Design load distribution member!
Design load distribution member!
(OP)
What is the proper way of designing size of HSS load distribution member, as shown in attached sketch? Do we need to check the thickness of HSS for localized bending effect? If so, how? I would appreciate your help.






RE: Design load distribution member!
RE: Design load distribution member!
The detail you show with the tube spreader doesn't feel right to me, and the loads seem too concentrated to accomplish what you want. Plus, the spreader is being loaded on its weak axis which is inefficient.
Mike McCann
MMC Engineering
RE: Design load distribution member!
Thanks for the response. Let me make things little bit clearer. The studs above and below are already designed (just DL and LL, not lateral load). I have designed shear walls for lateral loads. My concern is the design of HSS load distribution member. The detail I had attached previously is the most common detail in load bearing CFM stud walls design.
H57, yes, I have already checked the HSS section as a whole for bending. Worst case scenario, I designed HSS for simply supported beam of 16" span and point loads from Hambro joist and stud above (11,5000 lbs total). That turns out to be okay. Now I checked HSS member for the plate thickness (horizontal portion of HSS tube) of 1/8" (thickness of HSS member) supported by two vertical sides of tube (3" deep in our case) for localized effect of point load on HSS tube, it did not work. However, I am not sure this is the proper way of designing the load distribution member or not.
RE: Design load distribution member!
RE: Design load distribution member!
Conservative way: 11500# load concentrated at middle, designed as simply supported. I would use a width equal to the width of the joist.
I would check it this way first as a quick check. If it worked move on - if not review more closely.
The 11500# is really distributed over an area decreasing the moments in the plate. The load would distribute laterally as well so the effective width will be greater than just the joist bearing width. The joist seat will also distribute the load and provide rigidity to prevent bending of the top plate. The edges really aren't pinned so they are somewhat fixed.
I guess what I'm saying is there are alot of areas that I would start to look at. Not saying that I would use all of the above, but I may consider some of them depending on individual cases. This really gets into engineering judgement at individual connections.
RE: Design load distribution member!
RE: Design load distribution member!
I agree with msquared.
I would either put a small pipe or tube under the joist, or at least double or triple up the stud below the joist end. And call out on the drawings that this double or triple stud must be directly below the joist end.
I may be mistaken here, but to assusme that the load from the joist will be distributed out evenly to the studs below may require a fairly stiff distribution member. Off the top of my head, I am not sure you can get there with only 2" of depth to work with. I think the stud under the joist end ( or closest to the joist end) will likely see most of the load from the joist. And very little of this load will distribute to the adjacent studs.
Could be wrong on that. Been a while since I have done deflection vs. stiffness compatibilty analysis.
RE: Design load distribution member!
RE: Design load distribution member!
If you "heard" it on the internet, it's guilty until proven innocent. - DCS
RE: Design load distribution member!
1. Must specifically consider shear, as well as combination involving shear (such as bending & shear).
2. Members fail rather than "deflect" and allow redistribution.
IF I were dealing with a typical construction in timber, I would often be comfortable taking 1/2 of the load comming from the wall & OWSJ above and put it into the adjacent studs, simply because the centre post will deflect and allow this....
ie: __ <-- 1/4
|
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TOP 1 -->|__ <-- 1/2 BOTTOM
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|__ <-- 1/4
However, CFS has no plastic capacity... They also have little to no reserve capacity. You need to design for all of the load going into the stud below the OWSJ:
ie: __ <-- 0!
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TOP 1 -->|__ <-- 1 (full load) BOTTOM
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|__ <-- 0!
It's the relative stiffness & inability to redistribute any load or permit deflection that prevents the previous assumption.
Please note: I don't know if this is supported or contracdicted by any research, however it is my best opinion and how I carry out my work when dealing with CFS.
Potential Solution: Faced with this problem, I would simple use a double stud (back to back CFS) at each OWSJ support point, presuming a double stud suffices.
Let us know how it goes,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: Design load distribution member!
ie: __ <-- 1/2
|
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TOP 1 -->|__ <-- *FAILED* BOTTOM
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|__ <-- 1/2
Or use a header (spreader) that is stiff enough to actually distribute the actions)... Something like a W-section (I-beam), but this would be horendously inefficient!
Cheers,
YS
B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...
RE: Design load distribution member!
YS: Good Post!