Through Holes Steel Structural Column
Through Holes Steel Structural Column
(OP)
Hello,
I have concern regarding a hollow steel structural column that has recently been altered. At 4 separate height sections (all of which are separated by about 3 ft from the bottom), 3/8" through holes have been drilled through two given parallel faces. There are two holes at a given cross section, separated at roughly 3.5 inches apart (center to center). The hollow column itself is 7" x 7", with a 1/8" thickness. The column itself is between 70-80 ft tall and helps support the roof. I have included an image to give you an idea of what I am describing. Yes, it would be best if these holes were non-existent.
With an assumed factor of safety of 4 for structural steel construction (http://www.engineeringtoolbox.com/factors-safety-f...) at a given cross section of the column, taking into consideration compression loading (F/A), a new factor of safety was calculated at the new weakest given cross section. This cross section is the point where the entire diameter of each hole (2) has been removed from the given uniform square cross section. This new factor of safety was calculated to be 3.6. We have not included buckling within this calculation, as we do not see buckling being an issue at the hole location given how close to the bottom of the column they are.
I am curious if this is something to be concerned about. We have plans on welding these holes closed later. Thanks!
I have concern regarding a hollow steel structural column that has recently been altered. At 4 separate height sections (all of which are separated by about 3 ft from the bottom), 3/8" through holes have been drilled through two given parallel faces. There are two holes at a given cross section, separated at roughly 3.5 inches apart (center to center). The hollow column itself is 7" x 7", with a 1/8" thickness. The column itself is between 70-80 ft tall and helps support the roof. I have included an image to give you an idea of what I am describing. Yes, it would be best if these holes were non-existent.
With an assumed factor of safety of 4 for structural steel construction (http://www.engineeringtoolbox.com/factors-safety-f...) at a given cross section of the column, taking into consideration compression loading (F/A), a new factor of safety was calculated at the new weakest given cross section. This cross section is the point where the entire diameter of each hole (2) has been removed from the given uniform square cross section. This new factor of safety was calculated to be 3.6. We have not included buckling within this calculation, as we do not see buckling being an issue at the hole location given how close to the bottom of the column they are.
I am curious if this is something to be concerned about. We have plans on welding these holes closed later. Thanks!






RE: Through Holes Steel Structural Column
How did you back-calculate a FS of 4.0 for compression? Buckling?
Reducing a factor of safety from 4.0 to 3.6 based on that small a pair of 3/8 dia holes holds only if you are comparing area with the 4 hole against area without the 4x 3/8 holes.
RE: Through Holes Steel Structural Column
Under this FS=4 assumption, the force was calculated to be around 31,000lbf. Not sure how practical this is - currently not able to get a true weight estimate.
An assumed FS, along with known area and yield stress allowed for back calculation of the weight.
Essentially, the four equations below were used. Thanks!
A=known
A_New=known
P_yield=known
FS=Assumed to be 4
F=back calculate via assumed FS.
P_old=F/A
P_new=F/(A_new)
FS_old=P_yield/P_old
FS_new=P_yield/P_new
I agree with you that this new FS seems quite affected - however my main concern is the overall idea of having these holes in the first place. The particular numbers are important, however I am after a more general consensus about what others think, as I see altering structural supports as NOT good.
RE: Through Holes Steel Structural Column
RE: Through Holes Steel Structural Column
RE: Through Holes Steel Structural Column
RE: Through Holes Steel Structural Column
RE: Through Holes Steel Structural Column
RE: Through Holes Steel Structural Column
If you're truly concerned, do a "take off" of what the column is having to support to have an educated guess of the load and run the numbers.
All that being said, if this was a column that was design appropriately to AISC/ASCE codes, I would not worry about the holes.
RE: Through Holes Steel Structural Column
How often is this column braced in both directions? A 70' long 7x7 column cannot support anything without buckling. Critical stress is calculated based on the material yield stress and the elastic buckling stress. If your column is braced at very long intervals, you could theoretically be at 100% capacity and your holes just put you over the 100% mark (though this is probably unlikely).
Knowing the unbraced length is needed to evaluate the column capacity, not just the overall length.
RE: Through Holes Steel Structural Column