If you are interested in learning more about trusses and truss design, check out Truss Fun, Second Edition from Amazon. I’m a fan of keeping things simple, but it is possible that your unique bridge project would benefit from one of the more exotic designs. You can do a web search for truss design and see many more examples. There are other, more complex, designs that aren’t shown here.
I have chosen to highlight these four examples of different trusses to get you started with some very solid examples that you can easily use on your bridge. Perhaps you will end up not using any of these designs but creating something on your own based on the principles of force transfer. Take some time to read up on each of these designs before deciding on one to use for your bridge. Each of these designs does that in a different way. As I mentioned earlier, the key for us model builders is how these designs transfer forces throughout the bridge and eventually to the bridge supports. Common trusses used in model bridge buildingĮach of the following truss designs are very common in both real and model bridges because of their sound engineering and ease of construction. This short section is meant to whet your appetite, but now we turn to the application of truss design to model bridge building. Both the Pratt and Howe patents were very much concerned about methodology of construction more so than the actual design.īridge history is fascinating, and there is so much more to learn. This is a bit of a mystery to me, but you can see semblances of the original designs in the modern depictions. These two designs, which you can see from the original patent images, do not look exactly like the truss designs that we associate with those names today. The Howe and Pratt trusses in particular were designed to incorporate iron rods in the truss. With iron and steel, and the expansion of railroads that carried heavier and heavier loads, new bridge designs were needed. Wood was the primary material available in these early years, but iron and then steel came along and changed everything. Skilled carpenters were needed, and most of the engineering was practical and not theoretical. Interestingly, building bridges in the 18th and early 19th century was more about quality of construction. These men came up with practical solutions for bridge building, and did not know or have access to the theory behind their designs. Theodore Burr came up with a design that was used in many iconic covered bridges, and some are still standing today. These men, along with other bridge builders who followed them, designed and built many bridges, especially in New England. Three names stand out as true pioneers in these early truss bridges: Timothy Palmer (1751-1821), Louis Wernwag (1770-1843), and Theodore Burr (1771-1822). The need for bridges to span longer distances in this era, as well as to hold increasingly heavy loads, brought about many creative solutions in the form of new truss designs. While trusses have been used for both roofs and bridges for many centuries, there was an explosion of truss advancement in the 19th century in America. Now let’s take a quick look at the history of truss design, particularly in the United States. These terms will be helpful to keep in mind as we talk more about truss design. You will see examples of the most common designs further on this page. The way these triangles are arranged or shaped is the essence of truss design. The truss members are simply an arrangement of triangles (most of the time) that transfer the force/s put on the bridge to the ground. Now we will add the truss members, which are shown in black in this diagram. Practically, you might use different sizes or shapes of wood for each of these parts due to the force being put on each part is different. This diagram shows the frame in an expanded view so you can easily see each part. The frame is made up of several parts: Top chord, bottom chord, and two end posts. The frame is the outermost parts of the truss.
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Let’s define a couple terms to help you understand how to study truss design.
Without a truss, you simply have a beam bridge. The purpose of a truss is to help a bridge support a load (car, train, person) from any point along the span of the bridge. A truss is typically made up of a lot of triangles, but some uncommon truss designs don’t have any. A “truss” is what you see when you look at a truss bridge from one of its sides.
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