Morandi Bridge: analysis of the Ferrometal CCTV video clip in six enhanced sequences

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This study suggests that the root cause of the failure sequence is given by the rupture of the south-eastern concrete cable stay in proximity of the top of the A-pylon.

The analysis is based on six short sequences extracted from the "Ferrometal" video clip as published by "Guardia di Finanza Genova" on July 1st, 2019.

By Kristian Hasenjäger on July 4th, 2019 (updated: July 8th)

Introduction and methodology

About the six animation sequences extracted from the Ferrometal CCTV clip:

This research analyses the CCTV video clip recorded by the company Ferrometal S.p.a located in Via Lorenzi Nicola 11/N.
The video clip, hereafter nicknamed "Ferrometal video", was seized by Italian authorities "Guardia di Finanza Genova" immediately after the incident (August 14, 2018) and was declassified on July 1st, 2019. The released video is available here.
The author of this analysis has uploaded an edited version to youtube, adding a frame counter for later reference (see below) and applying minor image enhancements for better clarity.
Six short sequences were extracted from the original clip
Each frame (1920px x 1080px) constituting the six sequences was adequately enhanced (gamma correction, sharpness, rotation, and crop to subject) avoiding adding/amplifying bias or removing valuable image information.
The six short sequences shall help to convey the absolute maximum amount of information the original clip embodies.
Each frame has its frame-number imprinted in the upper left
The frame numbering is sequential in the original Ferrometal clip
Bridge failure starts with frame 000
The original Ferrometal clip consists of many identical redundant frames, usually 7 to 8 consecutive identical frames succeed each other before new content follows.
Therefore, the animation sequences below consist of non-redundant frames only. As a result, the frame counter increment between frames may differ
After removal of redundant frames, the CCTV clip can be subdivided into several sequences, each consisting of 3 to 6 unique frames (there are no more non-redundant frames in the original clip)
The six most meaningful sequences are shown below as animated GIFs
The frame rate of the animated sequences is 4 fps, while the original video came with 25 fps.

Sequence 1:

Sequence 1 (5 frames): The bridge deck starts flexing

Frame 000 marks the beginning of the bridge failure
The bridge deck starts flexing on both sides of tower 9. In parallel, a sag suggesting a loss of tension in the supporting cables along the southern side of the bridge can be observed.
However, a careful inspection of the amount of vertical drop shows that the out-most eastern section (on the right) drops further than the west-most section (on the left).
The slight flexing (a few pixels only, observe carefully) southward pointing top cross-beam indicates that the cause might be a rupture of the south-eastern cable stay in proximity of the cross-beam.
At this point the system is not balanced anymore, the (half) weight of the western bridge deck pulls the top of the "A"-shaped tower, without the previously counter-balancing eastern bridge deck (right on image).
Unfortunately, the south-most top corner of the "A" with the supporting concrete cable beam is not visible, it is right outside the camera frame. Therefore, the rupture of the cable in that location remains a hypothesis among others.

Note that the steel cables inside their thin concrete beams are routed through the A-tower top crossbeam. However, it seems they were "somehow" fixed inside the cross-beam as the single steel cables seem not to have been pulled through as it could be expected. Questions may arise here concerning the rupture of the cables inside their beam ("strallo" in IT).

Sequence 2:

Sequence 2 (3 frames): Initial collapse of western- and eastern bridge decks

The south-eastern (right) concrete cable stay is now likely to be entirely disconnected from the top crossbeam and accelerates its fall
The south-western (left) concrete cable stay is still attached to the cross-beam
The cross-beam can not withstand the unbalanced pulling force of the south-western cable beam
The cross-beam therefore breaks away, including a top section of both legs of the southern "A"
The northern concrete cable stays seem still to be effective
Therefore, high torsional forces around the carriageway axis are twisting the bridge deck girders

Sequence 3:

Sequence 3 (3 frames):

The topmost part of the southern A-shaped tower (which then will be catalogized as "reperto 132") continues to fall, including parts of the cross-beam.
The eastern concrete cable stay seems ripped off from the top cross-beam, underlining the hypothesis laid out above (sequence 1). The eastern concrete cable beam seems to have been cut-off right at the cross-beam. A short wild strand of steel wires can be distinguished on "reperto 132". The encapsulating concrete is blasted away.
This strand of wires can be identified in all three frames 55, 63 and 70, reducing the possibility of misinterpretation due to compression artefacts or other disturbances.
The central bridge deck section located between the tow "A" towers appears to have fallen a few meters (compare its vertical position with sequence 2), but remains horizontal until here.

Sequence 4:

Sequence 4 (6 frames):

*TBD*

Sequence 5:

Sequence 5 (4 frames): The northern A-tower tilts southwards with its concrete cable stays still attached

**TBD**

Sequence 6:

Sequence 6 (3 frames):

Conclusion

This short analysis suggests that the bridge collapse initiated as a consequence of the rupture of the south-eastern concrete cable stay in proximity of the top of the A-pylon.
The resulting imbalance has induced a strong momentum in the south A-pylon and in its top cross-beam.
Apparently, the forces required to break away the top of the southern "A" tower with its connecting cross-beam were rather low. In fact, forces transmitted by the south-west concrete cable stay were not sufficiently high to pull the short remaining sections of steel cables from/through the saddle sitting on top of the southern "A" tower.
The other three concrete cable stay sections remained effective during the initial collapse phase.

Open questions:

Why did single steel wires/cables not slide through the top cross-beam after weight was released on one side?

Critique:

The core of the argument is based on interpretation of sequence 2 consisting of the three frames 55, 63 and 70. The author assumes that what can be identified and "explained" in those image frames is what existed in reality (esp. the residual strand of wild cables on "reperto 132"). However, this may not be the case. Information conveyed by the images may be corrupted due to poor visibility (heavy rain), motion picture compression artefacts, image correction applied afterwards or other unknown reasons
The exact initial rupture location of the concrete cable stays can not be identified by this or any other known (CCTV) camera. Therefore, additional initial failure hypothesis shall be considered and weighted, i.e., the rupture of the top south A-tower with (initially) intact concrete cable stays.

Comment on this page...

1: Guest - 5.5 years ago

Aug 30, 2019, 3:57:07 PM

Why did single steel wires/cables not slide through the top cross beam after 
weight was released on one side?
My 2 cents: according to what is possible to understand from public drawings, it 
is possible that the lenght of the cable binded by concrete (at least 70 cm if 
I'm not wrong) was sufficient to make it totally fixed to the beam. In other 
words, during the construction there was 1 single stay passing on the top 
(Morandi talks about some curved steel plates to make it stable), but after 
tensioning and filling with concrete they became fixed as if they were 2 
different stays.
Just a guess