J-series joist

[hbarreto]

I am looking into a new project in a two story building that was built sometime around 1979. The intention is to use the second floor as storage over an existing bar joist system runing across a span of 35 feet.
The joists' depth is 24" and are 24" o.c. I also got a tag from one of the joists with this legend: 74 2J 3.
Can anyone tell me what this tag means so I can determine the lbs/sf this system can support?.

 

[JLNJ]

The "J" on your tag may not tell you the joist size but rather it may just be a factory-assigned erection mark number.

I'd start with the lightest 24" joist and see where that puts you compared to the required capacity.

 

[MiketheEngineer]

JLNJ is probably correct!!

If you can get very accurate sizes of all the members - go to

http://www.steeljoist.org

and they have a "calculator" that will help you - maybe.

Good Luck

 

[jike]

2J3 sounds like a joist mark that refers to the shop drawings not a joist size. Sometimes(not always) there may be multiple tags on joists.

 

[hbarreto]

Thank you everyone.

 

[ChipB]

hbarreto,
Had to do this before as well:
Measure the top and bottom chord angles to determine their size and area (A)
Calculate the distance between the center of gravities between the angles (d)

Calculate the allowable moment (approximate):
30kips * A_bottom * d = Allowable Moment (in*kips)

Then back calculate "w"

This should get you really, really close. If you don't have a 60 year joist manual, post the info, and I'll look it up for you.

 

[archeng59]

for what it's worth, the 60 year joist manual is one of the best reference books to have on your shelf.