Steel beam to column shear connection with short slotted holes - Bracing the column?

[MCip]

Hello

For a typical shear connection of girder to column, AISC allows the use of short slotted holes perpendicular to the direction of the load (shear). However, my doubt is: can the beam be considered as a lateral brace for the column? The brace force will be parallel to the slots.

Similarly, for filler beams to girder. If a short slotted shear connection is used, can the filler beams be considered as bracing the LTB of the girder?

Thank you

M

 

[Hokie93]

Is there a diaphragm associated with the beams and girders at the floor level in question? If so, then I would say the presence of short-slotted holes is of no consequence. If no diaphragm is present at the level in question, I would say you have three options: One, convince yourself that it is highly unlikely that every bolt at the connection/s in question in the direction under consideration will be 'perfectly' aligned in the short-slotted holes so as to permit the maximum horizontal movement (1/4"). Two, provide pre-tensioned connections (that is, provide some degree of frictional resistance, though indeterminate). Three, pry open the client's wallet and provide slip-critical connections at the connection locations in question.

 

[KootK]

I'm cool with it. On a 3/4" bolt, a short slotted hole is only 3/16" wider than a standard hole. Grab a ruler give yourself a sense of how small a dimension that is in the grand scheme of things in a steel frame. Even if you get extremely unlucky and end up with all of your tolerance working against you, I contend that 3/16" is still a "micro" thing relative to the more "macro" phenomena of LTB or column buckling. Things may have to shift a bit to fully engage but, generally, that's okay.

To add to Hokie's list, any beam with any serious load on it will produce end reactions whereby the bolts plow into the substrate and it's pretty tough to get any slip anyhow. Sometimes that works against us as in the attached article.

Old as dirt but you might find some useful information here: https://www.google.ca/&httpsredir=1&article=1246&context=engr-civil-environmental-fritz-lab-reports]Link[/url]



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.

 

[Mjkkb2]

AISC only allows it in one of the two connected parts so you will typically have slots on the tab but STD round holes in the beam web. Even if the bolt landed in the worst place (up against the edge of the slot) the movement like KootK said is a small fraction compared to the frame and its tolerance allowance.
This never crossed my mind in the last 15 yrs of doing steel buildings.
I think you will be fine

 

[MCip]

All,

thank you very much for your responses.

I did convince myself that bracing of the column is guaranteed if the bolts are pre-tensioned, since enough friction will be developed even if the surfaces are not prepared according to the slip critical surfaces. I believe that also AISC is saying the same (although in a very indirect way) with the clause on Chapter J.1.10 "Joints with pretensioned bolts shall be used in connections of all beams and girders to columns and any other beams and girders on which the bracing of columns is dependent".

Thank you again,

M

 

[BridgeSmith]

"...enough friction will be developed even if the surfaces are not prepared according to the slip critical surfaces."

From the commentary, Article C6.13.2.8, of the 7th edition AASHTO Bridge Design spec:

"On clean mill scale, this research found that even the smallest amount of overspray of ordinary paint, i.e., a coating not qualified as Class A, within the specified paintfree area, reduced the slip resistance significantly. On blast-cleaned surfaces, the presence of a small amount of overspray was not as detrimental...It was found that all curing [of paint coatings] ceased at the time the joint was assembled and tightened and that paint coatings that were not fully cured acted as lubricant. Thus, the slip resistance of the joint was severely reduced."

The provisions of the spec have a reduction factor for "For oversize and short-slotted holes" of 0.85.