Galvanized Faying Surface - without wire brushing?!?
Galvanized Faying Surface - without wire brushing?!?
(OP)
Any suggestions?
A project with completed erection, with many connections designed as Class A slip critical. The project is galvanized, so the coating is not Class A certified and the coatings are not blocked. What can be done if the erector failed to wire brush the faying surfaces?
The required slip coefficient is 0.33, for Class A. I think galvanized surfaces without wire brushing are approx. 0.15.
Some of the connections have OVS holes, so "bearing" connections are not an option. And they are not overly conservative to account for the difference in mu values.
A project with completed erection, with many connections designed as Class A slip critical. The project is galvanized, so the coating is not Class A certified and the coatings are not blocked. What can be done if the erector failed to wire brush the faying surfaces?
The required slip coefficient is 0.33, for Class A. I think galvanized surfaces without wire brushing are approx. 0.15.
Some of the connections have OVS holes, so "bearing" connections are not an option. And they are not overly conservative to account for the difference in mu values.






RE: Galvanized Faying Surface - without wire brushing?!?
Can you remove some members and go through RCSC's testing procedures to determine what your actual slip coefficient is? Maybe it's closer to 0.33 than you expect.
You've probably thought of the obvious fixes, like welding the connections, replacing the bolts with higher grade ones, and reaming holes and putting in bigger bolts.
RE: Galvanized Faying Surface - without wire brushing?!?
All of your suggestions are on the table. And yes both of these issues are on the same project. Luckily we are only consulting on the possible solutions. There other issues, but these are the most difficult.
Bigger bolts will require reviewing 100's of connection calculations for the changes in net section.
Welding is an option. But is never fun with galvanizing.
I had not considered testing the actual faying surface without wire brushing. I have read that the galvanized surfaces are rather generally "slick".
http://www.FerrellEngineering.com
RE: Galvanized Faying Surface - without wire brushing?!?
I have always wondered how effective it really is.
Some of the recent galvanized projects I have done the galvanizing was really rough in spots and smooth in others. Some spots super shiny and others very dull.
It seems to me that the galv roughness depends on the thickness of the material.
I might tend to agree with Nutte about a possible test.
RE: Galvanized Faying Surface - without wire brushing?!?
I got them to provide flange plates and weld the connection together. Since then, whenever shop drawings are submitted I always make the special not to the fabricator to ensure he fully understands what needs to happen with surface preparation and installation.
RE: Galvanized Faying Surface - without wire brushing?!?
I got them to provide flange plates and weld the connection together. Since then, whenever shop drawings are submitted I always make the special note to the fabricator to ensure he fully understands what needs to happen with surface preparation and installation.
RE: Galvanized Faying Surface - without wire brushing?!?
Is there any way you can carry out a test on the exposed surfaces to check this?
RE: Galvanized Faying Surface - without wire brushing?!?
I'm not so sure I agree with your contention that adding larger bolts will require recalculation of all the connections. Yes, it will stiffen the connections, but it seems to me that you could check a few and make sure that the redistribution of stress doesn't throw a load where you don't want it....as unlikely as that might be given the application. Welding would do the same thing.
My inclination would be to replace the bolts, using plate washers for oversized holes or, preferably, using larger bolts.
As much as it gets poo-pooed, I prefer using a calibrated wrench method of tightening. If you use a direct tension indicator such as a Skidmore-Wilhelm device, along with actual jobsite bolts, you can establish a reasonably consistent and relatively accurate torque value that relates to the actual tension developed in the bolts, without guessing or conversion calcs.