×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

FLITCH BEAM BOLTING - SIZE AND SPACING

FLITCH BEAM BOLTING - SIZE AND SPACING

FLITCH BEAM BOLTING - SIZE AND SPACING

(OP)
In designing flitch beam bolting, for size and spacing, do you analyze shear flow for steel to lumber, or just divide the total shear stress for each bolt equally.
Is the NDS value for the bolt to lumber controlling (not much, just 580 lbs when parallel to grain.)?

And for spacing, is there also a controlling value for unbraced steel to consider in a drop header?

RE: FLITCH BEAM BOLTING - SIZE AND SPACING

Quote (PT99)

In designing flitch beam bolting, for size and spacing, do you analyze shear flow for steel to lumber, or just divide the total shear stress for each bolt equally.

1) For flitch beams, the center of gravity of the plate is usually coincident with the center of gravity of the lumber, or very close to it. When that is the case, there really is no appreciable shear flow and you only need to supply bolts to transfer the transverse, applied loads from the point of application of the loads to the various plies in proportion to the EI values of the those plies.

Quote (PT99)

Is the NDS value for the bolt to lumber controlling (not much, just 580 lbs when parallel to grain.)?

2) Because of #1, you'll be concerned with bolt capacity perpendicular to grain.

Quote (PT99)

And for spacing, is there also a controlling value for unbraced steel to consider in a drop header?

3) I don't know how much attention this gets in practice but, I agree, it ought to be a consideration. And I've seen detailing where the bolts are spaced more tightly on the compression edge than the tension edge which, to me, suggests a concern for plate buckling. In the past, I've just considered little strips of plate running from bolt to bolt in the compression zone as little plate "columns". Then I'll compare that to some of the tabulated stuff that I've seen out in the wild (shared below).

Another question becomes what you're unbraced length ought to be for lateral torsional buckling. And, frankly, I don't know how to answer that question rigorously so I simply do not use flitch beams unless compression edge bracing is copious and convincing.

Some resources that you may find helpful:

Gang Nail Manual: Link

NAHB Manual: Link

StructureMag Article: Link





HELP! I'd like your help with a thread that I was forced to move to the business issues section where it will surely be seen by next to nobody that matters to me: http://www.eng-tips.com/viewthread.cfm?qid=456235

RE: FLITCH BEAM BOLTING - SIZE AND SPACING

To add to Kootk's #1, you also need to consider long and short term E for the timber to bound the issue. In the short term timber is stiffer, so higher load percentage carried by the timber, over time creep effects shed a proportion of the load to the steel, lessening the load in the timber. This results in larger overall deflections. It's conservative to just check the plate alone for deflections though which makes things pretty simple if you aren't shapening your pencil on the calculations.

For global lateral buckling, I've just estimated the behaviour as being equivalent to a solid timber member of the same overall dimensions. I suspect this is overly simplifying things though because of the much larger load carrying capacity of the flitch plate and hence amplifying any out of plane buckling forces compared with equivalent timber member. But I guess its better than nothing (which people sometimes do).

RE: FLITCH BEAM BOLTING - SIZE AND SPACING

In addition to the bolts to take the load from the timber into the steel, don't forget near the ends to provide additional bolts to take the load back into the wood if the wood is delivering the reaction in bearing. This is emphasized in the Jim DeStephano article which KootK linked above.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources

Ebook - Mastering Tolerances for Machined Parts
When making CNC machined parts, mastering tolerances can be challenging. Are general tolerances good enough? When does it make sense to call out for tighter tolerances? Do you need a better understanding of fits, datums, or GD&T? Learn about these topics and more in Xometry's new e-book. Download Now
eBook – How to Choose the Correct Corrosion Testing Method
When designing a metal component, engineers have to consider how susceptible certain alloys are to corrosion in the final product’s operating environment. In a recent study by NACE (National Association of Corrosion Engineers), it was estimated that the direct and indirect costs of corrosion in the United States is approximately 6.2% of the GDP. In 2016, that cost exceeded $1 trillion dollars for the first time. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close