My Bridge

For my physics class, I need to make a bridge to support quite a bit of weight. We must use balsa wood and only glue as an adhesive. Also, the bridge can't way anymore than 100 g total. I'm not that far into the process. I have created a diagram with all the measurement for each piece and I started making the base of the bridge. I'm planning to make a Warren Truss bridge with 5 supports underneath to help even out the pressure and help absorb the the compression from the weight. There are two things that I'm worried about. One of them is not going over 100 g. And the other is hoping my bridge won't break before the competition. Other than those two things, I feel pretty confident with my designs.

Bridges

There are four key structural components that a bridge must have: beams, arches, trusses, and suspensions.

1. The beam is the base of the bridge where the cars would drive over. A beam bridge would look like this:

2. The arch distributes compression and diverts weight onto the two column making the arch. An arch bridge looks like this:

3. Trusses provides a more rigid structure and it also helps distribute the weight load more evenly.  Truss bridge look like this:

4. Suspensions are ropes or cables that hold up the roadway. A suspension bridge would look like this:

Bridges all have to deal with two problem: tension and compression. When cars or other weights are placed on a bridge, they compress the bridge downward due to gravity. Therefore, as the bridge is compressed down, it is pulled both ways by the structures at the end and the bridge's tension increases. The tension increasing could be related to tug-of-war game where both sides are pulling at the rope.

Static Equilibrium

Static Equilibrium is a physics term used to refer when the total amount of force acting upon an object adds up to zero. It could be related to a tug-of-war game. In tug-of-war, both sides pull the ropes toward themselves, but if both sides pull with the same force, the rope won't move. Static equilibrium doesn't mean there aren't any force acting on the object, it just means the forces are balanced.

As you can see, both sides pull with the same force, and as a result, the rope doesn't move.

The static equilibrium can be found using a force table. Force tables use vector forces to balance a ring in the center of the table. Someone is able to find the static equilibrium using trigonometry and Pythagorean Theorem given two forces and two angles. A more detailed lab of this procedure could be found here. Anyway, when the ring is not touching the center piece, it has reached static equilibrium.