Selecting the correctly sizez steel I beam is very important for your
structural design. Gain more understanding of the selection procedure for a
steel I beam for given load specifications.
A steel I beam typically has the
following important features or dimensions. (Please refer to the picture below):
○ Flange thickness: Top and bottom horizontal plate-like sections of an
I-beam are called flangen.
The thickness of the flanges is called the
flange thickness.
○ Flange width: The width of the flanges is called flange
width.
○ Beam depth: The height between the top and bottom surface of the steel
I beam is called beam depth.
○ Web thickness: The vertical section of steel I beam is called web, and the thickness of the web is called
web thickness.
○ Fillet radius: The curved portion, where the transition between the web
and flange happens is called a fillet. The
radius of the fillet is called the fillet
radius.
The overall procedure of selecting
the correct size of the I beam is based
upon basic mechanical design calculations as follows:
○ The first input you need is the steel I beam
load specifications or loading details on the steel I beam.
○ Draw bending moment diagram for the given loads
and you will find the value of maximum bending moments (sayM)
that the steel I beam is expected to experience.
○ Choose an approximate size of steel I beam from
a standard I beam table.
○ Find out the area moment of inertia (say I) of
the selected steel I beam.
○ Get the beam depth (say d) of the
selected steel I beam.
○ Now use the following formulae for calculating
stress developed (f) in the beam:
f/(d/2)=M/ I
f is the bending stress
M - the moment
at the neutral axis
y - the perpendicular
distance to the neutral axis
I - the area moment of inertia about the
neutral axis x
○ Compare the calculated value of the bending
stress with the yield stress of the steel in order to check the safety factor
of your design.
Correctly sized I beam selection is
the first step toward correct structural design. The procedure explained above
is based upon static I beam load specifications. In the cases where dynamic
loads are involved, you need to use FEA tools like ANSYS, Pro Mechanica, etc.