reinforcing pipe columns

huangyhg

reinforcing pipe columns
anyone have any ideas on reinforcing steel pipe columns?  i've got 4" nominal diameter steel pipe columns, wall thickness unknown.  they dont work with the new loads applied (nor do they work with the original loads..).  so, to reinforce, i've come up with welding 4 l2x2's to the pipe, or trying 2 l3x3's to the column.  with (4)-l2's, i have a symetrical x-section, but twice as much welding.  with (2)-l3's, i have half the welding, but still weak in one direction.  
anyone have any other ideas besides welding angles?  welding other shapes to the pipe?  maybe reinforcing isnt cost effective, and replace the entire column with an adequate size?
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i've used 2 steel channels with the toes welded to the column to increase the allowable axial capacity
replacement with with an adequate size is probably your best option - not dependent on quality of workmanship and more predictable behavior of the   
if you haven't already done so, you might want to check out the previously posted question on 4-17-04 on "steel column reinforcing" and the replies for additional considerations...food for thought.
lppe, is it for a building column?  if possible, replace the column with proper/adequate size.
for telecommunication towers, some times adding new secondary bracings to reduce effective length will do the job.  in some stubborn cases welding shaped semicircular plate to the column is done, but that is extremely painstaking and expensive job.
i have read about filling the column with concrete is also a viable option, but did not do it personally.  cidet [forgot the number] standard gives design recommendation for concrete filled steel columns, may be some other standards do that too.
again, to me the best solution is to replace the leg with proper size [assuming available construction facilities will allow you to do so.]
good luck, am
my opinion is if the undersized column is a single-story and the connections to the structure or anchor bolts are easily accessable......replace the column.
if it is a multi story column........reinforce.  
single story column.  exposed structure, so no room to reduce the effective length.  the steel girders cantilever over the column, so the top of the column would be easy to replace.  the bottom of the column is embedded in the concrete slab (presumably on a footing...).
the most economical way is to add one or two channels (c4 or c5) to the pipe with the legs faced in as chipb suggested.  however you can attach the channel(s) to the pipe by screwing or powder actuated fastners to brace the the channel in it weak direction and for load sharing as welding behind the channel to a round   
i would use four (4) angles to form a square cross section with the pip in the middle. i have used this in the past. of course you are lucky it is steel, you can work and make many configurations to reinforce this column.
regards
can you put additional cols. in to cut the loads in half?
lppe,
just a reminder as we sometimes focus on one and forget the other.  all this reinforcing for the column due to increased loads, have you checked the foundation's capacity for the increase?
chip