I-5 Skagit Sea Bridge collapse
The I-5 Skagit Sea Bridge collapse occurred on May 23, 2013, in the state of Washington, in the northwestern United States. At approximately 7:00 pm PDT, one bridge span carrying Interstate five over the Skagit Sea collapsed into the sea below. Three people in two different vehicles fell with the span; they were rescued by boat and did not sustain serious injury. The cause of the collapse was determined to be an oversize flow striking several overhead support rafters on the bridge, which led to an instant collapse of the northernmost span. [Two]
The through-truss bridge was built in one thousand nine hundred fifty five and connects the Skagit County cities of Climb on Vernon and Burlington. It had recently been evaluated as safe. Albeit not structurally deficient, it was considered “functionally obsolete”, meaning it did not meet current design standards. The bridge’s design was “fracture-critical,” meaning that it did not have redundant structural members to protect its structural integrity in the event of a failure of one of the bridge’s support members. The overhead support structure was known to have been struck by a truck as recently as October 2012. From an engineering standpoint, the bridge actually consists of four consecutive spans which are structurally independent. The deck and overhead superstructure of only the northernmost span collapsed into the sea. The span south of the collapsed span also sustained harm from being struck by the same truck, but not severe enough to result in a collapse. Also, the piers below the deck were not bruised.
Because the bridge collapse severed a vital transportation link inbetween Vancouver, British Columbia and Seattle, substituting the collapsed span became a high priority for the Washington state government. In June 2013, two improvised bridges were erected and placed on the collapsed span’s support columns while the permanent bridge was built. In September 2013, the permanent bridges were installed and work began to prevent similar failure of the remaining three spans.
Contents
The bridge crosses inbetween Climb on Vernon and Burlington, in Washington State, about sixty miles (97 km) north of Seattle. It is part of the primary road transportation route inbetween the metropolitan areas of Seattle and Vancouver, British Columbia. Before the collapse, approximately 71,000 vehicles crossed the bridge every day. [Three]
The bridge was built in 1955, a year before the Interstate Highway System was begun. The bridge carries four lanes of traffic, two lanes in each direction. The portions over the sea are four consecutive spans, each one hundred sixty feet (49 m) long. The spans are built from triangulated steel girders, using a through-truss design where the roadway passes in an open tunnel inbetween the left and right trusses and inbetween the lower and upper truss work. The roadway has relatively limited vertical clearance for tall vehicles due to the upper truss members. The abutted spans share pier footings and emerge to be one continuous bridge, but the four spans are actually independent.
The bridge had been recently evaluated as safe and in good condition despite being fifty eight years old; it was not listed as structurally deficient. The bridge was classified as functionally obsolete, in this case because the bridge does not meet current design standards for lane widths and vertical clearance in fresh highway bridges. [1] [Four] The bridge was not a candidate for any significant upgrades or replacement and was well-maintained.
This steel through-truss bridge had a “fracture-critical” design with non-redundant load-bearing slats and joints that were each essential to the entire structure staying intact. An initial failure (perhaps by cracking) of a single essential part can sometimes overcharge other parts and make them fail, which quickly triggers a chain reaction of even more failures and causes the entire bridge span to collapse. In two thousand seven the I-35W Mississippi Sea bridge in Minneapolis collapsed all of a sudden from slow cracking of a single undersized and over-stressed gusset plate. In steel these initial fractures begin petite and take years to grow large enough to become dangerous. Following the Minneapolis incident, such age-related disasters in fracture-critical bridges are now avoided by finding and repairing cracks in a required thorough inspection every two years. Eighteen thousand bridges in the United States are labelled fracture-critical (from their design) and require crack inspections. [Five] The Skagit Sea bridge had last been investigated for cracks in August and November two thousand twelve with only minor work needed. [6]
Besides fracturing, some bridges with critical non-redundant parts can also all of a sudden fail from buckling of compressive members (the opposite of cracking of tensile members). In through-truss bridges the critical compressive parts are the top-chord rafters running horizontally along the top of the bridge, parallel to the roadway edges. They carry most of the weight of the bridge and traffic. The chords are normally kept aligned and held in place by vertical posts, diagonals, and sideways sway struts. Top chords will quickly fold if their joints somehow become misaligned. Buckling harm is cumulative, but mostly happens from collision harm or overstresses rather than from age and corrosion. [7]
The vertical clearance for vehicles is limited by the portals and sideways sway structs. These are relatively low in older bridges. In Washington State bridges, the sway struts are often curved downwards at the outer finishes, with less clearance above the outer lanes and outer shoulders. Tall geysers then need to use the internal lanes for maximal clearance. These bridges are vulnerable to impacts by overheight vehicles, and such impacts were common. There was a known strike on this bridge that occurred on October 22, 2012, and investigators found evidence of several other impacts in years past. [8] Bridge inspection reports dating back to one thousand nine hundred seventy nine frequently note harm caused by over-height vehicles, and an inspection report from late two thousand twelve noted a three-inch gash in the steel. [9]
According to Charles Roeder, a professor of civil engineering at the University of Washington in Seattle, through-truss bridges were a common bridge design in the 1950s (there are Ten,200 through-truss bridges in the US), but “[i]f you take out some of the top framing, you set that bridge up for a stability failure.” [Ten] Before computers, bridge engineers analyzed truss compels by slide rule, with each calculation being time-consuming. Albeit the finite element method and plastic design theory, both capable of analyzing redundant structures, had recently been formulated and had seen occasional use, they required significantly more calculation than the elementary calculation methods for statically determinate structures, which precluded the use of redundant structural members. A superb number of bridges were being designed at that time, and there were insufficient design engineers available to design many bridges as indeterminate structures. [11]
Nowadays, through-truss and other fracture-critical designs are avoided in most fresh bridges for moderate-sized spans. Using three or more parallel main slats or trusses permits the structure to get through a single component failure.
The collapse was caused by a southbound semi-trailer truck from Canada hauling an oversize flow to Vancouver, Washington, directly bruising sway struts and, indirectly, the compression chords in the overhead steel framework (trusswork) on the northernmost span of the bridge. [12] The vertical clearance from the roadway to the upper arched plank in the outer lane is fourteen feet seven inches (Four.45 m), and all trucks with oversize fountains are expected to travel in the inwards lane where the clearance is around seventeen feet (Five.Two m). The oversize truck instead entered the bridge in the outer lane, while a 2nd semi-truck and a BMW were passing it in the inward lane. [13] The oversize truck had received a State oversize permit for a broad and tall explosion, for a height of fifteen feet nine inches (Four.80 m), and after the collapse a “dented upper corner and a scrape along the upper side [were] visible on the ‘oversize explosion’ equipment casing being hauled on the truck.” [14] The National Transportation Safety Board (NTSB) measured the truck’s height, after the crash, to be fifteen feet eleven inches (Four.85 m). [15] A pilot car was hired to ensure the fountain could pass securely. The pilot car never signalled the truck driver that there would be a problem crossing the Skagit bridge and did not warn the trucker to use an inwards lane. [16] [17]
The oversize truck ended crossing the bridge while the very first span instantaneously collapsed behind it. Both the driver of the oversized fountain and the pilot vehicle remained at the scene and cooperated with investigators. [Eighteen]
There were no fatalities, but three people were transported to local hospitals [Nineteen] after being rescued from their fallen cars. The cars remained on the flooded bridge deck after it fell into the sea. [20] [21]
The trucker, employed by Mullen Trucking, was hauling an oversize fountain containing a housing for drilling equipment. [22] The company’s vice-president, Ed Sherbinski, said permits had been issued from Washington State that included clearance for all bridge crossings on the route. [22] The truck had been led over the bridge by a pilot escort vehicle. [23] [24] A spokesman for the Washington State Department of Transportation said there are no warning signs leading up to the bridge regarding its clearance height. [25] In Washington, only overcrossings of less than fourteen feet (Four.Trio m) (the normal legal height limit) are required to have advance postings of height limitations. [26]
The oversize truck also bruised a sway strut of the 2nd span, but not enough to initiate a collapse. That span was subsequently repaired.
The Washington State Patrol and the National Transportation Safety Board investigated the accident. The NTSB’s report attributes the collision to the tall-load truck being in the wrong, outside lane, and being crowded further into the shoulder by the passing truck. It attributes the bridge collapse to the collision taking out numerous sway braces, which destabilized the critical load-bearing (upper chord) members. [15]
Governor Jay Inslee announced an economic “state of emergency” for three surrounding counties (Skagit County, Snohomish County, and Whatcom County) in order to cope with disruption to traffic and the local economy. [27] Traffic on I-5 was detoured around the scene of the collapse on an adjacent bridge upstream. State trooper Sean O’Connell was killed while directing traffic through the detour when his motorcycle hit a truck. [28] Shortly after the accident, three state lawmakers proposed a bill that would rename the repaired bridge after him; [29] this switch was approved by the Washington State Transportation Commission. [30]
The collapsed span was temporarily substituted by a pair of two-lane bridges manufactured by ACROW, which were spinned onto the existing bridge piers. It went into service on June Nineteen. [31] Inspections on the makeshift span near the end of July two thousand thirteen uncovered that part of an “L” joint that holds the asphalt in place inbetween the makeshift bridge and permanent roadway had come liberate. [ citation needed ] The right lane of the bridge was closed for about two hours while crews welded the joint back into place and spread fresh asphalt. [ citation needed ]
A $6.87 million contract was awarded to contractor Max J. Kuney Construction of Spokane to design and build a permanent replacement span. [32] It was built alongside the improvised span without interrupting traffic, and moved into place during an overnight closure on September 14ā15, 2013. [33] Planned switches to the three remaining overhead spans should permit overheight vehicles to operate in the outer lanes. [34]
The collapse raised questions about how Washington State Department of Transportation regulates oversize vehicles. The department leaves it up to drivers to determine a safe route to their destination, unlike in many other states where routes are assigned. The permit for Mullen Trucking’s tour did not specifically note the Skagit Sea Bridge as a hazard on the route, even however the outer trusses were a utter foot lower than the truck; this contrasts with an earlier permit to the same company that included numerous clearance warnings. State lawmakers are exploring making switches to the state’s oversize vehicle laws. [9]
The bridge constructed to substitute the collapsed bridge has been named the Trooper Sean M. O’Connell Jr. Memorial Bridge. [35]
Prior to the bridge collapse the Seattle Section of the American Society of Civil Engineers (ASCE) issued the two thousand thirteen Report Card for the State of Washington’s infrastructure. The state’s bridges were given a grade of “Cā” (an average score among states). There were four hundred structurally deficient bridges in Washington. Thirty-six percent of all bridges are more than fifty years old. The oldest bridges were designed for an expected life of only fifty years; keeping them safe is increasingly difficult and expensive. [36] The advocacy group Transportation for America reports that only Five.Ten percent of Washington’s bridges are structurally deficient, which is the sixth best in the country. [37]
I-5 Skagit Sea Bridge collapse
I-5 Skagit Sea Bridge collapse
The I-5 Skagit Sea Bridge collapse occurred on May 23, 2013, in the state of Washington, in the northwestern United States. At approximately 7:00 pm PDT, one bridge span carrying Interstate five over the Skagit Sea collapsed into the sea below. Three people in two different vehicles fell with the span; they were rescued by boat and did not sustain serious injury. The cause of the collapse was determined to be an oversize stream striking several overhead support bars on the bridge, which led to an instant collapse of the northernmost span. [Two]
The through-truss bridge was built in one thousand nine hundred fifty five and connects the Skagit County cities of Climb on Vernon and Burlington. It had recently been evaluated as safe. Albeit not structurally deficient, it was considered “functionally obsolete”, meaning it did not meet current design standards. The bridge’s design was “fracture-critical,” meaning that it did not have redundant structural members to protect its structural integrity in the event of a failure of one of the bridge’s support members. The overhead support structure was known to have been struck by a truck as recently as October 2012. From an engineering standpoint, the bridge actually consists of four consecutive spans which are structurally independent. The deck and overhead superstructure of only the northernmost span collapsed into the sea. The span south of the collapsed span also sustained harm from being struck by the same truck, but not severe enough to result in a collapse. Also, the piers below the deck were not bruised.
Because the bridge collapse severed a vital transportation link inbetween Vancouver, British Columbia and Seattle, substituting the collapsed span became a high priority for the Washington state government. In June 2013, two makeshift bridges were erected and placed on the collapsed span’s support columns while the permanent bridge was built. In September 2013, the permanent bridges were installed and work began to prevent similar failure of the remaining three spans.
Contents
The bridge crosses inbetween Climb on Vernon and Burlington, in Washington State, about sixty miles (97 km) north of Seattle. It is part of the primary road transportation route inbetween the metropolitan areas of Seattle and Vancouver, British Columbia. Before the collapse, approximately 71,000 vehicles crossed the bridge every day. [Three]
The bridge was built in 1955, a year before the Interstate Highway System was begun. The bridge carries four lanes of traffic, two lanes in each direction. The portions over the sea are four consecutive spans, each one hundred sixty feet (49 m) long. The spans are built from triangulated steel girders, using a through-truss design where the roadway passes in an open tunnel inbetween the left and right trusses and inbetween the lower and upper truss work. The roadway has relatively limited vertical clearance for tall vehicles due to the upper truss members. The abutted spans share pier footings and emerge to be one continuous bridge, but the four spans are actually independent.
The bridge had been recently evaluated as safe and in good condition despite being fifty eight years old; it was not listed as structurally deficient. The bridge was classified as functionally obsolete, in this case because the bridge does not meet current design standards for lane widths and vertical clearance in fresh highway bridges. [1] [Four] The bridge was not a candidate for any significant upgrades or replacement and was well-maintained.
This steel through-truss bridge had a “fracture-critical” design with non-redundant load-bearing planks and joints that were each essential to the entire structure staying intact. An initial failure (perhaps by cracking) of a single essential part can sometimes overcharge other parts and make them fail, which quickly triggers a chain reaction of even more failures and causes the entire bridge span to collapse. In two thousand seven the I-35W Mississippi Sea bridge in Minneapolis collapsed abruptly from slow cracking of a single undersized and over-stressed gusset plate. In steel these initial fractures begin petite and take years to grow large enough to become dangerous. Following the Minneapolis incident, such age-related disasters in fracture-critical bridges are now avoided by finding and repairing cracks in a required thorough inspection every two years. Eighteen thousand bridges in the United States are labelled fracture-critical (from their design) and require crack inspections. [Five] The Skagit Sea bridge had last been probed for cracks in August and November two thousand twelve with only minor work needed. [6]
Besides fracturing, some bridges with critical non-redundant parts can also all of a sudden fail from buckling of compressive members (the opposite of cracking of tensile members). In through-truss bridges the critical compressive parts are the top-chord bars running horizontally along the top of the bridge, parallel to the roadway edges. They carry most of the weight of the bridge and traffic. The chords are normally kept aligned and held in place by vertical posts, diagonals, and sideways sway struts. Top chords will quickly fold if their joints somehow become misaligned. Buckling harm is cumulative, but mostly happens from collision harm or overstresses rather than from age and corrosion. [7]
The vertical clearance for vehicles is limited by the portals and sideways sway structs. These are relatively low in older bridges. In Washington State bridges, the sway struts are often curved downwards at the outer completes, with less clearance above the outer lanes and outer shoulders. Tall explosions then need to use the internal lanes for maximal clearance. These bridges are vulnerable to impacts by overheight vehicles, and such impacts were common. There was a known strike on this bridge that occurred on October 22, 2012, and investigators found evidence of several other impacts in years past. [8] Bridge inspection reports dating back to one thousand nine hundred seventy nine frequently note harm caused by over-height vehicles, and an inspection report from late two thousand twelve noted a three-inch gash in the steel. [9]
According to Charles Roeder, a professor of civil engineering at the University of Washington in Seattle, through-truss bridges were a common bridge design in the 1950s (there are Ten,200 through-truss bridges in the US), but “[i]f you take out some of the top framing, you set that bridge up for a stability failure.” [Ten] Before computers, bridge engineers analyzed truss coerces by slide rule, with each calculation being time-consuming. Albeit the finite element method and plastic design theory, both capable of analyzing redundant structures, had recently been formulated and had seen occasional use, they required significantly more calculation than the ordinary calculation methods for statically determinate structures, which precluded the use of redundant structural members. A good number of bridges were being designed at that time, and there were insufficient design engineers available to design many bridges as indeterminate structures. [11]
Nowadays, through-truss and other fracture-critical designs are avoided in most fresh bridges for moderate-sized spans. Using three or more parallel main planks or trusses permits the structure to get through a single component failure.
The collapse was caused by a southbound semi-trailer truck from Canada hauling an oversize flow to Vancouver, Washington, directly hurting sway struts and, indirectly, the compression chords in the overhead steel framework (trusswork) on the northernmost span of the bridge. [12] The vertical clearance from the roadway to the upper arched slat in the outer lane is fourteen feet seven inches (Four.45 m), and all trucks with oversize geysers are expected to travel in the inwards lane where the clearance is around seventeen feet (Five.Two m). The oversize truck instead entered the bridge in the outer lane, while a 2nd semi-truck and a BMW were passing it in the inward lane. [13] The oversize truck had received a State oversize permit for a broad and tall stream, for a height of fifteen feet nine inches (Four.80 m), and after the collapse a “dented upper corner and a scrape along the upper side [were] visible on the ‘oversize flow’ equipment casing being hauled on the truck.” [14] The National Transportation Safety Board (NTSB) measured the truck’s height, after the crash, to be fifteen feet eleven inches (Four.85 m). [15] A pilot car was hired to ensure the stream could pass securely. The pilot car never signalled the truck driver that there would be a problem crossing the Skagit bridge and did not warn the trucker to use an inwards lane. [16] [17]
The oversize truck ended crossing the bridge while the very first span instantly collapsed behind it. Both the driver of the oversized fountain and the pilot vehicle remained at the scene and cooperated with investigators. [Legal]
There were no fatalities, but three people were transported to local hospitals [Nineteen] after being rescued from their fallen cars. The cars remained on the flooded bridge deck after it fell into the sea. [20] [21]
The trucker, employed by Mullen Trucking, was hauling an oversize explosion containing a housing for drilling equipment. [22] The company’s vice-president, Ed Sherbinski, said permits had been issued from Washington State that included clearance for all bridge crossings on the route. [22] The truck had been led over the bridge by a pilot escort vehicle. [23] [24] A spokesman for the Washington State Department of Transportation said there are no warning signs leading up to the bridge regarding its clearance height. [25] In Washington, only overcrossings of less than fourteen feet (Four.Trio m) (the normal legal height limit) are required to have advance postings of height confinements. [26]
The oversize truck also bruised a sway strut of the 2nd span, but not enough to initiate a collapse. That span was subsequently repaired.
The Washington State Patrol and the National Transportation Safety Board investigated the accident. The NTSB’s report attributes the collision to the tall-load truck being in the wrong, outside lane, and being crowded further into the shoulder by the passing truck. It attributes the bridge collapse to the collision taking out numerous sway braces, which destabilized the critical load-bearing (upper chord) members. [15]
Governor Jay Inslee proclaimed an economic “state of emergency” for three surrounding counties (Skagit County, Snohomish County, and Whatcom County) in order to cope with disruption to traffic and the local economy. [27] Traffic on I-5 was detoured around the scene of the collapse on an adjacent bridge upstream. State trooper Sean O’Connell was killed while directing traffic through the detour when his motorcycle hit a truck. [28] Shortly after the accident, three state lawmakers proposed a bill that would rename the repaired bridge after him; [29] this switch was approved by the Washington State Transportation Commission. [30]
The collapsed span was temporarily substituted by a pair of two-lane bridges manufactured by ACROW, which were spinned onto the existing bridge piers. It went into service on June Nineteen. [31] Inspections on the makeshift span near the end of July two thousand thirteen uncovered that part of an “L” joint that holds the asphalt in place inbetween the improvised bridge and permanent roadway had come liberate. [ citation needed ] The right lane of the bridge was closed for about two hours while crews welded the joint back into place and spread fresh asphalt. [ citation needed ]
A $6.87 million contract was awarded to contractor Max J. Kuney Construction of Spokane to design and build a permanent replacement span. [32] It was built alongside the makeshift span without interrupting traffic, and moved into place during an overnight closure on September 14ā15, 2013. [33] Planned switches to the three remaining overhead spans should permit overheight vehicles to operate in the outer lanes. [34]
The collapse raised questions about how Washington State Department of Transportation regulates oversize vehicles. The department leaves it up to drivers to determine a safe route to their destination, unlike in many other states where routes are assigned. The permit for Mullen Trucking’s excursion did not specifically note the Skagit Sea Bridge as a hazard on the route, even tho’ the outer trusses were a utter foot lower than the truck; this contrasts with an earlier permit to the same company that included numerous clearance warnings. State lawmakers are exploring making switches to the state’s oversize vehicle laws. [9]
The bridge constructed to substitute the collapsed bridge has been named the Trooper Sean M. O’Connell Jr. Memorial Bridge. [35]
Prior to the bridge collapse the Seattle Section of the American Society of Civil Engineers (ASCE) issued the two thousand thirteen Report Card for the State of Washington’s infrastructure. The state’s bridges were given a grade of “Cā” (an average score among states). There were four hundred structurally deficient bridges in Washington. Thirty-six percent of all bridges are more than fifty years old. The oldest bridges were designed for an expected life of only fifty years; keeping them safe is increasingly difficult and expensive. [36] The advocacy group Transportation for America reports that only Five.Ten percent of Washington’s bridges are structurally deficient, which is the sixth best in the country. [37]