shear tab with axial load
shear tab with axial load
(OP)
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.....
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.....





RE: shear tab with axial load
Essentially, the reduction factor applied to the tension "limit state" capacity is = (1-R/Rv)^2.
where: R = actual shear end reaction
Rv = allowable shear capacity for the particular "limit state" considered.
Hope it helps.
JWB
RE: shear tab with axial load
Some considerations:
slots require slip critical bolts
bolt eccentricity
weld design (note this is not simply based on the end reaction)
weak axis bending of the plate
plate buckling
are stability plates necessary
adequacy of supporting member
http://www.FerrellEngineering.com
RE: shear tab with axial load
Good point about the weld design and slots requiring slip critical bolts. I am curious, how do you design for the combined tension and shear forces in the shear tab when a connection is subjected to an end shear reaction and a drag axial force?
JWB
RE: shear tab with axial load
Pa/Pn/omega + Va/Vn/omega + Ma/Mn/omega < 1.0
moment is from small eccentricty from bolts to face of column....
shear is from beam end rxn
Pa or Ta is from axial load
or would you analyize stresses with state of plane at a point from strength of materials
RE: shear tab with axial load
Shear Plate
plate stresses - shear, tension, bending strong-axis, bending weak-axis (combined stress interaction)
net fracture limit states - block shear for shear forces, block shear for tension forces, net capacity of plate for shear, tension, and bending
Beam Web
block shear, beam web tear-out
Bolts
plate/web bearing, bolt eccentricity (vertical and horizontal)
Weld
IMHO - I check the welds for the actual shear and axial forces. But use at least 5/8 x plate thickness (upto 1/2" plate w = 5/16 max). For thick plates, design for the plastic moment capacity of the plate (I think this is conservative, but in accordance with AISC's intent)
Disclaimer...
This may not be the complete list of design considerations
http://www.FerrellEngineering.com
RE: shear tab with axial load
RE: shear tab with axial load
If there is restraint in place, composite beam with studs or horizontal bracing, to resist out of plane movement, then weak axis bending would not apply.
http://www.FerrellEngineering.com
RE: shear tab with axial load
If so it depends if the connection is considered to be "Conventional Configuration" or "Extended Configuration."
If you have the "Conventional Configuration" with "a" less than or equal to 3-1/2" and less than 10 bolts, eccentricity can be ignored on the bolts for the vertical shear. To include the axial load I would determine the resultant horizontal shear to each bolt taking into account any horizontal eccentricity.
With these two forces (vert. & horiz.) I would find the resultant force in each bolt and check bolt shear, bolt bearing, etc. Use Slip Critical Bolts if you specify SSL holes.
You could than apply the same priciple to the design of the "shear tab" (plate) and the welds of the plate to the supporting member.
Please see pages 10-101 to 10-104 for additional information and requirements.
RE: shear tab with axial load
By applying shear and axial to the single plate (shear tab) connection, the tabulated single plate connections and design method does not apply. This design (with no eccentricity) applies to shear only. This was based on lab tests of shear only single plate connections. The design required is similar to the extended plate design, and the eccentricities are relative.
And FYI, the single plate tables and design method will change again in the 14th Edition Manual, later this year.
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RE: shear tab with axial load
I am not suggesting that the tabulated values (pages 10-105 ff.) be used. My point is that the effects of the horizontal force from the axial load be combined with the vertical shear, and the bolts, plates, and welds be evaluated with the combined loads.
My reference to page 10-101 was to point out that you need not consider eccentricity on the bolts due to the vertical shear if the conditions on pages 10-101 & 10-102 are met.
RE: shear tab with axial load
RE: shear tab with axial load
If the plate is welded to the column flange, relatively close to the centerline, then I don't think flange bending will control.
http://www.FerrellEngineering.com
RE: shear tab with axial load
I am trying to check the extended shear tab for combined moment and axial load. What would you calculate to be the moment in the plate?
The connection engineer is suggesting that there is no moment and that all of the eccentricity is being taken by the bolts, and as such bending in the shear tab is not an issue.
Even if the shear reaction is at the end of the shear tab welded to the HSS column, we would have some bending in the plate as we go towards the bolts...
RE: shear tab with axial load
Also sounds like a lot of force for a HSS face welded shear plate. Did they check the column wall for concentrated force. Would a through plate not represent the load path better?
http://www.FerrellEngineering.com
RE: shear tab with axial load
You are correct we do have through plates for the vast majority of these connections. The only exception is where we have pass-through forces crossing each other. Do you have a recommended detail for this situation?
We have concrete filled columns so compression is not an issue. I believe that this would help prevent local yielding of the column face under tension as well.
RE: shear tab with axial load
I don't know of any AISC examples for concrete reinforced columns. Chapter K provides the formula for checking the HSS wall for concentrated force.
I have designed connections for large axial load where column lines intersected. Cruciform through plates were used, with one plate continuous and the intersecting plates welded in the middle. This is not difficult at the top of column or baseplate. But, requires the columns to cut and spliced at intermediate floors.
Depending on the bracing forces, it can also be difficult to design the bracing gusset connections without through plates. The eccentricity for the vertical component is to the centerline of the column. Unlike a simple shear plate connection that considers eccentricity to the face of the column. The gusset plate is shop welded to the beam flange and field bolted to extended plate connection considering the eccentricity (or axial/moment with UFM)
The joy of connection design with HSS sections...
http://www.FerrellEngineering.com
RE: shear tab with axial load
I agree with the bolt eccentricity, and the net bending eccentricity. But I would put the gross bending eccentricity on the first line of bolts as well. By the time you get to the second line of bolts, you've removed load from the plate.
RE: shear tab with axial load
http://www.FerrellEngineering.com
RE: shear tab with axial load
For the OP's case of combined vertical shear and axial load, where is the weak-axis bending in the shear plate coming from?
Is it due to the slight axial load eccentricity between the shear plate and beam web centerline?
RE: shear tab with axial load
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??
RE: shear tab with axial load
Your statements are correct. However, if applicable, weak axis bending will govern the plate thickness.
http://www.FerrellEngineering.com
RE: shear tab with axial load
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.
RE: shear tab with axial load
RE: shear tab with axial load
http://www.FerrellEngineering.com
RE: shear tab with axial load
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://lar
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://lar
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.