concrete clamp plate

[bangerjoe]

Hello Forum

I have a beam which terminates at a concrete wall.

I do not know much about concrete design.

What are your thoughts on analysing it like a friction grip?

I could drill through the concrete, put a backing plate on and pre-tension the bolts. See the sketch below.

What is a suitable coefficient of friction for concrete on steel?

Thanks for any help you may provide.

 

[KootK]

You can do that. It essentially becomes a shear friction connection and you should consider consulting that section of ACI 318. You'll also find a recommendation on the appropriate coefficient of friction there.

If it were my design I'd use a connection plate on the face of the wall, either cast in or fastened with post installed anchors. ACI 318 Appendix D can help you out with that if you decide to pursue it.

With pretensioned through bolts, getting a reliable, verifiable level of pretension can be a challenge.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

Structural steel friction grip connections are steel to steel. Introducing a concrete member between leads to uncertainties (such as relying on KootK's shear friction).

I have used through bolt connections like this many times, and would design the connection for the top bolts to carry the tension, and the bottom bolts to carry the shear. You could also cast in adequately developed bolts.

 

[bangerjoe]

Hi Hokie66

the through bolt is feasable as the wall is existing.

can you please elaborate on Hokie's comment that top bolts carry tension (is this from moment at the terminating end of the beam) and bottom carrying shear from the beam shear at the point?

my concern is about the concrete, what checks can i do to make sure it can hold up to the tension in the bolts, and failing that, the bearing from the bolts on the concrete wall itself.

I've had a look at ACI318, what i can find is S11.7 which appears to deal with shear within the concrete itself, rather than a steel on concrete μ. Sorry if i'm not being clear, or interpreting the code correctly.

 

[hokie66]

Yes, you interpreted my comment correctly. The moment is resisted by the T-C couple of top bolts and bottom flange bearing. That leaves the bottom bolts to carry the shear. This is greatly simplified from what actually occurs, but conservative.

For the concrete as related to the bolts, for your detail it is just a bearing check. In addition to that, you need to check that the wall itself is capable of resisting the applied bending from the beam.