Frictional Force 2

[531234]

We are designing a three storey wood structure that will sit on a concrete foundation. My question is, can frictional force be used to resist base shear or sliding of the structure?

 

[JAE]

I think the codes specifically state, and engineers who are wise agree, that you don't rely on friction. A positive connection is highly recommended.

 

[CELinOttawa]

No. It cannot safely be the basis of your design. Besides, it is most likely that the Architect will require a barrier between the timber and concrete, so there will be little friction at any point, and as JAE stated, no friction you can rely upon in design anyways.

 

[boyze]

one of the first things a new engineer will learn about friction: when you want it, you can't count on it. when you don't want it, you can't get rid of it. ;-)

Have Fun!

James A. Pike

http://www.xl4sim.com

http://www.erieztechnologies.com

 

[531234]

Thanks for the responses, we will definitely put hold-downs and shear connectors for the lateral forces. I just thought of hearing some opinions if there is any practicing SE that would consider friction as a contributing factor to resist lateral forces.

 

[BAretired]

Friction between the footing and the soil may be considered.

BA

 

[FEM4Structures]

Have used frictional resistance between concrete and cylindrical steel tanks to come with effective shear resistance needed to design anchor rods. Your case is bit tricky as there are lots of unknowns.

Thanks,

FEM4Structures

 

[AELLC]

Don't you mean sill plate anchor bolts for the shear and hold downs for uplift at shear walls?

Hold downs aren't rated for lateral shear.

 

[chrislaope]

In some very specific situations, you can, and you have to rely on frictions to resist sliding.

Here is an example: say in design a 90' diameter by 100' tall grain storage silo in a seismic "D" zone, you have to rely on the friction between bottom of the silo and concrete to resist the huge base shear.

 

[531234]

AELLC, yes hold-downs attached on ends of shearwalls ( chords )for uplift, and sill plate secured to concrete with anchor bolts for shear.

 

[BadgerPE]

I have never used the frictional force of wood to concrete to resist base shear. Base shear is resisted as AELLC mentioned. Holddowns for uplift and sill plate anchor bolts to resist base shear.

In my neck of the woods, it is common to use some sort of base sealant (often a slippery foam) that adequately fills in the differences between the wood and the concrete. Therefore, I could see the frictional coefficient approach 0 for the wood-foam-concrete interface. W/o testing it would be difficult to assume any real frictional resistance of this connection.

This is a perfect example of where the OP (not beating you up 531234) needs to include more information up front. There are engineers talking about wood/concrete friction and some talking about concrete to soil. Hope this helps in the future.