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8/14/2019 Chapter 8 PVR
http://slidepdf.com/reader/full/chapter-8-pvr 1/34
C h a p t e r 8
D E
F L E C T
I O N S D
U E T O
B E
N D I N G
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C o n t e n t s :
T h e m o m e n t c u r v a t u r e r e l a
t i o n
I n t e g
r a t i o n o f m o m e n t c u r v
a t u r e r e l a t i o n
P r i n c
i p l e o f S u p
e r p o s i t i o n
L o a d
- d e f l e c t i o n
d i f f e r e n t i a
l e q u a t i o n
E n e r g y m e t h o d s
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D e f o r m a t i o n o f a n e l e m e n t o
f a b e a m s u b j e c t e d
t o b e n d i n g m o m e n
t s M
T h e m o m
e n t c u r v a t u r e r e l a t i o n :
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( 8 . 2 )
( 8 . 1 )
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( 8 . 3 )
( 8 . 4 )
M o m
e n t c u r v a t u r e r e l a t i o n
W h e r e E I i s f l e x u
r a l r i g i d i t y
o r b e n d i n g
m o d u l u s f o r b e a m
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I n s o l v i n g b e a m d e f l e c t i o n p r
o b l e m w e w i l l
u s e t h e
t h r e e s t e p
s o f ( 2 . 1 )
S t u d y
o f e q u i l i b r
i u m t o o b t a
i n M b a s a
f u n c t i o n o f x
M o m e n t c u r v a t u
r e r e l a t i o n g i v e s
a p p r o x i m a t e c u r v a t u r e a s a f
u n c t i o n o f x
I n t e g r a t i o n o f t h e m o m e n t c
u r v a t u r e
r e l a t i o n
g i v e s t o t a l d e f l e c t i o n
a l o n g x . T h e
g e o m e t r i c c o m p a t i b i l i t y w i l l b
e h e l p f u l t o
g e t
t h e c o n
s t a n t s o f i n
t e g r a t i o n .
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F i x e
d s u p p o r t
M
b ≠ 0
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S i m p l y s u p p o r t e d b e a m ( a ) b e f o r e a n d ( b )
a f t e r a p p l i c a t i o
n o f l o a d
W E X . 1
F i n d t h e d e f l e c t i o n
c u r v e
o f t h e d e f o
r m e d
n e u t r a l a x i s
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F r e e b
o d y d i a g r a
m o f b e a m
a n d s e g m e n t
o f b e a
m
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E x p r e s s i o n f o r b e n d i n
g m o m e n t
u s i n g s i n g u l a r i t y
f u n c t i o n
( a )
D e f l e c t i o n c u r v e
f o r n e u t r a l a x i s o f
t h e b e
a m
( g )
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E x . 2 A w o o d e n b e a m w i t h a m
a x i m u m
c o n c e n t r a t e d l o a d a t t h e c e n t r
e h a s f o l l o w i n g
s p e c i f i c a
t i o n s . F i n d
m a x i m u m
d e f l e c t i o n a n d
s l o p e
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r a d
E I
W
m m
E I
W
L
d x d v
L
x L x
0 0 4 2
. 0
1 6
(
0 0 5 1 8
.
0
4 8
2
0
3
2
) )
(
− =
−
=
−
=
−
= =
=
ν
( g )
T h e m a
x i m u m d e f l e c t i o n a n d
s l o p e i s
g i v e n b
y
T h e d e f l e c t i o n c u r v e
f o r a b e a m
i s g i v e n b y
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( 8 . 4 )
M o m e n t c u r v
a t u r e r e l a t i o n
I n
s o l v i n g b e
a m d e f l e c t i o n p r o b l e m
w e h a v e u s e d t h e t h r e e s t e p s o f ( 2 . 1
)
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E x . 3 F i n d t h e d e f l e c t i o n
δ a n d t h e
s l o p e a n g l e φ
a t B d u
e t o t h e s e l o a d s .
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F . B . D i a g r a m o
f e l e m e n t
( a )
1 ) E q u i l i b r i u m r e q u i r e m e n t
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2 ) F o r c e
d e f o r m a t i o n r e l a t i o n
( b )
3 ) G e o
m e t r i c c o m
p a t i b i l i t y
( c
)
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T h e d e
f l e c t i o n δ a
t B i s
( g )
T h e s l o p e φ a t B
i s
( h )
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S u p e r p o s i t i o n
T h e t o
t a l d e f l e c t i o n i s t h e s u
m o f d e f l e c t i o n s
d u e t o i n d i v i d u a l l o a
d ( M )
T h e d e f l e c t i o n s i n t h e s t a n d a r d c a s e s a r e
g i v e n i n t a b l e 8 . 1 . T
h e s o l u t i o n
o f t h e o r i g
i n a l
p r o b l e m
t h e n t a k e s
t h e f o r m o f a s u p e r p o
s i t i o n
o f t h e s e s o l u t i o n s .
D e f l e c
t i o n o f a b e a m i s l i n e a r l y p r o p o r t i o n a l
t o t h e a p
p l i e d l o a d .
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T h i s l i n e
a r i t y d e p e n
d s o n t h e f a c t t h a t w e
a r e
c o n s i d e r i n g l i n e a r e
l a s t i c m a t e
r i a l
M o m e n t – c u r v a t u r
e r e l a t i o n s . ( a ) L i n e a r ; ( b )
n o n l i n e a
r
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T h e l i n e a r i t y b e t w e e n
c u r v a t u r e
a n d d e f l e c t i o n
i s b a s e d o n a s s u m p t i o n t h a t
D e f l e c t i o n s a r e s m
a l l
m a t e r i a l i s l i n e a r l y
e l a s t i c
T h e l i n e
a r d i f f e r e n t i a l e q u a t i o n f o r d e f l e c
t i o n i s
( 8 . 4 )
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F i n d t h e d e f l e c t i o n
a t t h e f r e e
e n d
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I l l u s t r a t i o n o f s u p e
r p o s i t i o n p r i n c i p l e
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R e f e r r i n g t o t a b l e
T h e c o m
p l e t e d e f l e
c t i o n c u r v e c a n b e
o b t a i n e d b y a d d i n g
d e f l e c t i o n s a s f u n c t i o
n
o f x
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T h e L o
a d – D e f l e
c t i o n D i f f e
r e n t i a l
E q u a t i
o n
A n a l t e r n a t i v e m e t h o d t o s o
l v e b e a m
d e f l e c t i o
n p r o b l e m
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• A u n i f o r m
c i r c u l a r
b a r o f l e n g
t h L a n d d
i a ‘ d ’
e x t e n d
s b y a n a m o
u n t ‘ δ ’ u n d e r a t e n s i l e p u
l l ‘ p ’ .
F i n d t h
e m a x i m u m
d e f l e c t i o n i n t e r m s o f ‘ δ
’ a n d
‘ p ’ , i f t h e b a r i s u s e d a s a s i m p l y s u p p
o r t e d
b e a m a t i t s e n d s a n d c a r r y i n g a
c e n t r a l l o a d
‘ w ’ .
• A l s o
f i n d
t h e r a t i o
‘ ν ’ m a x
/ δ
, i f L = 8 0 d
a n d
M a x i m u m
b e n d i n g
s t r e s s d u e t o ‘ W ’ i s e q u a l t o
0 . 9 t i m
e s t h e t e n s i l e s t r e s s d u e
t o p u l l ‘ p ’ .
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