Steel spindle to timber stringer detail

[seconb]

I have a client who is proposing a stair balustrade that has nice sleek spindles that disappear neatly into the timber stringer, please see 3D views attached.

My question is how do you prove this detail works. It is only domestic loading (0.36kN/m) but the post surely cannot act as a cantilever. I don't know a connection detail that would work. Instead do you prove the handrail acts as a stiff beam as it runs continuously.

If anyone has any experience/ thoughts on this please let me know.

[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1729151606/tips/Opt_C2_-_3d_Views_Compiled_annotated_twht2t.pdf[/url]

 

[BAretired]

I can't read that file.

 

[phamENG]

The file doesn't open, but I think I know what you're talking about. And the answer is: a little bit of both. Embed the balustrades into the stringer deep enough to create a fixed reaction. Then the handrail at the top will act as a beam to spread the load out. So when you push on it, you're not engaging just one of those little steel posts, but several. How many? Dunno. You'll have to run the numbers. It's a question of relative stiffness of the handrail vs the posts. You could probably come up with an elastic spring constant for the posts, convert it to a linear spring, and then look at the handrail as a beam on an elastic foundation.

 

[seconb]

Thanks both, I have added a link for the image.

@phamENG you've got it. Your approach makes sense as well, I was just hoping it would be simpler haha

 

[KootK]

Will you be able to screw a stanchion base plate to the top of the stringer? Or are you intending to actually embed the post in an epoxy filled hole or something? I might have some issues with the latter approach.

I don't feel that there's any way to sidestep cantilever behavior here. The load sharing may reduce the base moments that you have to deal with but it wont eliminate them.

I know of a good document that speaks to the load sharing if you're interested.

 

[seconb]

Only if the connection can be hidden after finishes are added. I agree, the latter doesn't feel right. Current strategy is to weld the post to a vertical plate and then bolt that to the side of the stringer.

As for load sharing I am currently creating an FE model to account for some load sharing between posts. Interested to have a look at the document you suggest though. Cheers

 

[KootK]

I agree, the latter doesn't feel right.

I'd need to see the final proposal before passing judgment but I worry that the embedded connection would generate local cross grain bending and tension perpendicular to grain stress that might not perform well over time.

Current strategy is to weld the post to a vertical plate and then bolt that to the side of the stringer.

Love it. Do that if you can.

Interested to have a look at the document you suggest though. Cheers

I'm thinking of NAAMM's metal stair manual. Who doesn't like a sexalicious monograph? Your FEM would be just as valid, if not more, of course. This might just serve as a useful check.

Only if the connection can be hidden after finishes are added.

See one option below.