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Buckling due to lack of bolts and improperly placed bolts said cause of Mexico City metro collapse

Mexico City, Mexico — After a lengthy investigation, experts have determined that the collapse of the elevated Line 12 section of track between the Tezonco and Olivo stations on May 3 occurred as a result of buckling in the north and south beams, facilitated by the lack of functional bolts.

The report goes on to say that the lack of bolts caused part of the elevated span to lose its composite structure. The report was delivered Monday to Myriam Urzúa Venegas, head of the Mexico City government agency and to the Secretary of Works and Services, Jesús Antonio Esteva Medina.

The Norwegian-German company DNV (Det Norske Veritas) reported their official findings, which have determined that the two beams were working as two independent parallel beams, a concrete beam and a steel beam that experienced loading conditions for which they were not designed.

The report also indicates that the lack of functionality in the bolts was due to missing bolts, bolts with poor welds or incorrectly positioned, as well as deficiencies in the mechanical properties of the beams.

Regarding the 8.9 cm fatigue crack observed, it was the consequence of the vertical displacement of the beams, and although it does not represent the cause of the collapse, it could be a secondary cause of the collapsed section.