Bracket plate calculation

[derim01]

I need some advice regarding design of bracket main plate. I need some guidance how to check this plate for moment resistance around major axis with respect to buckling (BS EC3 preferred).
I was reading several sources but I am not sure in this. Example showing something similar will be helpful.

Picture is attached.

 

[JStephen]

The latest AISC code has information on flat bars (not tapered) bent the hard way, and that would be one way to approximate it.

 

[Splitrings]

AISC LRFD 3rd Edition Section 9 is the design of connection elements. It covers tee sections mounted on concrete. Another option could be FEA.

 

[JAE]

Well - I think he needs BS standards - not AISC.

anyone?

 

[chicopee]

can you post a jpeg picture instead? I can't open you gif file.

 

[derim01]

In attachment there is picture in jpeg.

Main problem I have is section classification and determining ultimate resistance with respect to buckling. So in general, question is how to calculate ultimate moment resistance for plate with moment acting around major axis.

If it is I or tube section then it would be clear to me.

In area where I am working AISC is also accepted but since I am not too familiar it will take time for me.

 

[JStephen]

JAE, I figured if the code in question had a section about "Tapered plates bent the hard way", he wouldn't be asking the question. If it's not covered in the code in question, then any information at all on the buckling strength ought to be useful, as bars buckle the same way on one side of the ocean as they do on the other. And the AISC code is (or at least was) a free download, thus the suggestion to refer to it.

 

[ToadJones]

Section F11. of AISC 360-05 or 360-10
"Rectangular Bars and Rounds"

I guess with a tapered member, it will be tricky to determine what depth to use in the calc.

The other thing is, since this apparently is supporting a monorail, you will have some loading which will cause weak axis bending of the plate so the plate really needs designed for combined stress. This is covered in section H1 in the same specification.
As others have mentioned, its a free download from

http://www.aisc.org

 

[JAE]

JStephen - yes - good point and I agree. I was just trying to be a bits sensitive to non-US participants here.

 

[dhengr]

Derim01:
I can finally see your detail. That’s an interesting buckling problem and about the best I can offer is that you look at the development of width/thickness ratios and bucking vs. allowable compressive stresses, for unstiffened outstanding plate edges in compression. The various codes just don’t cover every possible detail with its own formula and design examples, yet; although it seems they are trying to do that and should have them all codified in another code edition cycle or so, and another 23 design guides.

I don’t happen to think that that buckling problem is the worst of your worries on the detail you have shown. I think you should look further at the following: (1) the two top chemical anchors always loaded in tension (epoxy creep over time) with the fatigue problems associated with cantilever tip loads of 1300kg or 1625kg, that’s 1.6tonnes at 38", right; (2) how are you really going to make your connection out at the monorail/canti. tip for shear, torsion and dynamic axial load parallel to the rail; and don’t forget those same loads in designing your cantilever; (3) what’s the funny little trapezoidal web piece at the bottom near the concrete wall for; (4) and finally, how do you make a good weld to the 16mm base plate on the wall without it just unzipping from the top due to the combined shear and tension stresses, the base plate flexure (prying on the weld) and poor weld termination conditions; you will have very high combines stresses in these welds right at their terminations? (5) The torsional loading on your 200x700mm concrete beam.

I would be inclined to fabricate those brackets out of thinner web material, but put top and bottom flanges, 50-75mm wide, or some such, on the web. These would act as stiffeners and allow for a proper weld to the base plate at the wall. You might make these by splitting a std. beam web diagonally, and adding the second (bottom) flange, or if you can resolve your buckling problem, maybe the bottom flange isn’t needed. You can also make these by cutting a std. beam to 950mm length, then cutting a triangle out of the web, near the bottom, but above the flg./web radius; then bending the bottom flange up and rewelding the web.

 

[RFreund]

Possibly check Salmon and Johnson if you have their text 'Steel Structures Design and Behavior'. They mostly refer to AISC but I believe they did some research on these types of brackets as well and give a discussion regarding their behavior. I'll see if I can find my text and look thru it for anything useful.

EIT

 

[kingnero]

I need some advice regarding design of bracket main plate.

I'd agree with dhengr and design something with either, and preferably both, top and bottom plates...

 

[derim01]

Thank u all for replies.
In this case I am just checking the design of this bracket.
If I did the design from the start I would put top & bottom flange or use a tube section.
This design is made by our subcontractor for window cleaning system. The fact is that in their design documents they didn't provide valid calculation for above problem and that's why I was wondering.
In this case I will return their documents and ask for valid calculation of main bracket plate and discuss about problems that dhengr noted.

 

[SAIL3]

I certainly would not approve of this conn. For all the reasons dhengr mentioned plus the following. I would have no confidence at all in the lateral stability as regards the lateral fixidity of the tapered pl where it is connected to the base pl. There will be weak axis rotation there that would be almost impossible to caculate with any degree of confidence.
Instead of shopping for a recipe in the code that you can shoehorn this into, what about using and trusting your own engineering judgement, afterall, that is why we run the gauntlet of an engineering curiculum. The real danger in the spirit of the codes today is that they are encouraging cookbook engineering and stunting the growth of engineers when it comes to independent judgement and analysis.