Stiffener for eccentrically loaded Column Flange 2

[StuSE]

Hey you guys;

I am loading a structural column eccentrically for connections for the cladding of a building. This will cause rotation and bending in the column flange. I'm familiar with the web stiffener provisions, but am trying to determine at what point I need to add a flange stiffener to keep the flange from being overstressed.

Perhaps a simple bending analysis of 'x' width of flange would be appropriate, but I wouldn't mind pointing my finger at something specific. Do you guys have any tips?

Stu

 

[dhengr]

I’ve got a tip. Instead of pointing your finger, why don’t you give us a hint as to what you are talking about with a sketch; sizes, loads, dimensions, etc. Is the cladding loading on the column less than 95% of the total load on the column? Just imagine the infinite number of sketches and details which could be generated, each needing a slightly different design and analysis approach, but still complying with your limited description of the facts.

 

[StuSE]

Are there provisions for calculating when a stiffener is required to resist eccentric loading on a column flange. Is anyone familar with articles that address this situation.

I found an article on beam flange bending on Modern Steel Construction.

http://www.modernsteel.com/steelinterchange_details.php?id=499

 

[hokie66]

I read your first post, didn't know what type flange bending you were referring to, so didn't answer. Dhengr is correct...a sketch might help.

 

[paddingtongreen]

There are at least sixty two ways to load a column flange. That's my last contribution to this thread.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[rscassar]

StuSE

I would be happy to apply the theory which you attached in that link to modern steel construction. I am not as familiar with LRFD/AISC (whatever steel code is used in the US) and the steel design code which I use only covers web stiffeners when the web is subject to compression. I did do the calculations for a channel lately where I assumed a bending width of 100mm (4"). There was no engineering equations put to this, I based it on my engineering judgment. As it turned out, the flange of the channel exceeded it's capacity and I detailed a web stiffener to stiffen the flange for bending.

I found it interesting that modern steel recommends using b*d^2/6 for plate bending. I have always used b*d^2/4.

But to answer your question directly, I would follow the recommendations listed in the article which you posted.

All the best.

 

[PMR06]

What a warm welcome guys... It doesn't take paragraphs of unprofessional ramblings to say "Sketch please"!

StuSE: I'd use the local flange bending criteria also. Perhaps you could break your bracket moment into a couple and use a pair of stiffeners to resist the forces? If that doesn't sound like it would work... sketch please.

 

[ToadJones]

Kik-

bd^2/6 is just the elastic section modulus of a rectangle; commonly called Sx in the USA

bd^2/4 is the plastic section modulus; commonly called Zx in the USA.

In the US, Zx would often be used when using LRFD design.
Sx would be used in an allowable stress design, or ASD.

 

[ToadJones]

...my point being, you can use bd^2/4 if you are using a plastic moment approach.

 

[BAretired]

Sketch, please.

BA

 

[ToadJones]

no way I'm sketching how to figure out section modules BA.

 

[BAretired]

Toad,

I meant StuSE should provide a sketch illustrating his question.

BA

 

[ToadJones]

i know....it was a bad joke. :~/

 

[BAretired]

BA

 

[paddingtongreen]

PMR06, you don't see the whole story, the mods don't acknowledge when they edit.

Michael.
Timing has a lot to do with the outcome of a rain dance.

 

[StuSE]

Thank you mods. Thank you "Other Posters" I apologize about my lack of detail. Enclosed is a detail I am using. I am the cladding subcontractor and I did not want to leave it up to the Structural Engineer to tell me to put stiffeners everywhere, so I wanted to be able to calculate when I needed stiffeners and when I did not.

I am familiar with the web stiffening provisions used in moment connections, but that was not my concern. I am also familiar with torsional effects on the column, but obviously there are other forces aside from my cladding the SE has to consider. MY concern was how do I figure 'flange stiffeness' or "flange strength". Was there something out there in the engineering community or was it to simply check the bending stress of the flange, and if it is simply bending stress what are the reasonable assumptions. The Modern Steel Construction article gave me some info I am able to use.

If I run into trouble, I can use the plastic modulous, which I had not thought of. Thank you Kik! Any other information or articles you could point me to would be benficial,

 

[dhengr]

Since I seem to have started this mess by yanking StuSE’s chain to get his attention and try to get him to ask an intelligent question, let me try again. Stu.... your question isn’t a dumb question you just asked it in a really dumb way. As Paddington suggested when he was so rudely interrupted (or reinterpreted) there are some mighty smart people here who are willing to help and give of their time to do that, but they shouldn’t have to waste their time guessing what you want, when you are too lazy or not smart enough, about your own problem, to ask an intelligent question in a way which will elicit meaningful answers. You were looking at a sketch or detail which we couldn’t see from here, so how would we have any idea how you are loading the flange, the magnitude of the load, the dimensions, etc., etc. The MSC article is good conceptually, for their particular flange loading condition, but I can think of a number of ways which it falls far short of helping you solve your problem, and you still don’t give us much chance of helping you, for lack of problem specific info. I would not use the plastic modulus or stresses associated with that (of that magnitude) for your design and you should do your details so you don’t run into trouble.

You want to provide a cladding support detail which doesn’t require any, or darn few, web or flange stiffeners, since this part of the steel fabrication happens far removed from your involvement. And, nobody likes adding these type stiffeners because of your detailing. Who’s detail is this, your’s or someone else’s? I would show this detail to the EOR for his approval, so he can take this kind of loading into account in his column design. Does your cladding span btwn. column center lines, or is it also connected btwn. columns, a very different condition? Your cladding support detail will not apply much gravity loading to the column, the long cantilevered coil rod just can’t transmit much vert. load to the column. Your detail will only transmit significant loads perpendicular to the plane of the cladding and that will induce a torsional moment (loading) in the column and outer flange of the column. But, you don’t give a hint as to the magnitude of that load or the size of the columns you are dealing with, or if that’s a wind or earthquake load. And, I would try my darnedest to minimize the eccentricity (w = 1'-01/2") wrt the column web. This will impart a couple on the flange; with one force being into the bldg. and the other being outward; they will be separated by the flange width, and applied by your two 1/4" fillet welds. I would use 5x5x1/2 plates at the TS to facilitate improving this e.

You provide reasonable adjustability; 1" in each direction, in the x and y directions in the plane of the cladding; and also in the z direction perpendicular to the plane of the cladding, and that’s good. But, are coil rods and nuts at all susceptible to loosening over time, vibration, varying loads and temps., etc? Is the cladding really set 1' away from the outer flange of the column? How is the gravity load of the 5-6" thick cladding panel supported, and what does it weigh? I trust you keep the nut open and clean during casting, and install the 18" coil rod at the job site.

 

[BAretired]

Is the cladding a precast panel supported vertically at the foundation? Is the only force transmitted to the column an axial force in the 1" dia. threaded rod?

If so, there is bending and torsion on the column as a whole. There is also bending on the web. Bending on the flange is not an issue because (a) there are two flanges resisting the applied force, (b) they are each thicker than the web and (c) they are both reinforced by a HSS6x3x1/4.

The effective portion of web resisting the applied moment is probably about 6" + 2k where k is a dimension from the steel handbook. If the web has a thickness of t, it has a bending strength of 0.9Fy*(6 + 2k)t²/4 or thereabouts.

Why don't you use a detail where the precast is laterally supported at the center of the column and avoid all of this complication?

BA

 

[StuSE]

This is only a lateral connection. The bearing and longitudinal connections are elsewhere on the panel. The eccenentric loading is not a desireable item but a necessary item due to the locations of the panels in relation to the column. (someone please slap the architect for me!)

I had not considered the web to absorb the moment. This is likely considered in overall design of the structural steel colummn and not in my perview. I have recieved many responses to help me address when a stiffener makes sense due to cladding loading.

The loads for the shape portion of design is 4500lb, and I am applying it at the coil rod location. (as opposed to the weld....if I multiplied it by e and divided by flange width it would all come out the same) Using the MSC article, I am in the clear and I find this to be a suitable solution.

Thanks you guys!

 

[BAretired]

Torsional moment, Mt = 4500*12.5 = 56,250"#
Factored torsional moment, Mft = 1.5*Mt = 84,375"#

Resisting moment of web, Mr = 0.9*50,000*(6 + 2*1.5)t²/4 = 101,250t²

t required = 0.913"

You would need a web thickness of 0.91" to resist a force of 4,500# applied at a 12.5" eccentricity. My guess is that you need a stiffener on one side of the web.

BA