pipe penetration on structural members

[RLC32681]

Hi guys, I need to prepare pipe penetration (vertical and horizontal) details on structural members (beams, slabs, walls and staircase). Any reference that you can suggest? Is there any standard details that can be follow? E.g., for beams, penetration is allowed at some distance from the support. How about if pipe sleeves is not place prior to pouring, can it be drill in the beam? at what particular locations? Can you suggest construction methods?

Thanks in advance.

 

[asixth]

It is best to know the location of any conduits prior to pouring the slab so the reinforcement can be suited to pass around it. It is possible to core through structural elements after the concrete has been placed. I would not recommend coring near a support, it will reduce the punching shear capacity at the support and it is the most highly stressed region of flat slab construction, so if reinforcement is cut it is will significantly reduce the strength of the section.

If you need to locate the reinforcement after the slab has been placed, it is best to use a ground penetrating radar, it will be able to locate reinforcement accurately to a depth of 300mm (12") if it is operated by a competent user. The JRC Handysearch looks like a good piece of equipment. I had a sales rep demonstrate one for us last week.

Otherwise, try and locate openings in regions common to two middle strips. The concrete society put out a paper titled the provision for openings in reinforced concrete beams that may also be worth a look at.

 

[csd72]

Google

Floor Openings in Two-Way Slabs
By Mota, Michael C

It is an article in structural engineer or structure so it will be somewhere in the archives. This will help with your understanding of the issues.

You have not said what the material is that you are doing these in, I have assumed it is RC.

 

[RLC32681]

How about pipe penetration on wall, staircases and elevator shaft, it is possible? I hope someone can recommend construction procedure how to do it or any reference for possible details.

 

[asixth]

If the opening in the wall is small, then the interrupted reinforcement can be displaced or additional bars can be placed either side of the opening. This will create a band which will strengthen the wall around the opening.

This is a detail, I prefer to see interrupted bars re-positioned either side of an opening opposed to trimming around the opening with shorter bars. You need to prove the concrete can span around it.

 

[RLC32681]

In case for future use, do you recommend coring for pipe penetration? I have a lot of pipes, the largest is 160mm dia. How about I have 3 pipes place side by side? Any help for the detailing.

 

[Bagman2524]

most detailing of rebar around penetrations I've seen also includes diagonal bars at each "corner" of the penetration

 

[hokie66]

RLC,
Your question has no one answer. Holes have to be located with respect to the way the structure works. Areas to avoid are adjacent to columns in flat slabs and flat plates, and near columns in beams. For holes made prior to casting, analysis or at least assessment should be done of each proposed penetration. For holes cores in hardened concrete, same procedure.

 

[TXStructural]

As a general rule, reinforcement is there for a reason, so coring should be planned to avoid rebar. One exception is minimally-reinforced, one-way slabs, which can usually handle single bars being cut by penetrations.

Sleeving through beams can be done anywhere, so long as you have considered the loss of section in your design. It may require additional section (deeper, wider, haunches) to maintain shear capacity near supports.

ACI 318 allows slab and wall reinforcing to be displaced (i.e., in plan for slabs) up to 3 inches to accommodate penetrations. Where openings are larger, corner bars are used to avoid cracks from re-entrant corners. Generally, added bars, equivalent to those which are discontinuous through moderate size openings, are placed to either side of the opening and developed by laps.

Cutting an opening in an existing slab requires a firm grasp on the actions of the slab and the pathways for forces. In new design, you can tell the forces where to go by design, but in existing structures, they are where they are, and dramatic changes can result in serviceability and strength problems.

 

[RLC32681]

Thanks for the info guys. I still have one question, we have a portion in which slab is hollow core. what I am planning is to inform the supplier that they incorporate this sleeves prior to fabrication. At some portion of the building, I have some problem on clear height, thats why I am taking in to consideration to pass thru some pipe penetration on the beams. Is there any limitation for the pipe diameter? Or any reference. How about if it is for future used, Can you recommend coring? what is the maximum diameter of pipe that is possible.

 

[TXStructural]

It sounds like you are talking about precast, prestressed hollow core, and the answer to coring these is an unequivocal "NO".

You can sometime core through cast in place, post-tensioned, but the risk if damaging a tendon, and/or losing critical section is frequently not worth it. In precast members, the manufacturer would need to approve location and size. You cannot risk cutting or grazing a tendon (other considerations aside.)

 

[RLC32681]

exactly, almost 90% of slab are precast. Yah I already send querry to the supplier if possible to have coring or if they incorporate the sleeves prior to casting.

Any suggestion on how to do (construction method) coring on other structural members like RC beam, stair, and elevator shaft.

 

[TXStructural]

A coring contractor will generally use a hammer drill up to one inch, and a daimond coring bit on a coring rig over that. For horizontal boring, the rig will usually be mounted to the surface of the material being cored using concrete anchors.

It was unusual, but I did have a guy core drill a PT slab with a hand rig, so he "could feel if anything wasn't right", like maybe a misplaced tendon.

You will need to know where the reinforcing is for most structural members which are not just reinforced with minimum steel. GPR can work for most cases, but I did have to get radiographs for at least one case (misplaced PT in a beam.)
Up to 6 or 8 inches, you might be able to use Ferroscan, Profometer, or another magnetic or inductive scanner.

There are several NDT methods for locating bars and tendons, so it might be best to hire a competent inspection firm to locate the reinforcement.

 

[RLC32681]

TXStructural,

Using hammer drill can be core up to one inch. How about for larger holes? I have a service pipe with diameter equal to 160mm.

Can you reccomend core more than 1 hole? e.g. 3 holes place side by side passing thru beam. What would be the maximum pipe diameter that you can reccommend and what would be the clear distance between pipes? Is there any need to put reinforcing steel between pipes?

 

[TXStructural]

The method used for drilling is typically up to the contractor. Any reputable coring contractor can easily core 6 inch (150 mm). (Core drilling and hammer drilling are different methods to similar ends.)

Since you are designing these in, do not design for them to be cored, rather, sleeve the penetrations. Side by side is fine, as long as you have considered the penetrations when calculating strength. Horizontal penetrations through a beam, for instance, might require stirrups to be placed between the penetrations. Also, plan for horizontal penetrations to be outside the compression block in sections with heavy flexural stress. Horizontal penetrations may interfere with longitudinal reinforcing placement, so look carefully at this. DO NOT attempt to relocate prestressing strand to avoid penetrations - move the penetration. Avoid penetrations near post-tensioning anchorages.

Vertical penetrations through beams may require the beam to be wider to accommodate the loss of section, both for flexural strength and shear. You may be able to offset a loss of concrete (Vc) with additional shear reinforcement (Vs). Again, a 160mm pipe might be sleeved at 170 or 180 mm, which will probably interfere with longitudinal reinforcement, so look carefully at this. Make the beam wider if needed.