Elevated Bridge B/C

[sewforlife]

I just tested my div. B bridge today.
The mass: 8 grams
It held: 8.5 kg
Approximate efficiency: 708.
!

The efficiency of your bridge is 8500/8 = 1062.5

oops. I corrected it. thanks for catching that.

[nejanimb]

From what you suggested before about your design, that 1/8 by 1/8 lamination is a piece in tension. That also would make sense if it broke when the glue came apart - I can imagine why it would begin to unglue if that piece was in tension.

Using that gigantic piece for a tension member seems like a bad idea. I think it's a bad idea to ever use anything laminated for tension, and I also don't think it's a good idea to use 1/8 by 1/8 in tension even non-laminated. I think if you changed that member, that might help your design a lot.

Do you have pictures of the bridge, before and after? One thing we've started doing this year too is to take video of the bridge tests. It's good not only to watch the frame-by-frame of the breaking point, but because you can scrub quickly through the whole test sequence. When you're watching the test, it's very hard to see what's happening since its all so slow. When you scrub quickly through the video in fast forward, you can see the bridge compressing under the weight - it's actually pretty cool - and see what parts are shifting around and where there is deflection.

[croman74]

just finished the second side of the bridge. Right now I'm looking at around a 14-15 gram bridge, which I'm pretty happy with at this point, because there are definitely areas where I could make the design lighter. I feel like it will be a pretty good bridge for the first bridge of the season.

[sewforlife]

From what you suggested before about your design, that 1/8 by 1/8 lamination is a piece in tension. That also would make sense if it broke when the glue came apart - I can imagine why it would begin to unglue if that piece was in tension.

Using that gigantic piece for a tension member seems like a bad idea. I think it's a bad idea to ever use anything laminated for tension, and I also don't think it's a good idea to use 1/8 by 1/8 in tension even non-laminated. I think if you changed that member, that might help your design a lot.

Do you have pictures of the bridge, before and after? One thing we've started doing this year too is to take video of the bridge tests. It's good not only to watch the frame-by-frame of the breaking point, but because you can scrub quickly through the whole test sequence. When you're watching the test, it's very hard to see what's happening since its all so slow. When you scrub quickly through the video in fast forward, you can see the bridge compressing under the weight - it's actually pretty cool - and see what parts are shifting around and where there is deflection.

thanks. I'm going to try building the next one without the lamination.

Is it just me, or my computer malfunctioning? Because I can't get my pictures uploaded.

[Bert92]

hey, im bert from pemberto twp high school in new jersey. i have been worrking on some designs for my bridge. anyone have any ideas or anything

[cypressfalls Robert]

What do you have so far, basic design?

[Bert92]

Yes,see im a steel fabricator and structual engineer so this comes easy to me, but i hit a major delimma, the measurment qualification changed and i dnt have the new ones

[cypressfalls Robert]

if you mean the dimensions thhen it should have a 45cm span, minimum height being 12.5 cm, max height being 20 cm and 5 cm bearing zone on both ends of the 45 cm span

[Bert92]

thank u. r u in the competition?

[croman74]

the clearance block is 30 cm wide and 12.5 cm tall