Elevated Bridge B/C

[blue cobra]

Here is my new bridge.

The compression members with a green line next to them worry me. They don't really have anything to press against. Could making it one long piece, as indicated by the purple line, help?

Also, I was going to use paired strips of 1/32 bass for the tension members, gluing on the highest stressed pieces first. That means the middle piece gets glued on first, the the horizontal members next to it, then the near vertical ones above it, then the near vertical ones below it. Is it a good idea to stack this many pieces on top of each other? Also, I think I have 1/32 balsa. Should I use that for the near vertical members? And should I use balsa or bass for the spacers?

Thanks

[AlphaTauri]

The compression members with a green line next to them worry me. They don't really have anything to press against. Could making it one long piece, as indicated by the purple line, help?

I think that if you glue it solidly enough, you won't have a problem. I'm not sure that extending them would be the best idea because it seems that doing that would just add more stress to the middle of the legs, potentially making those give out earlier than they should.

[RandomPerson]

So I am back from my elevated bridge tryout, they had a written test based on the specifications (which I forgot to say you need to bring goggles, and I forgot to say the height of the loading block is 2cm) and I told the guy about my design which he called 'interesting' so hopefully it will do well on saturday when they said they would test it somehow.

[fmtiger124]

I also got the loading block size wrong...though I got it all wrong I said 4x4 random at least said 5x5 which is almost right. Though the really dumb mistake I made was when he asked me if a beam was tension or compression I said tension and now looking back it was really obviously compression.....nervousness I guess.

[sewforlife]

The compression members with a green line next to them worry me. They don't really have anything to press against. Could making it one long piece, as indicated by the purple line, help?

I think that if you glue it solidly enough, you won't have a problem. I'm not sure that extending them would be the best idea because it seems that doing that would just add more stress to the middle of the legs, potentially making those give out earlier than they should.

I think you're right, extending the piece might give more pressure to the side members.
cobra: I made a design almost exactly like that (I think the angles might be off by mere degrees) for states, and I built it with extended members, your "purple" pieces. I also made the main horizontal member two pieces of 1/8 by 1/8 laminated. It's efficiency was only about 200.

[nejanimb]

I love the idea of having a test on rule specifications. So important! It's very, very easy to make mistakes in Bridges, but there's no reason to do so.

Random, I really like your design. It looks like you do a very good job putting it together too. I actually think the single-piece legs could work quite well. I'm curious to hear how it goes!

Blue Cobra, are those tension members going to be used as all the same density or piece? From the lines you have, it seems like it'd be possible to have 3 tension members that simply cross at the nodes you indicated. One of my favorite parts of designing bridges is figuring out the layers. I loathe butt joints, and so a major part of my process is thinking about the different planes in which pieces exist to be joined together. I usually try to limit it to a maximum of 4 or 5 layers, but I think you have some interesting options with the truss design you have pictured. I disagree with your worry about the green highlighted pieces though. They definitely do have something to press against!

[AlphaTauri]

Meh, I don't really like the idea of testing people on the specs- that's what the rulebook is for. (Although, I could probably recite last year's specs from memory from staring at it for so long.)

I'm actually not competing in Bridge this year because I have 5 other events, but I can still help with questions.

[RandomPerson]

I love the idea of having a test on rule specifications. So important! It's very, very easy to make mistakes in Bridges, but there's no reason to do so.

Random, I really like your design. It looks like you do a very good job putting it together too. I actually think the single-piece legs could work quite well. I'm curious to hear how it goes!

Blue Cobra, are those tension members going to be used as all the same density or piece? From the lines you have, it seems like it'd be possible to have 3 tension members that simply cross at the nodes you indicated. One of my favorite parts of designing bridges is figuring out the layers. I loathe butt joints, and so a major part of my process is thinking about the different planes in which pieces exist to be joined together. I usually try to limit it to a maximum of 4 or 5 layers, but I think you have some interesting options with the truss design you have pictured. I disagree with your worry about the green highlighted pieces though. They definitely do have something to press against!

Meh, the good thing on the test about specifications is that it can weed out students who aren't cut for it, who didn't spend enough time on the event. But at the same time, it was kinda nitpicky, especially with the loading block, which didn't come up in my testing because of just building one side.
*shrugs*

Thanks btw, apparently they're testing them on the weekend, so I'll find out then. Looking at the other designs today (The bridges were left out in our head coach's room, who is also my chem teacher), mine is different for the rest, which could be a very good thing, or a not so good thing.

[sewforlife]

One of my favorite parts of designing bridges is figuring out the layers. I loathe butt joints, and so a major part of my process is thinking about the different planes in which pieces exist to be joined together. I usually try to limit it to a maximum of 4 or 5 layers, but I think you have some interesting options with the truss design you have pictured.

hmm. I like what you said about layering. A lot of people don't even see that when they first start building, but it's interesting to think about. All of my bridges have three layers, so that each layer is built around a central layer.

[lllazar]

Hello, im new to this forum and i had a few questions for u " pros"

1. What's a fixed node and rolling node?

2. How do i solve compression and tension (is there anything i can do to make the bridge stronger if i face this)

3. Is bass better for points of tension?

How much more does bass cost than balsa?

Thank you