Anchor Bolt Bending for Stand-Off Conditions

[WJA]

I'm trying to figure out where the attached method for assessing anchor bolts/rods installed in stand-off conditions comes from (section 3.1.6.9 Bolt bending - Strength Design). i.e. shear force applied to base plate puts anchor bolts into bending (no grout between base plate and concrete)

I can't seem to find anything covering this condition in CSA A23.3 or ACI 318, and Hilti doesn't provide a reference. Is the method shown in the attachment supported by a code? They are essentially ensuring that the shear force applied does not result in the bending capacity being exceeded, but I'm wondering why the ultimate strength of the bolt is used in the flexural resistance. I would have expected the flexural resistance to be controlled by yield strength.

 

[jhnblgr]

This is likely covered under AASHTO standards. Sign structures typically have this type of anchor bolt design.

 

[bones206]

Hilti references ETAG Annex C for this.

 

[WJA]

Thanks! I found the ETAG standard, which is helpful. Any idea if there is a North American equivalent?

Regarding AASHTO - any idea where this situation might be covered? AASHTO LRFD Specifications for Structural Supports for Highway Signs, Luminaires, and Traffic Signals, Art. 5.16.3.1—Double-Nut Connections states that bending stresses can be ignored if the gap between the leveling nut and concrete is less than 1 bolt diameter. However, my situation does not fall within this limitation. They also make reference to a research paper but I'm wondering if that's all there is.

 

[Lomarandil]

Yes, if the standoff distance is more than one diameter, bolt bending should be considered.

I don't know if this is the logic used in this particular circumstance, but high-strength alloys used in bolts are often evaluated using ultimate strength (not yield) because those alloys have less well defined yield plateaus. So it's more reliable to use ultimate strength and a larger factor of safety.

 

[Boiler106]

its been a long time since ive searched through this but does this pdf help?

Link

 

[bones206]

Any idea if there is a North American equivalent?

There is some discussion in Section 3.5.3 of AISC Design Guide 1. Basically amounts to using statics to find bending moment and shear in the rods, then checking against AISC combined bending and shear provisions.