Engineered Lumber Deflection including Shear Modulus

[WoodDesignCat]

Does anyone here include the shear modulus in their beam deflection calculations? I've worked at two different small structural engineering firms and as far as I know no one included shear deflections in beam calculations. Also the design software we used didn't include a way to check shear deflection, so it would have had to be an addition hand/Excel calculation.

How far off can calculations be by ignoring shear deflection in engineered lumber? Does anyone have a resource to better understand Shear Modulus of Elasticity and shear deflection?

 

[Shotzie]

I've never checked it for beam deflections. I'm very curious to know of a situation that would warrant it, not to say that I think definitively it should be ignored, just curious when it would be best to consider, if ever.

 

[WoodDesignCat]

@Shotzie, That's what I'm wondering as well. If no one else has better insight I will try to run some examples with and without shear deflection and see how much it changes the deflection, when I have some free time.

 

[JoshPlumSE]

If span to depth ration is greater than 5, then you don't generally have anything to worry about. Shear deflection < approximately 5% of flexural deflection. Usually, we're more like 10 or 20 for wood. Therefore, shear deformation rarely comes into play

 

[IDS]

Shear deflection is usually small, but if you are using software that allows shear deflections to be included I can't think of any good reason why you wouldn't include it.

Doug Jenkins
Interactive Design Services

http://newtonexcelbach.wordpress.com/

 

[hokie66]

You are fooling yourself if you think deflection calculations of wood members are that precise. It is not like steel, where the Modulus of Elasticity is not variable.

 

[XR250]

Yea i never check it but I am usually very conservative on the deflection limits for engineered lumber so it would not matter anyway.

 

[dik]

I can't think of any good reason why you wouldn't include it.

It gives you an exact answer to how many grains of sand there are on the beach... I do it too, for programs... I'll have conversion factors to 14 decimal places... just because I can. The answer is no more correct, but most compilers default to 'double' and 'single' is slower.

Dik

 

[KootK]

In sections that are solid or solid webbed, the shear flexibility is too low to warrant consideration in most practical situations where span to depth ratios are as JoshPlum described. This is probably especially true with wood members as their shear strength is relatively low.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.