×
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

Contractor-fabricated GL Arch

Contractor-fabricated GL Arch

Contractor-fabricated GL Arch

(OP)
Have a proposed job to look at involving a built-up wood arch spanning 48 feet with a 24 foot high ridge, spaced at 12' centers forming a kind of quonset structure.  

The contractor/owner wants to fabricate it on site using DF#2 material with special jigs, glues, bolts, and construction equipment.  Considering the low stress grade of DF#2 for 1" members, has anyone found any allowance in the codes/standards, other than testing, to increase the bending stress above the standard 1000 to 1200 psi range, into the range of a laminated GL beam - 1600 to 2400 psi?  I highly suspect not without special testing, inspection, and certification, but I thought I'd ask anyway.  ponder

Mike McCann
MMC Engineering

RE: Contractor-fabricated GL Arch

Mike,
I believe that the only stress grades that go above Fb=1500 psi is Machine Stress Rated (MSR) Lumber. The design values are found in Mechanically Graded Dimension Lumber (Table 4C in the 2001 NDS Supplement). But, I don't know if they run MSR for 1x wood.

You might give the APA in Tacoma a call at (253) 620-7400  

RE: Contractor-fabricated GL Arch

(OP)
Thanks - I'll give it a shot.

Mike McCann
MMC Engineering

RE: Contractor-fabricated GL Arch

I would not be too comfortable with an owner/contractor fabricating these...too many variables beginning with glues, temperature, humidty, etc - much less having a good design.

RE: Contractor-fabricated GL Arch

Douglas Fir is easily upgraded to higher stress allowance with scarfs and finger joints to eliminate checks, knots and voids.  A laminated sample tested to ultimate and then used at 1/3 the test strength would be appropriate,(flexural of extreme fiber).

RE: Contractor-fabricated GL Arch

I agree with MiketheEngineer.  Most people under estimate the amount of clamping force required to develop the proper glue bond in a laminated beam. I would be skeptical that a contractor field fabricating laminated beams would be able to develop the proper bond.

For 40' arches spaced 12' o.c. I am surprised that anyone would try to field fabricate the arches.  Glulam plants are set up to do this sort of thing on a daily basis.  It would be hard to imagen that the contractor could same money by gluing up the arches in the field.  Particularly now with our slow economy, plants should be hungry for work.



 

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