Different Composite Deck Capacities - Vulcraft vs. New Millennium 7

[cfox142]

I am looking at an existing building with composite metal deck and composite beams (shear studs). I am looking at the floor for some additional equipment to be added. From this I noticed that the composite deck capacities from Vulcraft and New Millennium vary quite a bit. The floor system is:

3" 20 Ga. Composite deck 5 1/2" total slab thickness spanning 10 ft over W16 beams with shear studs

In New Millennium this has a capacity of 203 PSF
In Vulcraft this has a capacity of 159 PSF

Does anyone know why the big difference? I assume the slab capacity is governed by the shear transfer at the slab to deck. Are the indentions in New Millennium deck larger or something? I look at the indentions in the deck as equivalent to shear studs on a beam i.e. larger sizes or quantities get a larger capacity until at some point you crush the concrete or yield the deck.

Thank you,

 

[dhengr]

Cfox142:
A crazy thing has happened on the way to the total-internet-world. The phone has completely stopped working for anything meaningful or really useful, and we have decided never to enquire of the people or organizations who should really know some/the answers to our questions. And, now Google must have all the answers, and a Tweet should be long enough to explain everything on everything, with some characters left over. Why not call the two companies? Do not e-mail if you expect something meaningful. Ask each for someone from their engineering dept. who is familiar with their deck products, deck testing programs, and their tabulated load values, etc. Spend a little time studying both sets of materials you have and listing your questions and issues, so that you do come across as an intelligent engineer who understands what he is doing and talking about. Then, ask Co.A why their product shows higher values then Co.B’s values, all else seeming to be equal; ask for deeper, meaningful reasons, not just a bunch of sales pap. Then turn the question around when you call Co.B. Look and listen for common sense engineering explanations, code justifications, real superior product qualities, not slick sales bad mouthing. Where they agree in approach and sound engineering fundamentals and give good sound engineering explanations, you are probably on the right track. Ask about any differences or misunderstandings in these areas, without really revealing the other party’s position. Ask them what they recommend to increase the slab cap’y. One thing you might do is put the new equip. on a couple beams which span the 10' btwn. beams to take the slab out of the picture. Assume, of course, that you can make the beams work. At least the beams have (10' by x')(100 lbs/sq.ft.) less LL on them, or they can be reinforced from below. But also remember, with the newer codes and the way we are manipulating loads and other factors these days, and the way clients are demanding cheaper bldgs., there might not be much fat left in the structure for the future, larger loading. They got what they paid for and wanted in the first place, and can pay the piper now.

 

[JoshPlumSE]

Gosh, don't be such a grump....

Sure, the best information about this may come from the manufacturer's themselves. But, it's a legitimate question and if he (or someone else) finds out the answer. I'd be truly interested in knowing it. Seems like exactly the kind of thing that I read Eng-Tips for....

 

[dik]

We need more information...

Does the deck have the same number of flutes or is the spacing of the flutes different? Is the one deck stronger than the other (Fy?). For 10' span I would not think that it would be a shear issue except for the number and sizing of the flutes.

Dik

 

[JedClampett]

dheng, I'm also a believer in the telephone. But in today's world, it's become very difficult to talk to anyone on the phone, and even more difficult to talk to anyone who knows what the heck is going on. Voicemail menus have replaced people. Push 1 for English and 2 for gibberish. Heck, you need the internet to find the phone number of the customer service department.
But I did call Vulcraft or Verco, I can't remember which one, about differences in the shear values between manufacturers a while ago. The guy on the line was a little sheepish, but he blamed the differences on testing. It seems that 20 gage deck with a certain profile should all test the same, but he insisted that it's a test and you could come up with different values.

 

[Once20036]

I appreciate your post DH...
The way I see it, if there's a problem you're facing that you've thought through, mulled over, discussed with colleagues, otherwise tried to solve, and can't make any progress on - bring it on. This forum has an incredible wealth of people who like tricky problems and will provide thoughtful, educated, and thorough responses.

On the other hand, if you haven't bothered to make an effort and expect strangers to solve your problem for you, maybe a grumpy response is exactly what you should expect.

 

[mijowe]

It is my understanding that Vulcraft publishes lower values, possibly based on their own testing. What is interesting to me is that (at least at one time) they use to publish the standard SDI capacity equations with no adjustment factors, ie the calculated value based on the equation did not match their tabulated values.

It should be noted that their values do not include the stud per foot, many catalogs include both values. I asked Vulcraft for span charts that included studs (at various spacing 1', 2', 3') and when they supplied these charts they more closely represented both the SDI equations and other manufacturers charts. I assume that they may have had tested values for no studs but with studs they just used the calculated values.

You should also verify that you are comparing the same steel strength, these vary from from chart to chart as well.

 

[dhengr]

I too believe that participating in E-Tips is a great learning and mental exercise experience. I’m not trying to be particularly grumpy. I’m just imagining that getting the facts straight from the horse’s mouth might be better than getting 15 guesses from a bunch of engineers, some pretty smart and knowledgeable, others less so, but none of them knowing the details of the testing, or the calc. methods or codes used, etc. etc. Of course, this presupposes that someone in the product manufacturer’s company knows what they are talking about, and that is becoming tougher to come by, as this work is being handed off to a voice-bot, press #7, or the computer does it all without the operator having the vaguest what’s really going on. And, we seem to be getting more and more products, to sell to the world; with less and less real knowledge and long term experience with each product, but we sure do have a thick product catalog. Heck, these days, you probably spend as much time studying product sales literature, maybe more meaningful engineering reports, ICC product reports, dozens of footnotes in each, for each RFI or change request, than you do designing some major parts of the structure. And, half these new and improved products don’t improve the final bldg., they just add to the design and approval complexity, and provide an additional product variation to sell.

Let Cfox142 come back and tell us what he finds out, if we really want to learn something, and he would be so willing/kind to really participate in the give-n-take here on E-Tips.

In today’s world, I would never want to get my info. straight from the horse’s mouth (original source). We are teaching cooperation and collaboration, thus, 15 semi-informed opinions, kinda averaged, and manipulated to fit your wants, is always a better solution and shows you care about other’s opinions and FEELINGS. Right or wrong, we are all entitled to a bunch of those, and certainly in a real democracy, a knowledgeable opinion should be given no more weight than any other opinions, feelings again. And, the guy who actually has the facts, he probably wants to bend those to fit his needs too. You do have to be smart enough to know when any one of the groups is trying to blow smoke up your leg, or when to devalue unknowing opinions when coming to a conclusion. They are not all equal in value.

 

[JLNJ]

I am always wary of composite deck tables. Very, very, wary. Especially in industrial uses. In fact, I don't use composite action with the deck for any moderate or heavier industrial loads.

Vulcraft's table says that their loads are suspect (my wording) for concentrated, dynamic, or long term loading. What else is there? Short-term non-dynamic? Small office workers stepping quietly?

To answer your question more specifically, my guesses are:

1) Vulcraft's material yield stress is lower. Maybe they take a conservative approach to the beneficial effects of rolling/strain hardening.
2) The two companies distribute the positive/negative slab moment differently or they look at the end span conditions differently.

 

[cfox142]

Thanks for all the input. Because of the speed of this project and not knowing which deck was used for the slab we ended up building a frame on top of the slab to take the loads directly to the framing members. I will update once I contact Vulcraft and New Millennium since we may by changing our specifications after noticing the big difference in capacities.