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StructuralEng, Consultant
Category: Structural Engineering
Satisfied Customers: 7315
Experience:  Structural Engineer
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My question is regarding drilling a set of ¼” holes in the

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My question is regarding drilling a set of ¼” holes in the flange of an I-beam with 7/8” flange thickness, 12” flange width, and 36” depth. I hope that the small diameter of the holes compared to the flange width results in negligible impact to the strength of the flange. Here is more about my application. I have a 66.5 foot long horizontal I-beam supported at each end. The I-beam holds up my church roof. Directly under the web of the I-beam are the building windows. In other words the “front” of the I-beam is the interior of the building, and the “back” of the I-beam is the exterior of the building. I want to install window shades, and the only way they can be installed is to mount them somehow to the I-beam. The shades will be mounted to brackets every 9.5 feet. I want to bolt each bracket directly to the I-beam flange and drill four 1/4” holes into the I-beam flange to bolt the bracket to the I-beam. Each bracket needs to support only 75 pounds. The 4 holes would be in a square pattern, 1 ¾” on a side, 1 ¼” back from the edge of the flange. An alternative would be to weld the brackets to the I-beam, but the weld itself may weaken the I-beam? A final alternative would be to use beam clamps (like used for hanging conduit) at the front of the bracket, and a single ¼” hole at the back edge of the bracket, 3.5” back from the edge of the flange. Keep in mind that this pattern repeats every 9.5 feet for a total of 8 brackets. Thanks for your help!
JA: OK. Is there anything else the Structural Engineer should be aware of?
Customer: I believe I covered all the parameters.
I can help with this. Do you happen to know the grade of steel? If not I can check it for the most common
Customer: replied 29 days ago.
I don't know the grade of steel. Please check for most common. Thanks!

ok. I'm going to check it out now.

The holes check out as ok, but you'll probably want to consider the beam clamps for ease of installation and cost. If you've never tried drilling holes in steel that thick, it isn't easy.

Customer: replied 29 days ago.
Got it. Thanks for your help!

No problem. I'm happy to help. Good luck with your project.

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