Hole in plate girder web

[MotorCity]

I recently designed a plate girder approximately 5 feet in depth with a 5/8" thick web, the span is 30'. It supports a 5" concrete floor and 2 steel columns above. The contractor wants to drill a 4" hole 4 feet from midspan and 1/3 of the way up from the bottom. Does anyone know of a method to check this condition that can be done simply with hand calculations (i.e. not FEA)? I was also interested in determining the impact of torch cutting or wet drilling the hole. Any thoughts?

 

[RockEngineer]

Your web in the girder does very little for bending but is the main resisting element for shear. Check to make sure that you have adequate shear area which should not be a problem. P/td (P=shear at the hole t=web thickness d=beam depth) I wouldn't have the least concern over a 4" hole in the web of a 5 ft deep girder. It is not uncommon on plate girder to put web holes in the center of the beam that are 1/2 the depth of the beam. On larger holes you provide flat bar reinforcement around the hole just to help in web buckling.

 

[ChipB]

Moment is carried in the flanges, shear in the web. Check the shear at that location on the reduced section. I'd lay odds, your plate girder is ok with the hole.

 

[LPPE]

Do not torch cut. Unsmooth, random edge leads to stress concentrations.

 

[JAE]

You need to get AISC's Steel Design Guide Series No. 2 - Web Openings in Beams and Composite Beams. This is geared toward rolled WF sections but should apply to girders as well.

http://www.aisc.org

 

[CWIC]

I respectfully disagree that thermal cutting processes are not recommended. If the cutting operation complies with the requirements of the D1.1 code, Section 5 (subsection 5.15), then the cutting is not an issue unless performed improperly.

I have a project right now that requires girder penetrations for moment frames. The openings are carefully inspected for compliance with the code and any additional project-specific requirements. If this is a concern, you may specify mechanically-assisted cutting (not freehand), surface/edge profiles whcih exceed the code, NDT, etc. for the cut edges.

 

[cap4000]

There are several references you must get. AISC Engineering Journals by John Bower 1971, R.G Redwood 1972, Kussman and Cooper 1976. There are load, hole and beam parameters charts based on the shear and moment at the hole location.