Equivalent Ix for Steel Member with Holes

[EngDM]

Hey all,

I'm wondering if there is a procedure for the calulation of member deflection for a member with holes at 32" on center. This is for a channel supporting lateral loads with holes through the web.

 

[Celt83]

if you have regular openings where you are approaching an almost castellated beam profile check AISC Design Guide 31 and associated references.

 

[jayrod12]

We're talking like 20mm diameter holes every 800mm? A pair of or a single hole(s)? Are the lateral loads reversible? Is the web intended on being in tension or compression, or if reversible, both?

 

[HDStructural]

Agreed with Celt83. I believe DG 31 calls for using 0.9 * I_net to calculate deflection

 

[EngDM]

We're talking like 20mm diameter holes every 800mm? A pair of or a single hole(s)? Are the lateral loads reversible? Is the web intended on being in tension or compression, or if reversible, both?

10" channel, probably a 2" hole right in the middle of the web. Loads reversible, section in tension/compression but for very little loading. The holes are to fill a concrete infill block wall with grout at 32" o.c. cores.

My hole is so close to the NA that I can't imagine it has very much effect on my overall Ix.

 

[EngDM]

if you have regular openings where you are approaching an almost castellated beam profile check AISC Design Guide 31 and associated references.

Holes not that large to consider it castellated.

 

[HDStructural]

Holes that small would have a negligible impact on moment of inertia. I would ignore the holes for deflection considering the hole size, channel size and hole spacing.

 

[XR250]

Holes that small would have a negligible impact on moment of inertia. I would ignore the holes for deflection considering the hole size, channel size and hole spacing.

Same.

 

[RattlinBog]

I can't imagine that hole is too different from having a couple standard size holes for bolts. Maybe you could check tensile rupture, but bending is probably fine.

 

[jayrod12]

Agreed with all that you're likely putting too much thought into it.

 

[EngDM]

Agreed with all that you're likely putting too much thought into it.

I'm more just making sure that there isn't any more thought to put into it. My initial reaction was to just not worry about it.

 

[jayrod12]

In terms of how I'm justifying that opinion in my head, it's likely that the channel capacity is governed by the situations where the tips of the flanges are in compression. (I guess I should clarify when you indicated it's subject to lateral loading, I'm assuming that means weak axis bending) As such, I'm anticipating that the stresses in the steel will be far lower than Fy even if the hole was at the location of max bending, which also is unlikely. There will be far more steel still remaining in the web area than the flanges for weak axis bending even when accounting for the hole.

 

[EngDM]

In terms of how I'm justifying that opinion in my head, it's likely that the channel capacity is governed by the situations where the tips of the flanges are in compression. (I guess I should clarify when you indicated it's subject to lateral loading, I'm assuming that means weak axis bending) As such, I'm anticipating that the stresses in the steel will be far lower than Fy even if the hole was at the location of max bending, which also is unlikely. There will be far more steel still remaining in the web area than the flanges for weak axis bending even when accounting for the hole.

Channel is on the flat, so strong axis bending. I guess saying lateral does imply weak axis bending, apologies for the confusion. My holes are so close to the NA that I'm not worried about it. Channel bending is goverened (like all beams really) by the flange area.