bme204_supplement lecture on moment of inertia
Post on 08-Mar-2015
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Geometric Properties of Plane Areas
-From Appendix C of CD- centroids
- second moment of area (i.e. moment of inertia, polar moment of inertia)
-second moment of inertia about inclined axis-parallel axes theorem
- Mohr’s circle method for MOI skipped
First Moment of Area-Centroid
First moments of area:
Centroids: zandy
First Moment of Area-Centroid
• Composite areas– Subdivide– Select coordinate axes– Find the overall area– Apply the composite
centroid formula
Second Moment of an Area
Moment of inertia, appear in the bending of beams
Polar moment of inertia appear in the torsion of beams
Second Moment of and Area• Moment of inertia of a rectangle
Second Moment of an Area• Polar moment of inertia of a circle about its center
Second Moment of an Area• Parallel axis theorem: shift the coordinate axis away
from the centroid, what will be the new MOI?
Second Moment of an Area• Calculate the MOI wrt y’.
Second Moment of an Area
• Composite areas– Subdivide– Establish centroidal
reference axis for each subdivision
– Apply parallel axes theorem for each division
– Sum them up
(Iy)i
Second Moment of an Area
• Product of inertia: required in the bending of asymmetric beams
Parallel axis theorem
Composite areas
For the rectangle about y-z axes:
Second Moment of an Area
• Moment of inertia about an inclined axis
2sin2cos22' yz
zyzyz I
IIIII
Second Moment of an Area
• Principal moments of inertia: the angle at which formulations in the previous slide for primed axes attain a minimum and a maximum.
Second Moment of an Area
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