How the Crimean Bridge explosion caused multiple spans to collapse
11 OCT, 2022 BY
ROB HAKIMIAN
A structural engineer from the University of Sheffield has explained why an explosion on the Crimean Bridge caused such a catastrophic collapse along the structure.
This weekend’s explosion on the Crimean Bridge, which connects Krasnodar in Russia with Kerch in Crimea, saw several spans of the bridge plummet into the water.
University of Sheffield department of civil engineering blast and impact dynamics research associate Andrew Barr said that this was because the spans were connected by a single beam.
Destruction of the 17km bridge, which is in fact two separate but parallel bridges carrying road and rail, occurred at around 6am local time on Saturday. Footage shows a huge fireball erupting on the road bridge, engulfing the whole road and some of the train bridge. Subsequent images have laid bare the extent of the damage, which extends about five spans on one side of the road bridge with three ending up in the water.
“The road section of the affected part of the Crimean Bridge has a composite slab orthotropic deck, supported on 3.2m deep steel plate girders over the 64m span between its concrete piers,” Barr said. “An important detail in understanding the extent of the damage to the bridge, with three visibly collapsed spans, is that these are not individual 64m sections. Instead, the spans are grouped together in sets of four, formed from a continuous beam which passes over the tops of the piers.”
Barr added that the continuous nature of the beams means that when the explosion caused the deck to fail and collapse into the water it pulled on the entirety of the beam and the bridge deck from both sides downwards with it.
“It appears that the explosion occurred near the centre of one of the bridge spans, and was sufficiently large or shaped in such a way as to cause a complete failure of the deck,” he said. “This created two new cantilevered sections of deck, which could not support their own weight and buckled over their supports. As these sections of deck fell into the water, potentially also provided with significant additional momentum from the explosive loading, they will have pulled on the surviving spans on either side.”
Between each beam there are gaps where expansion joints are inserted to allow the surface to expand and contract depending on the weather. The tensile and flexural load could therefore not pass through the expansion joints, causing the ends of the four-span beam to be displaced towards the damaged area, Barr explained. This wrenched the deck away from the bearings, causing a failure across four spans. While one span remained atop its piers, the other three collapsed into the water.
“The surviving intermediate span still stands, but has likely suffered significant damage near the zones where the adjacent spans have buckled, as well as being unseated from its bearings,” he added.
Despite there being theories about the cause of the explosion, neither the footage nor the images of the blast damage are conclusive as to whether the blast occurred above or below the deck, Barr said. “Some clues such as the adjacent road surface being blackened and its cantilevered wing sections appearing to be bent downwards may appear to favour a detonation on top of the deck, but ultimately the interacting pressure waves created around a bridge structure during an explosion are very complex,” he explained. “It would require a careful local investigation of the damaged bridge to unpick what has happened.”
The entirety of the four spans on the damaged beam will need to be replaced. The connecting span seems largely intact and could continue in use, but it might have suffered some damage when the connecting deck pulled away from it as it fell into the water. Only closer inspection and metallurgical sampling will reveal the extent of repair needed on it.
There was a tanker train adjacent to the explosion on the rail bridge, which was partly engulfed by the explosion. This caused fuel within the train to ignite and it remained burning for several hours, with fire spreading across the tankers and dripping down onto the rail bridge, melting the steel sections of the structure, including weakening of the girders. Images show burns on the concrete piers, which may also have been weakened, potentially making its reinforcement more susceptible to corrosion, Barr said. This will also need to be further examined by investigators.
Russia has reported that traffic has now resumed across the side of the Crimean Bridge that did not collapse. It is unclear the extent of safety inspection carried out on the bridge before allowing cars and buses to resume use, with head of Crimea Sergey Askyonov admitting that it still needs “to undergo the full inspection procedure”.
While it is likely safe, reopening it this soon seems to be an attempt at a show of strength from Russia. “The low weight of this traffic is less likely to instigate a further collapse, but allowing any use of the bridge before a detailed assessment of the structure has been carried out is very unusual,” Barr said. “It is indicative of the intense political pressure for the bridge to be seen as operational.”
The rail bridge does not appear to have resumed use. Floating cranes have been pictured lifting the burnt tanker train off of the track.
. The orange was a Ukrainian blue yesterday 
