficult to incorporate with either one. I think concrete is a much better option, whether poured through a hole in the top of the RCP, pumped in under pressure, or sprayed on.

Even if I use shotcrete, I would still need to epoxy dowel my rebars into the existing RCP wall.

Wouldn't it be difficult to epoxy dowel rebar into the circular wall?

It seems that it has been indicated early in this thread that doweling into the existing RCP would be difficult to have a contractor do?

 

[dhengr]

Oengineer:
There is more to this problem than has been expressed yet. It seems to me that you need access to the inside of the 36” RCP pipe from above and an ability for an upstream cleanout system, at a given location. The upstream reach will collect grit and debris for lack of sufficient flow and might need regular cleanout. This probably means a manhole or access box of some sort. The access box could be cast concrete with the 14” opening on one side and the 36” RCP on other. In terms of the closure/restrictor structure, you might think in terms of a 4x4 (whatever size) stainless steel angle ring, probably in two halves for fit-up in the RCP, etc., which can be anchor bolter to the RCP, and can transmit the shearing load down the length of the pipe. Can this occur at a normal joint in the pipe, where we could weld shear lugs to the 4x4 angle ring which fit into the joint to transfer the shear loads in a more positive/uniform fashion? The closure wall can be several wythes thick, with one face (down stream) built as a tension wythe, maybe a round stl. pl. and other wythes as compression and moisture protection wythes, maybe even arching action if many wythes. The advantage of a masonry wall, as in old sewers, is that it is less susceptible to corrosion. There could be some sort of a bonded moisture membrane in the wall makeup. If this wall was at the manhole it could be cast concrete, with ability to remove forming from both sides, and a need for some top closure system over these two flow sides.

I would like to know more about why this restriction is needed. They are trying to limit the downstream flow for handling reasons during a sudden overloading, and have the storage capacity upstream? They are trying to increase the downstream flow velocity, at some normal depth, to transport solids downstream? You should talk with the hydraulics guys about this as it may influence the structural considerations or the shape of the 14” opening.

 

[oengineer]

I would like to know more about why this restriction is needed.

To be honest, I am not sure on the exact reason for the specific restrictor.

I received a request from an engineer to provide a design.

Based on the previous comments in this thread, i am leaning towards non-reinforced brick or shotcrete for the restrictor. My main concern is determining how to ensure the restrictor remains in place.

I am new to this design, but seeing this detail means to me that there is a solution to provide such a restrictor.

 

[oengineer]

It seems to me that you need access to the inside of the 36” RCP pipe from above and an ability for an upstream cleanout system, at a given location. The upstream reach will collect grit and debris for lack of sufficient flow and might need regular cleanout. This probably means a manhole or access box of some sort. The access box could be cast concrete with the 14” opening on one side and the 36” RCP on other.

Regarding where this pipe will be located, it will be punching/attached into a curb inlet.

I believe this is the access that you are asking about.

 

[BridgeSmith]

Wouldn't it be difficult to epoxy dowel rebar into the circular wall?

I don't see how it being circular would cause a problem. The main issue, as I see it, is the thickness of the wall. You'll only be able to go maybe 3" deep without breaking through everywhere. Even then, it could still happen. For this reason I would suggest using a mechanical anchor of some type. If it was me, I would probably spec a wedge type bolt anchor, like a Hilti Kwik-bolt, with a coupler sleeve and a few inches of all-thread to extend them into the restrictor wall 6" or so for stability. You won't need tension capacity; only shear, so you don't need the depth required for pullout capacity, just enough to prevent shear breakout from rotation. If you use small anchors, you shouldn't have a problem with them breaking out of the pipe wall.

Rod Smith, P.E., The artist formerly known as HotRod10