A bridge walked into a bar. The bartender said, 'Why the long span?'
A bridge walked into a bar. The bartender said, 'Why the long span?'
Bridges using hollow rectangular or trapezoidal sections that provide excellent strength and torsional resistance.
Total in US
70,776
Poor Condition
4.6%
Avg Sufficiency
65.6
Average Age
39 yrs
Box beam bridges use hollow rectangular, square, or trapezoidal cross-sections as their primary structural elements. This closed-section shape provides exceptional strength and stiffness, particularly in resisting twisting (torsion), making box beams ideal for curved alignments and bridges subject to eccentric loading. They are widely used for highway overpasses and elevated roadways across the United States.
The box shape can be constructed from precast prestressed concrete, cast-in-place concrete, or steel. Precast concrete box beams are especially popular because they can be manufactured in a controlled factory environment, trucked to the site, and placed quickly with a crane, minimizing construction time and traffic disruption. Adjacent box beam bridges, where beams are placed side by side to form the entire deck, are one of the most common bridge configurations for shorter spans.
Steel box girders are the choice for longer spans and curved highway flyovers, where their superior torsional stiffness prevents the deck from twisting under uneven traffic loads. Many of the sweeping interchange ramps on major highways use steel box girder construction.
Box beams resist loads through bending, just like standard girders, but their closed cross-section gives them a crucial additional capability: torsional resistance. When a load is applied off-center (eccentrically), it creates a twisting force. An open I-beam has very little resistance to twisting, but a closed box section is extremely stiff in torsion because the shear flow can circulate around the entire closed perimeter. The top and bottom flanges of the box resist bending compression and tension respectively, while the webs carry the shear forces. In a concrete box, internal diaphragms at intervals provide additional stiffness. Prestressing (pre-tensioning or post-tensioning) the concrete allows box beams to span farther and carry heavier loads by introducing compressive forces that counteract the tensile stresses from bending.
The interior of large steel box girders used in long-span bridges is often big enough for a person to walk through standing up. Engineers use these interior spaces for inspection walkways, and some box girders even house mechanical and electrical systems.
Confederation Bridge (Canada, 12.9 km precast box girder)
San Mateo-Hayward Bridge (San Francisco Bay Area)
Coronado Bridge (San Diego, CA)
I-35W Saint Anthony Falls Bridge (Minneapolis, replacement)
Route 9A Viaduct (Manhattan, NY)
| Rank | State | Count | % of Type |
|---|---|---|---|
| 1 | Illinois | 9,515 | 13.4% |
| 2 | Ohio | 8,687 | 12.3% |
| 3 | California | 8,410 | 11.9% |
| 4 | Pennsylvania | 7,344 | 10.4% |
| 5 | Indiana |
There are 70,776 box beam 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.
| 5,042 |
| 7.1% |
| 6 | Kentucky | 4,510 | 6.4% |
| 7 | Texas | 3,038 | 4.3% |
| 8 | Michigan | 2,997 | 4.2% |
| 9 | Tennessee | 2,993 | 4.2% |
| 10 | New York | 2,952 | 4.2% |