shear tab with axial load 1

[rnorth]

how does AISC 13nth edition handle connections (simple two bolt shear tab) with combined shear and axial load?

in section 9-3 discussion is made about not combining stresses. user is refered to spec J to design connection elements.

would spec H be used for connection elements?

thanks in advance.....

 

[abusementpark]

Eccentricity in the bolts from the weld line to the centroid of the bolt group. Gross bending to the same eccentricity. Net bending to the first line of bolts.

I am assuming that for the gross bending check, Fy is used, and for the net bending check, Fu is used. Otherwise, if Fy were used for the net bending check, it would always govern over the gross bending??

 

[connectegr]

Abusement
Your statements are correct. However, if applicable, weak axis bending will govern the plate thickness.

http://www.FerrellEngineering.com

 

[abusementpark]

connectegr,

With regard to the weak-axis bending, I wouldn't have thought the bending force due to that small eccentricity would be significant enough to consider. Similarly, we usually neglect this same eccentricity in the design for vertical shear force, otherwise we'd have to check the shear plate for torsion.

If it is a design consideration, I'm not sure if I understand the rationale for neglecting the weak-axis bending when there is a diaphragm, since this only restrains the beam (and usually just the top of the beam), not the shear plate.

 

[iponom]

Can anyone tell me if it is necessary to use Extended Shear plate tmax configuration guidelines (from AISC 13th) at bracing connections (w. axial)?

 

[connectegr]

tmax is a ductility consideration, which is conservative as shown in the shear plate design. We use a maximum plate thickness based the moment capacity of the bolts. In a bracing connection, it can be argued that the connection lacks flexibility due to the combined depth of the beam and gusset connections. Therefore ductility should not be a concern.

http://www.FerrellEngineering.com

 

[LSM76]

The weak axis bending resulting from the eccentricity from the center of the plate to the center of the beam is often not considered in the design of the plate, since the beam, especially when connected to a diaphragm, will be much stiffer than the plate and therefore will take the lion’s share of the moment.

I check gross bending with an eccentricity measured from the face of the support to the first line of bolts not the centroid. Some of the load will be transferred from the plate into the beam at this first line of bolts. Though it can’t be proven mathematically (to my knowledge) I have looked at the force distribution on the bolts using the instantaneous center of rotation method, and in every case I have looked at the critical section is the full load at the first line of bolts and not the reduced load at the centriod.

The tmax requirements in the Manual are there for ductility, as has been stated. They are necessary to accommodate the simple beam end rotation. Further discussion and derivations can be found here:

http://larrymuir.building.officeliv...d Extended Single Plate Shear Connections.pdf

When a beam transfers significant axial load the simple beam end rotation is often small, so it can be argued that this requirement need not be met. For this reason and the reason stated by connectegr the tmax requirement does not apply to shear tabs used in bracing connections. More information concerning the use of extended tab with bracing connections can be found here:

http://larrymuir.building.officelive.com/Documents/extended tab vertical bracing.pdf

Until something better is published, I would combine the axial and moment based on Chapter H. I would combine the shear and normal stresses by squaring the ratios of the demands to the strengths and comparing to one, as is done in the Muir and Hewitt paper above. Of course in this case the normal stress would be the combined axial and moment.