A325 bolts in bending 2

[JAE]

Do any of you know whether there are any provisions or recommendations anywhere (from AISC, etc.) pertaining to high strength bolts in bending?

I know that the entire RCSC bolt spec never mentions flexure (tension and shear only) and also seem to recall that these bolts are typically never meant to be bent but only used in tight connection assemblies.

However, I was asked this question yesterday and didn't find anything in my references or online to specifically answer this question.

The detail in particular is a case where a high strength bolt is being used as a vertical pin, extending through an embedded seat plate, through an elastomeric pad, and into a slot on the bottom of a precast concrete member. Thus, if the precast member moves laterally, the elastomeric pad will flex just a bit and put some bending on the high strength bolt "pin".



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[Leftwow]

Doh, JAE asking a question, must be serious!... bump.

 

[jayrod12]

Wouldn't you treat it like prying action?

 

[KootK]

I haven't a clue. However, I've had some really good experiences asking very technical question of the folks at Portland Bolt (Link). They're very knowledgeable and eager to help.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[hokie66]

Bolts are used as pins in many cases, usually where a relatively small size will work and the architect doesn't want something fancy. You just have to treat the pin as a beam.

http://www.tboake.com/SSEF1/pin.shtml

 

[Ron]

You can bet you a$$ if JAE asks a question, it won't be a simple one!

JAE...my thinking is along the lines of yours....the literature only considers that high strength bolts are placed in direct tension, shear or both, but not bending.

This consideration would require a separation of the restraint and shear planes by a sufficient length to create bending. I've had to deal with that in structural applications for aluminum where material isolation was necessary but the bolts were typically stainless steel of sizes such that upsizing to accommodate bending was not such a big deal.

 

[UcfSE]

Have you tried any mechanical books with fasteners, such as Bickford or Shigley? I'd go there next. I can't think of anywhere I have seen bolt bending in structural literature like AISC. Hilti treats this, but I can't say how the procedure would change for a HS bolt.

 

[PMR06]

Anything in the NDS codes that might be similar? The bolted connection equations consider bolt bending/hinging at various locations within the timber elements.

 

[JAE]

Well, we know that there are given bending/flexural capacities for round rods found in AISC but I think that is only meant to apply to A307, A36, or F1554 type materials.

We could also assume that with bending you really end up with material compression and tension across the section, but there just wasn't anything explicit about flexure of A325/A490 in the literature.

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[hokie66]

My old Gaylord and Gaylord Structural Engineering Handbook has a worked example of a pin design, but it does not use a high strength bolt. Just a beam, where the forces are conservatively applied as point loads on the pin.

 

[TLHS]

I've done it on some types of pipe supports and machine supports where they need an adjustable screw base.

Honestly, I've just made sure the factor of safety is really big. Especially if there's a possibility of load reversal.

I'm pretty sure I've seen some information on bending in anchor bolts in european standards. I believe they take bending inside the grout pad into account. Other good places to look would be documents on the design of light pole bases and similar monopoles.

I'm not clear from your description whether you're intentionally putting the lateral load on this pin or not and where/how it's restrained. Is this simply supported at the top and bottom with the elastomeric pad applying a force in the middle? Is it cantilevered off the seat at the bottom somehow, maybe with a bolt on the top and bottom of the seat?

 

[SlideRuleEra]

JAE - Here is a lead from a paper about A325 & A490 bolts on the website of the National Science Foundation, Network for Earthquake Engineering Simulation:

Although bolts aren’t typically designed for bending, bending stresses are
often present due to misalignment, non-perpendicular holes, joint prying and other
causes. The stress in a bolt due to bending is the same as for any other typical
member...Coupled with the pretension and tension due to loading, the bending stresses can
be critical. The commentary to the LRFD addresses the bending of fasteners by
using a relatively low resistance factor of 0.75 for strength calculations (AISC,
1994).

See Chapter 3, Paragraph 3.7.4 Bending
at this link:

http://nees.org/data/download/NEES-...ertation by James A Swanson/dissertation.html

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[SAIL3]

I don't understand what the problem is, unless there is a concern about brittleness....bolts of much higher strength which are heat-treated may require further research....I believe A325 is not heat treated....

 

[manstrom]

http://www.awc.org/pdf/tr12.pdf

NDS has stuff for bolts and lags spanning a gap. It is a place to start.

Generally, I would try to avoid it in a high load connection. All those threads would create points of stress concentration.

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[graybeach]

If you have calculated bending I think your bolt falls outside of the RCSC Specification. I have seen A325 material used for anchor bolts that have bending. In that case, you treat bending the same as you would for any anchor bolt.

 

[Hokie93]

I agree with graybeach. Anchor rods used to resist shear loads bend within the thickness of the base plate. This is covered in AISC Design Guide 1 (2nd edition); see Example 4.11 in particular. Being as how anchor rod material can be high-strength (ASTM F1554 Grade 105, ASTM A449, ASTM A354, etc.), the procedure in AISC DG1 should be applicable to high-strength bolts.