Pullout Capacity - Steel Handrail Embedded in Concrete 4

[codySTR]

Exhibit A: A 1.5" I.D. steel pipe is used as a handrail and as the vertical posts connected to the handrail). Per the Landscape Architect's detail, said handrail posts are to be embedded X inches into my reinforced concrete stair slab / beam. The concrete base will be core drilled, the steel pipe post inserted into this void, and the gap between pipe and concrete filled with non-shrink grout with a higher f'c than the concrete, which has a f'c=4000psi. How on earth do I quantify the pullout capacity of the handrail post?!

This seemed very simple to me until I started looking for equations, etc.... The pipe is smooth (i.e. not rebar with deformations). I thought there'd be an equation in ACI 318-14, but I haven't seen one.

 

[r13]

If pull out is the concern, provide a small plate to the end of the pipe to be embedded, and do the calculation.

 

[XR250]

Once the pipe rusts and spalls out the concrete, your calculation will be a lot easier.

 

[codySTR]

Retired13, that was my initial idea... the problem is that this detail has already been implemented on the project.

Pullout is only a concern in the sense that I don't want some jack-knob to decide he/she wants to "test the pullout strength" because it seems fun and incidentally yanks the post out of the concrete. I highly doubt that will happen if there's ~6" or more of embedment, but I'd like to quantify that gut feeling.

XR250, interesting point.

 

[jittles]

Looking for some sort of bond strength value between steel and concrete, perhaps look into some of the composite design sections in AISC? Not beams w/ studs, but rather things like concrete-filled pipes and tubes.

Just an idea, not an area I have experience with.

 

[r13]

Unless you provide tie-downs (anchors), the posts eventually could be lifted out of the hole by bare hand. Another food for thought is to get the specification of the grout, many non-shrink grout's volume actually expand rather than constant, thus develop shear friction on the embedded pipe through lateral compression. However, the shear friction is not reliable though.

 

[human909]

Anchor epoxy seems like a better but more expensive choice. Also core drilling results in much lower wall friction than other drilled holes.

 

[KootK]

With non-shrink grout, or maybe even slightly expansive grout, I'd be inclined to not worry about this. Ever look into the "development" lengths for steel H-piles into pile caps? They're unfathomably short somehow.


Consider playing chess with me on the Social Chess app at iTunes. Same handle. Fear not, I suck.

 

[dhengr]

CodySTR:
Braze or weld a couple wraps of 12ga. steel wire around the lower 4” of the posts. Just don’t ask me how to calc. the pullout strength, but you’ve provided your own deformations. Just don’t make em perfect, so they can’t unscrew the post. Didn’t they used to fill that annular space btwn. the pipe and conc. with melted sulfur? Maybe ask some of the epoxy or grout suppliers what they recommend.

 

[JLNJ]

Why are you worried about the pullout capacity? I would be more worried about flexure fixity.

 

[r13]

Don't feel too bad if it is already done, and you couldn't find any simple method to justify the installation (lift per se). I remember that for handrail design, the code only requires placing forces vertically and horizontally, no uplift, unless the code has changed.

 

[codySTR]

dhengr, interesting suggestion! If I could change the design, I'd slap a cap plate on the end and weld a headed stud to the cap plate. Embed that in grout. Either that or weld an oversized plate to the end of the pipe (like a cap plate) to achieve some bearing if someone tries to pull up on the post. Some of these handrails are already in place, however. So no chance

JLNJ: The handrail just needs to stay there. Bending and deflections aren't a real concern. There are code minimum loads on it. Posts every 5'-0" per the LA's detail and the handrail is 3'-0" above the base. Considering no flexural rigidity of adjoining posts, a single post taking 200lb 3'-0" above the base results in M/S = 600lb-ft*12/0.309in^3 = 23,300 psi > Fy/S.F = 36,000psi/1.67 (ASD) = 21,560 psi, but I'm not super worried about that in this particular case.

 

[Tomfh]

Don't worry about it. The uplift bond force will only be a few psi. Allowables psi for concrete/steel bond is upwards of 150psi depending on which reference you look at...

 

[Ron]

I usually use 25 to 50 psi shear bond strength for embedded metals. As Tomfh notes, the pullout force will be quite low; however, since you are likely working under the International Building Code or a state subset of same, you still have to comply with the general requirement of a 200 lbf concentrated load applied in any direction (including up, however little sense it makes)or 50 plf applied the same way. So for a 200 lbf uplift on the post, you will need 200/25 or 8 square inches of embedment area....should be easy to get that.

 

[codySTR]

Ron, thanks. Do you have a source for that?

Also, as an update (especially to my response to JLNJ): I checked M/S when I should have checked M/Z. TLDR: the pipe is OK in bending.

 

[JLNJ]

cody

It's not the pipe flexure to which I was referring, it's the breakout of the concrete under the action of providing the fixity to the bottom of the post.

The post is nice and ductile and strong. The concrete is brittle and may or may not be strong enough, depending on the embedment geometry. My guess is that, no matter what the geometry, the first point of failure would somewhere be the concrete.

 

[r13]

codySTR,

I found a non-shrink grout spec on line. Pay attention to "Typical Volume Change" unser "4. Technical Data". Hope this helps.

Link

 

[codySTR]

Ah, I follow you, JLNJ. In this particular application, it'll be OK by inspection. The pipe CL is 6" from the closest edge of concrete with 8" embedment. There will also be a #5 longitudinal bar enclosed by #4 stirrups to resist breakout. I don't think concrete pullout will happen before the steel slips out due to bond failure and, with 8" embedment, I don't think pryout is a factor either.

 

[BridgeSmith]

If pullout capacity is a concern, a simple solution, similar to what we do for anchor bolts, is to deform (indent) the pipe in a few places, like a swedge.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Gerber_EIT]

I would consider adding a few drilled holes in the base of the embedded pipe (say at 4" or 6" from the bottom) to ensure the grout will be inside of the pipe. That'll add some additional pullout strength by actively engaging more of the grout, not just in shear friction between the grout and the pipe surface. No idea how to actually quantify this though. This would also help to limit the corrosion at the base of the pipe due to condensation.