Single Bolt To Connect Pedestrian Rail Post to Concrete

[dhoward26]

Pedestrian railing...standard dimensions but the post connection to the stem wall is a little odd to me.

I haven't seen a design like this before. An architect and contractor are asking me to look at it for a peer review. Analyzing seams pretty straight forward: bolt shear, bolt bending, tension, post shear/bending.

Has anyone else designed something similar? If so, how was the performance?

 

[connectegr]

Frequently we design posts as core drilled and grouted into the concrete. However I have never seen this detail. I don't know your loading or post spacing, so I cannot comment on the adequacy. But, a practical consideration is poorly set threaded rods. There is no tolerance for a miss-located or sloping rod. Also, why use a set screw if rods are threaded.

http://www.FerrellEngineering.com

Providing fabrication and erection efficient structural design of connections. Consulting services for structural welding and bolting.

 

[MikeHalloran]

This is probably not in the spec, but it's not resistant to the average high school football team. ... maybe not even a middle school team.

Lateral load applied to the handrail is multiplied into tension in the allthread/epoxy joint because the 3/4 square bar's lower edge acts as a fulcrum, at least to some extent.

The team may also have understimated the difficulty of tapping 1/2" diameter through 6" of steel.

... and I'm not sure exactly how the setscrew is supposed to help anything, but I really really hate setscrews.




Mike Halloran
Pembroke Pines, FL, USA

 

[IsaacStructural]

I'm just wondering what is left after you tap a 1/2" diameter hole into a 3/4" square rod. That leaves 1/8" of material if the hole is exactly sized and dead center, if it is off at all, you've got about 1/16" of material. Seems like it could easily wear out from fatigue, corrosion etc.

M.S. Structural Engineering
Licensed Structural Engineer and Licensed Professional Engineer (Illinois)

 

[dhoward26]

I agree with all. My recommendation will be to drill a hole and embed the post. 1/2" diameter bolt probably won't work.

 

[BAretired]

I don't think a 1"x1" HSS is adequate in bending even if fully developed.

BA

 

[dhoward26]

Yeah, probably not, I need to check it. As drawn in the attachment, it can't be more than 1/8" thick, which definitely won't work. I guess I'm baffled someone would spec out a 1/2" all-thread. Ever put any pressure on a 1/2" stick of rebar sticking 3' out of concrete? And that is almost double the strength of the bolt.

 

[dhoward26]

Just found out that the Post is aluminum. Wow.

 

[hokie66]

Typical wooly thinking architect. Designs something that can't be built, and even if it could, wouldn't be strong enough. Sympathies, dhoward.

 

[dhoward26]

hahaha, yeah, frustrating sometimes. The sad thing is, he probably won't like my recommendation and go find someone else until that someone else tells him it works...or get frustrated and end up spending a lot of money for a very easy fix.

The amount of accuracy involved in getting this to come out perfectly straight is pretty amazing. Not to mention some little kid coming along and seeing a lose set screw and removing it.

 

[hokie66]

What is the set screw about, anyway. With the bar tapped for the bolt, what is going to turn, the footing or the whole length of railing?

 

[dhoward26]

The only thing I can think of for the screw is to keep someone from lifting the aluminum post up as there isn't any info on connecting the square rod that will be tapped to the aluminum post...only the set screw as near as I can tell.

 

[hokie66]

Hang on. The way I read it is that he wants the square (alumninum) post drilled and tapped to receive a threaded rod. As far as that goes, it is at least logical, except for the sizes and materials. The set screw is illogical.

 

[JAE]

I don't think you can get that all thread to work in bending for the required lateral guard rail force per code.

 

[XR250]

Agreed. It will NEVER work. Besides the structural issues, the practical issues are overwhelming as well.

 

[dhoward26]

Smallest HSS I could get to work was 1-1/2 x 1-1/2 x 1/8.

hokie66: They weren't wanting to tap the aluminum rod, they were wanting to put that as a sleeve over a 6" stick of solid steel that would be tapped.

I called the architect this morning and with a little moaning and groaning from him, I persuaded him to do an embedded post. He didn't like it being 1/2" bigger than what was originally there, but not much else a person can do!!!