William O. Douglas Betty Bowen Carl Maxey Chief Joseph Bertha Landes Buffalo Soldier Home
Search Encyclopedia
Advanced Search
Featured Essay
Home About Us Contact Us Education Bookstore Tourism Advanced Search
7099 HistoryLink.org essays now available      
Donation system not supported by Safari     Donate Subscribe


Cyberpedias Cyberpedias
Timeline Essays Timeline Essays
People's Histories People's Histories

Selected Collections
Cities & Towns Cities & Towns
County Thumbnails Counties
Biographies Biographies
Interactive Cybertours Interactive Cybertours
Slide Shows Slideshows
Public Ports Public Ports
Audio & Video Audio & Video

Research Shortcuts

Map Searches
Alphabetical Search
Timeline Date Search
Topic Search


Book of the Fortnight
Audio/Video Enhanced
History Bookshelf
Klondike Gold Rush Database
Duvall Newspaper Index
Wellington Scrapbook

More History

Washington FAQs
Washington Milestones
Honor Rolls
Columbia Basin
Walla Walla
Roads & Rails

Slide Show Library

< Browse to Previous Essay | Browse to Next Essay >

Bridges of Washington State: A Slideshow Primer of Technology Through Time

HistoryLink.org Essay 8860

Click here to start the Slide Show

In Washington, bridges are ubiquitous. As of August 4, 2010, there were 9,415 bridges on the Washington State Department of Transportation (WSDOT) inventory. These include all bridges 10 feet and longer, all bridges owned by state and local agencies, and docks and transfer facilities owned by Washington State Ferries. The inventory includes only a few federally owned bridges and it only includes railroad bridges that cross public roadways. Bridges are added and removed from the inventory every year at the rate of about 100 a year. Forest roads and hiking trails also incorporate bridges. This slideshow offers a brief overview of Washington bridges and bridge technology as it evolved over time.

Bridge design is always evolving. Even so, there are only a few basic types:

  • trestle bridge -- the span is supported by a row of simple towers with vertical supports (called bents) leaning toward each other and steadied by cross pieces.
  • beam bridge -- the simplest type is a log placed across a stream
  • cantilever -- a development of the beam bridge. You have two anchor spans, supported by piers. Then two arms, the cantilever spans, extend out from the anchor spans. Some of these bridges have a center span hung between the two cantilever spans.
  • truss bridge -- the supporting truss looks like a Tinker Toy structure: The connecting members or struts (straight pieces) come in different arrangements, such as triangles or an N shape.
  • arch bridge -- favored by ancient Roman engineers using stone and cement
  • moveable bridges -- these include swing bridges, lift bridges, and bascule bridges (or drawbridges) whose spans are raised and lowered like a see saw.
  • suspension bridge -- the deck is supported by cables suspended from towers. The cables run from tower to tower, and the deck is hung from vertical suspenders that hang from the cables.
  • cable-stayed bridge -- A different type of suspension bridge. The cables run from towers directly to the deck, forming an A shape.
  • floating bridge or pontoon bridge -- the original floating bridges may have been canoes tied together to reach across a river.

There are a few terms and concepts that bridge engineers and bridge aficianados and buffs commonly use.

The dead load is the weight of the bridge itself.

The live load is the weight of the traffic on the bridge, whether autos or pedestrians or sheep.

Bridges work by tension (pulling apart) and compression (pushing together). Take a rope or a towel in your two hands and pull it apart as hard as you can. That is tension. Put your hands together as if you are praying and push them together as hard as you can. That is compression. The struts in trusses are in tension and compression.

As you walk, bicycle, drive, or take the train whether in your home town or on a trip, being able to recognize bridge types and understand something of how they are put together will increase your enjoyment of these monumental icons of our built environment. All bridges must stand up and carry their load. Some are ordinary, even homely. Others in their grace and great beauty attain something approaching a work of art. 

Click here to start the Slide Show

Craig Holstine and Richard Hobbs, Spanning Washington: Historic Highway Bridges of the Evergreen State (Pullman:WSU Press, 2005); Paul Dorpat and Genevieve McCoy, Building Washington: A History of Washington State Public Works (Seattle: Tartu Publications, 1998); Eric DeLony, Landmark American Bridges (New York: American Society of Civil Engineers, 1993); Lisa Soderberg, "Historic Bridges and Tunnels in Washington State," typescript, Washington State office of Archaeology and Historic Preservation, Olympia, 1980, available online (http://www.dahp.wa.gov/gis/pdfs/1270.pdf); Richard L. Cleary, Bridges (New York: W, W, Norton with Library of Congress, 2007); Craig Holstine to Stephen Emerson and Priscilla Long, August 4, 2010, email in possession of Priscilla Long.

< Browse to Previous Essay | Browse to Next Essay >

Special Suite: Bridges |

Related Topics: Roads & Rails | Science & Technology |

Licensing: This essay is licensed under a Creative Commons license that encourages reproduction with attribution. Credit should be given to both HistoryLink.org and to the author, and sources must be included with any reproduction. Click the icon for more info. Please note that this Creative Commons license applies to text only, and not to images. For more information regarding individual photos or images, please contact the source noted in the image credit.
This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License

Major Support for HistoryLink.org Provided By: The State of Washington | Patsy Bullitt Collins | Paul G. Allen Family Foundation | Museum Of History & Industry | 4Culture (King County Lodging Tax Revenue) | City of Seattle | City of Bellevue | City of Tacoma | King County | The Peach Foundation | Microsoft Corporation, Other Public and Private Sponsors and Visitors Like You

Aurora Bridge (George Washington Memorial Bridge), viewed from Fremont (north) side, Seattle, February 2006
Photo by M. Anne Sweet, copyright 2006 by M. Anne Sweet

New (2007) Tacoma Narrows Bridge (right, with pedestrians) and old (1950) Tacoma Narrows Bridge, shot from tower of old bridge, July 15, 2007
HistoryLink.org Photo by Priscilla Long

Fred Redmon Bridge over Selah Creek, I-82, Yakima County, October 17, 2008
HistoryLink.org Photo by Kit Oldham

Dalles Bridge spanning Skagit River, Concrete Sauk Valley Road, July 18, 2006
HistoryLink.org Photo by Priscilla Long

Home About Us Contact Us Education Bookstore Tourism Advanced Search

HistoryLink.org is the first online encyclopedia of local and state history created expressly for the Internet. (SM)
HistoryLink.org is a free public and educational resource produced by History Ink, a 501 (c) (3) tax-exempt corporation.
Contact us by phone at 206.447.8140, by mail at Historylink, 1411 4th Ave. Suite 803, Seattle WA 98101 or email admin@historylink.org