1. Humidity affects the weight of your bridge. Keep your bridge in a closed container with a few grains of rice.
2. Go easy with the glue bottle. As a general rule of thumb, if you can see it than you are using too much.
3. Keep your hands clean! Oils and grease from your skin [...]

Now Updated and Expanded
Now you can download the 5 Steps to Building a Model Bridge PDF ebook. The ebook contains the expanded version of the outline below, plus a lot of helpful pictures. The ebook also contains 25 bonus tips.
Here is a condensed version of the table of contents:
#1: Know the rules!

Be able to define [...]

I was first introduced to the Bridge Designer by a civil engineer, who explained to me the usefulness of the free program. However, it took me, a 6th grader at the time, over a year of playing around with it to finally figure it out.
Link to the Bridge Designer
The Bridge Designer allows you to create [...]

How Changing Height Affects a Bridge
I found it slightly difficult to come up with the right title for this post. Perhaps a better one is What happens when you change the height of a bridge assuming nothing else changes. I am talking about the forces that act on a bridge, of course.
I get asked all [...]

I was looking at my logs this morning, and noticed someone found my website by clicking a link from a Yahoo answers page. Curious, I went to the page. Someone was asking how to build a Popsicle Bridge. Two people had answered the question. The first person mentioned my website along with a complimentary description [...]

Science Olympiad is bringing back the Bridge Building event in 2009, except in a modified form. The event for ‘09 is Elevated Bridge, which will provide an interesting and refreshing challenge. The draft rules that soinc.org are very interesting and make for a good read. Check them out as the new bridge event looks to [...]

If you have visited my Projects page, you probably have seen the Fernbank Bridge. It is coming up on a year since I built that bridge. Original Fernbank Bridge Which means, it is about time to build a sequel. Unfortunately, the date for the Atlanta Toothpick Bridge Competition (where I test the Fernbank Bridge) and [...]

Compression:
Compression is a pushing (compressing) force. You can take the middle a straw and squeeze it between two fingers, the straw flattens. However, if you hold each end of a straw and push together it is harder to make the straw compress, or flatten. The shorter a piece of wood is, the more compression it [...]

I have become enamored with the idea of building a suspension bridge. I am not exactly sure why, and I also need to finish my toothpick bridge. However, I have begun thinking about how I would go about it.
A suspension bridge would be the most difficult challenge so far for me. I am thinking as [...]

Upon request, I have written an analysis of the K Truss which you can read about on my truss design page. The K truss design deserves your consideration as a bridge builder.

Lateral What? Exactly. Perhaps the most important aspect of your bridge and you aren’t sure what it is.

Lateral bracing is the term I use to refer to any pieces on a bridge that help keep the top chord from bending horizontally. In the figure before, lateral bracing is red:

Why is lateral bracing so important?
As you [...]

An L-beam is more efficient than a square the same width. It is not going to hold as much, but it is going to be more efficient. An L-beam is also more efficient than a square with the same mass of wood. Of course, you have to count in the glue weight for an L-beam.Balsa, [...]

Today I found out what exactly a pony truss is. I had heard the term before, but never understood what it meant.In fact, it is quite simple. A pony truss is a truss bridge which allows traffic through the truss, but the top of the bridge is not joined together with cross braces.
Example of [...]

Objective: To build a boomilever with the greatest efficiency.
Basic Design:
There are two basic types of boomilevers. First is the tension boomilever, where the tension chord is longer than the compression chord.

Second there is the compression boomilever, which is the opposite of the tension.

It is generally accepted that the tension boomilever is inherently better than the [...]

Question:
What’s your take on the new scoring. Do you think the bridge should just aim at holding 15 kg… or try to build one that’s lighter and hold less possibly getting a higher efficiency score?
I used to think that you should go lighter, holding less. But now I think that you should aim at [...]

My first event was Circuit Lab, which I don’t know much about. My partner ended up doing most of the work, I helped connecting wires when I could.Rocks and Minerals went okay, or so I thought. Ended up with 7th.

My tower broke too soon, weighing 6.5 and only holding 6.8kg. At least I worried McIntosh [...]

Today was our Science Olympiad regionals. Being busy all day, I didn’t get a chance to watch but two towers being tested. But there weren’t any terribly impressive ones there, mine being 8.6 grams, and the next 12.4.
There was one major complication. Instead of being provided with sand to load our towers as the rules [...]

Many people come to GarrettsBridges looking for advice on building a toothpick bridge. And though I have thought much about it, I have not attempted to build one yet.

This is a Japanese toothpick bridge contest. You will find tips on how to make them, as well as pictures.
Toothpick Bridge Building Contest
Here is a father who’s [...]

Common trusses used in engineering:
Warren

Pratt

Howe

K Truss

The following figures are shown under a load. The numbers represent percentage, where the total load = 100. The numbers are rounded to the nearest 5. For absolute numbers, visit the Bridge Designer.
Red represents tension, blue represents compression, and green is no load.

On this Warren truss, each of the [...]

Yesterday (Nov. 11, 2006) was the Science Olympiad competition, the Westminster Invitational. This has to be one of the earliest tournaments in Science Olympiad. Normally the invitationals aren’t until January.
The boomilevers there were not impressive (including mine). Only one boomilever had an efficiency score over 200, which did happen to be mine. I placed first [...]

Probably the question I get asked the most is “What bridge design holds the most weight?” or “What bridge design is the strongest?”

The answer to that question is not simple and probably is not going to be what you expect. The truth is, I cannot answer the question. There are too many variables that [...]