Marshmallow Bridge Design Report

MARSHMALLOW BRIDGE DESIGN REPORT

Andra, Ibram, Naomi, Shannis

10 Centaurus

Physics

Summary

A bridge is a structure that provides a way across which connects two places which is originally seperated by water or lands with different heights. A bridge can be made of different materials. The materials are chosen based on their capability to change their shape whe there is a force acting on it. Bridges can be made of stone, wood, concrete, steel and bricks.

A bridge can stay standing. It can be explained by Newton’s Three Laws of motion which are:

1.    An object with a constant velocity or at rest will remain that way unless acted upon by unbalanced forces

2.    F=ma

3.    “To every force and action, there is an equal and opposite reaction”

Compression is a pushing force. It pushes an object in order to compress or shorten it. Tension is a pulling force. It is when two forces pull or move against each other to stretch the object. Shear force is 2 forces that acts on a thing in the same point but are put in different directions. Torsion is a force that causes the object to twist because it is a rotating force.  

There are several types of bridge. The early bridges are the beam bridges. It was usually made of wood from trees that have fallen. The main types of bridge are: Arch, Truss, Suspension, Beam and Cable-Stayed bridge.

This time, we are going to make a strong bridge which will stand still and powerful eventhough there are forces acted on it. Our bridge will be made out of toothpicks and marshmallows. The marshmallows will functioned as a glue in the connecting point of each toothpick.

We choose to make a Truss Bridge. Truss bridge is a bridge that has triangular units which are joined together  that create the skeleton of the bridge. There are several types of truss bridge: Allan, Howe, Pratt, Bailey, Warren, and King Post truss bridge. The truss bridge that we made is a simple truss bridge which is the Warren truss bridge. The Warren Truss Bridge is lightweight yet strong and is easy to build.

It looks like this:

So, this is our design:

= Marshmallows= Toothpick

Ensuring that the marshmallows connect the toothpicks strongly is important. The toothpick must have the same length to help the bridge to stay firm and balance when a certain amount of  forces are acted on it.

Introduction

In this bridge design, we decided to make “Warren truss bridge.” It’s a bridge that have a “X” design on the left and on the right side of the bridge. “X” design means that it has a brace on the two sides to make the bridge become stronger. The “X” design makes the bridge become stronger ever two times more stronger than the usual brace. Moreover, we’re going to make the bridge using toothpick and marshmallow. Our objective is to make a strong and powerful Warren Truss Bridge that is able to stand still when there are forces (Compression, Tension, Torsion and Shear) are acted on it.

Like what we said before, Warren Truss Bridge is lightweight yet strong, but easy to make. But, to make this bridge we need to connect a lot of toothpicks using the marshmallows and basically when one toothpick falls or disconnected then it will be hard to reconnect it again and it will affect the whole toothpick connection in the bridge to be weaker.

We actually thought of making a suspension bridge before, but we think that it is more complicated and it will not be strong enough. But, we decided to make a Warren Truss Bridge. We also think of an alternative design which is still a truss bridge but it is a different type which is the Howe Truss Bridge that looks like this:

We thought that the Howe Truss Bridge design may also be strong enough because there are vertical toothpicks that hold the triangles.

Our Bridge:

Discussion

The theory behind the creation of a truss bridge actually uses a few assumptions and the appliences of newton’s laws of motion according to the branch of physics known as statics. The problems that we encountered while constructing the bridge wass when we were about to attach the toothpick to the marshmallow, and we were having a hard time in getting the bridge standing firmly, based on the result, we analyzed that the bridge needs more marshmallow in order so that the bridge were able to stand firmly and indestructible when a compression and torsion happens,   so we were able to overcome this problem by attaching a bigger marshmallow to the toothpicks.

Conclusion

We tried to make the bridge using the “Warren truss bridge” design. We tried applying the compression and tension force by pressing the bridge from the top side. We tried applying the torsion force by twisting the bridge.

The result is not satisfying. The bridge cannot stand properly. The bridge is very fragile and it is destroyed. We cannot lift it up because the marshmallow were sticked on the paper/table and if we take it off, all the toothpicks will be detached.

We think that it is actually right to choose “Warren truss bridge” because it is a strong and good design, but the bridge can be destructed by the forces because the way we make the bridge is wrong. The connection point between the toothpicks are not strong enough. We should have used half of the marshmallow for the glue instead of using 1/4th of the marshmallow. We think the marshmallow was not too sticky and not strong, that is why the bridge did not stand properly. Maybe we should have used the Howe Truss Bridge design because it has vertical poles that will hold the triangular units of the truss bridge.

This Warren Truss Bridge is a good design. This kind of bridge will be useful when we want to connect places in short distance. With Truss Bridge, we can obtain high strength of the bridge using simple elements. The concept of this bridge also can be modified, it can be combined with design of arch bridge and it will make that bridge stronger. An example of it in real life is the Sydney Harbour bridge. In the future, trusses can be useful for railway bridges.

Trusses are an efficient bridge design.

Appendices