New Bridge design – 553lb (695 efficiency)
By AndrewL on March 2, 2009 - Modified February 25, 2011
Youtube video of the bridge test
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can u make one for me? i buy it for 25 bucks
Short answer: no! We prolly put a good 20 hours into our project. I don’t usually work for $1.25 per hour. If you have a thousand US dollars or so, I’ll think about it.
g.
I’ll offer you the broken one, that only requires some minor repairs for $100.00 plus shipping.
Grant, it sounds like you and your son built a really nice bridge. Thanks for posting your results. Your offer to sell the bridge made me smile. Did you happen to take any pictures of your bridge?
Hi Andrew,
I just wanted to let you know that my son & I built a bridge based on your design. Despite using assembly jigs, and trying to assist my 8 year-old in weeding out the sub-par material, our joinery wasn’t quite as pretty as yours. (I couldn’t very well reject my son’s work based on quality – It was after all a 3rd grade science project.) However, that said I was astounded by the result. We used a hydraulic press to apply the load as opposed to dead weight, and we first mapped out all the losses in the press due to friction & return springs – e.g. we recorded sytem pressure throughout the entire press stroke in 1/4″ increments. We also measured the cylinder pos’n at point of failure, in order to determine how much pressure to subtract from our reading. Although, I accept some margin of error in our test methodology, and we didn’t use calibrated test gauges, our bridge withstood an effective pressure of 57 lb/in^2 (90 psig – 33 psi loss) from a 4 in. dia cylinder. (57 * PI * 2^2 = 716 lb!!!!) Our version had a span of 24.0 in., & weighed 0.681 lb, for an efficiency of 1051. Ours might have come in a tad lighter due to me belt-sanding off some of the “high spots” that I thot would interfere with lateral brace bonding, not to mention load distribution at supports & mid-span.
The primary failure was shearing of all lap glue joints between the bottom members & one of the “vertical” leg members. About 6-7 sticks from one of the outside laminations blew off, but the bridge still appeared more or less in tact after testing.
Of course, this project was perhaps a little advanced for a 3rd grade project, but both my 3rd grader, and 5th grader thot it was pretty cool, and I’m sure they learned that it is important “how one arranges material” in order to build a strong structure.
Cheers!
OK, drawings for this bridge are now available. You will need Google Sketchup to get the 3D drawing. Once you have Sketchup installed and running, go to the 3D Warehouse and do a search for “553lb”.
To those wanting to know what kind of bridge this is, I say this: you really need to study those text books a bit harder…
Wow this bridge is a very well built bridge. Do you have any plans for a First time bridge builder that can hold somewhere to 200lbs and up? My daughter seems to be really interested in building a bridge somewhat like this. Could you email me sometime at malcolm_andrews@verizon.net??
Hey,
Im a highschool student and I have to build a bridge for extra cedit to boost my mark from an a to a b, ANd i think this one is relaly cool, but I have to explain the physics of it, what kind of bridge is this?
Tell me, what kind of bridge this is. Arch? Cantilever? Beam? Suspension? Please tell me.
hey i am a student in tennessee and i was just wondering how did you plan this because i go to school and in my science class we are building a popscicle bridge and i have no idea what i am doing so i was wondering if you could give me some tips… like how to plan for building or some other kind of things that might help me..
Thanks for your help. Kayce.
What were the exact length measurements of your bridge ??
Overall length is 670mm. Distance between support points is 600mm. Height is 185mm. Width at widest point is 63mm (29 stick thickness).
Top member consists of:
14 sticks
13 sticks
14 sticks
15 sticks (centre)
14 sticks
13 sticks
14 sticks
Diagonal members consist of:
13 sticks
14 sticks
13 sticks
Bottom member consists of:
14 sticks
Vertical support members consist of:
13 sticks
14 sticks
Member construction uses a “comb tooth” design as can be seen from the photo/video.
Diagonal sticks are glued to the top member on both the top (6 sticks) and bottom (4 sticks) surface to provide improved rigidity.
It is also critical that the lower joint is reinforced with part sticks to create a strengthening plate effect.
The vertical members did not have diagonal bracing sticks (like the top member) and it should have – I think this was the initial failure point.
As can be seen from the video, the bridge test was subject to quite a bit of movement (swinging) in the load which does not work in the bridge’s favour.
Andrew
ok i see your bridge and i have been analyzing it for quite some time. now you said that you know how to imporve it if you build it again. how would you improve it? and where are the cross braces on this bridge but i don’t see any.
cheers
-john
Im building a bridge for the first time on thursday. No plans, no clue wat to do/where to start. But what kind of bridge is this? Beam? Cantilever? Help?
Sorry, don’t have plans for the bridge – but you should be able to figure it out from the photo.
Tried several ways to make the bridge. Ended up building it in sections:
1. Top span in two parts.
2. Vertical struts (x 2)
3. Diagonal braces (x 2)
Then it was a matter of assembling the bridge with “joiner” sticks.
Finally, added cut sticks to the lower joins for additional strength and added the cross braces.
Andrew
what was your building process? where did you start and what part did u finish?
Hey, brilliant work, do you have plans for this? i would be interested in having a look, and possibly modifying them for my own purposes.
Cheers
Andrew C.
Wow! 695 efficiency!!
Very very great work !!
how come can you create the design??
please describe how the weight distribution on it . . . .
thank you . . .
The rules for this bridge design were a 400gm maximum weight (this bridge was 361.6gm), and had to span 600mm. The test load was specified as 25mm square bar placed centrally. The design was made around this central load point, trying to optimise the useful lengths of the sticks.
The neat thing about the design is the construction which basically constructs open “boards” from the overlapping sticks, so the design can be easily analysed in 2 dimensions. As the overlaps between the sticks create a binding across the board, only minimal additional cross-bracing was needed.
You can see from the photo that the design is six sticks along the top member, one stick long at the bottom, with the diagonal tension members from the end support points to the bottom member three sticks long. The two upright support members (main compression members) are two sticks long.
The ends of the bottom member are a complex join between the three different members, so fillet plate sticks were added to provide additional strength.
If you think of the bridge as being built up in layers, there are 17 sticks per layer, plus the partial sticks used for the fillet, so say 17.5 sticks total per layer.
The number of layers can then be changed up to the weight limit of the bridge, allowing for a modest number of cross-brace sticks (10 in our case across the top member – 6 on top shown in the photo, 4 underneath).
This bridge design had 13 complete layers, plus another “half” layer to create an appealing symmetrical design. Total of about 261 sticks.
The failure point appears to have been the main upright compression members, which probably should have had a couple of sticks for diagonal bracing. It is hard to say what damaged was caused by the stress and what was caused by the falling bricks.
Andrew
Amazing!! good work guys