The continuing look at the 14 Shoreline Highway state bridges between Elk and the Ten Mile River has shown that bridges built during the heady post World War II days are costing taxpayers more than $100 million now, with all needing retrofit repairs and three — the old Noyo River Bridge, the Ten Mile River Bridge and the Greenwood Creek Bridge — deteriorating badly; all to be replaced between 2005 and 2010.
Others, including three magnificent bridges built during the Great Depression, are near the end of their anticipated lives, but modern maintenance and inspection methods make them safe, Caltrans says. The event that launched this story, the Aug. 1 collapse of a structurally deficient bridge in Minnesota that killed 13 people, remains under investigation.
Albion River Bridge —
last of the tall wooden bridges
The most photographed bridge on the Mendocino Coast, is the 968-foot Albion River Bridge. It was finished in 1944 and despite its towering height and improbable reclaimed wood material, rates a 69.3 on a scale of 1 to 100. Its superstructure, substructure and deck all meet modern criteria and earn satisfactory ratings. The bridge is rated as “functionally obsolete” because of narrow lanes.
The worrisome flaw is not the timber that lifts the bridge more than 165 feet above the water but its steel truss-deck, the same design as the Minnesota Bridge.
While accounts in engineering magazines and major newspapers say the truss-deck design was to save money in the 1950s, it was done to save steel in the deck of the Albion River Bridge, according to a 1945 article in Engineering News-Record. Steel was needed at the time for the war effort, and it was patriotic to find ways to use less steel and concrete.
Salmon Creek has similar design,
rating to Minnesota Bridge
When the Minnesota Bridge fell on Aug. 1, the federal government launched a national effort to immediately inspect every other steel truss-deck bridge in the nation.
The problem with truss-deck bridges is that they have no redundancy in their design. Redundancy means when one system fails, another one can catch it, according to engineering magazines. For example, the Caspar Creek Bridge has big steel cables that could hold the blocks together if the simple girder system failed.
There are only 750 steel truss-deck bridges in the entire nation, most part of the interstate building boom. There are 69 of them in California and three in Mendocino County.
Just a few yards from the Albion River Bridge is another truss-deck bridge, the 682-foot-long Highway 1 Salmon Creek Bridge. (The other is Burger Creek Bridge near Laytonville.)
Completed in 1950, the Salmon Creek Bridge rates a 49.7 on the scale of 1 to 100 and is tagged as “structurally deficient,” thus qualifying for federal funds to replace it. It is not a current Caltrans priority to replace this bridge.
The Salmon Creek Bridge has a bright new green paint job, which shows that Caltrans is doing what is needed to keep the bridge safe. Painting often is a key factor in the life of any steel bridge, engineers said. But it needs other repair work, its National Bridge Inventory data shows.
The deck is in poor condition and the substructure rates “fair” in the inventory data.
“None of the deck problems currently pose any impact on the structural integrity of the bridge,” said Caltrans engineer Barton Newton. “Salmon Creek and Hare Creek have deck cracks and water stains on the underside of the deck. These problems will be corrected by the application of crack filler.”
Old Noyo River Bridge had short life
Completed in those post-war years between the Albion and Salmon Creek bridges was the old Noyo Bridge, one of the worst and shortest-lived bridges in coast history.
The old Noyo Bridge, completed in 1947, was rated a terrible 2 on the scale of 1 to 100 in 2002, and its superstructure was classified as “failed” in the National Bridge Inventory, a truly rare classification mandating replacement.
Towards the end of its life, the 1947 Noyo Bridge bounced noticeably every time a big truck or RV went over it. “The ranking of failed condition” for the old Noyo Bridge corresponds to a superstructure condition rating of failed paint system and corrosion of the steel,” Newton said.
Some of those who worked on the bridge at the end of its life dispute Caltrans” statement that the bridge was still safe.
The superstructure was so badly rusted that new rivets and bolts were installed to keep it together, as contractors worked as fast as possible to get the new bridge built. The bridge also has flaws that required retrofitting.
The new Noyo Bridge, opened in 2005, has a lower sufficiency rating than some much older bridges in the county. This illustrates how sufficiency ratings look at not just condition but what would happen if the bridge did break.
“The sufficiency rating is based on both condition and functional use,” Newton explained “The sufficiency rating of 80.6 is primarily due to the approximately 96-mile-detour length.”
Ten Mile and Big River —
twin monuments to mediocrity
Two matching bridges were built in the 1950s, extending the easily traveled area of the Mendocino Coast to the north and south: the Big River and the Ten Mile River bridges. They reflect the rushed, monetary and minimalist values of the day. Both bridges have troubled histories, and both have passed whatever cost savings were achieved in the 50s onto modern society, with a $45 million price tag to replace Ten Mile alone.
The Ten Mile Bridge is being replaced today as fast as environmental concerns will allow the project to proceed. So far only the falsework is in place, with work on the substructure starting.
The new bridge will be 1,479 feet long and 44.9 feet wide, with two 12-foot lanes and 6-foot shoulders.
The old bridge has a critical design flaw: Wooden footings placed on concrete pilings. This creates a hazard in an event of an earthquake with a Richter scale of 8.0 or more. A reading of all the specification data on the old bridge showed this reporter that this was truly a design mistake.
One engineer, interviewed for a previous in-depth story on the Ten Mile Bridge, believed that no such design flaw would have been slipped by when Harlan Miller was chief engineer during the first third of the 20th century, nor would it now, partly due to the environmental scrutiny given modern bridges.
There are many other problems with the Ten Mile Bridge beyond its vulnerability to an earthquake.
“Ten Mile River Bridge is designated as structurally deficient” due to its superstructure condition rating of 4 as a result of delaminations [soft spots] and spalls [large chips] with exposed and corroding rebar in the girders and bridge [underside],” engineer Newton explained. “These are minor problems that if left unrepaired could have significant structural issues.
“This bridge is now being replaced due to seismic, scour, bridge rail and shoulder width problems in addition to the minor superstructure deterioration.”
The Big River Bridge also had seismic flaws, which were corrected a decade ago. Other, unrelated superstructure problems kept Big River Bridge on the “structurally deficient” list even after the fix.
“The specific conditions described in the bridge report causing this rating are spalls [large chips] and cracks on the exterior girders and on the bottom of this reinforced concrete box girder,” Newton said. “The seismic retrofit project did not include minor repairs to the superstructure that are required to bring the superstructure rating up.”
Hare Creek — another postwar problem
Built in 1947, the 383-foot-long Hare Creek Bridge, located just south of the Highways 1 and 20 intersection, is structurally deficient, with a sufficiency score of 52 and a deck classified as “poor.”
Hare Creek used an older, more elegant design than any of the other post-war bridges. Its superstructure rates “fair” but its substructure rates “good.”
One popular post-war tactic was pre-fabricated bridges, which are the easiest to build. The James Creek Bridge over Highway 20 is one of those, built in 1962. But it is another problem bridge, rated “structurally deficient,” with a 63.9 sufficiency rating.
Unique little Pudding Creek Bridge
Another bridge that benefited from a seismic retrofit is the 300-foot-long Pudding Creek Bridge at the north end of Fort Bragg, which otherwise is one of the best bridges on the coast. Five coast bridges were to be part of an $8 billion retrofit program for 2,200 bridges.
Pudding Creek Bridge”s National Bridge Inventory numbers included a rare “very good” superstructure condition. Surprisingly, the 1959-vintage bridge scores better than current acceptable standards. It is wider than most and has a unique support system that incorporates two different superstructure designs in a way unique to this bridge. It has a sufficiency rating of 63.
County bridges
In 1997, nearly 1,400 bridges — about 6 percent of California”s 23,000 — suffered structural deficiencies, a data analysis shows. By 2006, that soared to about 3,000, or 13 percent.
Engineers interviewed for this story said the rapidly escalating costs of bridges and the even more rapidly rising federal budget deficit will make it difficult to ever replace these bridges. The Benicia Bridge came in at $1 billion over budget this year, and the Bay Bridge replacement and retrofit is over $5 billion and rising.
A bridge is defined as an elevated span of more than 20 feet.
Howard Dashiell, head of the Mendocino County”s Department of Transportation, said a five-person crew maintains the 157 county-owned bridges. Because California bridges are held to a higher (seismic) standards than those in other states and are inspected and maintained regularly, there is no cause for alarm over structurally-deficient bridges, he said.
The greatest bridge disasters locally come from huge flood events. “We lost a lot of bridges in 1964,” he said.
Dashiell pointed out that bridges created by the Romans are still in use in Europe.
“Usually a bridge is as good as its foundation. If you watch them and maintain them, they are fine. But if the soils are bad, things shift and move,” Dashiell said.
“If you maintain the bridge, and inspect the bridge, you can continue to use it, although it may need replacement of components.”
While engineering publications say about 50 to 60 years is the expected lifespan of a tall bridge in salt air, that can be lengthened by diligent maintenance, American Society of Civil Engineers board member Andrew Herrmann said.
For example, thanks to constant painting and maintenance, the lifespan of the Golden Gate Bridge is estimated to be another 100 to 200 years, a spokeswoman said.
Tall, long bridges, like the Albion and Noyo, face the greatest design and maintenance challenges, especially in the salt air. The Navarro and Little River bridges are low bridges classified by the National Bridge Inventory as low-risk.
Overall, all the 14 Coast Highway bridges examined here have comparatively high ratings, considering their size and exposure.
“The fact that they are rated so high is due to the vigilance and dedication of our bridge maintenance crew,” Newton said.
Caltrans performs routine bridge inspections on all local bridges owned by the agency. As bridge owners, the local agencies use the inspection data to schedule repair and rehabilitation work on these structures.
The City of Fort Bragg owns no bridges, said Dave Goble, head of public works.
The National Bridge Inventory data for all local agency bridges in Mendocino County is collected and maintained by Caltrans, Newton said.
A Highway 271 bridge over the South Fork of the Eel River at the extreme northern end of the county is the oldest bridge in the county and yet shows no serious problems. The 1917-built structure escapes the “structurally deficient” and “obsolete” designations and earns a 65.6 percent rating. It is described in the details as “better than minimum” standards. The National Bridge Inventory also shows that the bridge was updated in 1934.
The biggest bridge building project in Mendocino County history is under way at Confusion Hill, not to span a canyon but to avoid two miles of chronic mudslide that began moving about the time of the birth of Christ and has never stopped.
The south bridge is the highest in the county at 255 feet above the river and the longest too at 1,395 feet. By contrast, the roadway of the Golden Gate Bridge is 220 feet above the water (although the towers are more than three times that high).
It”s also the most expensive, nearly double the Ten Mile Bridge project. The $71 million Confusion Hill project features two new bridges, excavation and removal of more than 10 million cubic feet of the mountain, and the eventual relocation of the highway to the other side of the South Fork of the Eel River.
