LVL wood beam column

[ajk1]

I am checking a design done by others, for an LVL column ("4 ply built up 2"x6" Versa-Lam studs") that occurs in the exterior wall and extends from first floor to peak of an arched roof. The column is about 20.5 feet long. It carries both roof snow laod and about 7 foot width of tributary wind wind load. Can I use the procedures, factors and equations in Canadian Standards Association (CSA) Standard O86 Engineering Design in Wood", if I get from the manufacturer the basic properties like compressive strength fc, modulus of elasticity, etc., or must I go to the manufacturer for him to check it or perhaps they have tables, although the tables may not fit the conditions for this particular building.

If I do use CSA O86, one of my questions is what should I use for the size factor Kzb for bending? Same as for that size of lumber if it were sawn timber (which would be a 1.4 factor in bending for a 2x6), or would it be 1.0?

 

[XR250]

In the US, I would use the NDS to calc it.
I would check deflection first - you may have a problem there. I usually use 2x8 wall or a tube or flitch beam in these situations.

 

[ajk1]

ExcelEngineering (Structural) - yes I checked deflection at the very start of my calculations, and it had 50 mm (2") of deflection under a 0.65 kPa (13.5 psf) wind load! I calculated the wind load based on the small buildings part of National Building Code of Canada (NBC). Thank you for your comment and that you wold use 2x8. That's what I felt should have been used as well. Do you know if NDS has a "size factor" for sawn timber, and if so, would you use the same size factor for LVL wood products? Thanks. Your comments are very helpful.

 

[woodman88]

In the NDS the size factor only applies to the visible grades of lumber not the LVL, MSR, PSL, etc. grades.

This is because a #1 2x12 is a lesser quality lumber than a #1 2x6. This is why ripping visible graded lumber is not allowed under the NDS. But grade bending allowable in the NDS is based on the grade of a 2x12. So a size factor is used to increase the bending allowable of the smaller sizes such as the 2x6.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

 

[XR250]

I don't know about the size factor - good question. I don't think I have ever needed to use it for an LVL post.
Might want to add a p-delta moment to the beam-column as well due to the large deflection.

 

[ajk1]

Yes my calculation of course includes a moment magnication factor to account for the delta, as per the CSA Standard.

So to be perfectly clear, can I calculate the strength of LVL lumber in accordance with the CSA Standard for sawn lumber, but with the size facor set to 1.0, and the permissible stresses and modulus of elasticity as per the LVL manufacturer's data? Or are strength determinations basically in accordance with manufacturer's published load/wind tables?

also, do different manufacturers have different recommendations for permissible stresses?

 

[jayrod12]

If you talk to weyerhauser and tell them you want the canada tall wall calculator they'll send it to you to check your calculated capacities versus theirs for the same size columns.

I've never thought of the size factor for lvl's but woodman makes a good point. but since you get to increase the strength for a 2x6 because the quality is better why wouldn't you get to increase the strength of a LVL post? Unless the allowable stresses provided by the manufacturer's already account for the accuracy of their material specifications.

 

[hope9010]

jayrod12 (Structural) - ok, I will try to talk to Weyerhauser to try to get their Canada tall wall calculator. Thanks.

 

[hope9010]

Just to let you all know, I contacted Boise Cascade in Canada and they have special software for Versalam, and the special properties for Canada which are different than U.S. and of course the Canadian are LSD. Also, it is Chapter 13 of CSA O86 that deals with these proprietary wood products such as LVL. It is very different than the earlier chapters that deal with sawn timber. That is why I was having so much trouble with Kh system factor. That issue disappears in Chapter 13.

Lessons learned:

1. Contact the manufacturer at the start when designing or checking proprietary w2ood products;
2. Be careful in downloading stuff from the internet; it may not deal with the product used in your country, or be geared to the design methods used in your country;
3. Similar comment with respect to advice from this forum.

 

[hokie66]

ajk1 and hope9010,

Are you the same person, or working together? It makes it confusing when comments from two "handles" seem to be from the same source.

 

[ajk1]

If I enter from my office computer, the system assigns one name, and if I enter from my home computer, it assigns a different name. I have said that they are the same person in a number of earlier posts on other subjects, but I see that I did not on this. Sorry for the confusion. Hope this clears it up.

 

[Ingenuity]

Very confusing. I log into Eng-tips on at least three separate computers all as one handle. Sometimes I stay logged on with all computers simultaneously without issue.