Grade Beam - Bridging over pipes + Steps
Grade Beam - Bridging over pipes + Steps
(OP)
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
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






RE: Grade Beam - Bridging over pipes + Steps
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
RE: Grade Beam - Bridging over pipes + Steps
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
RE: Grade Beam - Bridging over pipes + Steps
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.
RE: Grade Beam - Bridging over pipes + Steps
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.
RE: Grade Beam - Bridging over pipes + Steps
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.