Conduits and pipes embedded in slabs

[ajk1]

CSA A23.1 clause 6.7.5.4 says:

"unless approved by the owner, embedded pipes or conduits shall not be
(a) larger in outside diameter than 1/3 the thickness of the slab, wall, or beam in which they are embedded;
(b) spaced closer than 3 diameters on centres; or
(c) so located as to impair the required strength of the structure."

Question:
Should pipes or conduits be in the middle third of the slab, or does that not matter much?
Is it practical to place in the middle third of the slab?

I ask this question in relation to my review of all our office typical details, and not in relation any any specific project.

 

[WARose]

Should pipes or conduits be in the middle third of the slab, or does that not matter much?

The middle 1/3rd is the rule I've always heard. Checking several sets of old concrete notes (from several different companies I've worked for) that is what is called out. The logic I have typically heard is: you don't want it in the compression zone (of flexural stresses), and you don't want it too close to the edge of the tension zone either (for crack control).

Is it practical to place in the middle third of the slab?

If it's small enough. In most cases (when this detail is covered by a note) the max. size of the conduit is limited to about 1.5".

 

[ajk1]

Thank you WARose.

 

[bob33]

I have found that the MEP contractors normally do not comb through the structural drawings and specs looking for items like this. It would be better if the MEP consultants could also cover this in their drawings and specs. Regarding slabs, it is standard practice to place conduit directly on top of the bottom reinforcement. Also some piping may be required to be at a specific level (ice rinks for example). Of course, there are many other structural coordination issues regarding piping and conduit. This is only the tip of the iceberg.

 

[Tomfh]

For general situations we nominate middle third, as this keeps it away from flexural compression stress.

In practice this means conduits etc are between the layers of steel.

Sometimes they put conduits on top of the top steel etc, and you have to reject it.