Friday, February 10, 2012

Study Outline, 1, GLULAM

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SO, here is what I want you to understand about glulam ... (particularly BEAMS)



1. It (GLULAM) is stronger and stiffer (for the most part) than sawn lumber.


2. It is a very efficient use of our lumber resource (now that glulam is highly evolved – as is here in America).


3. It can be made for use in either beams or columns.


4. A member intended for use as a beam can be used as a column ... just make sure that it isn’t cambered.


5. A member that is intended for use as a column can be used as a beam – and there are Design Values for such.


6. A beam can be loaded in the strong (x-) or weak (y-) direction (and there are Design Values for such).


7. It’s nice when the compression zone of a beam is laterally supported – as is by the floor or roof system it is supporting – as is most often the case for simple beams.


8. For cantilever beams, beams with overhangs, and continuous beams, where the compression zone of the beam is NOT laterally supported, we need to deal with the Beam Stability factor, CL (which is not much fun).


9. For columns we need to consider how there are braced, and in what directions.


10. We should also consider how columns are loaded (centrically, or not necessarily centrically).


11. Glulams may be loaded as beams and columns at the same time! (Contact your local engineer – I am in the phone book, I think.)


12. Glulams intended for use as beams have higher grade laminations on top and bottom.


13. Glulams intended for use as columns generally have uniform `layups’.


14. Glulams intended for use as beams fall into two categories:


 ... 1) Unbalanced

 ... 2) Balanced or Reversible


15. Unbalanced Beams are intended for use as simple spanning members


16. Unbalanced Beams are often `cambered’


17. If unbalanced beams are installed upside down or in continuous spanning conditions or with cantilever spans ... they theoretically have less `capacity’


18. Stock beams are generally unbalanced and have camber


19. Balanced beams are intended for use in continuous spanning and cantilever/overhang conditions


20. Balanced beams are generally manufactured straight (no camber)


21. Glulam may be made into curved shapes, tapered shapes, curved and tapered, etc.


22. Curved and tapered beams are `custom’, and the designer should interface directly with the manufacture on their design, etc.


23. Glulam beams made be made into a nearly unlimited variety of lengths, depths, shapes (curved, tapered, etc.) ...


24. The main limitations on glulam size and shape (curved, etc.) are imposed by transportation issues.


25. Generally we don’t splice wood members – but due to transportation issues we have come up with a `moment splice’ for glulam.


26. You should specify glulam in accordance with what is available.


27. Glulam specifications should include stress and appearance grades.


28. For simple drop-in-place and prop-in-place members (beams and columns) there is a lot of `design guide’ type information.


29. For custom stuff, like curved beams, get an engineer and the manufacturer on board.


30. Manufacturers of `stock’ glulam generally do not provide engineering assistance.


31. Manufacturers of `custom’ glulam, or glulam systems (trusses, etc.) ... might provide design assistance, even a `stamp’.


32. The American Institute of Timber Construction (AITC) and the American Plywood Association – Engineered Wood Systems (APA-EWS) are the main trade organizations with glulam – and they provide a lot of useful information.


THAT’S IT FOR NOW ... MORE TO FOLLOW!

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