Opinion requested re: column web stiffening proposal... 8

[Zylinderkopf]

Greetings, esteemed structural engineers:

The issue that I face as a mechanical engineer is one that pertains to the subject matter in the following context.

There is an existing structure utilized to support a hydraulic hammer; the hammer is being replaced with another model of 50% greater mass.

A person who identifed himself as a structural engineer in a recent meeting stated that the columns that support the subject equipment are requied to be stiffened.

His proposal is to weld a 1/4"-thick mild steel plate on the exterior of one (1) side of each vertical column web, (also mild steel), approximately 15-feet in height, thus (in section view):

XXXXXXXXXX -- column flange
XX ------ column web (3/8" thickness)
XXxx
XXxx ---- proposed plate addition, fillet welded
XXxx
XX
XXXXXXXXXX -- column flange

Again, as a mechanical engineer only having limited experience with structures, I thought that this proposed method appeared unorthodox. Additionally, I wonder if the heat added, via whatever welding process will be used in this case, would be detrimental to the web material characteristics --- I expressed my opinions but was esentially told to "mind my own business" and that this practice "is common"...maybe it is? Does the AISC address this in any regard in way of eihter condoning or frowning on this type of web "stiffening"?

Any opinions that you could share with me would be most appreciated...as I have written, my structural experience is not that advanced.

Best Regards,
Pete

 

[csd72]

Zylinderkopf,

This is a fairly typical column stiffening procedure. Normally you would do it to both flanges, but it does make sense to do it one side only if the bending causes more compresion in that flange.

For typical structural steel grades the welding does not cause any issues with the steel strength( concrete reinforcement is another matter). The welds each side should be intermittent(i.e. 6"@12" o.c. or similar) to avoid warping the column from heating one side more than the other.

If there is a specific AISC reference for this I am not aware of it.

regards

csd

 

[civilperson]

Not common to attach to the web, usually if weak axis needs strengthening the plate is boxed across the space between the flanges on both sides. If the flanges need additional area, then weld plate to flange. Steel area near the Neutral Axis does very little in increasing the I or S, (Moment of Inertia or the Section Modulus).

 

[hokie66]

Would have to know the loads involved to give an informed opinion if the stiffening is adequate, but the structural engineer's approach is appropriate in adding axial load capacity to the column, although he is not increasing the capacity by a large percentage.

The comments by csd72 and civilperson are pertinent if the bending capacity of the column needs to be increased, but that is not necessarily the case.

 

[csd72]

Sorry,

I should have read the OP more carefully. Connecting stiffener plates to the web is not a regular practice, connecting plates to the flanges is.

As hokie66 pointed out, we really cannot give you specific comments without all the details.

csd

 

[dik]

Can you weld the plates across the toe of the flanges, parallel to the web? Stiffens and strengthens...

Dik

 

[Lion06]

I would concur with everyone else's post. This doesn't seem to add much to the section. Without knowing the loading conditions, it is difficult to say, but this plate adds very little to the section lodulus in either direction and even less to the radius of gyration in either direction.

 

[hokie66]

True, but it does add to the area of the section, and thus the compressive strength. Possibly that is all that was needed.

 

[patswfc]

indeed hokie it does increase the area of the section and thus its compressive strength, however the compressive strength of the column may be based on buckling and the addition of this plate will not be very beneficial.
As you have already said its difficult to say without knowing all the parameters.

 

[Lion06]

hokie66-
agreed that it does add to the area, but if you assume the controlling "r" does not change (not an unusual assumption in this case) and the area of the plate is about 2 in^2 (0.25*8) then the compressive strength of the column in increasing very little (maybe 50-70 kips). This seems small when considering that the weight of the hammer is being increased by 50%.
Of course, maybe it was overdesigned to begin with and doesn't need much help.

 

[trainguy]

I agree with most of the above posts, but I can add this:

Once the owner has bitten the bullet and agreed to reinforce the column, I would reinforce, and make it really count, such as boxing the column or other obvious means. The numbers may say that the proposed web doubler is adequate, but I would just make it stronger by boxing it.

This conslusion only applies if we're talking about 1 column, not 300.

tg

 

[jetmaker]

I would agree with the majority of the posters here, in that the web stiffening provides little increase in strength comrpessive or column buckling strength. However, it is possible that the web suffers from local instability and this plate will help prevent web buckling under the compressive load.

It is hard to agree/disagree with the findings unless more details are supplied (i.e column length, profile, lateral stiffening, etc...).

jetmaker

 

[hokie66]

Suggest we stop this. Remember the original post was by a mechanical engineer questioning a structural engineer who we haven't heard from. And the mechanical engineer has not bothered to comment further.

 

[Zylinderkopf]

Greetings to "csd72", "civilperson", "hokie66", "dik", "StructuralEIT", "patswfc", "trainguy" and "jetmaker":

Thank you all, so very much, for providing your valuable comments in way of the subject matter.

As an aside, just today the proposed design for column reinforcement was altered to the "boxed-in" configuration in lieu of the initially-proposed web stiffener.

Thanks again for your time and advice.

Pete