PSL Columns

[StrucConsultant]

PSL Columns (like Parallam):
Does anyone know why there is such a big difference between calculated axial capacity loads (calculated with a software like WoodWorks or similar) and the axial capacity loads supplied by the supplier ? Sometimes, the value calculated with the software is more than double the value given by the supplier.

Does anyone has the formulas to calculate the values by hands?

When the supplier only got 1.8E species and the software only allow for 2.0E species, how do we make the transformation? A direct ratio?
There is also three different values for each column size : 100%, 115% and 125%, it is not so very clear when to use one or the other.

Thanks

 

[janderso12]

I don't deal with timber very much but I know manufacturer's put on a higher than needed factor of safety in their values that could account for the difference in capacities with a software program.

 

[w16x26]

To calculate by hand I would use the formulas in the National Design Specification for Wood Construction. The calculation is a little long but all the factors are straight forward.

 

[SkiisAndBikes]

In WoodWorks, you can customize your database using the Database Editor (DBEdit). You can input the specifics based on local supply and can also hide materials not readily available in your area. It takes a bit of time but worth it.

 

[OldPaperMaker]

StrucConsultant,
The percentages, 100, 115,125,160% are the Duration Factors for floor, snow,roof live load, wind/earthquake (in that order).
But, if you don't know about duration factors and how to calculate, by hand, the column stability factor, Cp, then you probably shouldn't be using software like WoodWorks to calculate the capacity of a column.

 

[Prestressed Guy]

The difference in calculated and table values is likely related to what was assumed for eccentricity for the tables and the value that you used in your calculations.

 

[msquared48]

I assume that you are using the same unsupported lengths in woodworks as the supplier?

Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask

 

[slomobile]

OldPaper has it nailed. If you cannot do it by hand, or do not understand what Load Duration Factors are... well...

 

[FishingFrank]

Most EWP column tables assume an eccentricity of 0.167 for the width and thickness. They also assume the column is only braced at the ends and the slenderness ratio is less than 50.

The NDS has all the design formulas and factors.

I agree with slomobile....if you cannot do it by hand....