Weakest component: COLUMN FLANGE - TENSION

[hoshang]

Hi
My friend asked me to check connections in his project according to:
Design of fixed beam-to-column connection
EN 1993-1-8:2005/AC:2009
I noticed that one column has weakest component at column tension. The project is under construction and the steel frame is installed. Please find the attached files.
How this can be fixed? I thought of adding stiffeners & brackets, this helped but not much. I noticed a diagonal crack on top of the RC slab projecting from this column for about 15cm.

 

[hoshang]

Hi
Find this file also.

 

[Agent666]

I noticed that one column has weakest component at column tension.

Can you maybe explain a bit more about what you mean by this? Your explanation isn't making a whole lot of sense without some sketches maybe illustrating your concern? Can you mark something up showing the structure?

The crack could be anything, maybe explain a bit more about the structure in that area? How wide is the crack, I'm assuming you're referring to the slight separation between the column and slab and what looks like a small tear emanating from each corner of the flange? Is it possible that it's just a crack due to the concrete being still plastic and column moving a little. I say this because the crack on the left kind of makes a sharp turn 90 gress away from the gap against the flange? It sort of looks like the column deflected and pushed some concrete out of the way before final set.

 

[hoshang]

Can you maybe explain a bit more about what you mean by this?

CONNECTION RESISTANCE FOR BENDING Mj,Rd
Mb1,Ed = 244.56 [kN*m] Bending moment (right beam)
Mj,Rd = ∑ hj Ftj,Rd

Mj,Rd = 205.93 [kN*m] Connection resistance for bending

Mb1,Ed / Mj,Rd ≤ 1,0
ratio 1.19 > 1.00

 

[Agent666]

And these numbers without context mean what in your scenario?

I get you are saying the joint does not have sufficient capacity to develop the beam actions, but based on "what" aspect is limiting this joint capacity?

weakest component at column tension doesn't mean much to me.

Previous post of mine was written while you posted that drawing. But you still have not provided details of the joints and what the current configuration is, and what limit state is failing? (stiffeners, panel shear, welds... etc).

Clearly you've looked at "stiffeners and brackets" and deemed these to not have an impact, but without knowing the actual problem it's hard to say what a solution might be.

 

[hoshang]

But you still have not provided details of the joints

Hi
Please find the attached file.

 

[Agent666]

and answers to the other questions?....

I take it you mean this joint from your drawing? The configuration does not look ideal for a number of reasons, but I'll wait until you tell us what is failing to make any further comments.

 

[hoshang]

what limit state is failing? (stiffeners, panel shear, welds... etc).

Please find the attached file.

 

[BAretired]

So the problem is at roof level? I thought it was at floor level because your first photo was showing floor slab. I think you need to find a local engineer with a better understanding of the problem.

BA

 

[Agent666]

Ok now I see, despite you still not explaining in words.....

The column flange is basically too thin for a moment end plate type connection. Column flange tension failure is a yield line failure in the column flange around the bolts. The only way to address this is to come up with a configuration that forces more yield lines (= more capacity), or increase plate thicknesses (= more capacity).

Have a look at the use of backing plates. Given you've noted it is already built, this may be the only solution? Have a look at SCI P398 for some design guidance.

What has been built though? The drawing you provided, or the design checks you provided? Quite different configurations?

 

[hoshang]

So the problem is at roof level? I thought it was at floor level because your first photo was showing floor slab.

Yes, the problem is at floor level. I uploaded a detail of the joint because Agent666 asked to provide such a detail. So far I have this detail only.

 

[hoshang]

Have a look at the use of backing plates.

Thanks.
If I come up with these bolts, there will be congestion because of existing and new bolts. Can I field weld instead of bolt since it's difficult to field drill?

 

[BAretired]

Is there a problem on the outside of the column as well? Is 244.56kN-m also the cantilever moment? If so, the repair must be made on both sides of the column.

BA

 

[BAretired]

Just had another look at Section A-A. Is that really a 30 cm thick slab?

BA

 

[Agent666]

If I come up with these bolts, there will be congestion because of existing and new bolts. Can I field weld instead of bolt since it's difficult to field drill?

I think you need to explain what is new and existing bolts in your scheme? And what you mean by 'these' bolts in tht context.

You can remove the column flange as another option, replace it with a similar plate thickness to the beam end plate?

What do you propose field welding? Completely remove the beam end plate and weld column directly to beam to remove the flange bending via bolts loadpath is the only way welding would work without more significant modifications.

Simply welding round the end plate to the column does nothing for the loadpaths through the connection.


I don't think anything in that drawings is remotely to scale.... so possibly.

 

[Agent666]

Adding a stiffener between each set of bolt rows is also another possibility (increases length of yield lines in column flange as I noted earlier).

 

[BAretired]

The drawings provided and responses to date do not inspire confidence that the OP knows what he is doing. Why would the roof girders be stronger than the floor girders, particularly if the floor has a 300mm (12 inch) thick slab?

It seems to me that any suggestions we might make could easily be misconstrued by the OP and the friend who asked him to check connections. It may be better to abandon this thread in the absence of a sensible explanation as to what exactly has been built and why.

BA

 

[hoshang]

I think you need to explain what is new and existing bolts in your scheme? And what you mean by 'these' bolts in tht context.

Your suggestion of column flange backing plate proposed using new bolts. My friend's beam to column connection has already bolts in it. So my statement of new and existing bolts. So my question about welding your suggested column flange backing plate instead of bolting.

Adding a stiffener between each set of bolt rows is also another possibility (increases length of yield lines in column flange as I noted earlier).

Thanks for your new suggestion.
I think adding an angle or a plate under the bracket can also help. What do you think?

 

[Agent666]

Provide a sketch, I don't even understand what element you are referring to as the 'bracket' and how adding a angle or plate to a bracket helps?


Prop and take out existing bolts and replace in a controlled manner with backing plates included if that works.

 

[hoshang]

Prop and take out existing bolts and replace in a controlled manner with backing plates included if that works.

Thanks. Instead of taking out existing bolt, can we take out only the nuts and maintain the bolts? This will be safer.