Shear Area Calculation
For rolled I and H sections the shear area is calculated as follows:
 Load Parallel to Web: A_{v,z} = max(A  2*b*t_{f} +
(t_{w} + 2 r)*t_{f}, η*t_{w}*h_{w}) (as it is
defined in EC3Part 1.1 §6.2.6(3))
NOTE: The η factor in the above equation is defined in National Annex. However,
the value of 1.2 is recommended
for steel grades up to and including S460 according to EC3Part 1.5 §5.1(2)
Note 2.

Load Parallel to Flanges: A_{v,y} = 2*b*t_{f} (conservative
assumption)
Section Classification
Four classes of crosssections are defined, as follows (EC3Part 1.1 §5.5.2(1)):
 Class 1: crosssections are those which can form a plastic hinge with the
rotation capacity required from plastic analysis without reduction of the resistance.
 Class 2: crosssections arc those which can develop their plastic moment resistance,
but have limited rotation capacity because of local buckling.
 Class 3: crosssections are those in which the stress in the extreme compression
fibre of the steel member assuming an elastic distribution of stresses can reach
the yield strength, but local buckling is liable to
prevent deve lopment of the plastic moment resistance.
 Class 4: crosssections are those in which local buckling will occur before the
attainment of yield stress in one or more parts of the crosssection.
The classification of a crosssection depends on the width to thickness ratio of the parts
subject to compression. Compression parts include every part of a crosssection which is
either totally or partially in compression under the load combination considered.
The various compression parts in a crosssection (such as a web or flange) can, in general,
be in different classes. A crosssection is classified according to the highest (least favourable)
class of its compression parts. Exceptions are specified in §6.2.1(10) and §6.2.2.4(1).
The following table defines the maximum widthtothickness ration for
both internal parts and outstand flanges in compression.
Maximum widthtothickness ratios for compression parts 
Class 
Internal compression parts (Web) 
Outstand flanges 
Subject to Compression 
Subject to Bending 
Subject to Compression 
1 
c_{w} / t_{w} ≤ 33ε 
c_{w} / t_{w} ≤ 72ε 
c_{f} / t_{f} ≤ 9ε 
2 
c_{w} / t_{w} ≤ 38ε 
c_{w} / t_{w} ≤ 83ε 
c_{f} / t_{f} ≤ 10ε 
3 
c_{w} / t_{w} ≤ 42ε 
c_{w} / t_{w} ≤ 124ε 
c_{f} / t_{f} ≤ 14ε 

c_{w} = h  2*(t_{f} + r) 
c_{f} = 0.5*(b  t_{w})  r 
ε = (235 / f_{y})^{0.5}, where f_{y} in MPa

f_{y} 
235 
275 
355 
420 
460 
ε 
1.0000 
0.9244 
0.8136 
0.7480 
0.7148 
References
 EN 199311 (2005). Eurocode 3: Design of steel structures.
Part 1.1: General Rules and Rules for Buildings.
CEN, European Committee for Standardization, Brussels, Belgium.
 EN 199311 (2005). Eurocode 3: Design of steel structures.
Part 1.5: General rules  Plated
structural elements.
CEN, European Committee for Standardization, Brussels, Belgium.
 Anwar N. and Najam F.A. (2017).
Structural Cross Sections (Analysis and Design), ButterworthHeinemann,
ISBN 9780128044438.