Why do engineers love bridges? They're outstanding in their field.
Why do engineers love bridges? They're outstanding in their field.
The most common bridge type in America, using horizontal beams supported by piers to carry the deck.
Total in US
241,624
Poor Condition
8.2%
Avg Sufficiency
62.8
Average Age
47 yrs
Beam and girder bridges are the workhorses of the American transportation system. They are by far the most common bridge type in the United States, accounting for a significant majority of all bridges in the National Bridge Inventory. The design is straightforward: horizontal beams or girders span between supports (piers and abutments), and the road deck sits on top of or is integrated with these beams.
The simplicity of beam bridges makes them economical to design, build, and maintain. They are the default choice for highway overpasses, river crossings under about 60 meters, and interchange ramps. Steel I-beams, prestressed concrete girders, and steel plate girders are the most common structural elements, with prestressed concrete becoming increasingly dominant due to its low maintenance requirements.
While individual beam spans are limited, multi-span beam bridges can cross considerable distances by using a series of piers. The Interstate Highway System relies heavily on beam bridges, and motorists cross dozens or even hundreds of them during a typical long-distance drive without giving them a second thought.
A beam bridge works through bending resistance (also called flexure). When a load is placed on the deck, the beam bends slightly, creating compression in the top flange and tension in the bottom flange. The beam's cross-sectional shape (typically an I-shape for steel, or a bulb-tee for prestressed concrete) is optimized to resist these forces efficiently, with material concentrated in the flanges where stresses are highest. The deeper the beam, the greater its spanning capacity. Simple span beams rest on supports at each end, while continuous beams extend over multiple supports, which reduces the maximum bending moment and allows for more efficient use of material. Composite construction, where the concrete deck acts together with the steel or concrete beams, significantly increases strength and stiffness.
The Lake Pontchartrain Causeway in Louisiana, at 23.83 miles long, is one of the longest bridges in the world and is essentially a continuous beam bridge with over 9,000 concrete spans. It takes about 30 minutes to cross, and for 8 miles in the middle, you cannot see land in any direction.
Lake Pontchartrain Causeway (Louisiana)
Chesapeake Bay Bridge (Maryland)
Seven Mile Bridge (Florida Keys)
I-10 Twin Span Bridge (Louisiana)
Governor Thomas Johnson Memorial Bridge (Maryland)
There are 241,624 beam/girder 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.
Bridges built from interconnected triangular elements, combining strength and material efficiency.
| 10,267 |
| 4.2% |
| 6 | New York | 9,035 | 3.7% |
| 7 | North Carolina | 8,616 | 3.6% |
| 8 | Kansas | 8,365 | 3.5% |
| 9 | Pennsylvania | 7,878 | 3.3% |
| 10 | Illinois | 7,872 | 3.3% |