horizontal shear in wood beams

[alan131]

Client wants to open up an interior bearing wall in a home. Was checking on the new concentrated loads on the existing house girder using a software program. Conditions are pretty standard: 24' deep house, (3) 2 x 10 center girder supporting First Floor, Second Floor & storage Attic with support walls; lally columns @ 8'-6" oc.


Program failed the beam for shear, not only for the proposed concentrated loads which was expected, but also for the existing conditions. Horizontal shear in wood beams is usually considered critical for high concentrated loads on short spans, whereas for longer spans, bending is usually primary.

Why is length of beam not a consideration in the calculation for shear in the sizing of wood beams? At what point is a beam considered short with excessive loads?
Also, for the existing uniform loading conditions, the program called for a 16" deep beam rather than the existing 10" which on the face of it seems ridiculous.

 

[hokie66]

Yep, that's it. The shear is maximum at mid-depth for a rectangular section, and wood doesn't have the uniform properties in all directions like steel, so you design for the maximum.

I know, twice this season. What a bummer!

 

[alan131]

Hey. . . 1 for the architect. . . 1252 for the Engineers.

At least the Hokies own them in football.

 

[a2mfk]

hokie66- My experience with architects practicing outside of their area of expertise has not been very positive to say the least. I know the rules in my state use the term "incidental to your area of practice", which is subjective, but is a major load bearing beam for a two-story house incidental? Not to me. Outside of a drip edge on a roof or some gypsum board call outs, I stay away from architecture and hire one of my buddies. The OP may indeed be a good guy, but part of being a good guy is making good decisions, including knowing what you know and what you don't know.

Wondering why a beam program is telling you "bad in shear" sets off some alarm bells for me. If he is just wondering for educational purposes and this is only for preliminary planning, then please forgive me. If he has every intention of having a SE do the final design, then my bad. But helping a non-engineer practice engineering is prohibited in my state's rules...

Also, from your perspective, and this may be generational (with all due respect), there was a time when architects received a lot of training and first hand exposure to structural engineering. I have heard of some older architects who said when they first started their career they did quite a lot of engineering, and with those individuals, it showed. There were small offices who had everyone under one roof and architects may actually do structural engineering. And I would say that if you are an architect who worked for 4 years under a PE, got your PE sponsorship, and passed the NCEES Structural 1 exam, I would have no problems with your practicing structural engineering, even getting your PE if they changed the rules...

Nuff said, not ranting, just have had some bad experiences with this specific subject.