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Chapter 4 Centroid - Distr. Forces

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Chapter 4

Centroids &
Distributed forces
Introduction
 In the previous chapters we treated
all forces as concentrated along their
lines of action and at their points of
application.
 “concentrated” forces do not exist in
the exact sense, since every external
force applied mechanically to a body
is distributed over a finite contact
area, however small.
Introduction

Volume Distribution
Line Distribution Area Distribution
CENTERS OF MASS AND
CENTROIDS
 Center of Mass
Determining the Center of
Gravity
Determining the Center of Gravity
Centroids of Lines, Areas,
and Volumes
 Centroids of Lines
Centroids of Lines, Areas,
and Volumes
 Centroids of Areas:
Centroids of Lines, Areas,
and Volumes
 Centroids of Volumes
Sample Problem
Sample Problem
Sample Problem
Centroid of semicircular&
quarter-circular
Composite Bodies and
Figures; Approximations
Sample Problem
Sample Problem
Solution
Theorems of Pappus
A very simple method exists for calculating the surface area generated
by revolving a plane curve about a nonintersecting axis in the plane of
the curve
Theorems of Pappus
Theorems of Pappus
 Ifa line or an area is revolved
through an angle θ less than 2π, we
can determine the generated
surface or volume by replacing 2π
by θ
Sample Problem
 Determinethe volume V and surface area A of
the complete torus of circular cross section.
Sample Problem
 Calculate the volume V of the solid generated by
revolving the 60-mm right triangular area through
180 about the z-axis. If this body were constructed
of steel, what would be its mass m?
Solution
Beams—External Effects

Beams are structural


members which offer
resistance to bending
due to applied loads.
This analysis requires
the application of the
principles of statics.
Types of Beams
Distributed Loads
Sample Problem
 Determine the equivalent concentrated load(s) and
external reactions for the simply supported beam
which is subjected to the distributed load shown.
Problem 1
 Calculate the
supporting force
Ra and moment
Ma at A for the
loaded cantilever
beam.
Problem 2

 Determine
the reactions
at A and B for
the loaded
beam.
Problem 3

Determine the
reactions at A for
the cantilever
beam subjected to
the distributed and
concentrated
loads.
Problem 4
 Findthe reaction at
A due to the
uniform loading
and the applied
couple.
Problem 5
 Determine the
reactions at A and B
for the beam
subjected to a
combination of
distributed and point
loads.
Problem 6
Determine the force and moment reactions
at A for the beam which is subjected to
the load combination shown.

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