We run a competition here at Albury High in Australia for our Yr 12 Engineering Studies students involving max. 50 popsicle sticks, PVA wood glue and 2m of extra strong thread. Structures have to span 400mm and are centrally loaded. Here’s a photo of our 2010 winner which weighed in at 69 grams and held 58kgs giving an efficiency using the formula on your website if I used it correctly of around 12000!

Thanks for sharing the photo.

The efficiency equation works like this:

Take the mass held: 58kg and covert it to grams, 58,000g. Then divide that by the mass of the bridge: 69g. That equals 841.

Yeah Garrett i dont really understand what you just said can you explain that?

The bridge efficiency is the ratio of the mass supported to the mass of the bridge.

mass_supported / mass_of_bridge = efficiency

In this case:

58000 / 69 = 840.58 efficiency

This is different to the original posters claim of 12,000 efficiency.

The use of string/thread in this design is a major structural element.

That is so cool but do you know if you can make one of those out of 200 pop sicle sticks.

this bridge is friggen awesome. I was surprised to see how many popsicle sticks you used and how much weight you put on there.

Hi, would you be able to show me some ropes as to how I can build a bridge like yours? For instance, what do I have to take into consideration in order to be able to build a strong bridge? Would appreciate it very much for your help. Thanks.

I’ve seen 5 level Baily bridges from WW-II that supported Sherman tanks using the same general design principals. Heavy cables where supported at the center by a built-up underside structure, as this level of arching was not possible. Still, the cables added hugely to the strength of the structure.

A 12,000 ratio would require it to hold 828kg, or 1,821lbs.

Wow Garrett,

just revisited the original post. Thanks for the correction. How did I get that so wrong! Lots of excitement at the time maybe.

I have since been building to a set weight of 22grams over a 600mm span. I find the efficiency formula a bit simplistic so include a % adjustment to any variation from the set weight. If the bridge is lighter I multiply the efficiency index by the % under 22grams and add. If the bridge is heavier than 22grams I minus it. This brings the efficiency results of the average performers back to a closer contest.

WHat does the string thread do for the bridge?

The string keeps the bottom of the arches from spreading out and breaking. Without this string, the bridge would be a lot weaker.