analysis of wood beams in weak axis bending

[charliealphabravo]

Hi all,

I am in the market for a wood design application. One particular feature I am looking for is a module that will allow the analysis or design of wood purlins, deck planks, and stair treads. These are commonly installed flat so that the members are primarily acting as beams loaded in the weak axis.

I have checked several popular wood design applications and even some that allow the definition of custom sections do not allow the beam to be specified with a width greater than the depth.

Thanks in advance.

 

[a2mfk]

Doesn't Enercalc allow you to change axes? I can check that out tomorrow for you...

 

[MiketheEngineer]

I believe RISA does also...

 

[msquared48]

Yep for RISA, and you can also specify and create your own sections (S & I) and materials (E)too.

Mike McCann
MMC Engineering

 

[csd72]

This is about as easy a hand calc as you could ever do, not sure why you would need a program for it.

Even easier, do some standard calcs kept in a folder ready to put a copy in your calcs - viola!

 

[a2mfk]

good point CSD, especially since laterally buckling will not control. Actually, having designed and built decks, its not even a bending stress issue, its all about deflection.

I designed a deck once when I first started out as an EI, a walkway structure like you see at every nature park... Did all kinds of fancy calcs, etc., then I think the carpenter just did 16" oc like he always did to keep the "bounce" to a minimum. <shrug>

 

[charliealphabravo]

It can be trivial I agree. But when I contemplate writing a spreadsheet that includes the lumber sizes/species/grades/design values that I might need, wet/flat/size/duration/repetitive use/temperature factors, multiple/single spans for pattern loads, load combinations with snow and wind, point loads and uniform loads, deflection criteria, and multiple codes checks...I begin to think maybe an off the shelf piece of software for the lowly purlin might be helpful for the grunt work.
Also I think that in litigation hand calculations attract more attention.

 

[huntley101888]

a2mfk - I designed my own deck last year. I basically just did calcs to confirm the building code span charts for the joists. I also had to design a fascia beam to span my driveway, since height limitations prevented a typical carrier beam configuration. I also oversized things a bit in case anyone gets the bright idea to put a hot tub or something on it.

 

[Ron]

RISA will allow you to rotate the member for such applications (as others have noted)...have to agree with csd72...hand calc or spreadsheet would be easier.

 

[LonnieP]

I also agree with hand calc's for a new engineer.

That said, if you want to check weak axis bending you need to remember how wood members are graded. They are usually graded for "normal" orientation with knots running from wide-face to wide-face as much as possible. If you turn one of these on it's side and have moderate sized knots it's easy to see the effective section properties won't be what you would assume.

As for commercial software, it might be worthwhile to ask how they handled this problem. Having a seperate table for members graded as DECKING is probably the only way this can be realistically handled. THEN, you need to make this distinction on your drawings.

 

[MiketheEngineer]

Check the NDS for "flat" use - usually get about a 10% bump depending on size...

This is really too easy to even bother with sofware unless you need to do it about 12 times a day.

If so - then just a simple span spreadsheet....