Composite Steel Floor Deck 3

[dik]

Is there a minimum end bearing value for steel floor deck. I would have thought 2" or something of that ilk, but cannot locate this. Is this a matter for the manufacturer. Canadian practice, and cannot locate anything is CSA Standards or CSSBI Standards.

Thanks, Dik

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[structSU10]

2" is pretty standard. US deck catalogs tend to specify that and will give web crippling values for different lengths as well.

 

[dik]

Is it a supplier preference/requirement?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[driftLimiter]

The section has a limit state for out of plane loads at the bearing. Verco has some design tools where you can set it manually but I don't recall seeing anything less than 2"

 

[dik]

I've got a couple of queries in to some deck suppliers... I'll let you know when I find out. I've always used 2", but don't know why... maybe a wise old engineer told me to use 2", fifty years back...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[jayrod12]

The Canam catalogue I work with indicates their web crippling resistance is based on 1 1/2" end support bearing length and 4" interior support bearing length. So that's what I would be basing my minimums on.

 

[dik]

Thanks, Jay...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BAretired]

Found this note using Mr. Google:

A minimum of 1-1/2″ of end bearing should be provided for metal roof decking or metal floor decking. If there is less than 1-1/2″ of bearing, additional fastening should be provided and the deck end load capacity should be checked.

 

[dik]

Thanks, BART.. is there a source for that? I've always used 2", but never had a source. It appears that 1-1/2 is OK.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BAretired]

Thanks, BART.. is there a source for that? I've always used 2", but never had a source. It appears that 1-1/2 is OK.

Not sure of the source, but the attachment below from Canam Steel indicates 40mm (1.6") bearing for their P-3615 deck.
But be careful; the Canam Steel Deck catalog provides factored reaction values for 76mm deck of 76mm, 100mm and 140mm bearing, so it cannot always be assumed that 38 mm is adequate.

 

[KootK]

 

[dik]

Thanks Koot...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[dik]

From the SDI, in answer to my question:

and the response:

Great response... I don't know how or if it deals with different gauges; this may be in the reference. Is there anyone that can scan/photograph the relevant part?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BAretired]

Canam lists Web Crippling resistance for several profiles, different gauges and different bearing lengths in their Steel Deck catalog.

 

[dik]

Thanks, BART...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BAretired]

From the SDI document:

 

[dik]

Thanks so much, BART... another SMath program coming up... any idea of how the coefficients A and B are determined? I'd have used a phi factor of 0.85 for all cases.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[BAretired]

any idea of how the coefficients A and B are determined?

I haven't a clue! Here is what I found:

The design expressions used in most cold formed steel specifications are empirical in nature, as there is a large number of variables involved in the resistance to web crushing. There have been many attempts also to apply theoretical analysis to these problems, and the buckling behaviour of webs in the presence of localised loads. Of note among these is Khan and Walker [7]. In recent years also the plastic mechanism approach has been used by different authors, e.g. Bakker and Stark [8], Setiyoni [9]to provide alternative formulations to the solution of web crushing problems. However, in cold-formed steel design the specifications are at present empirical.

The empirical nature of the design rules, as mentioned, has been occasioned because of the large number of variables incurred in evaluation of web crushing capacity. The empirical rules are very useful and permit rapid, and in general safe, analysis of web crushing capacity within their range of application. The AISI Cold-Formed Steel Specification [10]has equations dealing with a wide variety of conditions. The corresponding British Specification [11]has its web crushing rules completely based on those of the AISI specification, and thus uses substantially similar equations.

Two main drawbacks to the empirical nature of the design rules are as follows: (i) the rules are strictly confined to the range for which they have been proven, and (ii) it is often difficult to ascertain the engineering reasoning behind the different parts of the rather complex equations. It is perhaps because of this second point that in the final stages of the development of the new Eurocode dealing with cold formed steel member [12]the UK/AISI rules have been adopted, but applied to different conditions than those for which these are used in the AISI or UK specifications.

There could be advantages in having design rules which can be built up using engineering principles, and for which the possibility of extension of the range of application can be viewed with some background knowledge of what should be expected. This is the case, for example, with the Eurocode dealing with hot rolled steelwork [13]in which the behaviour of webs under localised transverse loads is treated as a buckling problem, incorporating an effective width of compressed web together with the European column curves. While the extension of such an approach to deal with members of general shape is perhaps a difficult task, the use of powerful analysis methods such as the finite element method provides at least one basis of approach to the derivation of more theoretically based design rules. A good start for the development of such rules is to ascertain how the rules set-up compare with the existing empirical design rules, as these are known to have reasonable accuracy within their range of application.

 

[hokie66]

The discussion is about criteria during construction, but how is the limited bearing length justified with the requirement for extension of bottom steel at end supports?

 

[structSU10]

Thats an interesting point - I have never seen anything about the development length for composite deck and such. It obviously works with the small bearing length but it would be good to understand how and why it differs from traditional reinforced concrete design principles for that condition.