Engr210 – Fall 2010
Lesson # 31: Centroids for Composite Sections
Today’s Objective:
a) Determine the location of
centroid for composite sections.
Instructor: Ahmed Abdel-Rahim
Page 1 of 2
Composite sections:
made up of connected “simpler” shaped parts
or holes [rectangle, triangle, circle, semicircle,
etc]
Composite sections
Knowing the location of the centroid, C, or
center of gravity, G, of the simpler shaped
parts, we can easily determine the location of
the C or G for the more complex composite
body
Using the equations:
x = ( Σ xi A i ) / ( Σ A i )
y = ( Σ yi Ai ) / ( Σ Ai )
The location of the centroid could be
determined
[Note: you could replace A with W, M, or L]
Procedures for the Analysis:
Divide the body into parts that are known
shapes. Holes are considered as parts
with negative weight or size.
Choose an origin and x and y coordinate
system [origin at the left bottom corner of
the shape]
Make a table to summarize the properties
of different parts
A
xi
yi
A xi A yi
A1
A2
A3
..
Σ A xi Σ A yi
Sum Σ A
Using values at the last row of the table
find the x and y for the whole section
Examples
Engr210 – Fall 2010
Lesson # 31: Centroids for Composite Sections
Example
Instructor: Ahmed Abdel-Rahim
Page 2 of 2