Bentley 2006 User Manual

Section 2 

 

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 
 

F

F

b

y

= 0 55

.

 

 
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

⎛

⎞

⎛ ⎞

=

+

⎜

⎟

⎜ ⎟

⎝ ⎠

⎝

⎠

≤

 

 
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 
 

F

F

v

y

=.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.