When axial loads due to torsion (ie. warping torsion) are included in
equation H1-3, to which allowable stresses should these stesses be compared?
Are they compressive stresses or flexural stresses?
From: Charlie Carter [mailto:carter(--nospam--at)aiscmail.com]
Sent: Monday, August 27, 2001 12:27 PM
Subject: RE: ASD biaxial bending allowable stress
>When calculating biaxial bending in
>beams, we generally use equation H1-3:
>fa/FA + fbx/Fbx + fby/Fby = 1.0
>which in many cases, allows us to
>use 0.66Fy as Fbx and 0.75Fy as Fby.
>However, we've recently reviewed calculations
>where Fbx and Fby are 0.60Fy,
>no matter what the compact length
>attributes of the beam are.
>Is the 0.6Fy in biaxial standard?
No. The ratios in the interaction check represent the percentage of the
total member strength used up by each component of the load. The strengths
(FA, Fbx and Fby, in this case) used in this check must each be calculated
as though the member were subject only to that individual component of the
total load. So the unbraced length will very much affect what column-only or
beam-only equation must be used.
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