single angle in compression with aisc 2005

huangyhg

single angle in compression with aisc 2005
i noticed some changes in the code (see aisc 2005, chapter e). the capacity calculation will consider load eccentricity through connection detail (through short leg or long leg) and whether the angle is a web of a 3d truss or a 2d truss, and calculate an effective slenderness ratio.  the single angle can then be treated as an axially loaded pinned-end member.
with some calculation comparison with those from aisc 2000 (lrfd spec for single angle members) the new spec seems like an evolution.  at the same time i noticed also that something is very significant. such as the capacity of angle web in a 3d truss increases substantially compared to that in a 2d truss.
for example, an l4x3x5/16 web member, 10ft span and a36 steel, in a box truss. the end connection is through the short leg. compression capacity is 19.9kips (see the calculation example 2 by leroy a. lutz in aisc engineering journal, 4th quarter, 2006). when put the member in a planar truss the capacity is 15.3kips (30% reduction). also for the same angle, if the connection is changed to the long leg the capacity will increase about 20%. i don’t know how these sound to your folks.