Equivalent Coefficient of Friction
Equivalent Coefficient of Friction
(OP)
Hello,
I have weight (140 kip +) that will be sitting on a precast plank (yet to be designed). The end goal is to have a system with an "equivalent coefficient of friction" of 1.0, so that 140 kips of weight can resist 140 kips of lateral force. It was suggested to place plates at the end of the precast plank that protrude into the ground. Is there a way to design such a plate as part of an "equivalent coefficient of friction" as opposed to strictly relying on code maximum lateral bearing pressure (contact surface is 6" of 3/4" crushed aggregate on top of 18" of pit run, on top of existing soil with mostly unknown properties).
I am afraid that using the AASHTO friction factor for concrete on gravel = 0.6, and designing the plates for 200psf/f of lateral bearing, the plates will need to be way too large or too much extra weight will have to be added.
Any help is appreciated.
I have weight (140 kip +) that will be sitting on a precast plank (yet to be designed). The end goal is to have a system with an "equivalent coefficient of friction" of 1.0, so that 140 kips of weight can resist 140 kips of lateral force. It was suggested to place plates at the end of the precast plank that protrude into the ground. Is there a way to design such a plate as part of an "equivalent coefficient of friction" as opposed to strictly relying on code maximum lateral bearing pressure (contact surface is 6" of 3/4" crushed aggregate on top of 18" of pit run, on top of existing soil with mostly unknown properties).
I am afraid that using the AASHTO friction factor for concrete on gravel = 0.6, and designing the plates for 200psf/f of lateral bearing, the plates will need to be way too large or too much extra weight will have to be added.
Any help is appreciated.






RE: Equivalent Coefficient of Friction
Richard A. Cornelius, P.E.
WWW.amlinereast.com
RE: Equivalent Coefficient of Friction
The coefficient if friction is NOT a function of AASHTO, or any other organization. It is a property of both of the materials which are in contact with each other.
It also does NOT depend on the area of that contact.
RE: Equivalent Coefficient of Friction
RE: Equivalent Coefficient of Friction
Also, how are the protruded plates part of the coefficient of friction? Aren't the plates all together separate from the friction between the weight and plank?
Fe
RE: Equivalent Coefficient of Friction
RWF7437: I understand that the coefficient of friction is not a function of AASHTO, but for lack of proper testing we are using the common values of different materials against soil which is listed in a chart in AASHTO. We were looking at "Concrete mass on gravel" which is 0.55-0.6
FeX32: I know that nothing reaches the ideal coef. of friction of 1.0, but our task was to create this system that would have an "effective" coefficient of friction of 1.0 (providing the same result as a coefficient of friction of 1.0).
I guess what I am trying to say is this:
Having a the concrete block with plates on ends seems like it should be able to provide more resistance than just the friction of the plank plus the lateral bearing pressure on the plates. Is there something that I am missing? Can the whole be greater than the parts in this example?
Thanks again for any help.
RE: Equivalent Coefficient of Friction
RE: Equivalent Coefficient of Friction
RE: Equivalent Coefficient of Friction
RE: Equivalent Coefficient of Friction
Examples being soft rubber on dry concrete (1.0 - 4.0) or copper on cast iron (1.05).
Just throwing this idea out there, but it seems on a micro scale that the soil/gravel act similar to ball bearings rolling against a smooth surface. Maybe you could prepare the surface with a sticky agent first.
Also, running tracks that use recycled rubber for their surfacing and pelletized rubber dirt used in artificial turf come to mind.
Hope this helps to spark some new ideas for you.
DFLewis
www.phoenix-engineer.com
RE: Equivalent Coefficient of Friction
RE: Equivalent Coefficient of Friction
RE: Equivalent Coefficient of Friction
RE: Equivalent Coefficient of Friction
Is it possible to attach the footings on opposite sides of the structure together to eliminate the thrust portion of the lateral load? Usually thrust is equal and opposite on the two sides on a structure. This can be done with steel rods or some other means.
RE: Equivalent Coefficient of Friction
We will be looking at using (30) 4.1kip blocks stacked in rows (no higher than 4 so as to not over stress the soil), all resting on a precast concrete block, with 3 or 4 plates protruding the bottom of the block to use passive pressure (all located as close as possible without interfering with each other so as to use the most of the "overburden").
This is by far the most complicated and ridiculous lateral system I have ever encountered, but when you can't dig or use piles for lateral you have to come up with something...