What type of bridge would work best?

Question

I need to build a truss bridge out of balsa wood.
It needs to span a distance and I need a design that supports the most weight relative to how much the bridge itself weighs.
The weight is going to all be distributed in the middle.
Please tell me what types of trusses are the strongest, and what types would work best for my situation.

My teacher said I can't use and arched bridge.
All parts have to be straight and supported with trusses.

So I can't steem and bend the wood or anything like that.

Answer 1

An arch truss is also called a bow truss. Read up on trusses, there are a lot of cool websites out there. The biggest thing to remember, is that the strength for bending is acheived by increasing the distance between the top cord and the bottom cord, so the further the two are apart, the more it resists bending.
The maximum bending stress occurs at mid span.

The other force you have to resist is shear. The shear forces are resisted by the diagonals of the truss. The maximum shear force occurs at the ends of the truss.

Answer 2

I think you be best using an A frame truss. The weight should be distributed to the ends of the truss where there is support base, not the middle. I assume you are allowed to use some glue and some base material as a footing. I remember my design took up to 65kg before the footing broke loose. The truss design basically looks like an 'A'. The load is applied to the top of the 'A' and transmitted to both legs. I think the span was 1m.

Answer 3

Use triangle shapes for strength and weight distribution. The triangle, when used in bridges, roll-cages, tube-chassis, skyscraper skeletons, etc. are extremely strong.

For a bridge center, the arch is the best. Look at old Roman aqueducts - the arch is extremely strong.

So, when making a bridge, make an arched center that is braced with triangles. Most small/medium bridges use these designs until you get into the very long bridges - then suspension is required.

Answer 4

Well its definately not a suspension bridge or cantilever bridge. How ever a typical arch bridge will have the road deck "hung" underneath the arch very much like the sydney harbour bridge. For the picture you have referenced it has dosent have the deck "hung" thus it casn be argued that it is a truss bridge. There is no rules limiting the shape of a truss bridge to the traditional box shape, but can be a range of shapes.

Answer 5

go to physics 24/7 or yahoo answers to get an answer I can help you only this much don't just expect so much from me I' not einstein or something. what are you thinking?