coefficient of friction 1

[Lutfi]

A quick one, does nay one have a value for Mu " static coefficient of friction" for painted steel on hot dip galvanized steel? I found all kinds of values in Marks handbook that vary from 0.78 to 0.27 for clean and dry to oxide film respectively.

I would appreciate it

 

[dik]

There is no easy way... the coefficient of friction can vary by a couple of hundred percent.

If it's essential, then the only way I know of is that the surfaces must be tested. This can be by means of a small hydraulic load cell to supply the force and another to move the surfaces against eachother. Using hydraulics and a recorder it's possible to measure the 'break' between static and dynamic friction.

Alternatively, on site, the nut can be removed and the bolt can be loaded with a small hydraulic device used to 'proof' clamping action of bolts and again, the part loaded until slippage. For small loads, a flat machined nut and washer can be used to minimize the error. Results should be obtained by rotating the washer 120 degrees for each load to estimate the degree of error.

 

[dbuzz]

Table C9.3.3.2 of the commentary to Australian standard AS4100 "Steel structures" (

http://www.standards.com.au)

gives the following guidance on indicative slip factors for various surface treatments:
- Uncoated
Clean as-rolled 0.35
Flame cleaned 0.48
Abraisive blasted 0.53
- Painted
Red oxide zinc chromate 0.11
Inorganic zinc silicate 0.50
- Hot-dipped galvanised
Clean as-galvanised 0.18
Lightly abrassive blasted 0.30-0.40

This may not be of help though, since you have two surfaces with two different surface treatments.

 

[Lutfi]

dbuzz,

Much obliged. This is a nice table. I suppose I would do what a conservative engineer would, use low values so I can go to sleep at night.

 

[RASmithPE]

I am reinforcing steel angle tower legs by clamping new HSS (steel tube) to each existing. I cannot drill or weld to the legs.

Analysis tells me that 111k will be taken by each new tube and 68k by each original angle leg.

per (

http://www.tensioncontrolbolting.com/TCB.pdf

)

If I use 28k per 3/4" A325SC Bolt, and a coeff. of static friction of "0.18" (Galv/Galv), is 36 the # of bolts required?

((0.18)(179k)/(28k/bolt)= 36 bolts.

I would need 27 A325SC bolts in slotted holes, single shear. (ASD)

Is it that simple or have I missed something major.