7 Types of Bridges
Bridges unite and bind us together, from Sydney Harbour to the Tower Bridge, and across the Thames to the Golden Gate. They are portals to discovery—and the way many of us get to work every day. Whether they are basic footbridges, effective toll bridges, or complex drawbridges, they serve an important purpose.
Bridges can range from the most basic buildings to massive, beautiful pieces of art — and everything in between. A bridge serves only one purpose: to get us across a span that would otherwise be difficult (if not impossible) to cross.
7 Different Types of Bridges
Arch Bridge
Beam Bridge
Cantilever Bridge
Suspension Bridge
Cable-Stayed Bridge
Tied-Arch Bridge
Truss Bridge
From the first tree stem placed over a creek bed, people have throughout time developed increasingly complex bridge designs. Waterways and canyons are now crossed by a variety of innovative structures and materials.
Massive, elaborate modern bridges that cross quite large distances are now commonplace. The $8.5 billion Danyang-Kunshan Grand Bridge in China is the longest bridge in the world and spans a high-speed rail network of more than 100 kilometers.
Through the use of a foundation (pillars, abutments, piers, and footings) that grounds the load into the earth and a superstructure (girders, trusses, etc.) that supports the bridge deck and its weight, bridges function by balancing the forces of physics.
In order to offer a solid surface for crossing a split, a bridge must be able to withstand movement. A bridge can remain standing by striking the ideal balance between sound engineering and bridge construction.
1. ARCH BRIDGE
The Pont-Saint-Martin bridge in the Aosta Valley of Italy is one of the more than 1,000 stone arch bridges that the Romans constructed; it dates back to the first century BCE. The design of this bridge is about 3,000 years old. Modern arch bridges are also constructed with concrete these days.
The weight of whatever a bridge is carrying in addition to the weight of the bridge itself—referred to as the live load—makes up its total weight. An arch bridge is supported instead of collapsing by the forces of gravity and load, which would otherwise cause the bridge to collapse.
In order for an arch bridge to function, gravity must be directed inward, toward the keystone, which sits at the core of the construction, as opposed to downward. The surface, or deck, above the arch below can be supported by this compression theory.
Temperature changes have the potential to destabilize fixed arch bridges, hence hinges are occasionally included to the arch design at each base and even in the center of the span. This aids longer arch bridges in adjusting to the material’s expansion or contraction in response to sharp temperature changes.
2. BEAM BRIDGE
The beam bridge, with its straightforward design, was the inaugural bridge type ever constructed. Even today, it remains the most economical option. Essentially, all it requires is a single crossbeam spanning the gap, buttressed by abutments on either end. A subtype of this design is the girder bridge, fortified with steel girders for added strength.
Constructing a bridge poses a unique challenge due to gravity’s omnipresence. Unlike buildings, where support is more evenly distributed, bridges contend with vast expanses of open space beneath them. Typically, a beam bridge relies on just two abutments—one at each extremity—to defy gravity and shoulder the entirety of its load.
However, beam bridges pose a significant risk as they grow in length and accommodate more traffic. As the bridge’s span increases and the volume of people, vehicles, and cargo it supports rises, so does the total load it bears. Moreover, the further apart the abutments of a beam bridge are positioned, the less stable the structure becomes.
To counteract this instability, additional supports are introduced in the form of piers or stanchions placed strategically along the span. By connecting sections between these supports, engineers can create extended yet sturdy bridge structures. Examples of such engineering marvels include the 3.2-mile Yolo Causeway near Sacramento, California, and the monumental 24-mile Lake Pontchartrain Causeway in Louisiana.
Within beam bridges, the force of compression directs the load inward onto the piers positioned at the bridge’s midpoint. Simultaneously, tension exerts a pulling force, stretching the load outward toward the abutments at both ends of the bridge.
3. CANTILEVER BRIDGE
Cantilever construction is employed in the creation of certain bridges, characterized by a vertical pillar securely anchored into the ground. From this pillar, a horizontal deck extends outward, often spanning the width of the gap on one or both sides. Notably, the load on these bridges is typically supported both from above and below, akin to the design of a diving board or platform.
Among these structures, the Quebec Bridge in Canada boasts the world’s longest cantilever span, reaching an impressive 1,800 feet upon its completion in 1919. This surpassed the previous record held by Scotland’s Forth Bridge, finalized in 1890.
In the United States, examples of cantilever bridges include the central section of the Conde B. McCullough Memorial Bridge over Coos Bay in Oregon, as well as the eastern segment of the San Francisco-Oakland Bay Bridge (distinct from the Golden Gate Bridge). Often, cantilever bridges are integrated with other bridge types to traverse a single span.
To enhance stability and load-bearing capacity, cantilever bridges commonly incorporate trusses for support. These trusses redistribute the load from the deck to the supporting piers and abutments, enabling the cantilevers to withstand both tension in the upper supports and compression in the lower ones.
4. SUSPENSION BRIDGE
Suspension bridges stand as perhaps the most iconic bridge type in the United States, epitomized by the renowned Golden Gate Bridge in San Francisco. Since its completion in 1937, this engineering marvel has attracted over 10 million visitors annually, drawn by its striking twin 746-foot orange towers and grand Art Deco aesthetics.
As the name suggests, suspension bridges rely on a system of vertical pillars or pylons linked by suspension cables for stabilization. These primary cables support smaller, vertical suspenders that uphold the bridge deck through tension, the primary force that sustains suspension bridges.
While early suspension bridges employed simple ropes to support wooden planks, modern suspension techniques enable the construction of lengthy spans over expansive waterways. However, as suspension bridges are anchored to the earth at only a few points—typically the towers or pylons—they are susceptible to swaying in the wind or vibrating under heavy traffic loads.
Wind or movement across a suspension bridge can induce vibrations, which, upon reaching a critical frequency, may trigger resonance—a phenomenon akin to shattering glass when subjected to a specific pitch. Intense vibrations have the potential to disrupt bridge crossings and even lead to collapse.
Furthermore, suspension bridges are susceptible to torsion, a twisting force often induced by environmental factors like wind. Excessive twisting of the bridge’s surface while in use can pose a hazard to travelers.
Similarly, shear forces can exert horizontal pressure on a bridge’s components, potentially causing breakage akin to snapping a stick between two hands. These environmental forces highlight the need for careful design and maintenance to ensure the safety and integrity of suspension bridges.
5. CABLE-STAYED BRIDGE
A cable-stayed bridge is a variation on the suspension bridge that connects the crossbeam or bridge deck directly to pillars or towers. There’s no main cable, just a large number of vertical suspenders affixed to the top of the tower. These suspenders use tension to help keep the bridge deck stable and in place.
The Strömsund Bridge in Sweden is considered the first modern cable-stayed bridge. The three-span structure was completed in 1956. Its steel and concrete deck is suspended by diagonal cables from two pylons.
The glass-decked Sundial Bridge, built in 2004 across the Sacramento River in Redding, California, makes use of the cable-stay technique in conjunction with elements of cantilever and suspension. The famed Brooklyn Bridge, which opened in 1883, is a hybrid cable-stayed and suspension bridge.
6. TIED-ARCH BRIDGE (BOWSTRING)
A tied-arch bridge melds elements of both arch and suspension bridge designs. It utilizes horizontal thrust from both ends to bolster an arched framework, reminiscent of a traditional arch bridge. However, unlike conventional arch bridges where the arch supports the structure from below, in a tied-arch bridge, the arch rises above the roadway. Vertical ties descend from the arch to enhance the support of the decking.
Due to their appearance resembling a bow when viewed from the side, tied-arch bridges are also known as bowstring bridges. This bow-like configuration leverages the tension of its vertical cables, along with the compression of the arch, to effectively bear the load and maintain the stability of the bridge.
One notable example of this architectural style is the Blackfriars Street Bridge in London, Ontario, Canada. This wooden-decked bridge served vehicular traffic from its construction in 1875 until its closure in 2013.
In the United States, several bowstring bridges stand as prominent landmarks. These include the Fort Pitt Bridge spanning the Monongahela River in Pittsburgh, the Lowry Avenue Bridge traversing the Mississippi River in Minneapolis, and the Daniel W. Hoan Memorial Bridge in Milwaukee.
7. TRUSS BRIDGE
A truss bridge efficiently distributes its load by dividing it across a sequence of small sections that are interconnected. These sections are composed of structural beams for smaller bridges or box girders for larger ones. Typically, bridge trusses are joined together through welded or riveted connections, forming a network of triangles.
Vertical steel or wooden supports play a crucial role in holding up the bridge through tension, while diagonal truss supports contribute to stability by applying compression. This arrangement directs the load toward the center of the bridge, akin to the function of an arch.
Truss bridges are renowned for their cost-effectiveness and have a long history. Initially constructed predominantly from wood during the 19th century, there was a subsequent transition to using iron and steel. One of the most recognizable truss designs is the Pratt truss, characterized by diagonal segments sloping towards the center of the bridge. This design was pioneered by Thomas Willis Pratt in 1844.
A quintessential example of the Pratt truss design is the Cottonwood River Pratt Truss Bridge in Cedar Point, Kansas. Constructed in 1916 by the Missouri Valley Bridge Company, it holds a place on the U.S. National Register of Historic Places.
Additionally, there are various other truss designs, including the Baltimore truss, Howe truss, Long truss, Vierendeel truss, and Warren truss. Among these, the Ikitsuki Bridge in Japan boasts the world’s longest continuous truss span, measuring 1,300 feet upon its completion in 1991. Another notable example is the Francis Scott Key Bridge over Baltimore Harbor.
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