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Section 2
2-31
It can be mentioned here that AASHTO does not have a
provision for increase in allowable stresses for a secondary
member and when 1/r exceeds a certain value.
Bending Stress
Allowable stress in bending compression for rolled shape girders
and built-up sections whose compression flanges are supported
laterally through their full length by embedment in concrete is
given by
FF
by
=
055.
For similar members with unsupported or partially supported
flange lengths, the allowable bending compressive stress is given
by
2
6
50 10
0.772 9.87 0.55
yc
b
cz y
xc yc
I
xC
Jd
FF
Sl I l
⎛⎞
⎛⎞
=+
⎜⎟
⎜⎟
⎝⎠
⎝⎠
≤
Due to inadequate information in the AASHTO Code, the
allowable tensile stresses due to bending for both axes are set to be
the same as the corresponding allowable bending compressive
stresses.
Shear Stress
Allowable shear stress on the gross section is given by
FF
vy
=
.33
For shear on the web, the gross section is defined as the product of
the total depth and the web thickness. The AASHTO code does not
specify any allowable stress for shear on flanges. The program
assumes the same allowable for shear stress (0.33Fy) for both
shear on the web and shear on the flanges. For shear on the
flanges, the gross section is taken as 2/3 times the total flange
area.