Ram Elements Wood Design Repetitive Member Factor Cr

The help topic for Cr indicates it only applies to dimension lumber (e.g. S4S) which is probably why it's not being considered here. 

Repetitive Member

This flag can be applied to joists, truss chords, etc. which are in contact or spaced not more than 24" on centers and fulfill the conditions specified in Section 4.3.9. of the Specifications.

This parameter defines the value to be used for the repetitive member factor (Cr) for dimension lumber.

You could possibly modify the .leo to force the program to consider your section as dimension lumber. I think it's the line that says FORMULATION='LUMBER' that matters here (vs. 'GLULAM')

Seth,

I checked the Bentley Leo SPCa.  If this helps, here is the header information:

//common parameters
UNIT='In'
TYPE='SOLID'
SHAPE='Spaced'
CODE='WOOD'
FORMULATION='LUMBER'
CONNECTION='CONTINUOUS'
COMMENTARY='(Rectangular section for columns spaced by blocks "Condition a")'

Page 235 of the Ram Elements manual "For wood members, the following formulations are available: LUMBER: This formulation should be used with rectangular and rounded sections. Spaced columns are also considered. This formulation is explained in Chapter 4 of the NDS-Specifications."

NDS 4.3.9 Repetitive Factor Cr applies to 3 or more members of dimension lumber that is "in contact or spaced no more than 24" on center.". Based on NDS, multi-ply beams and joists can use Cr as long as the members used are not timbers (Table 4D) or Glulam.  The commentary C4.3.9 specifically addresses multi-ply beams as long as there are 3 or more members.

The S4S lumber used here are standard sizes and have design values from Table 4A.  It looks like Ram recognizes that I checked the Cr box but then does not use it when you look at the Wood Design output.

Thanks, the results are the same for me, so it's not a matter of my version.  I'll check with developers to see why that repetitive member setting gets ignored. 

Here our findings. The Cr factor (Repetitive Member Factor) applies for dimension lumber 2” to 4”: But this section is 5” thick, so the repetitive member factor should not apply:

In RAM Elements the user has the option to indicate that a member meets the criteria regarding the member spacing (24”), but we are still checking the applicability of Section 4.3.9 regarding the limits of the thickness.

Seth, The reference you provided states that the members must be 2-4" thick and these members may be in contact or spaced no more than 24".  Also, there needs to be 3 or more members for this criteria to apply.  A beam with (2)2x12's would not meet the criteria, but a beam with (3)2x12's would.  This section has 4 members.  There are 2 members (1.5"+3.5"=5") in contact, a space and then two more members (1.5"+3.5") in contact.

I did another test file with 1 beam using your S4S Leo to make a beam with (4)2x12's.  I got the same result.  The member gets marked as a Repetitive member but the Cr = 1.00 instead of Cr = 1.15 in the Wood Design output.  Section 4.3.9 and the commentary C4.3.9 both indicate the Repetitive Use factor can be used here.

We have a different interpretation of that code section. We are looking at the total width of the section. It means that if you have, for example, 3 (or more) rafters spaced 24" on center (or less) and that the rafters are each 4" wide (or less) you can apply Cr. You could use a section made up of 2 x 1.5" wide shapes and those would still get the advantage of the Cr factor, because each is 3" wide, but if you make a section with 3 x 1.5" layers (4.5" wide) that would no longer qualify.  LIkewise a section using 2 x 1.5" sections with a 1.5" gap in the middle would also be too wide. 

I felt much the same way as you do until I read the NDS Commentary C4.3.9.  It is clear. The last paragraph reads:

"The repetitive member increase also applies to an assembly
of three or more essentially parallel members of
equal size and of the same orientation which are in direct
contact with each other (28). In this case the transverse
elements may be mechanical fasteners such as nails, nail
gluing, tongue and groove joints, or bearing plates. The
required condition is that the three or more members act
together to resist the applied moment. "

I felt much the same way as you do until I read the NDS Commentary C4.3.9.  It is clear. The last paragraph reads:

"The repetitive member increase also applies to an assembly
of three or more essentially parallel members of
equal size and of the same orientation which are in direct
contact with each other (28). In this case the transverse
elements may be mechanical fasteners such as nails, nail
gluing, tongue and groove joints, or bearing plates. The
required condition is that the three or more members act
together to resist the applied moment. "

That helps, my copy of the NDS doesn't have the commentary. 

We asked for a clarification to the NDS and they replied. The dimension limit should not be applied to assemblies. Therefore, we will implement and remove the size validation. In this way, the user will have the freedom to check it where it is required, but also will have the responsibility to check the size limitation when needed. 

Thanks for the update!