Structural Concrete Sewer Chamber
Structural Concrete Sewer Chamber
(OP)
Hey fellas,
I'm reviewing a concrete sewer chamber in which I have no prior experience. I'm looking for some experienced input. Please view both the plan view and secion. My thoughts are as follows:
1. The design seems to combine a chamber and a riser cone manhole, not sure how typical this is but it doesn't look right to me.
2. The W8 x 31s interrupt the rebar shown in the secion, creating a cantilever effect. The W8 x 31s also leave an area just adjacent to the manhole with no support, other than the small section of concrete the would pour around the W-shape.
3. I could remove the W-shapes and heavily reinforce the area around the manhole opening.
4. What prevents the conical section from failing due to shear under a truck load. I understand they are reinforced and manufactured in those shapes. Is the best to contact the intended manfacturer for this situation.
Thanks for any help!
I'm reviewing a concrete sewer chamber in which I have no prior experience. I'm looking for some experienced input. Please view both the plan view and secion. My thoughts are as follows:
1. The design seems to combine a chamber and a riser cone manhole, not sure how typical this is but it doesn't look right to me.
2. The W8 x 31s interrupt the rebar shown in the secion, creating a cantilever effect. The W8 x 31s also leave an area just adjacent to the manhole with no support, other than the small section of concrete the would pour around the W-shape.
3. I could remove the W-shapes and heavily reinforce the area around the manhole opening.
4. What prevents the conical section from failing due to shear under a truck load. I understand they are reinforced and manufactured in those shapes. Is the best to contact the intended manfacturer for this situation.
Thanks for any help!





RE: Structural Concrete Sewer Chamber
RE: Structural Concrete Sewer Chamber
I would try this without the wide flanges, I have never seen a manhole yet that required this sort of reinforcement.
RE: Structural Concrete Sewer Chamber
Just something else to think about.
Structural reinforcement of junction boxes isn't my bag, but I do see your concerns about those steel beams cutting off the rebar. Never seen beams like that in a detail before. I would think the thing to do would be to leave the rebar continuous across the whole section, and if necessary just beef it up. Fair warning, I haven't touched reinforced concrete structural design since undergrad.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Structural Concrete Sewer Chamber
RE: Structural Concrete Sewer Chamber
It looks like a structural engineer designed the chamber and then someone stuck a riser on top of it. There are no details on the riser but many on the chamber.
1. There are no details for the connection of the pipe to the chamber.
2. There is no flow channel shown.
3. Riser connections and gaskets are not detailed.
4. The VCP will have to be replaced if you are installing a new sewer under it.
5. The steps should be above the flow line of the sewer.
6. See the attached example.
RE: Structural Concrete Sewer Chamber
Perhaps our municipalities down here are simply the subject of malicious marketing? I've personally got no bad experience with the stuff, because I've never been on a project where we called it out.
Hydrology, Drainage Analysis, Flood Studies, and Complex Stormwater Litigation for Atlanta and the South East - http://www.campbellcivil.com
RE: Structural Concrete Sewer Chamber
cvg, I agree this should be done without the wide flanges and that the walls should be used as a bearings where possible.
bimr, If I use that detail the manhole base will need to engulf all 3 pipes which would greatly lengthen the concrete reducer cap. I'm concerned with how much load that cap would be albe to take if extended 'x' feet further from the edge of the wall.
Disregarding my particular design, does anyone have a procedure for analyzing openings in reinforced slabs and reinforced vertical walls. ACI 318-05 13.4 doesn't seem to go into much detail. If I punch a circular opening through a two-way slab reinforced T & B how many kips/ft can it take. Likewise, if I punch an opening at the corner of a manhole and the uniform load rests on the slab/wall how much liner load can it take?
RE: Structural Concrete Sewer Chamber
The manhole detail was uploaded to provide you with general arrangment details, not a a substitute design.
RE: Structural Concrete Sewer Chamber
RE: Structural Concrete Sewer Chamber
In reality it's also more complicated than the sample because most of the walls intended to bear the load also have pipe penetrations.
RE: Structural Concrete Sewer Chamber
The other WF breaks up the integrity of the top slab. Designer should have just used beam steel with a thicker slab if warranted. Delete that too.
As for the riser, the walls of the riser should align with the exterior walls of the vault to minimize impact on the top slab. The small concrete lateral restraint ring at the bottom of the riser is not necessary either. This cam be done with a small inset in the top slab to receive the riser rather than another small pour.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask