Anchor Bolts

[eisparky]

What is this 2.5 increase requirement for anchor bolt design. In most cases steel strength supercedes concrete strength. Meaning that if the concrete is not strong enough then their wont be ductile failure of bolts. Since this is always the case does this mean that I will need to reinforce the the concrete and or embed the anchor bolt a lot in order to make it work? Recently we have been getting comments from the building department that we need to apply this factor to the concrete strength. It just seems so rediculous the amount of reinforcement needed on an elevated 16ft tall Nitrogen tank on unbraced legs to make the concrete work.

 

[Lion06]

The 2.5 factor is required for SDC D and above (only for the seismic loads, obviously) when the controlling failure mode is not the (ductile) steel. You can usually use the steel that's already in the pier to make it work. It is a pain sometimes, but you've got to do it.

 

[Loki]

The 2.5 factor also applies in SDC C. It can be a challenge, especially where edge distances are small.

 

[Lion06]

My apologies......... it is SDC C or worse. It shouldn't be that difficult to get to work if you use steel across the plane, then the edge distances don't even matter (unless you're governed by blowout). There's usually steel there anyway, so why not take advantage of it?

 

[anchorengineer]

The 2.5 is a global seismic CYA for the code officials. An alternative to a ductile failure of the bolts would be a ductile failure of the attaching member (I forget the code reference). Make sure your bolts are "ductile". Other then that, go deeper or use more smaller bolts. Try Hilti's Profis program. It's easy to modify your bolt layouts.
Good Luck!

Clarke Engineering Services, PC
Construction Consulting & Anchor Testing

http://www.anchorengineer.com