Bridges

History of bridges : Wooden Beam Bridge

History of bridges – The Stone Slab bridge

History of bridges – Iron and Steel

Roman Bridges

History of bridges – The Stone Arch bridge

The building materials

In this project you were asked to design and make a bridge structure which would support as much weight as posible.  These weights would be strong enough to destroy the bridge, by doing this the true strength of the bridge can be found as there is a ratio calculated camparing the weight of the bridge and the weight it take to destroy it.

The building materials were restricted to eight art straws, some masking tape and a glue gun. There was also a jig which was used to help form the structure and side cutters to cut the straws.

The building process

This is the main jig used to create the framed structure.  The dowel rod pins are removal, the structure is made around this frame and the top and bottom are secured by using either masking tape or the hot glue gun.  If the glue gun is used be careful that glue does not get onto you hands as it is very hot and will give a sore burn. 

If you get glue on your skin then cool the area down very quickly under running water, this should be kept there for about ten minutes.

The Testing

When the bridges were built they needed to be tested and this was done by adding weights to the frame to see how much it took before being destroyed.

The first thing to do was  weigh the bridge in gramms and then to test the bridges to see if they were able to take the weight of the 3 bolcks weighing 350g, 550g and 750g.

If the bridge was able to take the weight of the blocks without collapsing then further weights were put on top of the bridge to see how much the bridge would take before being destroyed.

The final destruction

The bridge was placed in a frame and the weights put on top. If it took all the blocks then extra weights were put on and the results were recorded.

A ratio of weight to destroy the bridge/weight of the bridge was found and this information was also recorded.

How important is triangulation in the building of a structure?

“If you do not think that building your structure in the form of triangles then just have a look at the image opposite.

To date the bridge with the larges ratio is one which weighted 5.8g and it took 10800 Gms to destroy it and that gives a ratio of 1862:1.

This is a bench mark for other to follow.  Call it the present school record.

Remember that this bridge is made of only paper straws and glue, nothing more and look how much weight it is taking.  Just imagine what a metal structure will hold made in the same way.

This should give you some reassurance of the strength of frame structures.