Kerch Bridge Update

In the week following the explosion or explosions on the Kerch Bridge connecting Crimea with European Russia, there have been lots of questions and few solid answers. Initial analysis of the damage, even from informed engineers, was sanguine. For instance, as of this past Monday,

Observers have been left wondering: what was the effect of the blast and fire on the surviving bridge elements, what repairs could be required, and when is it safe to re-open a bridge after such an event?

As experts in bridge safety and blast engineering, we have (some) answers.

. . . In structural engineering, safety is not an either-or proposition. It is measured on a continuum known as the probability of failure, or more positively, the reliability index of a structure. . . . for key bridges such as the Crimean Bridge, it may be reasonable to accept a reduced level of safety when the costs associated with a disruption are very high.

Cranes have been shown lifting the fuel tanker wagon wreckage off the Crimea-bound rail line. It remains to be seen how the steel girders will perform under train travel. It is likely the trains will be instructed to go slow to reduce vibratory effects, and that wagons will not be fully-loaded.

Under normal circumstances, the blast and damage we have seen would result in an extended closure and repair works. Clearly, however, the circumstances are far from normal.

Official Russian statements as of Monday were also sanguine but vague:

A pillar and a part of the rail track of the Crimean Bridge, which was damaged on Saturday in a terrorist attack, will need to be repaired, Russian Deputy Prime Minister Marat Khusnullin said on Monday. Speaking at a meeting with Prime Minister Mikhail Mishustin, Khusnullin offered reassurances that the damage did not pose any safety risks to vehicles.

“As a result of the diagnostics, the need to eliminate damage to the expansion joint on one of the pillars was established. The preliminary deadline for repairing the damage to the pillar is the end of this week,” Khusnullin said.

. . . Metal structures for the repairs will begin being delivered by the end of the week from the cities of Tyumen, Kurgan, and Voronezh, the deputy prime minister said, expressing gratitude to everyone involved for their “prompt work.”

As for the railway portion of the bridge, Khusnullin said that a preliminary assessment of the tracks had shown that two spans needed to be replaced.“The repairs do not affect the delivery of goods and passengers,” he emphasized.

The head of Crimea, Sergey Aksyonov, has estimated that fully restoring the bridge could take about two months.

It was thought that the rail bridge that runs parallel to the highway bridge suffered the least damage, since it was farther from the blast, although the effect on the steel of the heat from the burning tank cars loaded with fuel was hard to calculate. The rail bridge has two tracks, with the track farthest from the blast thought to be able to carry trains at reduced speed and loads, as outlined in the first link above. An initial video showed a test train operating on this track, but as of Tuesday, there were no additional trains:

Day 4 and still no train runs on the Kerch Bridge. No (military) supplies for Kherson and Zaporizhzhia since 4 days, at least not in large quantities. Remember, war of logistics and every day counts. #Kerch #Crimea #Ukraine

— (((Tendar))) (@Tendar) October 11, 2022

Repair of the highway bridge is likely to be complicated by damage to one of the piers, visible in the photo at right. This means that restoring this section of the bridge will require more than just replacing individual spans; likely this pier will also need to be replaced, a much bigger job. The official Russian version was updated later in the week, and it appears to reflect the damage to the highway pier:

On Oct. 13, the Russian cabinet issued a decree identifying Irkutsk-based construction firm Nizhneangarsktransstroy as handling the repairs and ordering all work on the bridge to be complete by July 1, 2023. According to Khusnullin, the main work repairing the bridge expected to be completed by the end of the year.

"Technologies have been found to dismantle the existing destroyed bridge supports,” Khusnullin told the news agency. “I can say that the first supports of the new bridge have already been manufactured at factories and are going to the Crimean bridge.”

Howwever, this time line is considerably longer than the two month estimate for fully restoring the bridge that was given on Monday. There's no specific reference to the status of the rail spans, but the few discussions available on the web suggest that both tracks on the railroad bridge are supported by a single set of steel box girder spans, which means that the fuel fire would have damaged one or more spans supporting both tracks, which means the rail bridge will not be usable for some months.

The problem, of course, is that Ukraine has resumed a southern offensive in Kherson as of this morning, and Russian forces west of the Dnieper are already isolated from supply and reinforcement due to loss of bridges over that river. For now, it looks as though Russia won't be able to supply its forces elsewhere in Kherson or Crimea for a period of some months just as Ukraine begins a serious offensive in that area.