CULVERT

[Hira Malik]

I am trying to do the design of culverts (single and multi cell) using moment distribution method.

1. Confused about how to calculate horizontal and vertical moments in the wall. Which one will govern?

2. ACI 350-01 says use minimum shrinkage reinforcement ratio as 0.003. Which seems to result in #4 bars @4"c/c which seems too much.

3. Can anyone give me the link to download ACI 350-06 ?

4. Any excel sheet or document using moment distribution for culvert design will really help.

[UmarMakhzumi]

Hira,

On 2018-03-12 at 5:33 AM, Hira Malik said:

1. Confused about how to calculate horizontal and vertical moments in the wall. Which one will govern?

Goto this post and download the attachment that shows how to calculation horizontal and vertical moment in the wall.

 

On 2018-03-12 at 5:33 AM, Hira Malik said:

2. ACI 350-01 says use minimum shrinkage reinforcement ratio as 0.003. Which seems to result in #4 bars @4"c/c which seems too much.

Please see this:

 

On 2018-03-12 at 5:33 AM, Hira Malik said:

3. Can anyone give me the link to download ACI 350-06 ?

These requests can't be entertained as it violates forum posting policy. Please see forum posting rules here.

On 2018-03-12 at 5:33 AM, Hira Malik said:

4. Any excel sheet or document using moment distribution for culvert design will really help.

Please see answer to 1. The coefficients provided in the document are very easy to use. 

Thanks.

[Hira Malik]

25 minutes ago, UmarMakhzumi said:

Please see answer to 1. The coefficients provided in the document are very easy to use.

Those are for 2 way slabs types I guess ? My wall is 17m in span and 1.5m in height i.e. one way and main reinforcement will be along height... so it will be simply designed by taking soil lateral loads as (ka*unit weight*height) right?

[UmarMakhzumi]

On 2018-03-13 at 10:56 PM, Hira Malik said:

Those are for 2 way slabs types I guess ? My wall is 17m in span and 1.5m in height i.e. one way and main reinforcement will be along height... so it will be simply designed by taking soil lateral loads as (ka*unit weight*height) right?

(ka*unit weight*height)  is the base pressure of the triangular force. You need to use ka*1/2*Gamma*h*h as the force and then multiply the force by lever arm (I think its 1/3rd (likely) or 2/3rd height - see literature) to get the moment at the base. If you have got a long wall, you should also do a check for counterforts to see if they are required or not. I am not sure why you called this a culvert, if its a long retaining wall. If you have a slab on top level, then the design would be different. Can you share a picture or a drawing.

Thanks.

[Hira Malik]

Yes its a culvert with long walls and slab on top. And so it cant be designed as a retaining wall. But due to longer length, main reinforcement will be that along the shorter span i.e. height (vertical reinforcement). I was thinking it should be designed using attached formula for for FEM when performing Moment Distribution, and W will be same as we do for triangular load. I was just confused if I need to use the walls coefficient method but I guess that's for walls with 2-way action which isn't the case here.

 

Edited March 16, 2018 by Hira Malik

[UmarMakhzumi]

On 2018-03-15 at 11:07 PM, Hira Malik said:

Yes its a culvert with long walls and slab on top. And so it cant be designed as a retaining wall. But due to longer length, main reinforcement will be that along the shorter span i.e. height (vertical reinforcement). I was thinking it should be designed using attached formula for for FEM when performing Moment Distribution, and W will be same as we do for triangular load. I was just confused if I need to use the walls coefficient method but I guess that's for walls with 2-way action which isn't the case here.

 

There is something else that you need to consider. For the case when you have a top slab, that means that you will have two walls - one on each side with ta top slab. So technically speaking the lateral pressure from each side should cancel each other out. But your wall should still be designed to transfer the forces as they are part of load path. Long story short, yes you can use the formula specified but if your length is long, check for counter-forts so that you don't get two way bending of the vertical wall.

Thanks. 

[Hira Malik]

1 hour ago, UmarMakhzumi said:

So technically speaking the lateral pressure from each side should cancel each other out.

Not sure about this. Both walls will act individually won't they? Yes the inward water and outward soil pressures on each one wall will cancel each other but not completely. Therefore, I am considering the Culvert as empty to maximize the outward soil pressure.

[UmarMakhzumi]

Here is what I was thinking. If your culvert is a buried box with a top slab then the lateral pressure from both sides would cancel each other out. Is this the case?

Thanks.

[Hira Malik]

6 hours ago, UmarMakhzumi said:

Here is what I was thinking. If your culvert is a buried box with a top slab then the lateral pressure from both sides would cancel each other out. Is this the case?

Thanks.

Yes. And each wall will have soil pressure from outside and water pressure from inside.

[UmarMakhzumi]

4 hours ago, Hira Malik said:

Yes. And each wall will have soil pressure from outside and water pressure from inside.

So there could be times when the culvert is dry and you only have soil pressure acting on your walls. The net soil pressure would equal out (as applied on both exterior faces) assuming that the construction sequence is to backfill both walls at same time. That would help you with sliding and overturning. But you will still need to reinforce your wall for the case of when culvert is dry and earth pressure is on the wall.

Thanks.

 

 

[WR1]

For any retained wall, always use all applicable cases e.g. for a water tank;

case1: full tank, no backfill

tension on external side of wall at mid span (if top slab exists) check crack width for 0.27mm

tension on inside of wall at base and at top (if top slab exists) check crack width of 0.15mm

 

case2: tank empty (e.g. for cleaning); backfill exists

this is opposite of case1