The Howe Truss was designed by William Howe in 1840. It used mostly wood in construction and was suitable for longer spans than the Pratt truss. Therefore, it became very popular and was considered one of the best designs for railroad bridges back in the day. Many Howe truss bridges exist in the North West United States, where wood is plentiful.

The Pratt Truss was designed by Thomas and Caleb Pratt in 1844. It became popular for railway bridges because it was able to have long spans. The Pratt has many variations, most with their own unique name. For instance, the Baltimore, Pennsylvania, and the Parker are all based off the Pratt.

The Warren Truss was patented by James Warren in 1848. It has been around a while. The Warren Truss uses equilateral triangles to spread out the loads on the bridge. This is opposed to the Neville Truss which used isosceles triangles. The equilateral triangles minimize the forces to only compression and tension. Interestingly, as a load (such as a car or train) moves across the bridge sometimes the forces for a member switch from compression to tension. This happens especially to the members near the center of the bridge.

A well done introduction to the practical steps of truss design. Written in 2004. It has 448 pages and has an average of 4.5 star rating on Amazon. Contains Illustrations. Here is the link to purchase this book at Amazon: Design of Building Trusses (Parker/Ambrose Series of Simplified Design Guides)

I am always on the look out for good software to help design model bridges. My latest find, Dr. Software, is a series of programs that allow you to customize a design, put a load on it, and see what happens. Dr. Truss comes in 2D and 3D options. You can also get Dr. Beam, which allows you to word with a beam and not a truss

The K Truss design was a variant from the Parker truss design. The Parker, in turn, came from the Pratt truss. The idea of the K truss is to break up the vertical members into smaller sections. This is because the vertical members are in compression. The shorter a member is, the more in can resist buckling from compression.

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 are not being defined.

All the time I am asked “How tall should I make my bridge?” This article will attempt to answer this question by illustrating a principle in model bridge building. There is no cut and dry answer, as you should evaluate your bridge specifications and guidelines and conduct experiments to reach the best answer for you. [...]

Learn all the main types of trusses used in real bridges, and see how to apply them to model bridges. Learn the history of each common truss design. This page is designed to help you make an educated decision about what truss design you should use on your bridge.

The Bridge Designer is perhaps the greatest online tool for building model bridges. It allows you to design a virtual truss, put a load on in, and it calculates how the forces are spread out. Amazing.