Damaged Steel Column Capacity 2

[thaidavid]

What references are there for determining the real-world, remaining column capacitiy for steel columns with damaged or dislocated flanges (ie: flanges bent mostly by fork truck impact)? We need to assess the stability and safety of an existing structure, and make provisions for any needed repairs.
Thanks -
David Anderson

 

[Hariharan]

I am not sure about I-sections. Residual strength of damaged(dented)
tubulars has been studied and documentad in offshore industry, and
used as well. Similar concept should be applicable for I-sections as well.
Basically, the procedure assumes that the dented/damaged portion is
ineffective in carrying axial load, computes the effective section properties
over the damaged region, and calculates the buckling strength. This
value is used in the interaction equations. This is not fully correct
for axial + buckling interaction, but is the best we have. This approach
has been used to evaluate damaged underwater elements,
strengthening which is very expensive, and should be avoided if
possible.

In case of land structures, I would box up the damaged region,
so that the original strength is nearly ensured. If the flange is very
severely bent, it is not effective anyway. The damaged piece can be
removed and a new patch-up piece welded in, before boxing up.
It will also safeguard the section against future forklift collisions!

 

[Qshake]

I agree with Hariharan but I am at a lost for a specific reference to capacity for these cases. I do, however, want to point out that an alternative to replacing a section is heat-straightening. There is much information on heat straightening most of it by a Dr. Avent(sp?) of the Louisiana State Univ. (I think...the specific reference escapes me) In these references you will find some research data on the crippled section and the heat-straightened section as they are compared to ascertain the benefit of the method.

Additionally, the member should be protected either with ballastrades around the column or encase the column in concrete to avert further damage.

 

[Ron]

As Hariharan and Qshake I can't recall a good reference but a procedure we have used is to carefully plot the reduced section dimensions, much as you would for corrosion damage in industrial structures. We then compute new section properties and consider that the column is now carrying an eccentric load, since the dents/damage have either moved it off its original axis and/or there is preferential damage to one side. This can result in significant load capacity reduction for the section.

If you encase the column in concrete to a fixity point above the damage, you really don't have to worry much about the damage affect.

 

[Qshake]

Ron, as always, has a good point. With encasement, correcting the damage is wasted money. Go with the encasement if possible.

 

[JAE]

Be careful about heat straightening a column under load. With the damaged section and eccentric loading that results from the remaining "true" cross section, you could initiate a buckling failure by over-heating the steel.

We usually either encase with concrete or add new steel shapes to the old to provide an extended, stronger shape. This involves calculating a new set of section properties of the added steel with the "true" remaining cross section and ensuring that the new cross section has more stiffness and area than the original. In addition, the connection between the old/new steel should be looked at by ensuring that the full capacity of the new steel can be developed across the weld interface.

 

[Qshake]

Thanks, JAE. I should have pointed that out!

 

[yekta]

It has been long time I reviewed eng-tips. Some good conversations are going on.
Caution for over-heating whenever an existing structure is involved. Provide shoring if you have to use a lot of welding.