Ram Elements Wood Design Repetitive Member Factor Cr

I am using spaced wood sections defined by your Leo SPCa.leo.  There is one section in the standard United States group and we added several sections to a custom group for our office.

Our sections typically use 4 combined members.  The members are typically 2x12's.  So, we would have (2)2x12's nailed together with a space of 5.5" and another set of (2)2x12's on the other side.  The total width of the beam-column is 11.5".  These sections have bending in the major axis and axial stress.  I have attached an Output Report for a beam-column  that has a total of (2)4x12's and (2)2/12's as one example.

The program has a check box to apply the Repetitive Member Factor Cr in the Wood Design Parameters.  The output shows that the member is a repetitive member under the heading "DESIGN CRITERIA", but the section "DESIGN FOR FLEXURE" for M33 shows Cr = 1.00 instead of 1.15.  I checked the box to use 1.15.  Why is Ram Elements ignoring this factor?

On another note for the same type spaced sections using SPCa.leo, the program will let me set Lu, but the spreadsheet tools will not assign Le.  The error message says it only works for rectangular or circular sections.  Why?

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  • 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.

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  • 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.

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