strucutural steel angle versus bent plate

huangyhg

strucutural steel angle versus bent plate
hi all,
i am working on a project were we are designing 63' long and 53' steel trusses.  we will be fabricating these trusses out of s32205 stainless steel.  typically, i would design trusses of this nature out of double angles, but in this case, the angles may not be available in that grade of steel, due to its scarcity of use and the difficult of forming shapes out of that high grade steel.
so, we may have to use bent plate as our angle shapes.
should i design it for the exact same properties as angle?  (minus the lil' sharp corner if you have to be technical)
or do cold-bent shapes lose strength compared to hot-rolled angles?
one source told me that the strain-hardening of bending the plates would actually make them stronger?  is that true?
thank you in advance,
mike
i would use the properteries of the actual plate you specify, not the ones from the corresponding angle.  try estimating a size or two and compare the hot-rooled shape properties to one the is made from a bent plate. my opinion of course.
the aisi specification includes provisions for takign into account the strengthening affect of cold-working.  the idea they use is basically an increase in the design yield stress depending on such and such equations, geometry and steel used.  i don't know how well that would apply though to thick   
the strain hardening effect would be just right at the bend line, so it wouldn't strengthen the overall section equally.  i would ignore that effect.
in many cases, overall strength will be based more on elastic properties, anyway.
you might also reconsider your overall cross-section.  could you just form a single wide u-shape or c-shape or some other section that has equalivalent sectional properties, but is made from just one piece?
calculate the bent plate section properties, preferably inclucing the radius. the previously alluded to, aisi manual has really easy formulas for this.
i would skip any effect of cold work of forming. i know for a fact that at least one of the major metal building manufacturers doesn't even use this and we all know how competitive they are!
dbd
agreed - use the actual bent profile shape and ignore any strain hardening effect in the truss calcs.
make sure however that you do not weld of drill in the zone of possible strain hardening as the relaxation of residual stresses could generate a stress concentration and possible brittle fracture mechanism.
given that the material is still basically a steel, i'd be inclined to think that strain hardening effects would genuinely be small.