Stress Distribution in a Beam-Finite Element Method-Assignment Solution, Exercises of Mathematical Methods for Numerical Analysis and Optimization

This assignment solution was submitted to Amar Sharma for Finite Element Method course at Aligarh Muslim University. It includes: Stress, Distribution, Beam, Elements, Discretization, Structure, Variation, Field, Variable, Interpolation

Typology: Exercises

2011/2012

Uploaded on 07/08/2012

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(SOLUTION OF PROBLEM # 1.8)
PROBLEM #1.8
Find stress distribution in beam shown in figure (below) by using two beam elements.
SOLUTION
STEP 1: DISCRETIZATION OF THE STRUCTURE
In this step, we discretize the given structure so that we may apply interpolation model on each
of the part to get the variation of field variable within the domain.
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(SOLUTION OF PROBLEM # 1.8)

PROBLEM #1.

Find stress distribution in beam shown in figure (below) by using two beam elements.

SOLUTION

STEP 1: DISCRETIZATION OF THE STRUCTURE

In this step, we discretize the given structure so that we may apply interpolation model on each of the part to get the variation of field variable within the domain.

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Desretized beam is shown below,

STEP 2: SELECTION OF A PROPER INTERPOLATION OR DISPLACEMENT

MODEL

In this step, we choose a suitable model which represents the behavior of solution in the given domain. Let us assume a solution of the following type,

STEP 3: DERIVATION OF ELEMENT STIFFNESS MATRICES AND LOAD

VECTORS

From the displacement model given above, we derive stiffness matrix and load vector. For this,

Potential energy of beam is given by,

---------------------------------------- (1)

Where,

Where π is the strain energy given by,

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Then equation (3) becomes,

Now, simplify the above equation, we get

Now, writing the above equation in matrix form, as under

Where,

Now, we have to calculate all the entries of the above matrix,

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Similarly second term,

Similarly, all other terms are calculated below,

Now, put all these values in equation (6), we get

And equation (5) then becomes,

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And global load vector,

Put all above values in equation (7), we get

STEP 5: SOLUTION FOR THE UNKNOWN NODAL DISPLACEMENTS

From figure, we can see the following boundary conditions;

W 1 =W 2 =W 5 = W 6 =0. V 1 = V 3 =0, M 1 =M 2 = M 3 =0. Therefore,

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So the above matrix can be reduced to,

Now replace and and in above equation, we get

Simplify it, we get two equations

Solving above two equations simultaneously, we get

STEP 6: STRESS DISTRIBUTION IN BEAM

For bending stress induced at distance x from node 1and y from neutral axis is given by