Standard Strength of Z-Purlins

[kevanthurman]

Does anyone know what the standard strength for Z-pulins in 1982 was? 33ksi or 55ksi?

Any info on moment capacity tables for different sizes would also be helpful.

Thanks

 

[hokie66]

What country?

 

[kevanthurman]

Hawaii, USA

 

[audeuce02]

Are you sure it was a Zee in 82. I would expect lapped Cee's during that time frame.

 

[ash060]

What Gauge? If they are thinner than 16 ga. they will almost certainly be 33 ksi. I don't know many manufacturers that have 50 ksi steel in the very light gauges.

 

[kevanthurman]

I have the original shop drawings calling out Z-purlins. The drawings however do not call out the strength or gauge, but based on the thickness called out (0.064-0.069in) and the moment of inertia about the x-x axis (13.87 in^4 calc'd from cross-section dimensions) I would say it is either 14-16 gauge.

 

[audeuce02]

In the 80's the yield was most likely 46 ksi. The moment capacity would be a different animal because everyone was pretty much rolling their own shape with variable length and angle stiffening legs. Thank god for LGSI and some industry normalization. The closest thing that I can find would be a 10Z16 with an Ixx of 14.7 in^4 and Mr = 8.160 k-ft for pressure and 4.080 k-ft for suction. These values were based on the 1986 AISI, has the 4/3 capacity increase due to wind loading, and is based on fully braced compression flange. I probably have some stuff from the late 70s or early 80s, but it would all be CEE sections. Hope this at lease helps a little.

 

[structuresguy]

I'm sorry that I can't add anything to this discussion, ut I do have a related question.

Knowing the dimensions and gage thickness, which can all be field measured, you can calculate your section properties very easily. If we assume a yeild strength, then you can calculate bending strength. However, I don't know how to calculate allowable bending for condition where the compression flange is not fully braced. I am sure there is a way for light gage, I just don't know it. Can anyone point me in the correct direction?

I have new catalogs for C and Z purlins with allowable bending based on braced length. But for investigation of existing buildings, with odd shapes, not sure what to do if the shapes don't closely match my catalogs. This was recently an issue for us, where I could not make 8" girts work, since they would have too long an unbraced compression flange. So i made them put in 8" structural shapes, instead of light gage. But they were not happy at all.

 

[j19]

Some of the metal building manufacturers were using 55 ksi as far back as the 70's. I'm not sure about component suppliers. I would be willing to make a job site visit to check them out if all expenses would be paid. It'll probably take a couple of weeks to get it figured it out. I would also need to bring my assistant (wife).