Steel joist properties

Anyone know where I can get the cross-sectional properties of widely-used steel joists? I am using a structural software program and they don't have a built-in joist table (like for AISC shapes). They have a nice facility input prismatic sections by providing area, moment of inertias, etc. But where do I find tables for joists? I checked the 40th edition of the Steel Joist Manual from the Steel Joist Institute, but they only had load charts. No properties. I know steel joists are a bunch of angles and rods welded together thus, making their cross-section abstract, but aren't there standard shapes. Any help would be appreciated.

 

[Mattman]

In the "Deflection of Steel Joists" section of its "Joist Design Commentary," Vulcraft's design guide states that the moment of inertia of a steel joist = 26.767*WLL*L^3*10E-6, where WLL = red figure in load table.

A typical area of steel (y in^2) can be determined by the weight of the joist (x PLF)and the density of steel (490 PCF):

y (in^2) = x (PLF)*144 (in^2/FT^2) / 490 (PCF)

 

But for which axis is that about? Major or minor? And how do you calculate the section modulus if you don't know the cg? As well as the values for the other axis? The program is requiring me to input values for torsional constant, two moms of inertia, and the area. Thanks!

 

[steve111]

Are you trying to verify structural capacity of existing owsj, or designing new owsj members? There are alot of different systems out there, especially through the 50's, 60's, and in to the 70's, proprietiory and a number of them no longer in existence.

 

[steve1]

You're not going to find a table of cross sectional properties for steel joists because each manufacturer has their own system. Some use hot rolled shapes like angles and tees, other use cold formed sections. The information provided by Mattman is useful for global properties of the joists, but I think you are looking for information regarding properties of the componets (chord and web members). This information is usually proprietary , and can only be obtained either directly from the manufacturer or by field measurment.

 

[Mattman]

The momemt of intertia equation is about the major axis. The steel area equation will not give an exact answer, as the joist weights in the joist tables are approximate.

Steve1 is correct; the systems are proprietary and the complete section properties of the joists are not published. In fact,the exact properties of standard SJI joists can vary from manufacturer to manufacturer, even when they have they same designation.

 

[steve111]

all things considered though for verification of existing owsj, we use a simple pinjointed truss program to analyse. Section properties straight forward enough wrt to elements, panel points are set as the intersect of centroids of elements framing into a node, have to watch for eccentricities here and at bearing points, apply design loads, and check for top chord combined bending axial load, and web shear. Field Measure, checking splices, joint connections, visual inspection of welds, top chord lateral bracing condition, bridging etc, and assume fy=36 ksi throughout.
Where we can find SHOP DRAWINGS of the manufacturer or tags etc., we consult the manufacturer, we do the field measurements and they run they owsj for us. They're always helpful in these matters.