Mini project For M.tech Structural Engineering Deflection of Simply supported thin Rectangular...
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Transcript of Mini project For M.tech Structural Engineering Deflection of Simply supported thin Rectangular...
Deflection of Simply Supported Thin Rectangular
Plates
Contents1. Introduction of Plates2. Navier’s Method (Double
Series Solution)3. Levy’s Method (Single Series
Solution)4. Comparision of Navier’s and
Levy’s Method5. Conclusion
ABSTRACT When a plate introduced to external load
will have a deformation out of its own plane.
comparison of simply supported plate deformation using Navier’s solution and Levy’s Solution
Plates• A plate resists transverse loads by
means of bending, exclusively.• Plates may be classified into three
groups according to the ratio a=h, where a is a typical dimension of a plate
in a plane and h is a plate thickness.
Classification of Plates• Thick Plates - having ratios a/h 8 . . .10• Membranes - with ratios a/h 80 . . . 100• Thin Plates - Intermediate type of plate, a/h with 8 . . . 10 a/h 80 . . . 100.Depending on the value of the a/h.
Thin Plates• Thin plates are initially flat structural
members bounded by two parallel planes, called faces, and a cylindrical surface, called an edge or boundary. The generators of the cylindrical surface are perpendicular to the plane faces. The distance between the plane faces is called the thickness (h) of the plate
Behavior of Plates• The behavior of plates is similar to that of
beams. They both carry transverse loads by bending action. – Plates carry transverse loads by bending and shear
just like beams, but they have some peculiarities– We will focus on isotropic homogenous plates.
x
yzSimply supported edges
Sim
ply su
ppor
ted
edge
s
Behavior of Plates
x
yzSimply supported edges
Sim
ply su
ppor
ted
edge
s
q Plates undergo bending
which can be represented by the deflection (w) of the middle plane of the plate
u
vw
w(x,y) w(x+dx,y)
w(x+dx,y+dy)w(x,y+dy)
w/x
w/y
The middle plane of the plate undergoes deflections w(x,y). The top and bottom surfaces of the plate undergo deformations almost like a rigid body along with the middle surface.
Bending of a plate• A plate has a wide cross section
- top and bottom edge of a cross section remain straight y-parallel axis when Mx is applied
• When a plate is bent to a cylindrical surface, only Mx acts:
)1(12)1( stiffness Bending
0 0 0
2
3
2
2
2
2
2
2
2
EtEID
yw
yw
xwM xyx
Assumptions :Linear thin plate theory is developed under
the following assumptions: • The plate thickness, t, is much smaller
than the plates dimensions in the x-y-plane.
• Small deformations (less than 0.3 times the thickness).
• The plates material is linear elastic, homogeneous, and isotropic.
• Example :- • A rectangular plate of sides a and b is
simply supported on all edges and subjected to a uniform pressure P as shown in Fig. To Determine the maximum deflection using Navier’s Method and Levy’s Method.
• This solution method can be used for a plate that is pinned along all edges. The method gives the displacement function from an arbitrary distributed load.
1 . NAVIER’S METHOD (DOUBLE SERIES SOLUTION)
• this method can be used on a plate with pinned edges.
• The boundary conditions can then be formulated as:
w = 0 and w,nn = 0 (or Mn = 0) on all edges.
1 . NAVIER’S METHOD (DOUBLE SERIES SOLUTION)
Deflection(w) and Moments(M)
Transverse Shear Forces(Q) & Effective Shear Forces(V)
1 . NAVIER’S METHOD (DOUBLE SERIES SOLUTION)
The method consists of a Fourier series development of an arbitrary load P Then displacement:-
1 . NAVIER’S METHOD (DOUBLE SERIES SOLUTION)
• When the displacement w(x,y) is known, inner moment, shear forces and stresses can be calculated. This calculation method has quick convergence for load distributions that covers the entire plate.
• And the method is well suited for solution on computers.
• Another approach was proposed by Levy in 1899. In this case we start with an assumed form of the displacement and try to fit the parameters so that the governing equation and the boundary conditions are satisfied.
2. LEVY’S METHOD(SINGLESERIES SOLUTION)
Contd.
• This method is used for plates with at least two pinned edges. The other two can have arbitrary boundary conditions.
• Presently we are considering simply supported conditions on four sides.
2. LEVY’S METHOD(SINGLESERIES SOLUTION)
Contd.
2. LEVY’S METHOD(SINGLESERIES SOLUTION)
Contd.
2. LEVY’S METHOD(SINGLESERIES SOLUTION)
Contd.
The general steps in Levy's solution is therefore:• Calculate the coefficients in the load Fourier
series.• Establish the particular solution for all m.• Superposition of the homogeneous and
particular solution.• The boundary conditions on all the sides with
arbitrary support to determine the constants Am, Bm, Cm and Dm.
2. LEVY’S METHOD(SINGLESERIES SOLUTION)
Contd.
The displacement function must also satisfy the differential equation for the plate, and the boundary conditions at y = 0 and y = b. To establish a solution, it is practical to divide the displacement function into one homogeneous solution and one particular solution: w(x,y) = wH(x,y)+wP(x,y)
2. LEVY’S METHOD(SINGLESERIES SOLUTION)
• After some calculations, you will end up with an expression for the displacement:
• The expression contains four unkown constants for each m, Am, Bm, Cm and Dm. The boundary conditions on the two sides with arbitrary support is used to determine these constants.
• The method has quick convergence, and few parts are needed to establish a good expression for w(x,y). If moment and stresses are to be determined with a minimal error, more parts must be taken into consideration.
2. LEVY’S METHOD(SINGLESERIES SOLUTION)
Contd.
• Consider a square plate under uniformly distributed load then the results are obtained from the following sheet as
COMPARISION OF TWO METHODS
Results by Navier’s Method – Table 1
COMPARISION OF TWO METHODS
m, n ValuesW max
Ʃm, n Values uptoAt (a/2, a/2)
1 4.8220 4.8220
3 0.0298 4.8518
5 0.0112 4.8630
7 0.0003 4.8633
13 0.0003 4.8648
15 0.0000 4.8648
17 0.0001 4.8649
19 0.0000 4.8649
Results by Navier’s Method – Table 1
COMPARISION OF TWO METHODS
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 250
10
20
30
40
50
60
Variation of Wmax with m&n values
m and n values X axis Deflection in mm in Y axis
Note :µ is taken to be 0.3.(x,y) locations are chosen correspond to maximum deflection or stress resultant.• It should be noted from this table that the
rate of convergence of the series is very fast for w.
Results by Navier’s Method
COMPARISION OF TWO METHODS
• The accuracy of the one-term approximation for Wmax is very good (error with respect to the converged solution is approximately 2.4).
Results by Navier’s Method
COMPARISION OF TWO METHODS
Results by Levy’s Method – Table 2
COMPARISION OF TWO METHODS
m, n ValuesW max
Ʃm, n Values uptoAt (a/2, a/2)
1 4.8118 4.8118
3 0.0527 4.8645
5 0.0000 4.8645
7 0.0000 4.8645
9 0.0000 4.8645
11 0.0000 4.8645
13 0.0000 4.8645
15 0.0000 4.8645
17 0.0000 4.8645
19 0.0000 4.8645
Results by Levy’s Method – Table 2
COMPARISION OF TWO METHODS
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 250
10
20
30
40
50
60
Variation of Wmax with m&n values
Values of m & n X axis Deflection in mm Y axis
Results by Levy’s Method
COMPARISION OF TWO METHODS
Note :µ is taken to be 0.3.(x,y) locations are chosen correspond to maximum deflection or stress resultant.
Results by Levy’s Method
COMPARISION OF TWO METHODS
Conclusion:• I want to conclude that a comparision of
the above results with those of Table 1 reveals the superior convergence of Levy’s Method compares to that of Navier’s Method ; accurate estimates of both deflections can be obtained hereby considering just the first few terms.
BIBILOGRAPHY
• Analysis of Plates by T.K Varadan & K.Bhaskar.
• Class Note Book• Guidance from V.Ramesh Sir.
Thank You