Grade Beam - Bridging over pipes + Steps

[rscassar]

Hi guys

I am currently designing a grade beam and have encountered a few issues.

1. What is a typical detail to ensure than a grade beam can span over a pipe? When the pipe is below the grade beam I feel it is quite straightforward that the pipe is to support the wet weight of the concrete before it hardens and then the beam can span the pipe. Is common for a pipe to pass thru the grade beam or should this be avoided at all expenses? I do not want to pass the pipe thru the beam because this is a reactive site and the soil is expected to swell.

2. I know this has been discussed before but I can't find any related threads. How do I properly detail a beam which cranks in elevation where the positive (opening) moment is trying to straighten the reinforcement and spall the cover concrete?

All responses will be welcome on this. Thanks

 

[a2mfk]

A grade beam on piers is a lot different then a typical footing, where you can step it down and have rebar details for pipe penetrations. I believe you have to treat this like any other beam and avoid penetrations, but if they are required, you want to put them in the center of the beam where shear is the least, and near the center of the span (if its a simple span) for the same reasons.

I don't know where to direct you to in ACI for other details but I am sure others. Maybe CRSI manual has some examples?

HTH,
Andrew Kester, PE
Florida

 

[msquared48]

It is a big nono to pass the pipe through a grade beam where significant settlement can occur. Personally, I would never do it under any circumstances without a sleeve and a lot of clearance in the sleeve for the pipe.

Regarding the second wuestion, this sounds like a similar circumstance to a wtep in a PT slab where you have to use transverse stirrups to contain the induced tension force.

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[dhengr]

Kikflip:
Put a compressible void form btwn. the pipe and the underside of the grade beam to allow the grade beam to deflect and settle or for the pipe to move with the soil without loading the pipe and damaging it. On the sloped grade beam, run the top bars straight on past the knee (change in top surface direction) and into the member and bend them to follow the far face if that much development length is needed.

 

[rscassar]

Thank you everybody for your contributions.

I am not going to allow the pipe to pass thru the grade beam and there is already compressible/collapsible void formers below the grade beam.

I am going to run the top bars past the knee (as dhengr suggests). I don't believe there will be any need to bend the bars to follow the far face because I should achieve full bar development before the bar extends that far.

Thanks again.

 

[csd72]

kikflip,

2 simple rules for detailing reinfocement at corners

no bends at inside corners
make sure that all reinforcement iss fully developed before it passes the inside corner

Concrete detailing is easiest to think of in terms of truss analogy. All concrete is compression strut only and the only tension ties are the reinforcement.

I have given you the tools now to figure out most concrete detailing issues from first principle. Good luck.