connector spacing for built up members

[jtriezen]

I am trying to reinforce a 140' 12-sided pole. It is galvanized steel 5/16" thick at the base. I'd like to bolt on some plates in order to reinforce the pole.

The AISC LRFD spec J3.5 states that the longitudinal spacing for connectors shall not exceed 24*t or 12" for members not subject to corrosion.

I'm wondering if this applies here (although the pole is subject to corrosion it is galvanized). And if so, why is the fastener spacing so close. This pole is overstressed up to 100'. At a 7" bolt spacing thats a lot of bolts. I've checked the horizontal shear and checked the plates as a column and have come up with a bolt spacing of about 18". Can anybody comment about the reason for the 24*t requirement?

 

[nutte]

The commentary elaborates on the reasoning for the requirement. It's to hold the plates tight against each other to prevent water from getting trapped in between them, which would lead to corrosion. It mentions specifically in the case of paint failure, though. It doesn't address this issue for galvanized material.

 

[Lion06]

Isn't part of the reason also to prevent local buckling of the individual element before global buckling of the built up member?

 

[nutte]

You check that separately. This requirement is independent of local buckling.

 

[HgTX]

I assume this pole is in place already.

Probably a stupid question, but have you checked the cost of this swiss cheese repair against replacing the pole?

And how are you going to install the bolts with no access to the back side of the connection?

Hg

Eng-Tips policies: faq731-376

 

[jtriezen]

Yes, the cost of the reinforcements will be expensive. Its a pole for a wireless carrier with some existing antennas on it. Generally they opt for expensive reinforcement instead of bringing down the site temporarily.

I was planning to use Lindapter hollo bolts to secure the plate.

-JT