Eccentric moment on bolt groups 1

[palk7 EIT]

Hi,

Attached a pic from AISC girder web supports, I read that the bolt group has to be designed for the moment Re, does that mean that that moment should be resolved into force for the distance between the centre of top & bottom bolts and check it to the shear capacity of the bolt in addition to the regular shear capacity check due to the reaction R.Or how to check for that moment R*e on the bolt group?

Thank you

 

[palk7 EIT]

I meant to say, the resultant force F = sqrt of (F1^2+F2^2), where F1= R/3 and F2= R*e/L, where L is the length between top and bottom bolt, is this correct approach?

 

[rb1957]

why won't the 3 fasteners transfer only shear (= R/3) to the connection and the offset moment would be reacted at the welds (that connect the connection to the girder ?

the "truth" is way more complicated ... how much rotation does the beam want to do (if pinned) ? how much rotation does the girder want to do (if fixed) ?

if you pin at the girder, and transfer moment into the beam here, then you've increased the moment in the beam (assuming you analyzed it as a pinned beam between the fastener groups). Ok, it's a small increase, but it goes to understanding what your assumptions mean.

another day in paradise, or is paradise one day closer ?

 

[palk7 EIT]

Its a pinned connect. to the girder to transfer only the Reaction. With regards to offset moment to be reacted at the welds yeah true, I guess it should not be welded to the inner faces of the top and bottom flanges and only to the web of the supporting girder to take up at that reaction. In this scenario, I don't want the girder to take any moment from this incoming beam it should be a pinned connecion atleast for simplicity

 

[rb1957]

then yes, weld on the web only (well, maybe in your calcs ... who'd do that in real life ?)

but increase the length of your beam by the end offsets ("e" at both ends ?).

and yes F2 (couple due to offset moment) is Re/L, and vector sum the two components.

draw a FBD to see it clearly.

another day in paradise, or is paradise one day closer ?

 

[271828]

Recommend you check out the following paper. They show how to handle the eccentricities for such connections.

Fortney, P.J. and Thornton, W.A. (2016), "Analysis and Design of Stabilizer Plates in Single-Plate Shear Connections," Engineering Journal, AISC, First Quarter.

 

[palk7 EIT]

Wow! that was a gem of a video!! Thank you 271828!

 

[271828]

BTW, I typically design those as rectangular plates that are only welded to the girder web. Make the plate thicker if necessary for plate buckling per the AISC Manual Part 10 procedure. You can assess the need for stabilization (stabilizer plates) using the simple equation in the 14th ed. Manual; they're typically not needed. If the beam has computed torsional requirement or is unbraced by lack of deck/slab, then it's another matter. I don't use single plates without stabilizers for those.