How to make a strong bridge

Think about what shape is the strongest:

In a movie I saw, it quoted "The strongest shape is a triangle".
Triangles are the strongest shapes in the world because. No matter how much weight you put on it, the force is equal on all three sides.

We will try to re-create a model from the internet

For our first design our bridge can only take 20 weights. For our last design we used an idea from the internet but we added a modification by us. The last design can hold 50 weights.

Here is the result of our bridge: