huangyhg

w-beam web openings
i have a 16w77 steel beam in my garage that spans 32'(holds up a 2nd level workshop/loft). if possible, i have a need to go through the beam in 3 places, equally spaced with 2"wide x 3" high openings. will the openings weaken the beam? and where would the best location of the openings be, towards the top ,middle or bottom of the web? thanks for any help.
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the section you describe is quite 'beefy' for residential applications, but considering the span it makes sense. i would recommend hiring a strutural engineer to look at the beam and estimate the loading. from that, the engineer can evaluate the size and location of the proposed holes. placing the holes in the mid height of the flange is the best spot (bending stresses are the smallest at the mid height of the beam). unless of course, these holes are directly under a point load or near the supports where shear stresses dictate and may play a considerable role in the hole size. for most applications, the holes should be rounded, as oppossed to square. a square opening in the web can produce some issues with stress concentrations at the corners of the openings.
fyi, the web is 0.455" thick and may prove difficult to cut the holes with a hole saw. are the floor joist above the beam framed on top of the beam? if so, you might be able to find a 'pocket' to run your 'conduit' through as oppossed to cutting holes in the beam.
rule of thumb is put the opening in the middle third of the depth of the beam and in the middle third of the span of the beam.
better have someone check it, though.
rg88:
surely you meant to say mid-height of the web and not flange. wouldn't want to confuse our automotive friend.
thank you all for the quick response.
watermelon you are right. i don't know what i was thinking...i must not have had enough coffee when i wrote that. it is indeed the mid height (middle third) of the web.
cutting holes in the flange, as opposed to the web, is a completely different issue and must be treated carefully.
rg88,
just out of curiosity do you have any experience or reference for flange cutouts.
i've been looking around and the only reference i can find is reduced beam sections in moment frames - creates plastic hinges for earthquake resistant design.
have you seen anything else

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