Bridge Types

Bridges are constructed in many different ways and are often identified by
the materials they are constructed from and the method of construction. The
following images can be used to help identify bridges you may see in your
travels.

Concrete Bridge Construction

openspandrelarch

Open Spandrel Arch

closedspandrelarch

Closed Spandrel Arch

concretegirdert-beam

Concrete Girder (T-Beam)

concreteslab

Concrete Slab

Truss Bridge Types

throughtruss

Through Truss

ponytruss

Pony Truss

decktruss

Deck Truss


Truss Bridge Parts

diagram

The above diagram appeared in the 1908 publication The Design of Highway Bridges and the Calculation of Stresses in Bridge Trusses by Milo S. Ketchum. We have revised some of the terms to reflect modern usage.

Truss Bridge Configurations

Most of the following truss designs are adapted from those which appeared in J.A.L. Waddell’s 1916 book Bridge Engineering and for the most part they remain relevant today with only minor name and classification changes as noted below.

pratt

Pratt: The Pratt truss is one of the most common truss configurations.

s_pratthalf-hip

Pratt Half-Hip: Some Pratt pony truss bridges lack hip vertical members, and are known as half-hip Pratt truss bridges.

whipple

Whipple (Double-Intersection Pratt): This variation on the Pratt was common for longer spans in the 19th Century.

howe

Howe: Diagonals follow the opposite orientation as that of the Pratt. The Pratt was more common on metal truss, while the Howe was more common on timber trusses.

parker

Parker: A Pratt truss with a polygonal top chord. Used for longer spans.

camelback1

Camelback: A Parker truss with exactly five slopes to the top chord (including end posts).

baltimore1

baltimore2

Baltimore Truss: A Pratt truss with subdivided panels. Two common forms shown above.

pennsylvania2

pennsylvania1

camelback2

Pennsylvania (Petit) Truss: A Parker truss with subdivided panels. Two common forms shown above. Today, Pennsylvania truss bridges with five slopes of the top chord are usually called simply “Pennsylvania” trusses, but could be noted as “Camelback Pennsylvania trusses.” Pennsylvania trusses were used for long spans, including some of the longest simple spans ever constructed.

warren1

Warren: While Waddell’s book distinguished between a “Triangular” and “Warren” type of truss, today all varieties are known as Warren truss bridges.

warren2

Warren (With Verticals): Most Warren truss bridges display vertical members, although the frequency of the verticals can vary. Warren trusses (with or without verticals) were a common truss type.

doublewarren

Double-Intersection Warren: This design can be thought of as two Warren trusses superimposed and offset on top of each other.

lattice

Lattice Truss: Triple-Intersection, Quadruple Intersection, and Quintuple Intersection Warren trusses are commonly called simply “lattice trusses.”

k1

k2

K-Truss: Invented during the construction of the Quebec Bridge, the K-Truss can be arranged in several different ways, with two orientations shown above. The top chord does not have to be polygonal.

bollman

Bollman: An unusual truss design used on some of the earliest iron railroad bridges.

fink

Fink: An unusual truss design used on some of the earliest iron railroad bridges.

bowstring

Bowstring (Parabolic): This form of truss typically has a curved top chord and is sometimes called an “arch-truss” as well. Most commonly used in the 1870s as an early metal truss form.

kingpost

Kingpost: Used for very short spans.

queenpost

Queenpost: Used for very short spans. May or may not have the “X” pattern of diagonals in the center.

aframe

Waddell “A” Truss: This truss, sometimes called an A-Frame truss, was built in small quantities.

lenticular

Lenticular: Most examples in the United States were built to a patented design by the Berlin Iron Bridge Company of East Berlin, Connecticut.

kellogg

Kellogg: An archaic and rare truss form.

post

Post: An archaic and rare truss form.

pegram

Pegram: An archaic and rare truss form.

thacher

Thacher: An archaic and rare truss form. Exact form may vary slightly, no existing examples exactly follow the design patented by Edwin Thacher.

stearns

Stearns: An archaic and rare truss form.

Bascule Bridge Designs

Among movable bridge types, bascule bridges display the most variety in mechanical operation. The following bascule designs are adapted from those which appeared in J.A.L. Waddell’s 1916 book Bridge Engineering and for the most part they remain relevant today with only minor name and classification changes as noted below.

fixedtrunnion

Fixed-Trunnion (Chicago Type): The counterweight is fixed to the leaf, and the leaf rotates around a fixed trunnion. First used in London’s Tower Bridge, the design was modernized and made popular by the City of Chicago.

scherzer

Scherzer Rolling Lift: This type of bascule rotates on a track, and has a counterweight fixed to the leaf. Invented in 1893 by Albert Scherzer and popularized by his brother William Scherzer.

strauss2

Strauss Bascule: Joseph Strauss invented his variety of trunnion bascule bridge that is noted for having a separate trunnion for the counterweight. As such, the counterweight is not fixed to the leaf. This overhead counterweight design was also adaptable to a design where the counterweight was hidden below the roadway.

strauss1

Heel-Trunnion: This variation on the Strauss bascule is noted for its parallelogram shape and typically takes the form seen above. The counterweight is always above the roadway.

page

Page: A rare bascule design.

rall

Rall: A rare bascule design.

Swing Bridge Designs

A movable bridge type, swing bridges are typically classified into two major categories based upon how they rest on the swing pier as noted below. Most swing bridges are symmetrical (center pier) but if the pier is not at the center, then the bridge is a bobtail swing bridge and a balancing counterweight may be present at the shorter end.

rimbearing

Rim Bearing: Span bears upon the circular track around the rim. Typically has a dense series of numerous rollers around the rim.

centerbearing

Center Bearing: Span bears upon a single point at the center of the swing pier. As such, there may be less rollers around the rim as they only serve to guide the truss when moving, and are not load-bearing.