Mitigation of Stress Concentrations Around Holes Drilled In the Web of A Beam

You are not very precise are you? Big hole? Big beam?

If it is a bolt hole you can ignore it.

If it is a big hole it needs individual analysis and custom repair design if repair is needed.

A rule of thumb is that the cross-sectional area removed from the beam web must be replaced with a reinforcement pad of the same cross-sectional area. Often the pad o.d. is twice the hole diameter, with thickness equal to the beam web thickness, but variations can occur.

In the case of a railway rail:

A1: star cracks radiating from the hole at about 45 degrees to the axis of the beam in all directions.

A2: bolts are never in contact with the beam. There must be a gap between the bolt and the material it passes through.

A3: expand the metal around the hole so it has compressive stress in it.

A4: crop the bolt holes off and thermit-weld the rail to its neighbour.

One simple test would be to get 2 sections of I or channel beam stock, maybe something like the al used on a carpenter's level. Drill two holes in one beam, both an equal distance from each end, one reinforced with a nut-bolt. Then load both beams until failure.

Bret Cahill

I don't know anything about this sort of thing, but, these questions may be relevant.

Is the hole closest to the flange in compression or the flange in tension?

Is the hole too close to the flange to allow (flat) reinforcement all the way around the hole?

All of the answers have been good. one additional question. Was the beam designed to barely meet the structural strength needs, or was it a convenient size much larger than the needs?

If ithe beam is much larger than needed and the hole is small, ignore it.

If the hole is large, have a structural engineer look at it asap.

If the beam just met the needs, have a structural engineer look at it asap.

If you don't know the structural needs, or how the beam relates to them, have a structural engineer look at the beam with the hole and other beams in the area asap

There are closed form methods for solving this problem, but you must supply details of the beam, the hole, and the manner of loading in order to calculate a specific answer.

As a couple of others have noted, the beam loading has to be defined. The hole might be insignificant for a beam as a compressed column or it might be a failure point for a beam in bending or torsion. With the information given so far, and without assumptions, I think that the only valid answer is "it depends".

first i will address an incorrect answer, and that is that bolts are never in contact with the beam, this is not only far from correct, it is in fact the opposite, excluding a metal interface exclusion zone for avoiding two different metals touching, an insulation collar for electrical or heat sink purposes, the bolt should try to touch the beam. best example of the practice is the Sydney harbour bridge where hot rivets were used instead of bolts to ensure full contact and least possible movement.

now to the two main areas missed in the answers,

1) it is more important to know the lateral disposition of the beam not the size of the beam, EG: an i beam with the centre flat horizontal has one 5th the strength of the same beam with the flat centre vertical, as such a hole in the horizontal will, without reinforcement by a welded plate as noted by others as the best solution be fatal to the beam.

2) and most important is that a solid beam is not always stronger than a beam with holes or a hole, a bridge builder will tell you this in a second, an arc or arch is not merely a cheap way to support a bridge like the Sydney harbour but stronger than a single flat sheet made to fit the same area. the reason is that the stress is forced through the arch to control points, a flat sheet or single piece suffers basic physics, in short the path of least resistance by stress loads, so the area of a stress is unknown, a hole or an arc forces stress in a given direction to a control point, many machines have large beam structures with holes in them which cost a great deal more than just using a piece of flat steel through the centre because it is less likely to buckle than a flat sheet, or flat beam section.

On load bearing structures problems can and do occur. This is why the the use of the many crack detection systems are used particularly on oil rigs, ships, refineries,etc

This may be a fluorescent ink and UV light detection system. This is actually from a ship...........that's all I know about it.

Assuming OP is searching for an answer to the question, he must provide additional information such as beam material, dimensions, boundary conditions (manner of loading and restraints), etc. It's difficult to provide a specific answer to a general question.

That's pretty much what was sought.

Thanks.

Bret Cahill