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During the  summer of 2015 I taught an engineering class at Roosevelt H.S.

We started out with truss bridges.

Here's some basic terminlolgy:  the bottom part of the truss is called the bottom chord- shown here in blue.

The top chord (in red) goes along the top of the truss and than
angles down to meet the ends of the bottom chord

This through truss ( the cars, people, etc. go THROUGH  the truss) is made of thin strips of plywood connected at the joints with small nuts and bolts.

In trusses, the bottom chord is in Tension. That means it's being stretched. To show that, we replaced the center part of the bottom chord ( the plywood piece) with string and a turn-buckle.

For this through truss we used 2 lengths of thread for the middle of the bottom chord.

As the load increases and the threads stretch, they get tighter and the note they sound when plucked, gets higher.
We loaded the bridge to failure.

Next we built a deck truss- the deck is on top of the truss.

This cantilever bridge has a main span of almost 7 ft

Using just 1 tower of the bridge, we put a live load of 2 bricks on the end of the deck.

CRANES - We started off using this small crane.

The angle of the boom can be fixed at 30...45 or 60 degrees.

We used 2 cranes in tandem to make this lift.

Next we assembled this larger crane and tried to lift a pile of 19lb. concrete pavers, but without sufficient counter-weight, the crane started to tip over.

The kids learned the formula for TORQUE   Weight x Distance = Torque

Using this basic formula, we calculated the amount of counter-weight (and the distance from the pivot point) to ensure a safe lift of a 114lb. load

Now we felt we could lift Elias.

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