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 Design of Steel Structures

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Alex Thomas's profile image
Alex Thomas posted 11-09-2022 10:51 AM

For the design of steel structures what is the provisions in the codes of getting un symmetrical sections fully utilized since lines of action of force and axis of symmetry of the steel structures must be the same for it's.

James Williams's profile image
James Williams
1) What code are you referencing?
2) Do you have an example of the type and orientations of your connections?
3) Do you use AISC's Manual of Steel Construction? It does a great job these days of providing connection details especially tubing and pipes. AISC also provides a manual for Seismic regions, so the connection type may differ given the seismic folks like a little more joint movement for energy dissipation. I have not had the pleasure of using the Seismic manual.

Back when AISC had the red book (guess how long ago that was) I spent weeks researching the effectiveness of steel tubing sections when connected to other sections. AISC addresses all those types of connections. A great reference book is Blodgett's Design of Welded Structures. One of the most brilliant engineers I ever knew, R. Krumpen, introduced Blodgett to a lot of us young engineers starting out. It was a jewel. I used my Blodgett so much that it has duct tape holding it together.

[Note: Some may have businesses that provide consulting services, so a detailed answer may not be readily available.]

Steel plates aka gusset plates, stiffeners, chock plates or simply plates. Plates connected or embedded in one, both or multiple members. 

However, in some cases you will not be able to obtain 100% and have to reduce the effectiveness of your connecting member. 

By the way, in this era of modeling structures being able to produce a solid model of the connection and applying a unit axial, shear, torsional and bending forces individually should provide great reference numbers as well as the visual of stress concentrations easily identifying the effective regions.
Alex Thomas's profile image
Alex Thomas
It's Beuro of indian standard IS 800 1984 and IS 800 2007, consider angle equal or unequal legs center of gravity is out side the section, if it's a rectangular section bar center of is at the geometrical center, then if the line of action of the load is coincide with the center of gravity line Full section is used to resist the load. For an angle section a formula is given in the code for getting the effective area to resist the load. About 70% percent area is utilised. (IS 800 1984) . In IS 800 2007 a formula is given to get strength of the angle section, which gives 80%area is utilised.
Christian Parker's profile image
Christian Parker
Hello Alex,

I can't speak to the Indian codes, but I wonder if part of the reason you're not able to "fully utilize" the section is that stability limit states and flexure-torsion interaction govern the design.  In AISC 360 (US code for steel), single angle flexural members must be checked for yielding, lateral-torsional buckling, and leg local buckling.  A section which is continuously torsionally braced and compact will be governed by yielding, so you could consider the section fully utilized.  If your section is not continuously braced, LTB usually governs.  The capacities get low and the math gets ugly, especially for unequal leg angles.  If you're willing to sweat through the numbers, the best things you can do to get the most capacity is minimize support spacing and orient the section so that the toe is in tension (i.e. with the horizontal leg on top)--but even so, it's an inefficient section and you'll rarely get close to the yielding moment governing.  Channels do a lot better, but you still have to check the effect of torsion since the shear center is way out in the suburbs.

I hope that helps.
Alex Thomas's profile image
Alex Thomas
Channels do better, pipes and box sections are having a problem of corrosion inside because we can't protect inside by painting. Myself used the channels with inside filled with concrete used as lintels for renovation of a building.