Open Web Steel Joist yr 1983 capacity

[crackgerbal]

Hey there,

I am working on a project that is to add an eco roof to an existing building, built in 1983. The roof is currently supported by open web steel joists type 20H6 @ 8'-0" O.C. spanning 33ft. Newer versions of the Steel Joist Institute design manual do not have this type of joist listed in them.

Does anyone have a copy of the older versions of the Steel Joist Institute design manual with this joist type? I would like to know the capacity of this joist. If you know how the naming convention of the joists were changed that would be helpful too.

Any help would be appreciated.

 

[crackgerbal]

So I talked to a guy from Vulcraft and he had a copy of the design manual that would have been used. it is attached below if any one else needs it.

This is only for the H series though

 

[diggingdeeper]

80 YEARS OF OPEN WEB STEEL JOIST CONSTRUCTION is the name of a publication available from the Steel Joist Institute with this information.

 

[msquared48]

Better check the deck capacity too with that 8 foot span and the load from some of these green roofs now. Depending on the gage and depth, it may not be adequate.

Mike McCann
MMC Engineering

 

[crackgerbal]

Thanks for the tips guys!

I am in the process of checking the decking right now actually.

 

[StructTaco]

I'm not sure what part of the world you are in crackgerbal, but be sure to check additional seismic loading due to dead load of green roof as well. I've done a few of these, and with the ever-changing code and more and more windows, seismic retrofit is almost always going to need to happen, at the very least, checked.

Dave

 

[crackgerbal]

@Dave: StructTaco

Yeah the building is in Portland Oregon, and they have a provision that states that if the loading is increases 5% from the original design (which was 1950's) then the building will need to be seismically upgraded. We are calling around to get more info on this provision, since it doesn't state whether or not it means the seismic weight (as in seismic base shear) or the factored loads are to be kept under the 5% max.

The building is so old that retrofitting it will not be cost effective. The client may decide to abort the green roof idea as a result.

 

[StructTaco]

Check out the Existing Building Code in the back of the IBC, it has a relaxation on the seismic demands on older structures. I have always compared the 5% increase in mass to the existing building mass, not the seismic weight. If you are below that 5%, then no seismic analysis necessary. If you are increasing the mass by more than 5%, then an analysis would be warranted, and you would need to then account for all loads as they exist today, and use the current building code for that retrofit, which usually means larger loads, increased shear resistance, and foundation retrofit...to some degree. Good luck.