Combined Stress - Bending, Shear and Tension in Bolts

[RFreund]

Are there any references or suggestions for analyzing/designing a bolt subject to bending, shear and tension?

The bolts would be embedded in concrete/masonry and the applied load would be at a 'standoff' distance of around 4-6 inches just to give you some prospective on the situation.

EIT

http://www.HowToEngineer.com

 

[gwynn]

Typically I would design something like this as a pin per AREMA specifications. This is may be conservative, as railway bridges see fatigue loadings which you may not have, but upsizing the diameter one or two sizes shouldn't be a big cost item unles you have a large number of them.

 

[WillisV]

AISC Design Guide 1 provides recommendations for checking the steel strength of anchor rods for combined shear, tension, and bending. The bending strength is very small as one would suspect.

 

[RFreund]

Thanks guys.

I didn't realize this was in DG1, I'll have to take a look.

EIT

http://www.HowToEngineer.com

 

[RFreund]

So just to summarize/recap. The Tension stress from bending is found using the plastic modulus then added to the tension stress due to axial tension. Then checked against the allowable tension stress for combined Shear and Tension per AISC Eqn: J3-3

EIT

http://www.HowToEngineer.com

 

[rb1957]

why combined shear and tension ? you've only talked about tension loads.

so total tension = tension from bending + tension from axial (how does preload affect this ?)

 

[ash060]

Pretension does not affect the tension capacity, see AISC Commentary J3.6

 

[rb1957]

that assumes gapping at ultimate load, if you know you're gapped fine, but if not you're unconservative.

 

[RFreund]

rb - I'm unfamiliar with the term "gaped" could you explain.

The bolts would be subject to shear as well. Actually I would have shear in two directions, bending in two directions and axial tension.

I plan to use the force resultants for shear and bending. Apply all loads separately to find axial tension fa=T/A, shear stress fv=V/A (AISC DG1 uses no 'shape' increase in area) and bending tensile stress fb=M/Z.
Add fa+fb=ft

Use ft and fv in AISC equation for bolts subject to tension and shear. AISC Eqn: J3-3


EIT

http://www.HowToEngineer.com

 

[rb1957]

i was replying to the previous post ... preload doesn't affect the static strength of a bolt if the joint gaps (opens up) under the external tension load.
if the joint doesn't gap under ultimate load, then the load in the bolt will be higher than the applied tension.

my previous post picked up on the fact you have tension loads, and therefore i expected you'd be preloading the joint. if you do have a preload, and the joint is still closed up under load (ie not gapped) then the joint surfaces will be transferring the bulk of the loads (and not the bolt).

 

[RFreund]

ahhh... I see. Thanks.

EIT

http://www.HowToEngineer.com

 

[izax1]

"Are there any references or suggestions for analyzing/designing a bolt subject to bending, shear and tension?"

Generally speaking, a bolt should not be designed for taking bending loads. I am talking machinery where you will experience alternating loads. Thats why you need to ensure enough pre-load. When the bolted connection is separating and you have shear loads, you will get bending in the biolt. Also, remember that the max. stress from shear and the max stress from bending will not be at the same position in the bolt cross section.