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Attached is a paint file, Just imagine the bottom leg to be an arc.It buckles a lot during testing, but always manages to stay in tact until about 14kg. The way I make it, it is around 9-10 g.

I cannot visualize this... picture? creative drawing in Paint?

embokim wrote:Attached is a paint file, Just imagine the bottom leg to be an arc.It buckles a lot during testing, but always manages to stay in tact until about 14kg. The way I make it, it is around 9-10 g.

I cannot visualize this... picture? creative drawing in Paint?

I dont think an arc on the bottom is a good idea. This is because ideally you want to make your bridge top loaded, which means the bottom beam is under tension. Since the bottom beam is under tension you want to make it straight not curved. It seems odd to me that it worked better for you, maybe it had something to do with the cross beams connected to the bottom.

I made a slot in the bridge to allow for the loading block assembly to fit. The entire bridge is an elongated pyramid and the curve when pressure is applied to the top, naturally tries to revert back into a straight angle. The top of the triangle holds the arc back and thus allows for a load to be placed onto the bridge.

Use
a triangle
because it is
the strongest design
out of all of the designs
that I and my partner have tried.

XplodingCesium wrote:Use
a triangle
because it is
the strongest design
out of all of the designs
that I and my partner have tried.

Lovely poem! We need to have a forum for all the SciOly poets.

embokim wrote:hello, i have been recently trying out a new design, a triangle topped bridge but on the bottom instead of a straight line to connect the two legs of the triangle it is a curve. It has been working like magic, any thoughts?

I would suggest you do some research on the engineering principles involved in bridges... Identify which members are in compression, and which are in compression, then determine if the bottom chord should be arched or not.

I have done my research and I have consulted a structural engineer and according to him, this design is pretty accurate

embokim wrote:I have done my research and I have consulted a structural engineer and according to him, this design is pretty accurate

It sounds to me that your confidence in this design is pretty high, so you do not need our buy-in or approval... That being said, generally the top chords are considered to be in compression, as the load is applied to the top of them. A bridge MUST be in equilibrium, so this means that the bottom chord must then be in tension. That being said, if a member is "pulled" on both ends, a curved member would not be the most efficient design.

Now there are ways to reverse this premise, so that the compression members are on the bottom, where a curve could possibly work, ... but most involve some sort of buttress into the existing structure, which is not allowed in this competition. In any case, good luck with your design... Hope it holds the family Volkswagon!

dholdgreve wrote:

embokim wrote:I have done my research and I have consulted a structural engineer and according to him, this design is pretty accurate

It sounds to me that your confidence in this design is pretty high, so you do not need our buy-in or approval... That being said, generally the top chords are considered to be in compression, as the load is applied to the top of them. A bridge MUST be in equilibrium, so this means that the bottom chord must then be in tension. That being said, if a member is "pulled" on both ends, a curved member would not be the most efficient design.

Now there are ways to reverse this premise, so that the compression members are on the bottom, where a curve could possibly work, ... but most involve some sort of buttress into the existing structure, which is not allowed in this competition. In any case, good luck with your design... Hope it holds the family Volkswagon!

I would agree with dholdgreve. Also, I will add that arcs of any sort are almost impossible to build well with balsa (notice: I did not say impossible- it is possible, just exceptionally difficult). I would stray from arcs- you can have very, very successful bridges without any sort of arc.

JonB wrote:

dholdgreve wrote:

embokim wrote:I have done my research and I have consulted a structural engineer and according to him, this design is pretty accurate

It sounds to me that your confidence in this design is pretty high, so you do not need our buy-in or approval... That being said, generally the top chords are considered to be in compression, as the load is applied to the top of them. A bridge MUST be in equilibrium, so this means that the bottom chord must then be in tension. That being said, if a member is "pulled" on both ends, a curved member would not be the most efficient design.

Now there are ways to reverse this premise, so that the compression members are on the bottom, where a curve could possibly work, ... but most involve some sort of buttress into the existing structure, which is not allowed in this competition. In any case, good luck with your design... Hope it holds the family Volkswagon!

I would agree with dholdgreve. Also, I will add that arcs of any sort are almost impossible to build well with balsa (notice: I did not say impossible- it is possible, just exceptionally difficult). I would stray from arcs- you can have very, very successful bridges without any sort of arc.

I dont think any of the top 5 bridges at nats ever had arcs, but I guess there's a first time for everything.