Top Mounting Guardrail on to (E) Concrete Wall

[Respawn]

Does anybody have any good solutions for top mounting a 4x4 wood post guardrail to n existing 8" concrete wall? I have been dancing around different hardware but nothing works for a 200lb point load at the top. I am free to shift the post anywhere on the width of the wall.

 

[KootK]

Maybe take a length of 4x4 steel angle with a base plate, post install anchor the base plate to the concrete wall, and through bolt the wood posts to that. The fence in my back yard is pretty close to that setup and it feels sturdy. I'm not sure that it's 200 lbs sturdy...

 

[dik]

I'd use a couple of HDG angles as Kootk mentions with the post through bolted between. Leave 1/2" gap between the concrete and the wood to keep the end of the post from rotting out. If you need it for bearing, then a steel plate. Simpson likely has a connector for this.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[KootK]

The issue with most versions of this connection tends to be how to keep the thing snug when the wood post shrinks transversely. And my detail doesn't address that. One might have to return to the scene of the crime to tighten the bolts from time to time.

 

[phamENG]

I'm not even sure the post installed anchor idea really works if you're in the top of the wall. At only 8", missing rebar (or drilling through it and removing any sort of interaction between the rebar and anchor), etc. is going to be really hard period much less getting a sufficient moment arm to resist your 8.4kip-in (+/-) moment. A saddle plate could work. Go down several inches and then bolt into the side/through bolt through the wall.

As for the post shrinking...here's an idea most contractors would probably laugh at: either get kiln dried after treatment or have the contractor buy the material and then store it inside in a conditioned space until the EMC is down below your typical EMC for the region. Then when they install it, it'll grow and not shrink.

Another possibility is to core a hole in the top of the wall and set whatever steel attachment in that. But then you have to deal with the section loss of the wall at your connection, which may be considerable.

Can you post a sketch? Is this a cantilever retaining wall that needs a guardrail? Or is there a floor going on it? If a floor, I'd attach it to the floor somehow. It would be significantly easier to attach to a wood deck than to the top of an 8" wall.

 

[KootK]

At only 8", missing rebar (or drilling through it and removing any sort of interaction between the rebar and anchor), etc. is going to be really hard period much less getting a sufficient moment arm to resist your 8.4kip-in (+/-) moment.

I would say that depends on the kind of wall that we're dealing with. I was assuming a lightly reinforced retaining wall. Maybe two layers of #5 at the dirt side only or something like that.

One trick for increasing the likelihood of the post installed anchor setup being able to handle the moment is to take advantage of the fact that there will be a base plate compression block pushing down right next to the anchors that are trying to pull up. That will tend to alleviate pullout and make it more about direct shear and pry out.

There are very few situations in which I'm a fan of through bolting. That, because:

1) As far as I can tell, there's no accepted way to design those connections except for some weird CMU shear wall tech notes floating around out there.

2) Also as far as I can tell, most things that you could to with a through bolt could be done as well or better with an adhesive anchor. Most of the action happens near the concrete face in both cases.

3) Too often, through bolting seems to be used as an excuse to ignore concrete breakout failure modes.

Conceptually, I like the saddle setup but, as with the through bolts, it takes an annoying level of judgment to "design" such a connection.

 

[phamENG]

True, and if this were a 18" wall or maybe even a 12" I'd say adhesive anchors into the saddle...but at 8" thick I'm pretty sure your anchors would touch in the middle anyway. Unless you offset them - that could work.

 

[SJBombero]

I was able to get (4) Ø3/8" Hilti screw anchors to work with a 8" baseplate on top of an 8" wall. I was sure it wasn't going to work so I sacrificed the sleep to look at it. There isn't a easy way to mount a 4x4 to this though.

 

[KootK]

Yeah, I like the offset. Given that the anchors will be loaded in pure shear, I wonder if one might be able to get away with Hilti HUS or something like that. Adhesive is almost redundant when there's no tension on the anchor.