What is the standard spacing of A325 bolts on metric projects 1

[cliff234]

Structural bolts are typically spaced at 3" on center in the U.S. What is the standard metric spacing for bolts in other countries? (We are doing a project in South America that will be fabricated in China.) 3" = 76mm. A 76mm bolt spacing sounds odd. We will eventually get this dimension from the fabricator, but I wanted to find out beforehand. 80mm?

 

[CELinOttawa]

Increments of 25mm are not uncommon. Most metric countries were once imperial and have inherited the same "good old rules of thumb" as you'd have in your practice. If memory serves I was taught that rivets and bolts at 6" or less would minimize rust jacking, and that 4" and 3" were considered to be low maintenance installs. When I worked in New Zealand one of the old engineers was a former Ministry of Works engineer (long story) who provided me with a bridge detailing manual... It stated that bolts and rivets should be not wider than 150mm in an exposed and easy-to-inspect location, with 75mm being best where hard to inspect and paint regularly.

Just don't use any decimals in your drawings and you should be fine. Try to end all layouts and dimensions with "5" or "0" and people won't complain.

 

[Ingenuity]

70 and 90mm gauge lines are common, depending on bolt diameter, in Australia.

 

[KootK]

This is enormously frustrating, isn't it? I work in Canada and see 76 mm, 75 mm, and 80 mm regularly. Most often, the steel shop drawings come back as 76 mm (3"). Steel fabricators here tell me that plate is most often available in imperial sizes and fabrication settings tend to be set up that way as well.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[IDS]

I don't work with structural steel, but converting 3 inches to 76 mm, rather than 75 mm, strikes me as ridiculous.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[TLHS]

The standard shear connections in Canada have 80mm vertical spacings as per the yellow section of the CISC steel handbook.

This isn't something I'd stress overly hard about. As long as you're consistent on a project, don't use dumb numbers (end with a 0 or 5) and can actually physically get to all the bolts for fitup, I don't think it's a big deal with modern machining.

 

[KootK]

When I worked in imperial, I could detail something and expect that it would reflect reality within the bounds of normal tolerances. With soft metric dimensioning, a splice plate with six rows of bolts dimensioned at 80 mm o/c might be off by an inch when they come back at 76.2 mm o/c. And that's before tolerances. Is it a big deal on site? No. Does it make my engi-heart ache for the lost illusion of control? Yes.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.