Reg: Forces Sharing inbetw lapped purlins through Flanges

[VijayandVijay]

cold-Formed Zee purlins lap connection, we have bolting on webs only.
However, one of consultant raising the issue states that “When we achieve the continuous action there is a moment sharing between flanges and webs, but shows connection by bolts for purlins at web only” then how flange forces sharing to the adjacent lapped purlins.
Consultant requesting for Justification or supporting documents/Codes for the above issue.
Can anybody guide us.

 

[hokie66]

The flanges share the moment because there are two flanges. The member consists of two purlin sections, and does not attempt to develop any sort of composite action. Your purlin supplier should be able to provide loading tables, which are based more on extensive testing rather than on analysis.

 

[Archie264]

VijayandVijay, are you referring to Z sections aligned parallel to each other or in line with each other? And, if it's the later, are you trying to achieve a continuous beam by way of a moment connection?

Hokie, good to see you back posting.

 

[hokie66]

Thanks, Archie. Just been travelling, didn't have time or access in order to post here.

Vijay is talking about nested lapped splices, where there is no actual moment connection. The bolts through the web at the ends of the splice are in shear to deliver forces to the ends of the respective cantilevers.

 

[msquared48]

Actually Hokie, some (I did say some now) continuity is achieved over the mainframes for splice overlaps in the 4 foot range that I have seen in years past. As you say, these are supplier specific and the spans are tabularized for the splice length used. I would say that there is little to no moment development however to splices of a foot or two.

If the joists do not need the continuity to increase the span length, though, why worry about it?

Mike McCann
MMC Engineering

 

[hokie66]

Mike, I didn't say that there was no continuity as there certainly is, but I wouldn't call it a moment connection. Where I am, the typical splice length for smaller purlin sizes is 900, about 3 ft in your terminology. This provides a double section at the support, pulls the moment to that point, and reduces significantly the moment at midspan.

http://www.lysaght.com/files/dmfile/LysaghtZedCeesPart1v2Aug2010.pdf

 

[msquared48]

OK. Then I guess I would have to ask, if it is not a moment connection, then how is any continuity achieved?

Seems to me that the force couple on the web bolts do exactly that.

Mike McCann
MMC Engineering

 

[rowingengineer]

generally the roof screws the two flanges together and also provides some restraint at the lapped location, with the cleat providing the remaining. I have attached the general lapping configuration for purlins in Australia. These have been tested by many universities and found to be sufficient for laps between 7.5-15%, not so for laps less than 7.5%.

http://www.nceng.com.au/

"Programming today is a race between software engineers striving to build bigger and better idiot-proof programs, and the Universe trying to produce bigger and better idiots. So far, the Universe is winning."

 

[hokie66]

Semantics, I guess. To me, a moment connection involves splicing flanges. In the case of a lapped connection, each purlin acts as a cantilever with an end force imposed by the other purlin.