Earthquake could destroy 520 bridge, too, study says

An Article By LARRY LANGE

So you thought the Alaskan Way Viaduct was on shaky ground? Now you can worry about the state Route 520 bridge, too.

A recent engineering analysis, quietly discussed among state transportation officials and planners, says a magnitude-6.5 earthquake in the wrong spot could take out both structures.

The analysis says the viaduct fronting Elliott Bay and the bridge crossing Lake Washington have about the same ability to withstand the kind of major earthquake that occurs on average every 210 years. It is widely accepted that this region is at risk of catastrophic quakes.

To put it bluntly, a quake ranging in magnitude from 6.5 to 7.2, located close to the Earth's surface and near the spans, could destroy either structure or both.

The odds of this actually occurring have not been determined, state bridge engineer Patrick Clarke said.

Last year's major earthquake, centered near Olympia, registered a magnitude 6.8 but was centered 35 miles underground and 60 miles to the south -- too far away to destroy either span. Still, it was forceful enough to damage both, and to close the viaduct for several days for inspections and repairs.

Losing the bridge and viaduct, besides being deadly, could cripple traffic for years.

More than 225,000 drivers now use the two bridges every day, and would be forced to use side streets or other already-strained highways.

Rush-hour traffic backups could routinely extend south on Interstate 5 as far as the Boeing Access Road or east on Interstate 90 as far as Interstate 405, said Morgan Balogh, the state's regional traffic operations engineer.

"It gets ugly in a hurry, I'm sure," said Les Rubstello, manager of the state's Trans-Lake Washington study examining ways to improve mobility in the 520 corridor.

Replacing the 520 bridge could cost from $1.8 billion for four lanes to $7.4 billion for eight lanes, according to recent state estimates. Construction, depending on the option chosen, could last from nine to 11 years.

That the 520 bridge is as quake-vulnerable as the viaduct was startling news to some.

It was "new information for me," said King County Councilman Dwight Pelz, chairman of the council's Transportation Committee and a key player in planning a regional ballot measure to pay for major highway and transit improvements.

The quake analysis actually has been around for several months and was known to state officials and to some members of an advisory committee discussing whether to rebuild or replace 520's Evergreen Point Bridge.

Rubstello said the state didn't formally release details to avoid sounding "like we were crying wolf twice" after much-publicized reports about the viaduct's vulnerability to tremors.

In February, state Transportation Secretary Doug MacDonald urged legislators and Gov. Gary Locke to set aside money to plan replacements for both the viaduct and 520 bridge.

The letter did not mention the earthquake risk but said the 520 bridge is vulnerable to high winds and waves, which could break it apart.

"I've been flapping my lips at every meeting that it's an unsafe facility," said Redmond Mayor Rosemarie Ives. "Nobody wants to listen."

The quake analysis "serves to move 520 (replacement) up on the regional priority list," Pelz said.

Doing this, however, could reignite controversies about the effects of a bigger new bridge on the shorelines it connects. And some, including transit advocate Peter Hurley, want to see more detailed information before they agree that replacing the bridge makes more financial sense than retrofitting it to better resist earthquakes.

Engineers have long said that a major quake could fatally damage the viaduct, a 2.2-mile, double-deck structure that carries state Route 99 along the Seattle waterfront from the port docks to Aurora Avenue.

They have said the viaduct, which carries about 110,000 vehicles on an average weekday, could collapse if ground gives way under part of it, or if concrete cracks and support columns shear.

In a report issued a year ago, a team of engineers recommended replacing the viaduct, saying retrofitting it to meet modern earthquake standards didn't make sense.

That report came four months after an earthquake did more than $1.7 million in damage to the viaduct, cracking it and prompting crews to close parts of it for several days while it was shored up.

The same Feb. 28, 2001, earthquake that opened cracks in the viaduct did minor damage to the 520 bridge, loosening bolts in a joint on the western approach span.

A 1993 earthquake-evaluation study concluded that the tops of the 520 bridge's approach supports near each shoreline, filled with concrete five feet down from the top, would bend enough in an earthquake to hold up.

But that's no longer accepted. Below those solid "caps," the supports are hollow shells with 5-inch outer walls. State officials said researchers in California later became skeptical about how well hollow columns would hold up.

After a tug and barge hit and shattered one of the 520 bridge columns two years ago, Washington state engineers re-evaluated the earlier conclusion.

And in a memo three months ago, two state engineers said the caps wouldn't bend enough in an earthquake to keep the bridge supported.

That conclusion also was included in a brief internal state Transportation Department report in January. This said that even though the double-deck viaduct and the floating 520 bridge are built differently, the earthquake risks to the two structures when faced with the 210-year earthquake "are almost identical."

Rubstello said state analysts are just beginning to calculate how motorists would react to the simultaneous loss of both structures. Balogh, the state engineer, said backups would be longer on I-5 and I-90 and congestion would worsen on other highways as drivers tried to compensate for the loss of the two spans.

"You're not going to sit on the freeway for an hour. You're going to risk it on an arterial" (street), he said.

Some think the earthquake risk makes the 520 bridge a higher replacement priority. State officials have said retrofitting the 520 bridge for safety is not worthwhile because of its age, though they did do $1.14 million in retrofitting work in 1999.

Even people in Seattle's Montlake neighborhood, where the bridge's west approach is located, agree it should be replaced, said Jonathan Dubman, president of Montlake Community Club.

But the question is: With what? The advisory committee hasn't decided how many lanes a new span should have. That's a big issue in Dubman's neighborhood where, depending on the width of a new bridge, people living 200 feet from it now "could be as close as 20 feet to the new highway."

"The neighborhood would support an effective transportation solution that would improve the quality of life along the (520) corridor and through the region," Dubman said. "But we have some work to do to figure out a solution."

I-35W Bridge Collapse

A lesson which had made our bridge engineering safer.

I-35W Bridge History

• Built in 1964 by Hurcon Inc. and Industrial Construction Company.
• Steel trusses and deck were constructed by Industrial Construction Company in the summer of 1965.
• Bridge opened to traffic in 1967.
• Scheduled for reconstruction in 2020-25.

Stats

• Bridge carries 144,000 vehicles per day; including 4,760 commercial vehicles.
• Similar bridges in Minnesota include the Hwy. 123 bridge in Sandstone and the Hwy. 23 bridge over the Mississippi River in St. Cloud.

Design

• Deck steel truss is made up of three parts: deck, superstructure and substructure (the structure under water).
• Bridge has a split deck (longitudinally parallel to traffic) and is 113 feet, 4 inches wide.
• Size/length: 1,907 feet long, eight lanes.

Inspection History

• Had been inspected annually since 1993; before that, was inspected every two years
• Last fully inspected in 2006. Partial inspections were conducted in 2007; to be complete in fall 2007 (see inspection reports on I-35W bridge online at www.mndot.gov -- scroll to bottom of page to find documents)
• The 2006 Fracture Critical Bridge Inspection Report, prepared by a MnDOT bridge inspection team, describes specific problems that caused the superstructure (part of bridge above water) to receive a poor rating. The poor rating can be attributed to corrosion at some areas where the paint system has deteriorated, poor weld details in the steel truss members and floor beams, bearings that are not moving as they were designed to move, and existing fatigue crack repairs to the truss cross beam and approach spans.
• Deficiencies were acknowledged in the 2005, 2006 and 2007 inspection reports.

• MnDOT had taken several steps to address these deficiencies. Some cracking in the approach spans was repaired or was being monitored. The Bridge Office had contracted with the University of Minnesota in 1990 to evaluate the fatigue stresses within the truss. Field tests were conducted. Measured and calculated stress ranges were less than the fatigue threshold, therefore, it was concluded that fatigue cracking was not expected in the deck truss. The following actions were recommended:
• Structural components of the main truss with the highest stress ranges should be inspected thoroughly, every two years.
• Critical locations of the floor trusses had high stress ranges, and should be inspected every six months.

• Although the report concluded that fatigue cracking was not expected to be a problem for the weld details used on the truss, MnDOT contracted with URS (a private firm) in 2003 to do a more in-depth fatigue and fracture analysis, and to determine whether the fracture of any single truss member would result in collapse of the bridge or whether the traffic load would be safely carried by other members of the bridge. URS made three recommendations in January 2007:

1) Add redundant plating over the most critical 52 truss members,

2) Conduct a visual examination of all suspected weld details and remove measurable defects at suspected weld details of all 52 fracture critical truss members, or,

3) Do a combination of both 1) and 2).

MnDOT had begun inspection of the weld details and no weld cracks were detected. Therefore, MnDOT did not proceed with option 1 at that time. MnDOT intended to complete the inspection of the weld details on all of the remaining members after the completion of the current construction project.

Structurally deficient bridges

• A bridge is rated as “structurally deficient” when part of the bridge is found to be in poor condition. Many bridges in poor condition are still safe for use. As deterioration continues, engineering analysis is sometimes necessary to re-compute the safe load capacity of the bridge. If the safe load capacity is less than today’s legal truck load (80,000 pounds), the bridge is posted at the newly computed safe load capacity.

• The I-35W bridge was rated safe for legal truck loads and permitted overweight truck loads of up to 136,000 lbs. The bridge was not under any restrictions.

· The condition of different parts of a bridge is rated on a scale of 1 to 9 (7, 8, or 9 are good condition ratings, 6 is satisfactory, 5 is fair, 4 is poor, 3 is serious, 2 is critical and 1 is closed). A structurally deficient bridge is one for which the deck, the superstructure or the substructures are rated in condition 4 or less. For this bridge, the superstructure was rated 4.

• In Minnesota, there are 1,097 bridges that are considered structurally deficient and that have a sufficiency rating less than or equal to 80. Of these bridges, 106 are on the state trunk highway system and 991 are on the local system.

Federal report on bridges (NBIS database)

• The National Bridge Inspection Standards require states to annually report condition ratings for all bridges in their states to the Federal Highway Administration (FHWA). Each MnDOT district has inspectors who are trained to inspect and rate bridge condition. That information is forwarded to MnDOT’s Bridge Office where it is compiled and forwarded to the FHWA. The FHWA uses that data to determine which bridges are structurally deficient and functionally obsolete.

Recent work on the bridge

• Work involved concrete and joint repair, lighting and guardrail installation
• Work was scheduled to be complete Sept. 30.
• Cost for the work is $9 million.

Millau Viaduct – World's Tallest Bridge

Extreme Engineering Marvel

Mankind has certainly moved on to the next challenge of constructing on what was thought to be as the impossible by our predecessors. Credits to the Engineers.

To me there are few things more impressive than being on a man-made structure, such as a very tall building or a bridge, and viewing blue sky above and clouds below. Of, course for this to occur the structure has be be rather high and the clouds low.

This is why I was immediately impressed when a friend sent me pictures of the Millau Viaduct, which crosses the valley of the Tarn River valley near the city of Millau in the mountains of southern France.

Normally it is the high mountains that present a challenge to engineers building roads that connect two or more points. However, in case of the Millau Viaduct, the mountain area through which the A75 autoroute, also known as la Méridienne, passes is apparently rather high most of the way until it reaches the Tarn River valley.

Bridge with blue sky above and clouds below.

Bridge spans valley of the Tarn River.

 

A Joint Franco-British Project

As can be seen from the picture at the right, one has to traverse a long, winding road down the mountain on one side of the valley and then immediately repeat the process while climbing up the mountain on the other side of the valley.

In addition to the kilometers / miles and time added by the trip down into the valley and back up into the mountains, time was also lost in the past to traffic congestion in the town and on the two lane bridge across the Tarn River. It is estimated that the bridge over the valley has shortened the driving distance between the Paris and the Mediterranean coast of France by 100 kilometers (about 62 miles) and, during the summer tourist season, reduced travel time by as much as four hours.

Construction of the bridge was a joint Franco-British project with help from companies in other European countries. Financing for the 394 million Euro (U.S. $524) project was provided by the French construction firm Eiffage. As a result of corporate mergers*, the Eiffage frim includes the firm that built the Eiffel Tower in Paris which, at the time of its completion in 1887, was the tallest structure in the world. This is obviously a company with long experience in being involved with construction of structures of record setting size. British architect Norman Foster designed the bridge, which has come to be viewed both as a work of art as well as a construction marvel, while the French bridge engineer, Dr. Michel Virlogeux, provided the engineering design.

While planning began in the late twentieth century, actual construction did not begin until December 2001 and its 2005 target completion date was achieved a little early when it was formally dedicated on December 14, 2004 and opened to traffic on December 16, 2004.

The Millau Viaduct is an artistic and engineering marvel. It currently holds the record for having the highest piles (the pilers rising from the ground and supporting the bridge from below) of any bridge in the world with its highest being 244.96 meters (803.7 feet) and the highest mast (the pilers rising up from the top of the bridge and holding the suspension cables) which towers 343 meters (1,125 feet) above the roadbed of the bridge. It also has a claim to having the highest roadbed of any bridge in the world with its roadbed reaching 270 meters (885.8 feet) above the river below.

However, the roadbed of the Royal Gorge Bridge in Colorado in the United States tops this with its roadbed which towers 1,053 feet (321 meters) above the river below. Based upon height of roadbed, the Royal Gorge Bridge is the highest in the world while based upon mast height, the Millau Viaduct is the highest in the world. Regardless of which is the highest, the Millau Viaduct is the clear winner in terms of length and beauty.

Famous Bridges

Look back into history of some of the famous bridges around the world

Look up to the tallest bridge in the United States at the Royal Gorge Bridge in Colorado. It is the tallest suspension bridge in the world, looming above the Arkansas River at 1,053 feet. You can even walk across the bridge’s wooden planks, if you can deal with the vertigo you may experience. Only taking six months to build, it cost $350,000 in 1929. This bridge was built with tourists in mind, not as a transportation mode. It is at the top of the list for visited attractions in Colorado.

See St. Petersburg Cathedral, The London Eye, Canary Wharf and so much more from the London Tower Bridge walkways in London, England. The two towers span over the Thames River with two glassed in walkways for pedestrians to walk. Previously, the London Bridge was the only way in and out of England’s capital city. As the only movable bridge on the Thames, it moved up and down over 1,000 times a year after it first opened in 1894. Today, very few ships travel down the Thames River and it only opens about 100 times annually.

Cross the Brooklyn Bridge by car and you will be among 144,000 other vehicles daily. This bridge boasts several “firsts” in the world of bridges. It was the first suspension bridge to use steel cable wires in its construction, and it was also the first to use caisson devices in explosions. When it was built in 1883, it was the longest suspension bridge at 3,460 feet. However, today the Japanese Akashi Kaikyo Bridge at 12,626 feet is the longest suspension bridge in the world.

Ride in a railway car over the Garabit Viaduct Bridge from the Garabit valley to the south of France. This famous red bridge was built from steel beams with triangle shaped holes in a truss pattern. This allowed the windy area’s bridge to remain stable rather than swaying when the wind hit it. This bridge was designed by none other than Gustave Eiffel, known as the famous architect of France’s Eiffel Tower.

There is enough cable wire from the Golden Gate Bridge in San Francisco to circle around the world several times. The men that worked on the bridge had a special name attached to them, the “Halfway to Hell Club.” That's how dangerous their jobs were. A safety net was strewn under the workers. It saved the lives of 19 of the bridge builders during it’s construction. A million vehicles, and counting, have gone over the Golden Gate since it was built in 1937.

Observe the remains of the Tacoma Narrows Bridge at the National Register of Historic Places. Its remains were dredged from Puget Sound for safe keeping. After its demise, bridges were never built in the same way again. When this bridge was completed in the 1940s, it got the name “Galloping Gertie” because of its rocking action. It actually made drivers and passengers car sick while driving over it. Thankfully, no lives were lost when it finally fell apart in 42 mph winds and crashed into the water below. The solid girders used in the construction of the Tacoma Narrows Bridge caused it to act in the unstable manner. A new type of construction eased the wind and kept bridges from excessive swaying.