Two analyzes by independent experts show that the fall of row 12 Of Metro was due to inconsistencies and failures in maintenance, including administration Miguel Angel Mancera You Claudia Sheinbaum,
In the document to which REFORMA is a copy, the initial version has been questioned regarding the misplacement of “Nelson Bolts”.
One of the analyzes points to cracks, leaks, deformation, humidity, degraded concrete and corrosion in steel since 2015, all of which grew unnoticed. 2020,
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Another study also refutes that the problem was with Bolt.
It establishes that there could have been failures during rehabilitation between March 2014 and November 2015 weight overload Heavy material and maintenance trains, as well as the September 19, 2017 earthquake.
one of the analysis, signed by the engineer Sergio Montes de Oca OchoaPrior to a public notary, it was established that various cracks, leaks, deformations, humidity, degraded concrete and steel corrosion were detected since 2015 and that they grew without inclusion until 2020, Google of the collapsed section According to the images available on the map.
He points out that cracks appeared, indicating a lack of regular inspection and maintenance work in the section in question and emphasizes that the elements were sufficient to conduct inspection work to determine their cause and to know the actual condition. for maintenance. structural elements.
“These leaks proceeded without being addressed and repaired. This created problems with the structural elements which should have been inspected to know the actual condition of the elements.”
Sheinbaum believed that it was from the modifications that, after the collapse, cracks, subsidence, leaks, among others, were found, however, he attributed them to the construction and dismissed that they were due to lack of maintenance.
Another study was the causal analysis of failure of girders, based on analytical and computational models of event reconstruction, with a cause-effect method.
it was signed by Jorge Luis Gonzalez VelazquezA consultant represented by Mechanical Integrity and Engineering Services SA de CV (INMEYS), and denies that the problem was Bolt’s.
In its analysis, it establishes that there may have been failures that occurred during rehabilitation between March 2014 and November 2015, which introduced overloads in the overpass due to the use of heavy material and maintenance trains, which were heavier than the operational ones. Also the September 19, 2017 earthquake (19s,
Furthermore, it emphasizes that imperfections can be detected with in-depth review techniques such as X-rays, and not just with normal eyepieces.
“The fact that the collapse of the girders occurred under normal operating conditions and at the same time as a train was traveling on the south track indicates that the failure was gradual or gradual in nature and developed over time until The girder was not able to withstand the dynamic load induced by the passing of the train and failed to cause the accident,” he concluded.
The analysis emphasizes that the elevated section withstands thousands of times train passing, earthquakes of great magnitude and overloads introduced during maintenance work without any collapse.
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“The material of the composite girder, at least under normal operating conditions, was of sufficient strength to withstand the passage of a train,” he asserted.
For this reason, it ruled out that the material of the elevated section superstructure was not strong enough to withstand the normal stresses of operation or that the load on the overpass exceeded its actual structural strength.
And he pointed out that the only condition that could cause damage is that a condition was introduced after the overpass’s superstructure was built, which made its resistance equal to or less than that level. normal operating load,
“It is the only one which under normal circumstances can cause the passage of a train to cause the collapse of the overpass after supporting the passage of trains thousands of times, therefore, in the resistance of the superstructure after its construction.” Shortcoming is the only prevailing situation”.
INMEYS analysis refutes that a possible cause of failure was the lack of Nelson bolts or their poor installation.
“It was shown that there was a risk of collapse of the overpass due to insufficient or incorrectly installed Nelson bolts, with more than 70 percent of the bolts which, according to ‘built’ plans and related documents, indicate that they were actually installed “
And yet, he added, he could not believe that, if this 70 percent Bolt must have been the cause of the incident.
“In that case, not permitted, the superstructure would have failed in the first train journeys made after the commissioning of the elevated section or, in any case, when the superstructure was overloaded during rehabilitation.”
Maintenance Manual Elevated Section With Metal Structure The Line 12 Consortium establishes that after an earthquake of magnitude equal to or greater than 6.5, the structure should be amended; In case of doubt about the state, he says, inspection should be done via X-ray, ultrasound or penetrating fluid.
They cautioned that weld cracking can be caused by local failure due to inadvertent faults or uneven settlement of the structure during construction, stress concentrations due to exceptionally heavy loads, or large earthquakes.
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In the event of damage or indication, manual is too much, civil engineering management should be given immediate notice stc So that they review the status of the structure together with their representatives.