Truss Bridge School Project

[Jo_Burg]

Hi
I have to make a truss bridge from 30 wooden sticks 6mmx6mmx600mm.
the bridge has to span 650mm so our teacher recommended no less than a 700mm span. it can be no less the 100mm high or 50 mm wide.The bridge must hold a minimum of 30 kg though i am aiming for atleast 45. I was wondering if anybody on the forum had any ideas on how i could make this bridge as strong as possible within these constraints.
thanks for the help

[HurricaneHugo]

could have told us when it was due and what you had in mind and then we could have made suggestions, oh wells

[SHOFEAR]

Depends on where the load is being applied. Most "popsicle stick" bridge competitions apply the load on the top of the structure, not the deck surface. That basically forces you to design the bridge in a completely unrealistic manner because your not concerned about the load that can be carried by the bridge deck.

One thing to keep in mind is too avoid zero force members....which are basically T connections. They may seem to make sense, but when members are perpendicular to each other they can not spread the load because Force in the X and Y directions must be conserved.

If you really want to go balls out with it, download a basic structural program like S-frame and experiment by adjusting the orientation and placement of members to ensure each is carrying a load close to the failure point of the wood (i'm guessing Balsa).

[Jasonhouse]

Ha... I've won these sorts of contests every time I had one back when I was in school...

So the most important question from my perspective... What are the limitations on the types of glue you can use? Are there bonuses for making a particularly light structure that still holds up 30kg?

[mersar]

Originally Posted by SHOFEAR

Depends on where the load is being applied. Most "popsicle stick" bridge competitions apply the load on the top of the structure, not the deck surface. That basically forces you to design the bridge in a completely unrealistic manner because your not concerned about the load that can be carried by the bridge deck.

Yep, I learned that lesson the hard way in middle school. Came in under weight and it held the load fine when I had tested it on the deck, but the test in class put the load on the top and it crashed to the floor. It probably would have survived if it had been using popsicle sticks, but unfortunately the teacher decided that year that plastic straws were just as acceptable for the building material It's quite amazing how much bend some of the bridges that passed the test had in them.