Resisting Column Base Shear with Friction
Resisting Column Base Shear with Friction
(OP)
I generally only use friction to resist base plate shear loads for lightly loaded columns in non-seismic areas. For serious loads, I'll find a more positive shear transfer mechanism such as shear lugs.
The sketch below represents an as-built condition for a building currently under construction. It relies on friction to resist shear loads and the numbers work. On the one hand, it is very heavily loaded. Were it my design, there would probably be a shear lug for that reason alone. On the other hand, the situation is such that the shear load only exists if the vertical load does too. It's 100% reliable in that regard.
What do others think of this? Good or no good?
As a secondary question, how do we feel about steel shim stacks when we're utilizing base plate friction? Clean steel on steel gives a coefficient of friction of 0.5-0.8. Greasy surface come in around 0.16. So says the internet anyway.
The sketch below represents an as-built condition for a building currently under construction. It relies on friction to resist shear loads and the numbers work. On the one hand, it is very heavily loaded. Were it my design, there would probably be a shear lug for that reason alone. On the other hand, the situation is such that the shear load only exists if the vertical load does too. It's 100% reliable in that regard.
What do others think of this? Good or no good?
As a secondary question, how do we feel about steel shim stacks when we're utilizing base plate friction? Clean steel on steel gives a coefficient of friction of 0.5-0.8. Greasy surface come in around 0.16. So says the internet anyway.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.






RE: Resisting Column Base Shear with Friction
DaveAtkins
RE: Resisting Column Base Shear with Friction
RE: Resisting Column Base Shear with Friction
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Resisting Column Base Shear with Friction
What is the coefficient between steel and concrete? How can that be ensured? If the plate was toothed, or roughened, ok. Can the friction that you have assumed still apply if the plate "jumps" due to a seismic event.
I would add a steel shear key, embed the baseplate, or provide a crapton of bolts.
When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.
-R. Buckminster Fuller
RE: Resisting Column Base Shear with Friction
It is pretty common to use friction. Quality control on the mu value is an issue for sure. For this particular condition, ASCE 10-97 lets you use 0.55. In seismic zones, I believve that there is code provision precluding the use of friction in this kind of situation.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Resisting Column Base Shear with Friction
RE: Resisting Column Base Shear with Friction
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Resisting Column Base Shear with Friction