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I've built a number of models I use to teach engineering principles and applied math.

The 3-member truss................Method of joints and Free body diagram

Deck truss.................Method of Sections

Crane boom .............................Torque-- moment of force

This engineering model can be configured 3 ways.
1- as a beam, hinged at 1 end and supported by a cable at the other end-classic static problem.

Here the load is 46" from the pivot and the beam is at  31 degrees.

The cable goes over a sheave in the tower and connects to the load cell.

The windlass has an automatic brake so the beam can be safely raised to any angle and

A possible exercise might be : with a given load and beam angle and a 20 pound Tension

in the cable, what is the greatest distance from the tower the load can be placed ?

For another example go to ....Torque- Moment of force

2- As a cable-stayed bridge.  The deck is supported by 3 cables- either in a fan configuration

or a harp arrangement.

The tension in the 3 lines can be computed and then checked against the load cell.

The 3 lines can be linked to a single bar and then to the load cell

OR with more load cells, the Tension in each line can be read separately.

3- A bascule bridge - the deck is raised by the fall of 3 counter weight boxes.

The 3 ctwt. boxes are filled with enough scrap to overcome friction and inertia to start the lift.

As the deck rises and the distance from the CG of the deck to the tower decreases, so does

the required ctwt.

Then the lowest box hits bottom and its' weight is cancelled. The lift continues as the other boxes

hit bottom in turn and the deck rises smoothly.

The students can compute the moment are different deck angles.

Cantilever model.......................Cantilever bridges