Timber Roof Trusses: Supporting Domestic Residences

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A 32mm hole drilled through a 9"x2" timber joist, which supports a second-floor residence, raises concerns about structural integrity, especially given its proximity to a nail plate. The hole increases bending stresses near the center of the beam by approximately 30%, but it may not significantly impact the overall load capacity. Stress concentrations in wood can be unpredictable due to grain variations, making it essential to consult a professional engineer for a thorough assessment. The location of the hole near maximum shear stress further complicates the situation, necessitating detailed drawings for accurate evaluation. Overall, while there are concerns, the situation may not be critical, but professional advice is recommended.
markeo
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Dear all,

Situation:

plumber has drilled a 32mm hole through a 9"x2" timber joist. This is being used to support a second floor domestic residence.

ive been told the hole is central with in the section (ie: 9" thus 4.5" to centre) but its only 30mm from the nail plate.

Will this effect this beam as it lays a long on netral axis or do i need to look at the who truss as a structural element? I also have concerns over the close proximity of the nail plate, any practical remidies (ie: how to thicken or depend the section if required).


Regards

Markeo
 
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Looking at my stress concentration factors reference book, a 32mm hole drilled in a 9" beam (a d/H ratio of ~.14) will increase the bending stresses near the center of the beam by about 30%, but the maximum stress will still reside at the top/bottom surfaces of the beam, and therefore not significantly reduce the beam's overall load carrying capacity. These are assumed for a beam of infinite length and uniform material, neither of which your beam satisfies perfectly (since you're near one end, and it's made of wood).

Keep in mind- it can be very difficult to guess at stress risers in wood due to grain structures and irregularities. If you're afraid of reduced strength to a critical structural beam, you should consult a professional engineer specializing in construction to take a look at it and give his opinion (...and tell the plumber to leave the structural members alone!).
 
By "nail plate", do you mean the support? If so, he has drilled the 32 mm dia hole pretty much at the point of maximum shear stress. To answer this question properly, we need a good drawing with three orthographic view, if you can manage it, to show the connection in detail, and its location relative to the beam. Having said all that, however, it doesn't sound very critical.
 

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