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| HAER OR-104-19 (CT) 19. General view of Fremont Bridge, looking northeast. - Fremont Bridge, Spanning Willamette River, carrying Interstate 405 northbound & southbound, Portland, Multnomah County, OR |
"Opened in 1973, and the epitome of high-tech, the graceful Fremont Bridge is still [Sep 1999] both the longest bridge (main span) in Oregon and the longest tied arch bridge in the world. Its 6,000-ton center span lift was the heaviest anywhere, accomplished with techniques and technology never used before at that scale. This erection method was selected because it had the least impact on navigation and the lowest cost. Innovative features include a weight-saving orthotropic deck and welded box girder and welded arch rib sections, with the arch ribs fabricated from high-strength quenched and tempered (T-1) steel....The lift employed a hydraulic jacking system, placed on the completed side spans, to lift the 900' unit 160' from the transport barges to its final position in the bridge. The river was closed for navigation for only three days during the lifting operation." [HAER-data]
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| Bridges Now and Then posted Lifting the center span on Portland, Oregon's, Fremont Bridge, March 16, 1973. The span was built in California, shipped to Swan Island, 1.7 miles upstream from the bridge site, assembled, and floated into position. (Calvin Hess) Justin McDonald: World record heaviest lift at the time I believe. Bridges Now and Then posted Lifting the center span of Portland, Oregon's Fremont Bridge into place, March 16, 1973. (Calvin Hess) Dennis DeBruler The 900' long, 6000-ton tied-arch span was the heaviest in the world. It was lifted 160'. The total length of the arch between anchorages is 1,255.3'. |
"On 28 October 1971, while the center span was still at Swan Island, release of load by the contractor on the falsework under the west side span triggered a brittle crack at Panel Point 3 in the south tie girder. The crack occurred in the joint between the arch and the bottom flange of the tie girder. The tie girders are 18' deep by 4'2" wide box sections. The crack started in the 66" x 3-1/4" bottom flange of the girder and proceeded upward through the 24" x 2-3/4 and 48" xl" web plates. The fracture propagated upwards 6' in one side web, but only 2' in the other web. Both cracks stopped at welded splices between plates. The girder came to rest on the falsework, still in place, thus avoiding complete failure of the side span. Workers standing on the falsework at the time, located about 300' from the shore and 160' above N.W. Front Avenue, feared the entire span was going to fall." [HAER-data, p24]
The report also discusses the engineering advances of T1- steel and orthotropic decks in the United States and the use of computers for design. (The orthotropic deck design was developed in Europe after WWII to help replace the many bridges that were destroyed by the war. That design uses less steel. The first use of an orthotropic deck in the US was the San Mateo-Hayward Bridge in 1967. But after a burst of bridges in the 1970s that used this design, it fell out of favor because the fabrication is much more labor intensive than a concrete deck. However, it has been used recently for deck replacement projects.) [HAER-data, p30-33]
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| HAER OR-104 (sheet 1 of 1) HAER OR-104 (sheet 1 of 1) - Fremont Bridge, Spanning Willamette River, carrying Interstate 405 northbound & southbound, Portland, Multnomah County, OR [The addition of temporary arch supports to transport and lift the arch caught my eye.] |
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| Higher Resolution, written in Sep 1999 |
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| Bridges Now and Then posted Moving Portland, Oregon's, Fremont Bridge center span into position, March, 1973. (Fat Pencil Studio) |
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| Mount St. Helens Before 1980 posted Mount St. Helens with newly built Fremont Bridge from Portland, Oregon. Fresh snow coat 1972, with Mount Rainier in the background. Courtesy Francis Keyes. MSHB1980 Bridges Now and Then shared |
Interesting to see that during transport, the arch needs to be supported; and the central support has a diagonal bracing to reinforce the structure even more. In the finished bridge, the arch is of course stable, and the span below now is suspended from it.
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