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Truss Calculations with MD Solids

Enter the Enter the information into information into MD Solids. Before MD Solids. Before you press you press “Compute” , try to “Compute” , try to predict which predict which members are in members are in compression and compression and which are in which are in tension.*tension.*

*If necessary, refer to the wide variety of “MD Solids Help Documents” *If necessary, refer to the wide variety of “MD Solids Help Documents” included in the MD Solids software to help you get started.included in the MD Solids software to help you get started.

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Notice the gold Notice the gold colored members colored members labeled with a (C) labeled with a (C) are in are in compression, and compression, and the blue colored the blue colored members labeled members labeled with a (T) are in with a (T) are in tension. Did you tension. Did you guess correctly?guess correctly?

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Try to predict Try to predict which which members members here are in here are in tension and tension and which are in which are in compression.compression.

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The members in The members in purple are in purple are in neither tension or neither tension or compression. compression. Sometimes, Sometimes, additional additional members do not members do not help to support a help to support a load. These are load. These are called zero-force called zero-force members.members.

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Try to predict Try to predict which which members members here are in here are in tension and tension and which are in which are in compression.compression.

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Compare Compare your your predictions predictions with the with the solution.solution.

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Solve for the force in each member of the truss in this example to find whether the members are in tension or compression. Use MD Solids software.Start by replacing the supports with Start by replacing the supports with reaction forces:reaction forces:

A

C

3m

4m

D

B

3m

300 N

200 N

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Here the supports have been replaces with reaction forces:

6m

4m

CY

300 N

200 N3m

CX

AY

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This is how the problem looks when entered into MD Solids.

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The solution shows forces in each member and at each support.

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For of the following trusses:

1. Replace the supports with the appropriate reaction

forces.

2. Predict which beams would be in tension, which would

be in compression, and which would be supporting the

most force.

3. Draw the truss in MD Solids.

4. Record the forces at the supports and in each beam.

5. Were your predictions correct?

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• ••

• ••

• •

2 ft

2 ft

2 ft

• ••

#2#1

• •

3 ft

4 ft

• • •

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2 m

• ••

• ••

• •

3 m 3m

• • •

#4

• • • •

• ••

3 m

• •

4 m 4 m#3

* 1 KN = 1000N, therefore 5kN = 5000N

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Solution for #1

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Solution for #1

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Solution for #2

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Solution for #2

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Solution for #3

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Solution for #3

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Solution for #4

Solution for #4

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