Column Dents - To Fix or Not to Fix
Column Dents - To Fix or Not to Fix
(OP)
I'm peer reviewing some designs for column reinforcement where 8x8 columns have been whacked by forklifts about 18" above floor level. See the photo below. Our engineer has followed the lead of a previous firm and recommended angle reinforcement on the four corners of the column. My feeling is that no reinforcing is required. These three arguments inform my opinion:
1) The damage is far away from the mid-height of the column where full section stiffness is needed to prevent buckling.
2) There is no column "kink" to speak of. The column is still very straight. It just has the dents now.
3) While some of the cross section near the damage may be unable to carry compression due to P-Delta effects in the bent walls, I feel that I only need to demonstrate that there's enough undamaged section available to carry the load across the damage using squash capacity (As x Fy). I can get this done if I represent the four corners of the columns as imaginary 1.5" x 1.5" angles composed of undamaged HSS wall section. It doesn't take much. Moreover, there's probably some post buckling capacity to be had in the dented HSS side walls anyhow.
It might ultimately be prudent to fence off or concrete encase the columns to protect them from this kind of damage in the future. For now, however, I'd like to solicit comments regarding my "do nothing" proposal and the logic that I've used to justify it. The fact that reinforcement was specified by another firm in the past makes it apparent that one of us must be wrong in our thinking. Maybe it's me.
1) The damage is far away from the mid-height of the column where full section stiffness is needed to prevent buckling.
2) There is no column "kink" to speak of. The column is still very straight. It just has the dents now.
3) While some of the cross section near the damage may be unable to carry compression due to P-Delta effects in the bent walls, I feel that I only need to demonstrate that there's enough undamaged section available to carry the load across the damage using squash capacity (As x Fy). I can get this done if I represent the four corners of the columns as imaginary 1.5" x 1.5" angles composed of undamaged HSS wall section. It doesn't take much. Moreover, there's probably some post buckling capacity to be had in the dented HSS side walls anyhow.
It might ultimately be prudent to fence off or concrete encase the columns to protect them from this kind of damage in the future. For now, however, I'd like to solicit comments regarding my "do nothing" proposal and the logic that I've used to justify it. The fact that reinforcement was specified by another firm in the past makes it apparent that one of us must be wrong in our thinking. Maybe it's me.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.






RE: Column Dents - To Fix or Not to Fix
RE: Column Dents - To Fix or Not to Fix
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Column Dents - To Fix or Not to Fix
When you actually run the numbers the dents near the point of support don't impact the columns capacity by much, if any. I wouldn't be very concerned. If desired, encasing the columns in concrete has the double effect of protecting the columns and shielding them from future damage.
Maine EIT, Civil/Structural.
RE: Column Dents - To Fix or Not to Fix
Just adding a different perspective, but in the end I would follow your line of reasoning.
RE: Column Dents - To Fix or Not to Fix
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Column Dents - To Fix or Not to Fix
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Column Dents - To Fix or Not to Fix
Now, it's worth noting that this doesn't mean it can't fail. I've seen a large building column rust down to paper thin at the base and fail in buckling (dropped about 6 inches before secondary supporting members caught it and saved a building from coming down). However, it took about a 75% loss of cross-section before it did fail.
Maine EIT, Civil/Structural.
RE: Column Dents - To Fix or Not to Fix
This makes sense in that the middle 60% of the column works much harder to prevent buckling than the end 20%.
But don't tell the forktruck drivers about this!
RE: Column Dents - To Fix or Not to Fix
JLNJ commented on how little the bottom 20% contributes to buckling resistance. On many occasions, I've seen engineers place ground floor columns on much larger below grade piers in order to keep the KL from getting too long on columns where the footings must be deep for one reason or another. They treat the pier/footing assembly as though it were effectively rigid. However, if you look at the column as a single member from top to footing with the pier simply represented as a section with increased I, you find that you've improved KL very little. There's a bunch of other stuff at play out in the real world such as slab on grade restraint and passive soil pressure. Still, though, the logic is often flawed.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Column Dents - To Fix or Not to Fix
RE: Column Dents - To Fix or Not to Fix
I suppose you could present the case to the owner as arguing for complete repair OR addition of buffers/deadmen around the column.
Mike Halloran
Pembroke Pines, FL, USA
RE: Column Dents - To Fix or Not to Fix
However, and I think this is what the "other engineers" are doing; they are assuming a pinned base for the column. Thus, with a pinned base the column and pier do not act as one column and will have their own individual L values. But, you are correct that the piers will shift laterally and this may cause some secondary effects but these are likely negligible.
Maine EIT, Civil/Structural.
RE: Column Dents - To Fix or Not to Fix
@Mike: we stated that the columns were structurally okay but it would be prudent to protect them somehow. Similar to your recommendation. I was thinking about this issue at lunch. Initially, I worried that recommending a "do nothing" option would give them free license to run into the columns all they like. Then I came to realize that I don't really mind if they keep running into the columns over and over. As long as my three caveats at the top continue to be satisfied, my answer will always be the same. I accept your point regarding lawyers though. I make an active choice to not consider things in terms of future lawsuits. I find it paralysing to think in those terms. No doubt, my first lawsuit will change my tune.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Column Dents - To Fix or Not to Fix
I do consider that some angles should be placed on the corners supported by some springy flat bars as a guide for the crazed forklift operators.
Michael.
"Science adjusts its views based on what's observed. Faith is the denial of observation so that belief can be preserved." ~ Tim Minchin
RE: Column Dents - To Fix or Not to Fix
RE: Column Dents - To Fix or Not to Fix
RE: Column Dents - To Fix or Not to Fix