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Structural Failures Led to Fatal Mexico City Subway Collapse, Report Finds


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The accident on line 12 of the Mexico City subway, which left 26 dead in May, was due to failures in the work, mainly the lack of bolts (screws) in the area where the track fell, according to the assesment of the Norwegian firm DNV presented on Tuesday.

“The result of the analysis indicated that the collapse occurred as a result of the buckling of the North and South Beams made possible by the lack of functional bolts in a significant section,” Mexico City’s Secretary of Works and Services, Jesús Antonio Esteva Medina, said at the presentation of the report.

During the delivery of the Final Technical Report by the Norwegian company DNV, Esteva Medina pointed out that this was “what caused part of the elevated section to lose its structural integrity.”

Last May 3, a section of the elevated bridge between Olivos and San Lorenzo stations, in the Tláhuac district, collapsed between columns 12 and 13, causing the train with passengers to get stranded in a “v” shape, leaving 26 dead and a hundred injured.

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On June 16, the official preliminary assessment of the collapse of line 12 of the Mexico City subway revealed “structural failures” in the work, carried out during the administration of Marcelo Ebrard, now Chancellor.

This September 7, and after several delays for the presentation, the second report focused on these flaws in the infrastructure.

Esteva Medina explained that this lack of bolts led to the “structural integrity” to operate as two “independent parallel” beams, and these “experienced loading conditions for which they were not designed.”

As revealed in the previous report, the expertise highlighted defects in the welding of the bolts, missing bolts and misplaced bolts.

Also, in the tension and flexibility tests of the bolt welds that were inspected, certain requirements were not met.

Defects in the “mechanical properties of the beams” and in the “design of the cross frame of the structure,” which did not meet certain standards, may also have contributed to the collapse.

Among other findings, it was reported that the track and the facilities next to it, such as sleepers and rails, were in “good general condition,” so there was “no evidence” that they contributed to the failure.

Also, the structure was already in a “compromised condition” before the 2017 earthquake that struck the capital.

At the beginning of the event, the secretary of Integral Risk Management and Civil Protection, Myriam Urzúa, explained that this final assessment analyzes the “immediate causes” of the subway accident and the “failure mechanisms” of the materials, as well as the identification of the “factors” contributing to the incident.

He recalled that DNV was chosen for its “extensive experience” as independent experts in accident analysis with its own methodology. And he pointed out that analysts from Germany, the United States, Spain and Brazil have worked on this study.

The General Director of DNV Mexico, Eckhard Hinrichsen, explained that the second report contains “a conclusion on the probable direct cause of the collapse of the elevated section of line 12.”

Finally, he added that a third report, which will evaluate the “root cause” of the accident, will be released in the coming weeks.

The victims’ defense lawyer, Teófilo Benítez, was disappointed by the results of the report and accused both the government of President Andrés Manuel López Obrador and the mayor of Mexico City, Claudia Sheinbaum.

He said that both showed from the beginning no respect for the victims, null empathy and lack of commitment.

“They put more effort into maintaining their political stability and little commitment to comprehensive reparations for the victims,” the lawyer said in a statement.