Catastrophic collapses of major bridges are fortunately rare. Notable examples from the previous few many years include a crash I35-W in Minneapolis in August 2007and the collapse of the Morandi Bridge in Genoa 11 years later. When such events actually occur, public attention understandably focuses on the nature of the collapse, which may extend a whole bunch of meters in a matter of seconds, and its causes.
Whether attributable to extreme loading or an accident, these supposedly rare events in the life of a bridge still need to be assessed before they occur and mitigating measures taken in accordance with all potential consequences. This type of evaluation is known as a “risk-based consequence assessment.” The cost of taking additional measures in the near future may prevent serious negative consequences further down the line.
As many of these structures are over 50 years old, we often hear that the condition of the bridge can have deteriorated due to deterioration and increased traffic loads – each in terms of volume and frequency of vehicles. Additionally, older bridges were designed to standards that were replaced by recent knowledge and technology.
Although these aspects have helped persuade some politicians to increase infrastructure budgets, including through Bipartisan agreement on infrastructure in the US, the trend is to deal with stronger, more resilient recent construction and dearer maintenance of existing structures. The latter makes it easier for politicians to show that the money spent has had a positive effect since it leads to an overall reduction in the number of bridges considered obsolete or defective.
Given the enormous scale of the bridge maintenance problem – the American Highway Builders Association estimated that one in three U.S. bridges requires repair – it is smart to allocate available funds widely. However, this approach can have serious flaws if it doesn’t establish clear priorities based on the scale of the potential consequences of accidents and failures.
One of the two central pylons Francis Scott Key Bridge in Baltimore was rammed by a 300 m long container ship on March 24 at around 1:30 a.m., which led to the gradual collapse of the entire bridge lattice inside 4 seconds.
Although the bridge was 47 years old it was considered to be in “fair” condition last inspection in 2008 and, according to Maryland’s governor after the collision, were “fully compliant with regulations,” experts agreed that the catastrophic collapse was to be expected making an allowance for the magnitude of the ship’s impact. At that point, maintenance staff were working on the bridge, filling in holes, amongst others six people died.
Direct and indirect consequences
Bridge collapses due to ship collisions have happened before and can unfortunately occur again. In a similar incident in 1980 Sunshine Skyway Bridge in Tampa Bayalso a steel truss structure, was hit by a barge, causing the deaths of 35 people as a result of the collapse of over 400 m (1,300 ft) of its span.
The American Association of Highway and Transportation Officials reported 31 major bridge collapses worldwide as a result of ship collisions in the years 1960–2002, leading to the death of 342 people.
The latest was the destruction of the Francis Scott Key Bridge, which cut off one of three transportation links across the Patapsco River at the busy Baltimore Harbor. Given its importance as a transport hub, this can have serious economic consequences, which may very well be expected.
More than 30,000 vehicles that used the Key Bridge each day must now seek alternative routes. Importantly, the other two local crossings run through tunnels, which places restrictions on the type of traffic that may cross the river, as the transport of hazardous materials through tunnels is prohibited.
Shipping traffic to and from the Port of Baltimore has been suspended until further notice. Removing the debris shall be a complex operation and work to ensure secure navigation of the river for every kind of vessels will take time. Due to the construction of the recent bridge, further restrictions shall be crucial.
There are already signs that the bridge collapse is affecting supply chains around the world, particularly in the passenger automotive and light-weight truck, agricultural and construction machinery sectors.
Jim Lo Scalzo/EPA-EFE
The economic consequences of this catastrophic event shall be significant at each the city and state level. Early estimates of liability insurance payouts suggest the total cost may exceed $1.5 billion (£1.2 billion).
Judging by what happened after bridge collapses in the past, this might have a negative impact on jobs and the local economy: around 14,000 people work in the port itself, and one other 140,000 in related services.
First of all, six people lost their lives. However, the human cost might have been much higher if the incident had occurred during peak hours. If the impact occurred on a ship carrying hazardous materials, the environmental costs is also dramatic.
Given knowledge from previous incidents about the severity of ship-bridge collisions and major bridge collapses, it was clear that this bridge was critical.
For bridges, many mitigation options can be found, including installing safety devices around bridge supports (pylons) in the form of fenders or artificial islands to deflect the vessel or reduce collision energy.
In general, for bridges, there are measures that also can assistance on the ship side, comparable to requiring the use of tugs or introducing stricter speed limits, depending on the type of cargo and the size of the ship. However, it’s unclear whether this could have made any difference in the Baltimore bridge collapse.
First and foremost, by conducting a risk-based impact assessment every ten years or so, authorities chargeable for key infrastructure will help visualize evolving threats and prioritize their responses accordingly. For river bridges, ever-increasing vessel sizes, faster turnaround times and bigger cargo volumes have increased the risk – and price – of a catastrophic collision or collapse.
