Your browser does not support inline frames or is currently configured not to display inline frames. If you have 3" diameter logs, multiply all dimensions by 3 and dimensions will be in inches.
If you have 10cm diameter logs, multiply all dimensions by 10 and dimensions will be in centimeters. I used Basswood on this bridge because at the time, I believed basswood was inherently better than Balsa.
Just recently I got the bridge out and decided to test it again just to see how it would do.
Hey I have to wonder, being tested so many times, do you think possibly that the joints are weakened?
I’m new to bridge building, but I noticed that you said the bridge pictured spanned 35 cm. I was wondering if you thought a arched bridge like this was better than a rectangle like shape with a lot of equilateral triangles? The trick with bending balsa is to use thin strips laminated together to make a curved beam, rather than trying to bend a thicker beam. My arch bridge used an inverted arch under the load bed for the main beam (smile instead of frown), with warren-like truss members from each load point on the road bed to the beam. The following year I used a *very* simple, *very* light simple beam design that scored 2150 even though it always broke under a light load. My friend and I have been trying to make a bridge that can hold max weight and be at most 15g for an efficiency score of 1000. The bottom of this bridge is mostly empty because it only needs to hold weight at the very center.
Keep in mind that the Science Olympiad bridge rules change every year, so the what designs worked well back in 2005 may not work in following years. Also check or your rule book, as they may have differing info from the SciOly wiki.
So is the top chord made from 3 strips of bass wood laminated together and then bent or is it a single piece that was steamed and bent?

Hi Garrett, What is the highest efficiency you have heard for a 35 cm span, 5 cm min width, 15 kg max load bridge? My Science Olympiad Bridge team it trying to replicate your bridge on a larger scale (using 50 cm on the bottom), and wanted to consult you to find a good height for it, and how to spread out the supporting pieces accordingly. These bridge kits are complete as listed, with all required hardware, ready to just bolt together. I probably could have shaved off a couple grams and the bridge still would have held the entire weight. And if you were to rebuild the bridge using balsa (and test it) That i would do much better, considering that it is new built and the structure has not been weakened yet? This puts the longer arch member in tension and the shorter, straight loadbed member in compression. If I had to build it again, I would make the bottom chord smaller, and maybe make the top T Beam smaller as well. I’ve heard of great bridges built entirely from Bass, and others entirely from Balsa.
For most cases, you won’t need the strength of ProBond in SO, so I would stick with the CA glue. This bridge had an additional piece of wood that was glued to the inside of the bottom chord (1 on each side) that the loading block sat on.
We cracked some numbers, and came up with a length x width x height of 50 cm x 5 cm x 8.5 cm, with our total arch rounding out at 54 cm and having our supporting pieces every 3 cm apart from each other as they spread out on the sides. In order to post comments, please make sure JavaScript and Cookies are enabled, and reload the page. All the truss members held spread the load from the load point to various points on the arch. I could have taken off most of the weight on the arched chords, but also some on the bottom tension chords.
My wife won’t let me test it to failure though, she thinks of it as permanent decoration. These values don’t match, and I was wondering if the span and length of a bridge were different things.

I want to cut down on weight by making the bridge as narrow as possible, but at the same time, I don’t want my bridge to be unstable laterally and tip over on either side.
The national winner from the same year as this bridge was around 7.5 grams if I remember correctly. I’m making a bridge for Science Olympiad and was hoping to make something of this design since it seems to be extremely powerful.
I attemped to make a souped-up version of this bridge after the competition, but my enthusiam gave out and I never finished it. If the loading block sits on something glued to the bottom of the bottom chords, that would be very weak. This gives the bridge a new efficiency score of 1920, which is quite a bit better than before. This allowed the edges of the bridge to rest on the supports, with a little less than 1cm of overlap on each side. Similarly, it is very important to build your bridge perfectly vertical, with no lean at all. It increases the stiffness of a beam by having a larger cross section in both the x and y axis while cutting weight compared to a square beam. The best I had personally was the bridge on this page, although after this I stopped working on SO bridges.
I now have tested this bridge six times, and it is still going strong.And since the bridge is not broken, I may try and test it further later on. It may be able to get a score of close to 2500, which would put it close to the national winning bridge back in 2004.

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  1. SEQAL

    Collection for use by school and college students residence 2 hand-crafted projects from this begin out.


  2. killer457

    Does not must be entered every time.