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Weakest component: COLUMN FLANGE - TENSION

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hoshang

Civil/Environmental
Jul 18, 2012
497
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.
 
 https://files.engineering.com/getfile.aspx?folder=8a2baaa6-eade-42f7-8830-253b9e5524dc&file=viber_image_2020-12-12_22-13-30.jpg
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BA
 
Agent666 said:
Stiffeners won't fix the original root issue with the column flange not having sufficient capacity to resist the local bending from bolt tension forces. It may improve things a little, but it was failing by a lot.

The end plate on the beam appears to be even thinner than the column flange, so it too has insufficient capacity to resist local bending. A remedial detail gets a bit messy, but likely could be done with exemplary field welding, a service which may not be available on this project.

BA
 
The quality of welding is a big question.
 
Well the initial calculations provided by OP showed 20mm end plate and 13mm flange thickness. But I agree the thickness in the photos seem far more similar.

Add that observation to the longer list of issues that seem to be stacking up.

Perhaps OP was simply trying a thicker end plate in the calculations with a view to replacing it to see if the column flange could be made to work.
 
Thanks all.
I agree with you for the column orientation in the foundation. But I must proceed with the as-built on the field.
Anothe thought came to me. What about reinforcing the beam with a plate to absorb more moment?
 
So far I have failed to follow you on identifying the problem, as I don't wish to go over your worksheet, the number does not tell story without accompanied with a decent sketch. Please provide sketch, or identify the problem with remarks on the photos, so we can understand better.
 
hoshang said:
I agree with you for the column orientation in the foundation. But I must proceed with the as-built on the field.
Another thought came to me. What about reinforcing the beam with a plate to absorb more moment?

The same thought occurred to me, but I wasn't sure whether you needed some moment for lateral loads. If you need it only for gravity load, you could design the beam as a simple span, with positive moment reduced to suit end conditions.

The floor load, according to what you told me is 3 + 3 (D + L). I think you are a little light with dead load. A 150 slab weighs about 3.6kPa. Allowing for electrical, mechanical and possibly a ceiling, say 4.0kPa. The longest span is 9.8m which occurs 20m from the westernmost grid.

q = 4 + 3 = 7 kPa; L = 9.8m; spacing = 5m
Beam service load w = 7*5 = 35kN/m
M[simple] = wL^2/8 = 35*9.8^2/8 = 420 kN-m

I am not familiar with European sections, but I found the value of M = 212.36kN-m in the second table below. That is only about half of the simple span moment.

The beams nearer the west end are shorter, so they will be less critical. For the longest beam, I believe it is too shallow from a deflection point of view, so instead of a plate on the bottom, perhaps a 200 deep wide flange would be more suitable (I am guessing). A structural tee would be another option, but I don't trust your welders to carry out the weld properly.

The flange of the member should be wider than the 170mm flange of the existing beam to permit down hand welding.

The negative moment should be conservatively estimated. That will reduce the positive moment slightly, but material cost is likely to be the least of your worries.

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BA
 
hoshang,

Your calculation file named Column-tension-1, in which you claimed a connection resisting moment of 205.93kN-m is based on information not consistent with the floor beam used on the project. It is based on a total of 4 bolts between beam flanges. You have only 3. It is based on a beam depth of 400mm. Your beam has a depth of 360mm.

image_gk671f.png


hoshang said:
I agree with you for the column orientation in the foundation. But I must proceed with the as-built on the field.
Anothe thought came to me. What about reinforcing the beam with a plate to absorb more moment?

If you are relying on negative moment at each end of the beam in order to calculate the required positive moment, the above named file cannot be used. It is not valid. Also the quality of weld is highly questionable, so you should estimate the available negative moment with an abundance of caution.

EDIT: A structural design review and a construction review are desperately needed on this project before continuing to build.

BA
 
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