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Reaction Distribution to Hollowcore Precast Plank

Reaction Distribution to Hollowcore Precast Plank

Reaction Distribution to Hollowcore Precast Plank

(OP)
Please see attachment...

I need to fasten a CFS facade to bottom of existing cantilevered hollowcore precast plank. For clarity, the primary structural member, a 6.00 x 1.62 CF, is the only member shown.

At Exhibit A, my tension reaction is too high for the single anchor type i want to use.

At Exhibit B, my reactions go crazy!

At Exhibit C, may i install a steel plate to adjust the reaction as shown, or perhaps, from Exhibit B, may i adjust the reaction to: 2.41 - 1.85 = 0.56K?

Is this reasonable?

Can i apply this to multiple fasteners at the first node provided my transfer strut is significant enough?

Thank you!

RE: Reaction Distribution to Hollowcore Precast Plank

None of the above! Exhibit B is impossible. Better to provide a hanger to a steel angle above the hollowcore or alternatively a hanger anchored to concrete fill within the void of the hollowcore.

BA

RE: Reaction Distribution to Hollowcore Precast Plank

I could get behind C if you provided a spacer between the concrete and CF thing at the fastening locations.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Reaction Distribution to Hollowcore Precast Plank

(OP)
BA, thank you for you input.

Exhibit B provides the resultant reactions (according to the Enercalc program i am using). I'm struggling transferring forces with an intermediary support so-to-speak. If the Enercalc program providing an error? Or what am i doing wrong?

Doesn't my steel plate anchoring through the top flange of CFS member serve as the hanger or similar fixture? I suppose using an angle to fasten the CF web to would provide a sturdier connection also providing web-stiffening. But, with such low loads, i don't see that as necessary, but, i will reconsider.

Thank you!

RE: Reaction Distribution to Hollowcore Precast Plank

It seems Exhibit B just the unpleasant limitations of modeling that node as a pin? What result would you achieve if you modeled all these bolts as very stiff spring instead of pins? I had this work successfully on closely spaced bolts before, one just needs to ensure that the deflection of the spring is realistic and inline with the slip of a bolt.

RE: Reaction Distribution to Hollowcore Precast Plank

(OP)
KootK, why do you feel a spacer is necessary? And what material?

RE: Reaction Distribution to Hollowcore Precast Plank

(OP)
jwilki, what type of springs are you referring to? I understand the physical perspective, but, please keep in mind the cost feasibility. This is such a small facade that does not need to flex.

RE: Reaction Distribution to Hollowcore Precast Plank

If the pieces are in direct contact with the precast, you may get a prying effect that would amplify the fastener loads. I'm not sure what makes sense for spacers. Frankly, I don't think that it's even s practical solution. BA's concer sounds promising to me.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Reaction Distribution to Hollowcore Precast Plank

Sorry, I mean model this connection with stiff springs instead of static pins, such that the first 2 fasteners are in tension and not a couple as in diagram B. Overall, AS BA said a hanger from a bent piece of steel will do it.

RE: Reaction Distribution to Hollowcore Precast Plank

Yes - what jwiilki says.

There is no such thing as an infinitely rigid support so your reactions in Case B are totally unrealistic.

A Case D where you use two fasteners like in B but rotate the pair so they are on either side of the cantilevered member.

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RE: Reaction Distribution to Hollowcore Precast Plank

The A or C models are fine. I agree with BA about the anchorage...it can't be just through the thin bottom of the hollow core slab. Grouting the cores would be my choice.

RE: Reaction Distribution to Hollowcore Precast Plank

BSVBD:
Why not take your option “A,” and use the upward anchor at the tip of the precast primarily to hold the 6.00 x 1.62 CF in place laterally and longitudinally, or eliminate it? Then apply some sort of a clip angle to the side of the 6" CF and up the outer end of the of the precast; bend it over onto the top of the precast and pin it down to the precast. This clip angle will take the .43k reaction, and hold the 6" CF laterally.

RE: Reaction Distribution to Hollowcore Precast Plank

Just to appease my curiosity, what do CF and CFS mean?

RE: Reaction Distribution to Hollowcore Precast Plank

Hokie:
I think they mean cold formed (CF) and cold formed steel (CFS), but that’s just my best guess. But, they sure do make people sound knowledgeable and important, don’t they? I’m so damn sick and tired of looking up acronyms in an effort to try to help some of these guys, that I just quit reading those threads. If we use a few more acronyms in our communications nobody will be able to understand anything being said.

RE: Reaction Distribution to Hollowcore Precast Plank

(OP)
JAE - I also "perceive" that the reactions in case "B" are unrealistic. However, the reason i present them as such is simply because that is the way the numbers worked in the program. I also perceive that you are implying that we can reasonably apply our engineering judgement to understand that the actual numbers, in a case as such, can be "interpolated" (more reasonably: "interpreted", in this case). Am i correct in my perception? I also inquired about adding the positive to the negative to achieve the reasonable resultant which, essentially is what, i believe, you obtained by "rotate(ing) the pair so they are on either side of the cantilevered member." Again, is this a reasonable understanding? The only problem with rotating the pair is that they would not fit within the 1.62 flange. Thus, the contributing suggestions.

dhengr and hokie66 - Yes, CF & CFS stand for Cold Formed Steel, as in "steel stud"-type members.

dhengr, i like your suggestion of bearing on top, however, it seems more complicated than the contractors on the job would be willing to use and more expensive than the simpler solutions.

dhengr, please forgive me for the apparent appearance of arrogance. That was not the intent. CF and CFS are common acronyms in the area i work. A simple helpful answer to any question is all that is necessary within the environment of this forum.

Thank you all!

RE: Reaction Distribution to Hollowcore Precast Plank

Quote:

I also perceive that you are implying that we can reasonably apply our engineering judgement to understand that the actual numbers, in a case as such, can be "interpolated" (more reasonably: "interpreted", in this case). Am i correct in my perception?

Well not so much engineering judgement as simply modeling the system correctly. Using infinitely rigid boundary conditions in your program isn't accurate at all. There is some "give" in the fasteners, the plank will flex a bit, and the flanges of the CFS shape will deform a bit. Even if these are very stiff spring boundary conditions that you estimate, they are a VERY LONG WAY from infinity.

Quote:

I also inquired about adding the positive to the negative to achieve the reasonable resultant which, essentially is what, i believe, you obtained by "rotate(ing) the pair so they are on either side of the cantilevered member." Again, is this a reasonable understanding?

Yes I would think so. By rotating the pair your analysis becomes non-redundant (two supports vs. three) and you can solve for it directly....which the results, I think, would come closer to what you probably would get by using softer boundary conditions in the first place.

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