Collapse in Metro Line 12 was the result of buckling of beams due to lack of adequate bolts: DNV report

The lack or malfunction of these parts caused part of the elevated section of the Metro to lose structure.

MEXICO, (September 08, 2021).- The international company DNV presented on Tuesday the final technical opinion on the accident on Line 12 of the Mexico City Metro.

The accident occurred on May 3 and claimed the lives of at least 26 people. There were more than 100 injuries.

According to the executive summary of the project, which was read at a press conference by the Secretary of Works Jesús Esteva, the collapse that occurred between the Los Olivos and Tezonco stations was due to buckling of beams due to the lack of adequate bolts.

“The results of the analyzes indicated that the collapse occurred as a result of buckling of the North and South Beams facilitated by the lack of functional bolts in a significant length, which caused part of the elevated span to lose its composite structure.

“As a result, the composite structure was operating as two independent parallel girders, a concrete girder, and a steel girder, which experienced loading conditions for which they were not designed,” the report states.

All of the above created the conditions that led to the distortion of the central transverse frame and the initiation and propagation of fatigue cracks; the latter further reduced the structure’s ability to bear the load, the text adds.

DNV also noted that among the factors that contributed to the non-functionality of the bolts were poor welds on the bolts, missing bolts, and bolts that were misplaced.

“Possible factors that contributed to the collapse include deficiencies in the mechanical properties of the beams and in the design of the transverse frame that did not meet design standards,” he said.

The analyzes also found that fatigue cracks are not the primary cause of failure, but could be considered secondary due to missing or incorrect bolt placement in the midsection of the failed beams.

Source: El Financiero

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