It appears that the permanent repair will be a concrete girder span, rather than an overhead truss.
After installing a temporary Acrow Bridge in place of the collapsed span WSDOT reopened the Skagit River Bridge today. A permanent repair is currently being developed.
This is too sad and disturbing to see such failures. Respectfully, NTSB will decide, however there are a couple of technical points and observations worthy of mentioning here.
1-It is possible that truck impact on the strut was a significant, but rather consider it as trigger causing the collapse. The structural condition in addition to service deficiencies prior to collapse are too important to ignore.
1- The bridge rating was only 56. There superstructure condition rating 5 out of 9. It is reduced because of prior-damage and deterioration not just insufficient clearance. I would be curious to see bridge inspection report on load rating considering prior damaged members, and bearing conditions.
2- Look at the photos right after collapse showing significant vegetation right on the top of the pier
It shows pile of vegetation along the entire top of the pier and right next to the bearings. This is exactly where the expansion joint with large opening allowing water coming down causing the bearings (rocker or roller) but certainly subject to extensive corrosion. The floor beam corrosions are also very evident.
The vegetation was is all cleaned as NTSB photos show.
Note the spalling of concrete and anchor bolts failure at the top of pier.
3-The end sway from frame seem to have little or no damage, but first interior struts has significant damage. So It possible that pulling of the top chord associated with rotation of the vertical at this panel point cause instability. But remember the oversize truck is going south bond, it hit this brace the top chord will not be under maximum compression since truck is not in the mid span yet. So the collapse must have occurred under maximum load caused by other trucks or vehicles following that first truck hitting the strut.
4- Moving forward, it is best practice that all bridges with insufficient clearance and not having redundancy be subjected to progressive collapse analysis in case of a vehicle impact, then provide protection against impact or retrofit critical members. Just posting it for clearance limit without knowing the consequences of potential impact and mitigate it is not sufficient. Hope the policies and practice improve in maintenance and load rating to zero on risk for such failures. Hope there will be continued support to retrofit and replaced all deficient bridges. Neither slightest injury to public nor a grave cost of emergency replacement of a collapsed bridge should be tolerated.
I can tell you what caused the bridge to collapse. Driver error. Without a doubt, the WDOT issued a waybill listing restrictions on the drivers route, and it's common practice for bridges with limited clearance to have a sign in the middle showing the clearance there, and signs at either side showing the lesser clearance there. Either the driver was in ignorance of the height of his load, or he chose to ignore the posted warnings, or, most likely (based on my frequent dealings with over the road truckers) he arrogantly assumed that the rules of the road (such as speed limits) and load and height restrictions magically didn't apply to himself. I wonder if the State of Washington will hold that fellow personally liable for the cost of a replacement bridge.
When the finger pointing stops perhaps you'll ask what really caused the failure of this simple span. You have a clue. Notice how little damage was made to the load. I don't have the details, but I'm guessing there is an expansion bearing at this end of the bridge that supports that truss and allows movement forward and back. These bearings are not suppose to have a twist. This could have happened when the load made contact with that cross member. It may only have taken a slight twist to cause this failure. The State needs to rethink the way they issued permits.
Just found proof that a modern pre-stressed AASHTO girder bridge can collapse from collision: http://abclocal.go.com/wls/story?section=news/national_world&id=9116758
Even modern bridges cannot be fully protected from out-of-control or irresponsible vehicles.
A few comments. I agree that likely blame will be placed (unfairly) on the limited clearance of the truss. However, freeways are not just limited in clearance where truss bridges are present. Overpasses on the freeway, whether new and meeting standard height requirements or older with significant, posted clearance restrictions, are a fact of life on US freeways. Even non-fracture critical, redundant steel stringers or pre-stressed concrete bridges can be brought down by idiots on the road. Trucks have hit overpasses so hard they rip through half or more of the beams on a bridge. In Michigan, an overpass was destroyed when an accident caused a tanker truck to explode. http://www.denverpost.com/ci_12848139 Long story short, bridges cannot be completely idiot-proof. There is no excuse or alternative for responsible driving.
Also, someone asked to see what the truck looked like that caused the collapse. I attached a photo I dug up from WSDOT, as well as a photo showing damage to a span of the bridge that didn't collapse.
Well, the NTSB will decide. Looks like the truck cleared the portal brace but not the next vertical member's brace.
At any rate the NTSB will probably state that a concrete deck bridge is better because of infinite vertical clearance.
The NBI says clearance of 15.3', but that is assumedly in the center lanes only. From one article, the lowest clearance is 14.6' and the permitted height is 15.9'. That sounds like an "interference fit" to me. 8^P
The truss bridge is "functionally obsolete" because of low clearance and superstructure damage caused by oversized loads. Maybe they added to the deck material thickness since the permitted height was decided upon.
Especially with the previous damaged areas, you'd think height would be restricted to less than 14.6' to insure no contact with the overhead bracing.
So it comes down to someone's stupidity for allowing over height loads to weaken the structure(and ultimately destroy it), but the blame will be on too low overhead clearance of a through truss bridge.
Seeing the picture of the collapsed span and where the upper chord is deformed, here's what might have happened. Truck's oversize load hit the last sway brace before the portal strut on the way out of the bridge. Vertical member that brace attaches to was already pulled out of alignment slightly and weakened from previous (a yahoo news article showed photos of other sway brace-to-vertical member connections where the vertical member is deformed on the other standing spans) impacts. WDOT actually new about these damaged areas (according to the article) and had future plans to repair them. Not only does it hit the sway brace, it hits or hooks the sway brace enough to pull it, and the attached vertical with it. The vertical bends, and pulls the upper chord down at that point. Upper chord now deformed & unable to carry compressive load, compressive forces keep bending chord in direction it has been pulled & the span fails as a result.
Noticed something interesting. Turn the street view camera around 180° and zoom in on the truck at the entrance to the bridge. Looks eerily similar to the load that struck the bridge, and if you notice he is straddling the center line obviously where you need to be with an over tall load.
I think "truck-eating" bridges should have teeth/fangs and glow-in-the-dark glowering eyeballs painted on them. On the far right and far left of the bridge, keep score. "Trucks: 0; Bridge: (however many hash marks the bridge has to its credit)." I had not considered an undead motif and shall take it into consideration.
I think this trend in bridge collisions should be called: "the Zombie Trucker Apocalypse."
This page discusses the history of US 99:
Quote: "In the mid 1950s, a 4 lane US 99 expressway was built in the Mount Vernon-Burlington area. The Skagit River bridge on this expressway was built higher than the 1938 US 99 bridge, eliminating the need for a draw span on the expressway. This expressway was upgraded to freeway and is now I-5."
Meanwhile, Google Maps has already been updated to show a gap in I-5 at the bridge site.
That date comes from the National Bridge Inventory (NBI). There are a few bridges on the Interstate Highway System that pre-date 1956. One example, the Intercity Viaduct carrying I-70 through Kansas City, dates back to 1907.
Does anyone have a picture of the truck carrying the oversize (too tall load)? Or, did WSDOT allow them to continue on to the delivery point? It would also be informative to see a copy of the oversize permit that WSDOT issued to the operator. I'm thinking NTSB investigators would very much like to examine the suspect truck and its load. Just wondering...
Who says the the bridge was built in 1955? It's highly unlikely to have been built before the National Interstate and Defense Highways Act of 1956. It may have been built in the middle 1970s after the levees were raised, but not before I-5 came to Washington.
There will be lot's of talk about the crumbling infrastructure of Washington States Interstate highway system. Unlike Oregon, who has invested heavily in replacement of Interstate bridges on I-86 and I-5, as well as REPLACEMENT of damaged concrete roadway panels, Washington State continues with it's policy of grouting and surface grinding concrete panels, patching outdated truss bridge gussets with primer and half measures with expansion joint upgrades, siesmic assesments for bridge pier and approaches, as well as no plans for a strategy to replace or upgrade anything.
What is not being discussed is the nature of the I-5 corridor in Washington State which is mostly a mild upgrade of the old Highway 99 corridor which was mostly built in the Franklin Roosevelt era to enhance logistics to Fort Lewis in Pierce County Washington, an important Army and Army Airforce staging center during WW2. This is especially as bridges are concerned.
People are commenting that the Skagit River structure which failed yesterday was built for the I-5 improvement, the fact is, the bridge happened to be one of the newest bridges on highway 99 at the time the I-5 project was put through the legislature and because it was new, it was wide and strong enough to handle the traffic loads of the day on four wide (for the day)lanes. The failed bridge was one of the last truss structures on I-5 to have both North and South bound lanes on one structure. Washington saved a lot of money at the time, but we're gonna pay for it now as there is no bridge next to it to temporarily detour traffic to while repairs are made on the failed bridge. It will take months to repair the bridge - and don't get any hopes up they'll replace it, there's no funds to do so - they will replace the failed span, and promise a new structure - in a fairyland future which also contains a modern safe I-5 Interstate bridge from Vancouver to Portland
An example of a river crossing on the North fork of the Lewis River in Clark County Washington near Woodland, is an example where the Highway 99 Warren Truss structure built in 194O, although built to handle 4 lanes of traffic, could not meet the requirements of modern commerce. Instead of removing the obsolete structure, the legislature decided that at the time the improvements were needed, the structure was only 28 years old and had plenty of life left in it and chose to build an second Warren truss bridge East of it to dedicate to Northbound traffic in 1968, and the older bridge to Southbound traffic - three lanes each. Summary - Head to Portland from Seattle you cross the North fork of the Lewis river on a 73 year old structure, on your way back, on a 45 year old structure.
The Southbound structure also presents an issue for Class A commercial loads as the portals on the 73 year old bridge have a arch radius which is much closer to the road bead than the newer bridge next to it. Semis heading southbound are are required by law to move from lane 1 (where they belong) to lane 2, to be able to ensure safe entry onto the structure. Next time you are heading Southbound in this area and are approaching this structure take the time to look at the Northwest corner of the portal arch which is heavily damaged from a collision or two.
There are many of these Roosevelt administration era truss bridges like the South bound Lewis River bridge that were old highway 99 bridges which need to be replaced. Nobody wants to pay taxes, but we need to wake up an take the responsiblility to bequeath a safe commercial infrastructure in Washington State to our children.
Washington has a few of these simple span "continuous" bridges. They are exactly what Nathan described. They are simple spans that appear continuous, but have a break in the truss at the piers.
The Vernita Bridge is of similar design. (SEE PHOTOS 10 & 11)
I think the witch hunt to destroy truss bridges will fail, just like with the cantilever deck truss bridges in response to the I-35W Bridge Disaster in 2007. What the disaster will do is give law makers an incentive to pass a law banning oversized vehicles from travelling the roadways, period. This would force people and companies to reduce their load. After all, less is more, right?
Its a pity nobody on BridgeHunter got some more photos prior to collapse, since this is an interesting bridge. Hopefully someone can visit and get photos of what's left. I had to look at some of the collapse photos to get a sense of this very unusual bridge. It has inclined end posts at the far ends of the truss spans, but in between the end posts are vertical. It makes the bridge look continuous, but the bridge appears to be in fact simple spans. In this case, that appears to have been good, since when the span collapsed, it does not appear to have effected the other spans. If it was truly continuous, the collapse of one span would have damaged or destroyed the other spans.
Great. Now for the next 10 years I get to listen to DOTs and the media try to tell everyone that every single historic through truss is exactly like this one and if it isn't demolished and replaced immediately it will collapse, even though the collapse of this bridge was likely the result of a specific, unusual situation that has absolutely nothing to do with any other through truss.
If they find the remaining spans of the bridge structurally stable, they'll likely install a pre-fab replacement span to keep the bridge usable, like the replacing of the Kentucky Lake bridge span that collapsed after getting hit by a barge last year.
I suppose that if it was an oversize load that hit the overhead or portal bracing that would help explain where the failure occured, very near the portal.
WSDOT spokesman stated they are very confident the collapse is the result of an oversized vehicle hit. There are also reports of "No Fatalities". Hopefully this holds true.
There are accounts claiming that an oversize truck struck part of the structure immediately prior to the collapse. Yet to be confirmed.
There is an unofficial report that a truck crash was the cause. 'Crash & splash'?
The most recent inspection on the NBI is from August 2010. At that time, the bridge's sufficiency rating was 57.4, and the bridge was considered functionally obsolete, but not structurally deficient. The structural evaluation appraisal was given as 5, or "Somewhat better than minimum adequacy to tolerate being left in place as is".
I don't have the most recent inspection -- presumably from August 2012 -- but I'm really surprised this bridge has suddenly collapsed.
From news photos it appears that the north most truss is down. That being close to shore it appears the river is not very deep at that point allowing some cars to not be fully submerged. I hope that is a good sign and that there are not a large number of unseen, submerged cars. Keep fingers crossed! This happened just about at sunset so there are limited photos. Nearness to shore should help rescue effort. No indication why it failed.
News reports say that cars are in the water. More info as it develops at http://www.seattlepi.com/. Photo of collapsed bridge: http://ww3.hdnux.com/photos/21/65/77/4677622/4/centerpiecewide.jpg
The State of Washington is rated in sixth place for the lowest percentage of structurally deficient bridges - Only 5.1% of our bridges are in this category. Worst is PA with 26% of its bridges deficient. Considering that one of the best maintained states in the country had a collapse, I wouldn't drive anywhere in PA right now.
Thank heavens this did not occur on the start of the holiday weekend! Hope no lives are lost. only one section went down. It seems that we have very major bridge problems in the state of Washington.
We hope for everyone's safety after the collapse of this important bridge!