Flange reduction due to Bolts
Flange reduction due to Bolts
(OP)
In the AISC ASD 9th edition manual, there is a reduction in flexural strength of a beam if bolt holes are too big in either flange (B10).
If the holes are too big, ASD goes on to state that the member flexural properties shall be based on the effective tension flange area Afe.
My understanding of this section is as follows:
1. The holes can be in either flange, or both (compression and tension).
2. You end up with a “new” section that has a compression flange area as if there are no holes. You also end up with a reduced tension flange with the area Afe as stated above.
From this logic, I end up with a section that appears to be a Wide flange with large compression flange and little tension flange. In order to calculate the bending properties, I find the new neutral axis, second moment of inertia, and section modulus for top flange and bottom flange.
In the Volume 2 connections manual page 4-23, they actually reduce both flanges (it's a symetric moment connection). In doing this, you end up with an answer that is very close to my logic mentioned above, but not exactly the same (within 3% though).
How do you guys perform this task? Do you find this unsymmetrical shape, or just use a reduction technique similar to AISC in Volume 2?
If the holes are too big, ASD goes on to state that the member flexural properties shall be based on the effective tension flange area Afe.
My understanding of this section is as follows:
1. The holes can be in either flange, or both (compression and tension).
2. You end up with a “new” section that has a compression flange area as if there are no holes. You also end up with a reduced tension flange with the area Afe as stated above.
From this logic, I end up with a section that appears to be a Wide flange with large compression flange and little tension flange. In order to calculate the bending properties, I find the new neutral axis, second moment of inertia, and section modulus for top flange and bottom flange.
In the Volume 2 connections manual page 4-23, they actually reduce both flanges (it's a symetric moment connection). In doing this, you end up with an answer that is very close to my logic mentioned above, but not exactly the same (within 3% though).
How do you guys perform this task? Do you find this unsymmetrical shape, or just use a reduction technique similar to AISC in Volume 2?






RE: Flange reduction due to Bolts
RE: Flange reduction due to Bolts
I got aboout 75% to 85% of the gross section modulus this way. It is pretty conservative to assume that the holes occur exactly at midspan, but I did not want to bother detailing exactly where they occur.
Other thoughts here would be appreciated.
RE: Flange reduction due to Bolts
RE: Flange reduction due to Bolts
Is it ok to reduce the compression flange, if the compression flange has the holes in it? AISC makes it sound like any holes in either flange must be taken out of the tension flange.
I'm a little foggie here.....
RE: Flange reduction due to Bolts
For what it's worth, the Austr. Steel code AS4100 doesn't differentiate between top and bottom flange when reducing flexural properties due to holes.