latticed column vs hot rolled wide flange?

[delagina]

can someone give the advantage and disadvantage of latticed column as opposed to a hot rolled wide flange?

how do you design the latticed column if you are using risa or staad? do you model them as individual truss members? or as one member with "latticed properties"

this is not really a real project question but a curious question. i have not used latticed column ever in my industry. i do noticed specially for metal buildings, they use this a lot.

 

[KootK]

In general terms, I'd say that a latticed column makes sense where:

1) People are cheap an material is expensive and/or;

2) Scale is such that no commonly rolled section would do.

I think that you'd model such a column as a single member with composite section properties. Maybe dial down your flexural stiffness 15% for the axes affected by the latticework shear flexibility if you're feeling like a keener.

I suspect that you'd need to perform the member design largely by hand.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[dhengr]

Delagina:
At one time lattice columns and truss compression members were quite common. As Koot mentioned, labor and fab. hours were pretty cheap in comparison to the material costs and availability. Mostly we knew how to rivet and punch rivet holes, and I expect this method just derived from our knowledge of truss design, in a miniature version, using small, thin std. sized pieces of mat’l. Look in old steel manuals and handbooks for the design methods, and std. mat’l. sizes which were available. We also didn’t have the large WF sections, high strength steels or a very good handle on welding yet. If the PEMB people are using this approach, it is probably on a group of fairly standard members, in an attempt to save material weight, with min. thick smaller material pieces. And, it is most likely very highly mechanized in its fab. and manufacture.

 

[Lomarandil]

KootK and dhengr are spot on about the economics.

I'd definitely model it as a single representative member in FEA, with potentially some hand checks for local conditions depending on your application.

Axial design for a leaner column is fairly straightforward -- typically a modification to KL/r and neglect the lacing cross sectional area. There is some guidance for built-up member connections in AISC E6.

Flexural design is more complex. For bending with lacing in the plane of the web, you need to decide whether the lacing (and lacing connections) are adequate to develop the composite cross section that the geometry implies. In my experience, some existing members are able to act compositely, but many require a reduction in stiffness and strength, especially for single riveted lacing.

If (heaven forbid) you have to consider torsion in a laced member, that typically means resorting to finding research on similarly designed members, or complex FEA with plate elements.