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HSS Col-Beams from four sides
3

HSS Col-Beams from four sides

HSS Col-Beams from four sides

(OP)
I want to verify the changes I want to make to this attached obsolete detail. I have a HSS col with WF beams coming in from four sides. I can get a thru plate for connection from two sides but I am not sure about the other two sides. Could I use welded plates (as marked up) which are not thru plates? Thanks.

RE: HSS Col-Beams from four sides

Is this a shear-only connection?  If so, and if your plate thickness and HSS wall thickness satisfy the proper ductility ratio, you don't need through-plates at all.  The shear tabs could weld directly to the column face on all four sides.

RE: HSS Col-Beams from four sides

I prefer welding a WT section over a shear tab on the face of a tube. Bolt as if this were a shear tab. Make the WT a little bigger or a little smaller than the column width to allow for welding.

 

RE: HSS Col-Beams from four sides

(OP)
hawkaz, thanks. Use of WTs seems like a good idea, and cheaper too.

nutte: Its sort of complicated, I have moment connection (wind frame) from one side with 8k-ft moment, so not a lot. Rest are shear connections. Where would I find the ductility ratio info in the steel book?

RE: HSS Col-Beams from four sides

I agree with nutte..  We use shear tabs on HSS columns all the time. See AISC 13th Ed., Sec. K1.5 for the ductility check nutte mentioned. Remember, KISS.

RE: HSS Col-Beams from four sides

2
Depending on the HSS wall width and thickness, a face welded shear plate is the best option in most cases.  As noted this detail and design considerations are shown on the 13th Ed manual.  Your detail as shown with thru plates must be welded at the center intersection.  The partially inserted plates provide no advantage or reinforcement of a thin wall column.  In many cases it is more economical to increase the wall thickness, then to use through-plates.  Intersectting plates require that the column be cut and the welded cruciform plates inserted, then the column repaired/spliced.  This is obviously easiest at the top or bottom of the column.  The face welded WT detail has been shown in several publications.  Note however, AWS does not advise the use of fillet welds in prying.  The bending forces are concentrated at the top of the welds which can cause the welds to "un-zip".  The flange thickness of the WT must be adequately thick to eliminate prying.   

http://www.FerrellEngineering.com

RE: HSS Col-Beams from four sides

connect-
where is this noted in AWS?  

RE: HSS Col-Beams from four sides

Toad
I will attach references when I return to my office.  The issue is that prying applies concentrated forces at the top of the weld and at the root of the fillet.  These concentrated forces can propagate a crack, which significantly reduces the weld strength.    

http://www.FerrellEngineering.com

RE: HSS Col-Beams from four sides

okay...i was wondering for WT hangers.  

RE: HSS Col-Beams from four sides

Hangers would have the same prying concern. The flange thickness can be increased so that weld is in tension without prying.   

http://www.FerrellEngineering.com

RE: HSS Col-Beams from four sides

Toad
Page 8-15 in 13th Ed manual.  The detail advises against the use of one sided fillet welds in tension.  In the case of a WT flange the condition is similar, if the welds are separated by a distance and material in between allows bending.  Similar to the single plate, the toe of the flange rotates and the weld stress is concentrated at the root.  If the flange is designed for bending, the weld stress is tension only applied to the thickness of the weld.   

http://www.FerrellEngineering.com

RE: HSS Col-Beams from four sides

connect-
thank you.
I recently had a detail passed across my desk for a multitude of hanger type connections. The hangers were fabricated from WF shapes with the top flange being welded with fillet welds along the sides of the flange to a larger WF shape above.
I didn't care for the detail at all and asked the engineer whose did the design (another company) if he investigated prying-like forces on the connection. He was irritated and the conversation did not go well. He essentially cast me off as if I were inventing a problem. I could not remember where I had seen or read that this was a bad idea but at the same time I wasn't looking either.
He told me that the material had been order and cut for the hangers.
All I could come up with for a suggestion to eliminate prying was to cut the flange width down.  

RE: HSS Col-Beams from four sides

wow...sorry for hijacking the thread

RE: HSS Col-Beams from four sides

Toad
Another fix is to provide partial depth stiffeners.  Prying increases the tension forces on a bolted hanger connection.  It is not a stretch to expect the same with the welds located at the extreme width.   

http://www.FerrellEngineering.com

RE: HSS Col-Beams from four sides

Connect, how thick do you have to go to eliminate the "unzipping" force on the weld?  You can size the WT flange for bending, but no matter how thick it is, it will still deflect, however slightly.  How thick is thick enough?

RE: HSS Col-Beams from four sides

I think Connect is suggesting that the thickness to eliminate bolt prying is sufficient....but the bolt gage is narrower than the beam flange (obviously). That would lead one to believe that the thickness required for the welded condition would be larger than that for traditional prying of bolts.  

RE: HSS Col-Beams from four sides

When this detail cannot be avoided, we develop the thickness for bending.  Theoretically the bending check will allow some deformation.  But the bending allowables are conservative, and the thickness should be relatively stiff.  It should certainly provide enough stiffness to resist rotation at root of the weld.  We don't use the welded flange hanger detail or the WT shear connection HSS walls.  For the hanger detail we typically use a bolted connection, and design the flanges for prying.  For HSS column shear connections we use shear plates.       

http://www.FerrellEngineering.com

RE: HSS Col-Beams from four sides

Toad
The thickness for prying is insufficient.  The design for prying allows for flexibility.  But, the thickness required to eliminate (theoretical) bending is sufficient to use a welded connection.

http://www.FerrellEngineering.com

RE: HSS Col-Beams from four sides

A contrary view...although I respect connectegr's advice, I don't use face welded shear plates on HSS columns unless the loading is very light.  Through plates or tees for me.  Seems illogical to make the column thicker just to accommodate a simpler connection.

RE: HSS Col-Beams from four sides

Hokie-
I agree, but sometimes one column may have many many connections on it. A heavier column may lead to significant cost savings.  

RE: HSS Col-Beams from four sides

connect-
Let me be clear, I was referring to the thickness to eliminate prying.

RE: HSS Col-Beams from four sides

Reason we avoid the welded hanger detail...

The flanges become very thick, when developed for bending.  This requires "built" T's or pieces of much heavier sections to provide adequate flange thickness.  The supporting member may also require reinforcement.  This detail also requires overhead field welding, which is not for the typical iron worker.


I also apologize for leaving the thread topic.     

http://www.FerrellEngineering.com

RE: HSS Col-Beams from four sides

Hokie
I have attached our standard for single plate connections.  The shear capacities are pretty good for face welded plates.  Note, that we provide a detail for the width/thickness requirements, to adequately account for punching shear and weld capacity.  The thicknesses relative to wall width are pretty reasonable.  If you are using "soda can" columns, then I agree that through plates or other connections should be used.  


Thanks for getting back on the topic.   

http://www.FerrellEngineering.com

RE: HSS Col-Beams from four sides

Thanks for that, connectegr.  The capacities are surprising to me.  I'll try to do a comparison with Australian practice.

RE: HSS Col-Beams from four sides

I'm a little late here but good thread discussion.

Just so I have this right -

The eccentric load on the WT creates a moment at the connection. The Tension component of the force couple pulls the WT away from the HSS which puts the flanges in flexure. The rotation of flange then causes the root of the fillet weld to be stressed, which is not ideal.
Correct?
Where does the prying occur?
See attached for an illustration of the questions.

Thanks.

EIT

RE: HSS Col-Beams from four sides

RFreund, the connection you're talking about is a WT shear connection, where the WT acts the same way a shear tab does.  Here the weld is generally considered to be in straight shear, with no eccentricity.  The bolts are designed with the eccentricity.

The "prying" with WT hanger connections occurs when a tension force is applied to the web of the WT, and the flange of the WT is welded to an overhead support.  In this case, as the flange flexes, the weld sees tensile stresses at the root, which can lead to the unzipping effect.

RE: HSS Col-Beams from four sides

RFreund
Your details correctly illustrate my concern with the WT shear connection.  Current design examples for double angles and shear plates consider the beam web bolts to be in straight shear, but I am not aware of any design examples making the same consideration for the WT connection. As you have shown the eccentricity results in prying of the WT flange.  However, nutte is correct and I am sure the others using this connection are not checking prying in the WT flange.  The design example in the HSS manual does not address this concern.  It actual limits the flange thickness to provide beam end rotation.  The requirement for flexibility is also noted in the 13th Ed manual.  The design example considers eccentricity in the bolts, bending in the WT web, but no prying on the WT flange.  If the forces are large or the eccentricity is large, this tension at the top of the connection can be large.  Although we frequently use knife-angles to embeds with the outstanding legs welded, we avoid the use of the WT shear connections.  I prefer to consider the prying in the design, and expect that the supporting member will provide adequate ductility for end rotation.  

Clearly a personal bias.   

http://www.FerrellEngineering.com

RE: HSS Col-Beams from four sides

I don't have the benefit of all the latest codes and manuals, so I'm hard pressed to see the very same code sections or manual figures you guys are sighting.  However, for that end connection, on the simple beam that we are talking about here, basically assuming only a shear reaction, non end moment connection; you have the very same forces from the building and beam acting on the connection wether it is a WT or a single shear plate, they are just taken out differently into the HSS.  And, as I see it they both have some drawbacks or conditions which are kinda hard to rationalize from the stress or weld standpoint.

For the WT as a hanger with the web vertical and with a hanging load, you will have a prying action causing tension at the root of the fillets, not a good condition; as Rfruend shows in his Sec. A-A, if the only welds are out at the flg. tips to the supporting member.  But, you can start to alleviate this prying action by welding across the cut flg. on both ends of the WT to the supporting member.  Then the problem I have trouble rationalizing is a fairly high weld stress within an inch or two on either side of the WT web because of the way the stiff web transmits the load the weld on the cut end of the flg.  For the single pl. hanger you can certainly get enough double sided weld btwn. the single pl. and the supporting member, a good weld detail too, but now the starts and stops (terminations) of these welds have the potential of becoming highly stressed or stress raisers if there are any undercuts or craters, particularly if the load is not perfectly vert.

With the WT as a shear connection on the HSS you have the same considerations.  I would weld across the top of the WT flg. to minimize the prying action on the vert. welds out at the flg. tips.  The weld hard spot at the WT web becomes softer because the HSS face pl. is flexible, but this should still be looked at.  The forces applied to WT by the building and the simple beam are the same as those applied to the single shear pl.  We assume the rotation (some fixed end moment) will be taken care of by the slotted holes, but maybe not if the nuts are tightened.  Otherwise, you still have a moment applied to the connection as a function of the shear and its eccentricity, Rfruend's sketch pretty much shows it as I see it.

You can do the very same sketch for the single shear pl., and now any end moment (RF's, Td = M) plus Pe = another M, are acting with their max. stress in the shear pl., from any moment in the shear pl., right at the start or stop (terminations) of the double vert. shear welds, at the top.  And, without great care in welding and inspecting this is hardly a better condition than the prying on the WT.

I think Connecteng pretty will summarizes the problem, or quandary, by saying some worked out examples and some figures seem to ignore some of the forces or couples which might be acting on the connection.  However, the idea that    "The design example in the HSS manual does not address this concern. It actual limits the flange thickness to provide beam end rotation."    seems to fly in the face of what we are discussing here.  It seems that almost invariably we make a second problem by trying to fix the first problem, and it is left to us..., good, thinking engineers to try to pick the least of the evils, and then hope they don't slot the holes in the wrong direction, or some such.


 

RE: HSS Col-Beams from four sides

Every detail and connection we do should get this kind of basic scrutiny; in more detail as we are learning the ropes, and so we really do learn the ropes and learn to recognize good details; and with a somewhat lesser attention (or time required) as we gain experience and know when and where to look for problems.  As our buildings and details get more and more complicated and are expected to do more, at higher stresses, this is the exact place that an engineer or firm dedicated to these details will really shine.  They are doing this every day, and as Connecteng has demonstrated, they learn to know where and when to look more closely, or to make that extra calc., etc.  At the same time, this thread would seem to indicate that there a plenty of bright engineers here, who are basically able to do this themselves, on their own designs.

The problem I have with the way Structural Engineering is going these days, is we are starting to produce engineers who are 'one trick ponies.'  You do the positive moment on the beam, I'll do the negative moment, he can do the connection bolts, and we'll hire a firm to do the welding on the connection....   And, there isn't anyone who has a handle on, or control over, the entire design.  I don't bother checking your moment, or design, or shop drawings, I claim I just didn't see your error, or you just didn't consider what I had done to affect the design; but now I do have someone to blame now, other than me.  And, the attorneys and insurance providers love it.   

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