Why do engineers love bridges? They're outstanding in their field.
Why do engineers love bridges? They're outstanding in their field.
Bridges built from interconnected triangular elements, combining strength and material efficiency.
Total in US
7,293
Poor Condition
38.1%
Avg Sufficiency
45.7
Average Age
83 yrs
Truss bridges use a framework of interconnected triangles to distribute loads efficiently, making them one of the most versatile and widely-used bridge designs in history. The triangle is the simplest geometric shape that cannot be deformed without changing the length of its sides, making it inherently rigid. By assembling many triangles together, engineers create a structure that is both strong and lightweight.
Truss bridges dominated American bridge building from the mid-1800s through the mid-1900s, and thousands of them still serve highways and railroads across the country. They come in many configurations named after their inventors or structural characteristics: Pratt, Warren, Howe, Parker, Camelback, Pennsylvania, and K-truss designs each have distinct patterns of diagonal and vertical members.
The two main categories are deck trusses, where traffic passes over the top of the truss framework, and through trusses, where traffic passes between the trusses on either side. Through trusses are particularly distinctive, with their overhead bracing creating a tunnel-like passage that many travelers find memorable.
A truss works by converting the bending forces that would exist in a simple beam into tension and compression forces in individual members. The top chord of a truss typically experiences compression, while the bottom chord is in tension (for a simple span). The diagonal and vertical web members transfer forces between the chords, with each member carrying either pure tension or pure compression depending on its position and the loading pattern. This is remarkably efficient because each member can be sized precisely for the force it carries. Engineers analyze trusses by examining the equilibrium of forces at each joint (node) where members connect. The result is a structure that uses far less material than a solid beam of equivalent strength, making trusses economical for spans of 30 to 150 meters.
During World War II, the U.S. Army's Bailey Bridge, a portable prefabricated truss bridge, was considered one of the most important inventions of the war. General Eisenhower called it one of the three most important tools for winning the war, alongside the jeep and the C-47 aircraft.
Astoria-Megler Bridge (Oregon/Washington)
Huey P. Long Bridge (New Orleans, LA)
Commodore Barry Bridge (Pennsylvania/New Jersey)
Francis Scott Key Bridge (Baltimore, MD)
Ikitsuki Bridge (Japan, longest continuous truss)
Quebec Bridge (Canada, longest cantilever truss span)
| Rank | State | Count | % of Type |
|---|---|---|---|
| 1 | Ohio | 925 | 12.7% |
| 2 | Iowa | 646 | 8.9% |
| 3 | Nebraska | 576 | 7.9% |
| 4 | New York | 470 | 6.4% |
| 5 | Pennsylvania |
There are 7,293 truss bridges in the United States.
Iconic bridges with a deck hung from cables draped over tall towers, capable of spanning enormous distances.
Modern bridges where cables run directly from towers to the deck, creating a dramatic fan or harp pattern.
One of the oldest bridge forms, using a curved structure to transfer loads outward to abutments at each end.
The most common bridge type in America, using horizontal beams supported by piers to carry the deck.
| 455 |
| 6.2% |
| 6 | Missouri | 331 | 4.5% |
| 7 | Indiana | 287 | 3.9% |
| 8 | California | 276 | 3.8% |
| 9 | Oklahoma | 208 | 2.9% |
| 10 | Washington | 184 | 2.5% |