where can i find the friction coefficien

huangyhg

where can i find the friction coefficient?
awhile back i spoke with the precast concrete institute (pci) concerning the coefficient of friction between a precast concrete building and a cast in place or precast grade beam. his response was that the pci design handbook indicates a value of .80, but that the portland cement association (pca) recommends that a factor of safety of 2 should be applied to that, hence a value of .4 should be used
the coefficient is highly variable.
if one block of concrete is cast against another, even if it is smooth, there will be some keying between the surfaces that will produce a high friction.
however, after any movement between the surfaces, there will probably be grains of sand rubbed off between the surfaces.  these will tend to act like ball bearings, unless the pressure is enough to crush them, and then your friction will be only a fraction of what it was without the sand or dirt between.
as ribeneke says it is variable.  also, if you are looking at a repetitive friction interface, the comments from steve1 need to be heeded, as the friction interface will change with each action, resulting in a "ball bearing" condition as noted by ribeneke.
single action static coefficient of friction can be easily determined by a simple test.  see astm c 1028 and vary it to match the materials you want.