Lap Length on cold-formed Purlins and Girts

[SteveGregory]

I understand that the typical cold-formed purlins and girts on metal buildings are Zees and they are lapped to make them continuous. I assume that the nested zees provide a section modulus that is doubled to handle the negative moment at the building column or frame.

Is the lap length normally calculated so that the last row of bolts securing the nested zees occurs at (or beyond) the point where a single zee can carry the negative moment? Or is the lap length normally controlled by the bolted connection at each end of the lap?

How about the shear in the bolts at each end of the lap? Bolt Shear = Moment at column / Lap Length - Correct?

Am I on the right path?

 

[SrVaro]

Unfortunately you might be over-simplifying. The adjacent girts might be of different thickness, especially if one is an end bay. The laps could also verify on the left and right sides of the splices. Every manufacturer will have different thickness, shapes, lap lengthes, and connection type/locations.

In general they do add the two thickness to develop the design thickness and capacities.

 

[BAretired]

Here is what Lysaght uses. See attached.

BA

 

[hokie66]

Steve, you are generally correct. The lap lengths shown in BA's link are measured centre to centre of bolts.