Diaphragm Collector & Chord

Is there a valid way to model and design chords and collectors within RAM?

Way back when I used to disconnect column nodes from the diaphragm so the load was placed into the beams.  I found it to be a bit cumbersome and ended up doing my collector design outside of RAM.  Has anything been changed over the years to make collector design within RAM easier?

Thanks,

Larry

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  • There is still no easy way to model and design collector beams or drag struts with RAM Frame. In order to model a drag strut taking axial load, the beam needs to be a lateral member supported by lateral frames (probably with pinned ends). But, even if you model the whole framing line as lateral, the force from the diaphragm will still go directly to the nodes of the braced bay and not through the drag struts.

    communities.bentley.com/.../18616.ram-frame-criteria-diaphragms

    The only accurate process of analyzing and designing these members is to apply a complete lateral load as nodal loads in the modeler, elevation view, distributed along the length of the frame line. Then in RAM Frame, analyze the structure with the diaphragm criteria set to “none”. (A pseudo flexible diaphragm would also work if the forces are evenly distributed)

    communities.bentley.com/.../ramss-pseudo-flexible-diaphragms-faq 

    What most users do is print the frame story shear report from RAM Frame and then divide the change in shear value on this report by the drag strut length to come up with some uniform axial force to check the beams and diaphragm for manually. 



    Answer Verified By: LarryHD2 

  • How do you recommend getting the flexural DCR of a drag beam under seismic load combo? 

    Suppose I use the "story shear report" method. I will still need to know the flexural DCR of the drag beam under a seismic load combo (e.g., (1.2+0.2Sds)DL + f1L + OmegaE ) for use in interaction check. However, the Gravity Beam Design reports only show flexural DCR for governing gravity load combo (usually 1.2DL + 1.6LL). It seems to me that it would probably be conservative to to use the gravity load combo DCR, but in the case of high drag forces there is an incentive to take advantage of the f1 factor on live load. 

    Is there a way to get  moment demand on a gravity beam from just the load cases rather than load combos? Or would I need to pursue the method of defining drag elements as frame instead of gravity?

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  • How do you recommend getting the flexural DCR of a drag beam under seismic load combo? 

    Suppose I use the "story shear report" method. I will still need to know the flexural DCR of the drag beam under a seismic load combo (e.g., (1.2+0.2Sds)DL + f1L + OmegaE ) for use in interaction check. However, the Gravity Beam Design reports only show flexural DCR for governing gravity load combo (usually 1.2DL + 1.6LL). It seems to me that it would probably be conservative to to use the gravity load combo DCR, but in the case of high drag forces there is an incentive to take advantage of the f1 factor on live load. 

    Is there a way to get  moment demand on a gravity beam from just the load cases rather than load combos? Or would I need to pursue the method of defining drag elements as frame instead of gravity?

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