The collapse of a stage where a Citizen Movement rally was taking place in San Pedro Garza García, in the metropolitan area of Monterrey, has paralyzed the final stretch of the presidential campaigns in Mexico. The tragedy, which occurred after a windstorm that caused the collapse of the structure in front of which thousands of people gathered in one of Jorge Álvarez Máynez’s last campaign events, has left 9 people dead and 121 injured so far. The images of the accident have gone around the world and caused shock in a country where more than 98 million people are called to vote in an election day that will renew more than 20,000 public positions in less than ten days. With the investigation to determine responsibilities underway, the loose ends of the collapse are torn between inevitability in the face of the force of nature and versions that point to negligence on the part of the organizers and authorities.
A structure not suitable for the wind
For José Luis Garibay Reyes, a civil engineer expert in structures for shows, a series of errors, both in the choice and approval of the stage, and in the execution of the event in the face of adverse weather conditions, gave way to tragedy. The first point that stands out is the choice of the stage support: “We know this type of structure as a truss, it is the most common in the field of medium to low massive impact shows,” explains Garibay. This is a quick installation scenario, whose assembly usually does not take more than a day taking into account the work of a crew of 20 workers. It is a slender structure with a limited load capacity, whose supports fall on its legs. “The load is concentrated on the roof, which is known as the grill, the columns support that roof and all the work is done on the grill. rigging where the motors, the lights, the screen are mounted, all supported by the grill which in turn is supported by the perimeter columns that distribute or distribute the load towards the floor,” says the expert.
Although the truss system is one of the first options for medium to low impact events, Garibay considers that the most used alternative for massive outdoor events is a multidirectional scaffolding mechanism patented under the name of the Lahyer system. This structure, originally manufactured for construction, jumped into the entertainment world about two decades ago and became a top choice in the entertainment industry. “It is precisely this scaffolding system that is used so that the load capacities are much greater and the structure that makes up the stage is not so slender, making it more robust,” he assures.
From the perspective of Garibay, founder of a company with experience in massive events such as the Pa’l Norte Festival or concerts at the National Auditorium, the choice of a truss system on a multidirectional scaffolding was decisive for the collapse, which occurred once that the columns supporting the right side of the stage fell. With the columns defeated, the metal structure of the grill, with dozens of lights and horns, collapsed on the attendees who occupied the first rows.
Wind gusts and whirlwinds: an ignored weather forecast
Although the Civil Protection of Nuevo León attributed the fall of the scenario to the appearance of “gut and atypical winds”, the forecast of the National Water Commission (Conagua), the official weather forecast in the country published daily at 06:00 in the morning , warned of heavy rain, possible hail and strong to very strong gusts of wind in Nuevo León and Coahuila.
A second report focused on the conditions of the northwest region between 6:00 p.m. and 9:00 p.m. confirmed the storm conditions, pointing out the metropolitan area of Monterrey as one of the regions of the State that would experience wind gusts of up to 70 kilometers per hour, same as He assured, “they could cause trees to fall and advertisements to fall.” The updated forecast also warned about the possible formation of whirlwinds or tornadoes in Nuevo León, Coahuila and Tamaulipas.
“The wind is decisive in this type of structures [truss], which is not suitable for gusts like those that occurred there, which although they seem atypical, nothing exempts you from the possibility that they could happen,” Garibay explains in this regard. “Being very slender, a gust of wind of that magnitude was logical that it would not be able to withstand it for the simple fact that you have a roof and a canvas, in addition to the screen, which also causes a sail effect,” says the civil engineer, referring to the swinging of the giant screen in the center of the stage, which rises above the heads of the people in the stage just before the collapse.
![Alvarez Maynez](https://imagenes.elpais.com/resizer/v2/2C3PAWJPHNEMLPLNWYDGUR4V6U.gif?auth=d4c1573c9b90dc2921bb3005f9bfc05c3d84762eb37356dc7a8c61061ef71bf6&width=414)
Authorization for the rally
The candidates went up to the stage minutes before 8:00 p.m., while the rain increased in intensity and the wind began to wreak havoc on the stage, blowing away some blankets designed for the event. The effective holding of the rally, prior approval from Civil Protection and even after the forecast of bad weather, is another of the loose ends surrounding the tragedy of San Pedro Garza García. For a massive event of this nature (the organization estimated 10,000 attendees when requesting permission from the authorities), the approval of a Responsible Construction Director is necessary, a figure who acts as an independent consultant who monitors compliance with construction standards , as well as local Civil Protection. Both were approved to hold the rally.
“Of the few incorruptible things in Mexico, one of them is a Responsible Construction Director. “They have the power to tell Civil Protection that a structure does not meet the requirements,” says Garibay while listing a series of events in which, regardless of the budget invested or the number of attendees, the authorities have postponed or canceled for bad reasons. time. “We do not know the real circumstances that led to the event taking place, even when the announced weather conditions were adverse. Although I think that due to the type of structure, even if they had added a little more counterweights, they would not have been enough, since it was not designed to withstand a wind like the one that occurred.”
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