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-   -   Drilling vertically through structural beam? (http://www.diychatroom.com/f19/drilling-vertically-through-structural-beam-158606/)

dyi_sometimes 10-01-2012 05:28 PM

Drilling vertically through structural beam?
 
Is it ever OK to drill vertically through a structural beam? I have a 5x8 solid timber structural beam running the span of my basement supported by lally columns. Is there any location on this beam that can support a vertical hole through the beam?

I bought the house in January and the previous owner had a heavy bag hanging in the basement via a 1/2 eye hook that runs vertically through the entire 5x8.

This section of the beam is 200" wide and it spans a section from the wall to the intersection with another 5/8 beam running perpendicular. the hole is 56" into a 200" section of the beam. A lally column is 3 ft away from the whole on on side and the intersection with the the other beam 56" away to the other side.

I have read mixed information about vertically drilling and that it's never advisable but is ok if the hole is less than 1/3 the width of the beam (which it is) and must be in the center 1/3 of the beam (which it is not). I have read other info that says not to vertically drill at all. So I'm looking for clarification.

If it is NOT OK what remedies can I use? Do I need a Lally column directly below the hole?

Thanks for any advice you can provide.

tony.g 10-01-2012 06:08 PM

A 1/2" diameter hole down a 5" wide beam is not going to materially reduce its' strength.
If the hole is not too near the bearing (where the shear stress is greatest) nor too near the middle (where the bending stress is greatest) you won't have any problems.
If I've read your dimensions OK, your beam has its full quota of material where it needs it - mid-span and near the ends, so cross this off your list of worries.

Daniel Holzman 10-01-2012 06:42 PM

Drilling a 1/2 inch hole vertically in a 5x8 inch structural beam will reduce the moment of inertia of the beam by 10 percent, since the moment of inertia of a rectangular beam is 1/12bd^3, where b is the width of the beam, and d is the depth, and the 1/2 inch hole is 10 percent of the width of the beam. The reduction in moment of inertia will increase the maximum fiber bending stress on the beam by approximately 11 percent at the location of the hole.

In most cases, maximum stress in a beam occurs at the midspan of the beam. Since this hole was apparently drilled well off mid span, it is likely that the reduction in strength will not be a problem. HOWEVER, in some cases a beam is loaded with one or more point loads, in which case maximum stress DOES NOT occur at midspan. If your beam has point loading near the place where the hole was drilled, you could have a problem, which can only be analyzed by a careful analysis based on a site visit.

The rules you were quoting about 1/3 diameter etc. are applicable to horizontal holes, which have been discussed extensively on this forum. Do a search and you will find numerous threads. These rules DO NOT apply to vertical holes. The reason you can drill a horizontal hole through the center (in the vertical sense) is because the center of a rectangular beam loaded under constant vertical load (which is approximately the case for most wooden beams used in residential construction) is the zone of zero bending stress. The majority of load carrying capacity of a rectangular beam is carried on the outer 1/3 of the beam, so drilling a hole through the center has no significant effect on the load capacity of the beam in bending. Residential beams are almost never controlled by shear strength, so horizontal holes within code based limits are generally not a problem.

A vertical hole is completely different, since you are removing material from the top and bottom of the beam, which carry the majority of stress. This results in the remaining beam width (in your case 4-1/2 inches) being forced to pick up the load, which results in a significant stress increase (11 percent in this case). It is fair to say that you should always carefully analyze the effect of drilling a vertical hole in a structural beam, and you are not going to find blanket rules in the code books that permit drilling such a hole without analysis.

dyi_sometimes 10-01-2012 08:39 PM

Follow-up to Drilling vertically through structural beam? Reply to Thread
 
Thank you both for you replies!

Daniel, can you please further explain moment of inertia? Is that the beams resitance to rotation? Mean the beam is more likely to twist near the location of the hole or is a vertical stress?

What are my possible resolutions if there are point loads? would a lally column be sufficient or are there other less invasive remedies?

Would you be able to determine via a picture if there are point loads?

Finally, how concerned should I be about the 11% increase in load to the surrounding part of the beam? Should I have it inspected or are there signs/symptoms I should look for before having it inspected?

Thanks again for any information you can provide.

tony.g 10-02-2012 04:56 AM

Quote:

Originally Posted by dyi_sometimes (Post 1021546)

Would you be able to determine via a picture if there are point loads?



Just look upstairs in the area above the beam. If there are no walls/partitions crossing over it, and no columns directly above it, then it is carrying no point loads above.
Then check down below that there are no large beams supported off it.

tony.g 10-02-2012 06:07 AM

1 Attachment(s)
Is this the situation of your beam?

dyi_sometimes 10-02-2012 08:57 AM

Drilling vertically through structural beam?
 
Here is a drawing of the beam, hole, etc. Similar to yours but in reverse. Unfortunately, there is a wall roughly above the beam on the first floor. At this particular spot the wall has a large doorway from one room to the other so the wall is not actually touching the flloor directly above the beam.

dyi_sometimes 10-02-2012 09:12 AM

Drilling vertically through structural beam? Reply to Thread
 
1 Attachment(s)
Sorry, my last image was too large. 100kb is awfully small. Not sure you'll even be able to see this but basically my drawing is almost the reverse of yours. The hole is on the other side of the lally column from wall. The hole is 36" to the right of the lally column in your drawing and the end of the beam and another lally column is 56" to the right of that. The whole beam is 200" from wall to lally column support.

the beam is not supporting anything under or other beams just the floor joists above. There is a wall roughly above the beam but a large doorway spans the are of the flloor where the beam is so the load is actually being displaced on either side of the beam and I believe is supported by the floor joists.

tony.g 10-02-2012 04:05 PM

1 Attachment(s)
Yes,your pic is small, but I've sketched out what I think the layout is.
Assuming the beam is continuous over the central column, the graph below shows approximately how the bending stress varies along the beam.

It is at a maximum where the beam 'hogs' over the central column, falls to zero further out each side, and then rises to a lower maximum further along the beam. Finally, the stress falls to zero at the outer supports.

The hole seems to be approximately where the beam is stressed to about 2/3 its maximum stress. Bearing in mind that only 10-12% of the width of the beam has been removed at the hole, there should be no problem.

These values are relative and we don't know the load the beam is carrying (that depends -among other things -on the area of floor supported). Nor do we know the maximum permissible bending stress of the timber (that depends on the species). However, it's unlikely you will load the floor up to the maximum allowed in your code, and there are factors of safety built into their figures.

If this was my beam, I wouldn't loose a wink of sleep, but if it makes you feel better, get a couple of pieces of 2x8 about 4ft long and nail them fimly to each side where the hole is. (the trouble with this is that if you sell the house, buyers will think there is something wrong with the beam!).
You decide.

dyi_sometimes 10-05-2012 11:19 AM

Thanks for your response Tony! I really appreciate the feedback!

dyi_sometimes 11-01-2012 08:22 AM

Will the decrease in the moment of inertia cause the beam to bend upwards? Above Daniel states the moment of inertia has been reduced by 10%. Does that mean the beam will have the potential to deflect upwards? I have noticed that in the floor above the beam squeeks and after closer inspection I can actually stand (on the first floor) on either side of the beam and feel that is has pressed upward into the floor. What I don't know is if this was already the case due to "normal" loads or if the whole has caused the beam to deflect and is something that could continue to deflect upwards causing damage to the floor above?

tony.g 11-01-2012 09:18 AM

As DH pointed out, the 1/2" hole reduces the moment of inertia by around 10%.
The deflection of a beam is inversely proportional to the moment of inertia. For example, if your moment of inertia is reduced by 10%, the maximum deflection under any load will be approximately 10% greater.
However, this will NOT cause any upward deflection of the beam. If your beam has bowed upwards, it will almost certainly be the timber itself which has warped upwards ('crowning').
The squeak is probably related to how the floor deck is fixed to the tops of the joists (are they well and securely nailed/screwed?). And is there effective bridging between the joists?
In short, neither the upward bow nor the squeak will be related to the hole.

jcarlilesiu 11-01-2012 09:28 AM

Quote:

Originally Posted by dyi_sometimes (Post 1042290)
Will the decrease in the moment of inertia cause the beam to bend upwards? Above Daniel states the moment of inertia has been reduced by 10%. Does that mean the beam will have the potential to deflect upwards? I have noticed that in the floor above the beam squeeks and after closer inspection I can actually stand (on the first floor) on either side of the beam and feel that is has pressed upward into the floor. What I don't know is if this was already the case due to "normal" loads or if the whole has caused the beam to deflect and is something that could continue to deflect upwards causing damage to the floor above?

Per the loading diagram provided by tony, the maximum force on the beam IS upward at the lally column. Caused mainly by downward deflection at the beams midspans both sides of the column.

Is there any mechanical connection between the top of the column and the beam? If not, can you see the beam pulling out of the top of the column?

tony.g 11-01-2012 10:10 AM

Quote:

Originally Posted by jcarlilesiu (Post 1042331)
Per the loading diagram provided by tony, the maximum force on the beam IS upward at the lally column. Caused mainly by downward deflection at the beams midspans both sides of the column.


Good point; I'd forgotten that the beam was continuous and, as you say, that will cause a hogging moment over the column. It could then be the reversal of stress in the upper part of the beam which IS causing the squeak.

dyi_sometimes 11-01-2012 10:41 AM

The floor decking is under a hardwood floor so I can't see how well it is secured. The beam is not pulling off the top of the column. The beam is "continuous over the lally column but is only about 200". only a few nails connect the column to the beam. Per Tony's drawing the beam's left end is not really secured. It is sitting in a notch in the foundation with the joists above it so it would seem as though the beam could almost act as a cantilever? causing the left end (where the most noticible bowing is) to deflect upwards?

The bridging is across the joists (perpendicular)

With this information due you think any of the deflection is due to the whole? There are some uneven floors in other areas of the house so i'm not sure if it was there before the hole was drilled or not, but am looking to somehow minimize any additional deflection if that's even possible.


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