b b b
SOLUTIONS
, Contents
Preface ............................................................................................................................. iv
1. Vectors, Tensors, and Equations of Elasticity............................................... 1
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2. Energy Principles and Variational Methods ............................................. 19
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3. Classical Theory of Plates ................................................................................51
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4. Analysis of Plate Strips ................................................................................... 59
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5. Analysis of Circular Plates ............................................................................. 75
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6. Bending of Simply Supported Rectangular Plates ................................ 91
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7. Bending of Rectangular Plates with Various
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Boundary Conditions ......................................................................................... 99
b
8. General Buckling of Rectangular Plates ................................................... 115
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9. Dynamic Analysis of Rectangular Plates ................................................ 123
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10. Shear Deformation Plate Theories ............................................................ 129
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11. Theory and Analysis of Shells ..................................................................... 139
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12. Finite Element Analysis of Plates .............................................................. 157
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, 1
Vectors, Tensors, and b b
b Equations of Elasticity b b
1.1 Prove the following properties of δij and εijk (assume i,j = 1,2,3 when they are
b b b b b b b b b b b b b b b b b
dummy indices):
b b
(a) Fijδjk = Fik b b
(b) δijδij = δii = 3 b b b b b
(c) εijkεijk = 6 b b b
(d) εijkFij = 0 whenever Fij = Fji (symmetric) b b b b b b b
Solution:
1.1(a) Expanding the expression
b b b
Fijδjk =Fi1δ1k + Fi2δ2k +Fi3δ3k
b b
b
b
b
b
b
Of the three terms on the right hand side, only one is nonzero. It is equal to Fi1 if
b b b b b b b b b b b b b b b b b b
k = 1, Fi2 if k = 2, or Fi3 if k = 3. Thus, it is simply equal to Fik.
b b b b b b b b b b b b b b b b b b b b
1.1(b) By actual expansion, we have
b b b b b
δijδij = δi1δi1 + δi2δi2 + δi3δi3
b b
b
b
b
b
b
= (δ11δ11 + 0 + 0) + (0 + δ22δ22 + 0) + (0 + 0 + δ33δ33)
b b b b b b b b b b b b b b b
=3 b b
and
δii = δ11 + δ22 + δ33 = 1+ 1+ 1 = 3
b b b b b b b b b b b b b b b
Alternatively, using Fij = δij in Problem 1.1a, we have δijδjk = δik, where i and k are
b b b b b b b b b b b b b b b b b
free indices that can any value. In particular, for i = k, we have the required result.
b b b b b b b b b b b b b b b b b
1.1(c) Using the ε-δ identity and the result of Problem 1.1(b), we obtain
b b b b b b b b b b b b
εijkεijk = δiiδjj − δijδij = 9 − 3 = 6 b
b b b b b b b b b b b
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, 2 Theory and Analysis of Elastic Plates and Shells b b b b b b b
1.1(d) We have b b
Fijεijk = −Fijεjik (interchanged i and j)
b b b b b b
=−Fjiεijk (renamed i as j and j as i) b b b b b b b b b
Since Fji = Fij, we have
b b b b b
0 = (Fij + Fji)εijk
b b b b b
= 2Fijεijk b
b
The converse also holds, i.e., if Fijεijk = 0, then Fij = Fji. We have 0 =
b b b b b b b b b b b b b b b
b
Fijεijk b
b
1
= (Fijεijk +Fijεijk)
2
b b
b b b
b
1
= (Fijεijk − Fijεjik) (interchanged i and j)
2
b b b b b b b b
1
b
= (Fijεijk − Fjiεijk) (renamed i as j and j as i)
2
b b b b b b b b b b b
1
b
= (Fij − Fji)εijk
2
b b b b
b
from which it follows that Fji = Fij.
b b b b b b b
♠ New Problem 1.1: Show that
b b b b b
∂r xi
= b
∂xi r
Solution: Write the position vector in cartesian component form using the index
b b b b b b b b b b b
notation
b
r = x j ê j (1) b b
Then the square of the magnitude of the position vector is
b b b b b b b b b b
r2 = r ·r = (x i ê i ) ·(xj ê j ) = xixjδij
b b b b b b b b b b
= xixi = xkxk
b b b (2)
Its derivative of r with respect to xi can be obtained from
b b b b b b b b b b b
∂r2 = ∂
(xkxk)
∂xi ∂x
∂xik ∂xk
= x +x b
b
b b b b
∂xi k k ∂x
i b b b
∂xk
=2 xk = 2δikxk = 2xi b b
b b b b
∂xi
Hence
∂r xi
= b (3)
∂xi r
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