cc205 5 combined direct bending stress-copy
TRANSCRIPT
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Combination of Direct Stress and
Bending Stress
CC205 MECHANICS OF STRUCTURES
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Introduction
Axial Load
Bending Moment
Body
Direct
Stress
Bending
Stress
Single
resultant
stress
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Eccentric Loading
A load, whose line of action does not coincide
with the axis of a column or a strut is known as an
eccentric load
A load imposed on a structural
member at some point other than
the centroid of the section.
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Columns With Eccentric Loading
Load P acts at eccentric, e
Load P causes moment (P x e)
and also produces bending stress
Where e is a distance from
centroid to the ecentric point
e
P
P
d
b
e
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Eccentric axial load
The combination of direct and bending
stresses is a result of eccentric axial load
Direct
Stress
A
Pd y
I
Mb
Bending
Stress Max/Min
Stress
min/max
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Eccentric axial load
yI
M
A
P
min/max
Moment caused by eccentric loading
ePM .
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Columns With Eccentric Loading about
One Axis
e
P
max min
y
x x
e y
P
A B
C D
The maximum
stress will be at
the corners which
near to the load
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Columns With Eccentric Loading about
Two Axes
e
P
ex = Eccentricity of the load of about x-x axis
ey = Eccentricity of the load of about y-y axis
y
x x
ey
ex
y
P
A B
C D
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y
x x
ey
ex
y
P d
b
b = width of the column section
d = thickness of the column
ex = Eccentricity of the load of about x-x axis
ey = Eccentricity of the load of about y-y axis
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Formulae
Bending stress about x-x axis
12
3bdI x
2
dy
xx ePM .
Bending stress about y-y axis
12
3dbI y
2
bx
yy ePM .
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Formulae
xI
My
I
M
A
P
yx
min/max
Combination stress about x-x and y-y axis
bybxd min/max
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Example on column
with eccentric loading
about one axis
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Example 1
A column with a cross section
width of 200mm and thickness
350mm, carries an eccentric
load of 20kN, 5mm from the
centroid as shown in figure
below . Determine the maximum
and minimum stress that occur
in the cross section.
e
P
350mm
200mm
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A rectangular column 200mm
wide and 150mm thick is
carrying a vertical load of
120kN at an eccentricity of
50mm as shown in Figure
below. Determine the maximum
and minimum intensities of
stress in the section
e P
150mm
200mm
Example 2
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A rectangular hollow column
has a cross section of 0.45m x
0.6m. An eccentric load of 2MN
is applied at an eccentricity of
100mm from the geometric axis
of the section. Calculate the
maximum and minimum stress
intensities in the section.
0.45m
y
x
0.3m
0.45m
0.6m
e
Example 3
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Example on column
with eccentric loading
about two axes
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A short column 800mm x
600mm is subjected to an
eccentric axial load of 60 kN
as shown in figure below.
Find the stresses developed
at each diagonal of the cross
section.
800mm
600mm 50mm
25mm
A B
C D
Example 4
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A short column 350mm x
500mm is subjected to an
eccentric axial load of 120 kN
as shown in figure below.
Find the stresses developed
at each diagonal of the cross
section.
Example 5
350mm
500mm
2cm
3cm
A B
D C
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End of Chapter