inertia

1. MOMENT OF INERTIA OF
STANDARD SECTIONS

2. Moment of Inertia of
Standard Sections
The previous presentations defined moment of inertia and
the determination of moment of inertia for simple and
composite shapes. However, most construction is with
'standard sections' or 'standard structural shapes'
Both phrases typically refer to common structural steel
sections, but can also be used to define common aluminum
sections
2
Standard sections are
defined by the industry.
The common I-beam,
hollow circular tube,
hollow square tube,
and L-sections are
amongst the definition
of standard sections.

3. Moment of Inertia of
Standard Sections
Historically, wooden beams of any shape were built-up
onsite. As such, the idea of a standard section was never
really applied to structural shapes derived of wood material.
However, this has changed in recent years. Laminated
sections are available with standardized dimensioning.
3
To date, standard wood sections
are glued I-beam sections often
used as joists.

4. Standard Section
For our purposes, we will define a 'standard section' in terms
of a structural steel section. According to Wikipedia,
structural steel may be defined as follows:
Structural steel is steel construction material, a profile,
formed with a specific shape or cross section and certain
standards of chemical composition and mechanical
properties. Structural steel shape, size, composition,
strength, storage, etc., is regulated in most industrialized
countries.
Although this definition is for structural steel, structural
aluminum section may be similarly defined.
4

5. Standard structural shapes are designated with an alphanumeric
string that defines the shape, the depth (height) of the shape, and
the weight of the shape per unit length. Common alpha
designations are:
S – Standard section with sloped inner flanges
W – Wide flange section with parallel flange surfaces
ST, WT, MT – A T-section cut from a W-, S-, or M-Section
HP – Bearing Pile section with parallel flange surfaces and equal
thickness of flange and web
C – Channel section with sloped inner flanges
L – Angle sections (equal or unequal legs)
M – Miscellaneous I-beam section
MC – Miscellaneous channel sections
HSS – Hollow Structural Section. May be an RSS, CSS, or SHS for
rectangular, circular, and square structural sections respectively. These
designations are used frequently in the UK.
Structural Shapes
5

6. European standard sections carry different designations. They are
dimensioned in millimeters rather than inches and weighed in kilograms
per meter rather than pounds per foot. Typical designations are:
IPE – Parallel flange surfaces, height of 80 to 600 mm
IPN – Flange has 14% inner slope, height of 80 to 600 mm
HE – Wide flange, parallel flange surfaces, height of 100 to 1000 mm
HL – Extra wide flange, parallel flange surfaces, height of 920 to 1100 mm
HD – Wide flange column section,
parallel flange surfaces, section height of 260 to 400 mm
HP – Wide flange bearing piles, parallel flange surfaces, height 200-400 mm
L – Angles (equal and unequal length legs)
UPE – Channel with parallel flange, depth 80 – 400 mm
UPN – Channel with tapered flange, depth 80 – 400 mm
U – Channel with tapered flange, depth 40 – 65 mm
Structural Shapes
6

7. Examples of designations are:
W18x119 – A wide flange section with a nominal depth* of 18
inches and a weight of 119 lbs/ft
C15x50 – An American Standard Channel with a nominal depth of
15 inches and a weight of 50 lbs/ft
L6x4x7/8 – An American unequal leg angle with legs of 6” and 4”
and a thickness of 7/8”
UPN 100** - A European Channel with tapered flanges and a
depth of 100mm
L20x20x3 – A European angle with equal length legs of 20mm
and a thickness of 3mm
* The height of a section is referred to as depth
** Unlike American designations, European designations include only nominal height,
and do not reference weight. The sole exception are angle sections which are
designated in a manner similar to American designations.
Structural Shapes

8. Moment of Inertia of
Standard Sections
Since standard sections have defined geometry
as well as metalurgical properties, all of these
properties can be and are tabulated as
handbook data.
This data includes geometric dimensions as
well as elastic design properties, many of which
you will not use until a strength of materials
course. The elastic properties listed will include
the moment of inertia of the section.
Abridged tables are included in the appendix of
this online text. You can also visit
http://www.structural-drafting-net-expert.com/
for additional information on structural sections.

9. 9
Moment of Inertia of
Specialized Sections
Specialized industries
may also have 'standard'
sections for use within the
industry. For example, in
the marine industry, mast
and boom sections and
their properties are made
available to naval
architects for use in their
designs.

10. 10
Moment of Inertia of
Laminated Wood Sections
The same holds true for laminated wood sections. Although
moments of inertia still need be calcuated for unique sections,
'standard' sections are available with their properties as shown
in the table below.

11. 11
Examples for Moment of Inertia
In the end, moments of inertia for standard sections are
provided in handbook data and from the manufacturer. You
can simply look them up and apply them as appropriate
However, many structural sections are built-up from standard
sections. This is the topic of the next module