Mourning for a City: Why Did 11 Young Lives Die? Expert analysis of deadly perlite rock pile | building materials | insulation
On July 23rd, it rained for two whole days. In the scorching summer, Qiqihar is unusually cool.
At around 2 o'clock in the afternoon, the owner of a nearby snack shop at No. 34 Middle School remembered, "There was a loud 'thud' because it was raining, and I don't know if it was thunder." Soon, the command center of the fire rescue team received an alarm, and rescue personnel, vehicles, and search dogs rushed to the scene. It was then that he realized that the sound was the sound of the school gymnasium collapsing with a loud bang.
On the evening of July 24th, Qiqihar City held a press conference. Shen Hongyu, Secretary of the Qiqihar Municipal Party Committee and Mayor, reported that at 14:52 on July 23, a roof collapse accident occurred in the gymnasium of the 34th Middle School in Qiqihar. This is the most serious safety accident in Qiqihar in recent years, and a total of 11 teachers and students lost their precious lives.
Preliminary investigation shows that during the construction process of the teaching complex building adjacent to the sports hall, the construction unit illegally piled up perlite on the roof of the sports hall. Affected by rainfall, the weight of perlite soaked in water increases, leading to an increase in roof load and causing collapse. At present, the public security organs have filed an investigation into the relevant responsible persons of the construction unit of the teaching comprehensive building and taken criminal coercive measures in accordance with the law.
Entering from the school gate, passing through a plastic track playground, is the incident gymnasium. The search and rescue scene of the roof collapse accident at the No. 34 Middle School Gymnasium in Qiqihar City, captured on July 24th. Xinhua News Agency image
The Flower Sea and Snacks at the School Entrance
At 14:26 on July 24th, a female volleyball team member who survived the accident took a group photo to mourn: "All my best friends have left.". Half an hour later, she left a message in the comment section: "Ah Liang, next time we will have a lot of delicious food, and then drink milk tea. Don't forget it."
Citizens are also spontaneously remembering these young lives. In the early morning of July 25th, the rain that had been raining for the whole two days finally stopped. It was a bit damp and cold, and the school gate of Qishi No. 34 Middle School was surrounded by candles and a large sea of flowers on the ground.
"I specially selected sunflowers for the girls," said a citizen. Among the white and yellow chrysanthemums, there are occasional bouquets of sunflowers that turn yellow against the candlelight. Most of the citizens who come to send flowers and pay their respects are dressed in black, silent, and their eyes turn red. Seeing that a candle had gone out, they took the initiative to come forward and light it.
At around 12:30 in the morning, family members of the victims drove over and immediately got out of the car, crying uncontrollably.
A young man wearing glasses and a black T-shirt took the initiative to maintain order on site. To prevent candles from burning flowers, he occasionally arranges the placement of the bouquet.
The figure of the delivery rider also occasionally appears. "We ran over 100 orders at the school gate today." At 23:00, local rider Li Ming arrived with a whole box of 24 cans of canned peaches. He vigorously patted the bottom of the can, opened each can, and placed it next to the candle. He took a photo of the scene and sent it to the order taker, adding "Thank you for your love.".
Next to the canned peaches, there are also AD calcium milk, lollipops, cookies, and 11 cups of honey snow ice city milk tea with straws inserted.
The rescue has ended, but Gao Bin has not left the rescue site for a long time. Upon hearing the news, he rushed to the scene to help. According to the Weibo account of the National Fire and Rescue Bureau, at 14:56 on the 23rd, the command center of the Qiqihar Fire and Rescue Brigade received an alarm, and the brigade command center immediately dispatched 39 fire trucks, 159 fire and rescue personnel, and 4 search and rescue dogs to the scene.
After receiving a call from the emergency bureau at 16:00 on July 23, the Blue Sky Rescue Team dispatched 36 people to the scene.
"The collapse site was filled with cement and gravel, and heavy machinery such as tower cranes were unable to operate inside. They had to rely on manual labor to move and dig little by little." Gao Bin remembers that he spent most of his time moving perlite.
The rescue continued until near 11 am on the 24th.
Unsoaked perlite has reached the critical load-bearing value of the roof
At the press conference on the evening of the 24th, the preliminary investigation results of the accident were announced: during the construction process of the teaching complex building adjacent to the gymnasium, the construction unit illegally stacked the insulation building material perlite on the roof of the gymnasium. Affected by rainfall, the weight of perlite soaked in water increases, leading to an increase in roof load and causing collapse.
Professor You Jia from the School of Architecture and Urban Planning at Tongji University analyzed that "sports activities need to be carried out in the gymnasium, and the interior cannot be designed with columns, which will have an impact on sports activities. The roof structure is supported by columns, and the structural forms of large-span buildings are diverse. Grid structures are more common, and the stress performance is also relatively good. This building has been built for more than 20 years and is still in use, so its design should be no problem."
According to Youjia's analysis, it is not easy for large-span buildings to rely on their structures to solve their own spans. Although buildings like sports arenas are not very large, they are mostly designed and constructed with roofs that are not accessible to people. If a large-span building is designed as an accessible roof, the cost is relatively expensive. Generally, large-span buildings are not designed as accessible roofs.
According to the "General Code for National Standard Engineering Structures of the People's Republic of China" implemented by the Ministry of Housing and Urban Rural Development of the People's Republic of China on January 1, 2022, the standard value for uniformly distributed live load on roofs with access is 2kN/㎡, while the standard value for roofs without access is 0.5kN/m2, which is four times the difference between the two.
The General Specification for Engineering Structures, which will be implemented from January 1, 2022.
Hong Wen, a master's degree in engineering from Tsinghua University and structural designer, believes that according to the pictures, the perlite piled up on the top floor of the gymnasium reaches a height of about one meter to the waist of the workers. Under dry conditions, the weight is approximately between 80 kilograms and 250 kilograms per square meter, with an average of 160 kilograms. If it rains, the weight will at least double, and the density can reach 300 kilograms per square meter or even more.
The parapet wall of the gymnasium is not high and there are no protective measures, which indicates that the design of the gymnasium does not allow access to the roof. According to national regulations, the non accessible roof load should be at least 50 kilograms per square meter, which is for the daily maintenance of staff in the future. Due to the weather conditions in Qiqihar, the specifications require a snow load design based on a 50 year heavy line period, which is approximately 40 kilograms per square meter. In actual design, the load sub factor will be considered, which is 1.4. Overall, the gymnasium has a load-bearing capacity of at least 120 kilograms.
According to Hong Wen's analysis, based on the image data, it can be determined that the roof of the gymnasium is a grid structure. Unless there are special requirements, in the design of general grid structures, in addition to considering the weight of the upper roof waterproofing and insulation methods, as well as the load of snow accumulation and maintenance, the remaining usage load is generally reserved very little, generally not exceeding 50 kilograms per square meter. If other factors are not taken into account during the construction of the sports hall, the dry perlite is already at the critical point of overload.
Yujia believes that based on the current signs of collapse, the main cause of the accident in the sports hall is the collapse of the roof. From the surface of the damage, the walls are relatively good, more like the two sides of the roof tilting and collapsing towards the center. It can be said that the original structural design was not poor, and there was no wall collapse associated with it. However, there is no data to support this judgment at present.
Xinhua News Agency image
The construction unit has participated in nearly 20 school related project bids
According to the inquiry from the Heilongjiang Public Resource Trading Network by Shangkan News reporters, in 2022, the construction of a new affiliated comprehensive building on the campus of the 34th Middle School in Qiqihar City was publicly tendered, and Heilongjiang Jiamei Construction Co., Ltd. was ultimately selected as the pre winning bidder.
On a construction sign of the teaching comprehensive building of No. 34 Middle School, it is written that the construction unit of the project is Heilongjiang Jiamei Construction Co., Ltd.
The construction party and design drawings publicly displayed outside the school.
The construction party and design drawings publicly displayed outside the school.
According to data from Qichacha, the company was established on July 6, 2009, with a registered capital of 50 million RMB. The legal representative is Cheng Zifeng, and its business scope includes residential interior decoration, construction engineering, cultural relic protection engineering construction, and building demolition operations. There are currently two branches located in Keshan County and Nehe City, Qiqihar City.
Its total operating revenue in 2021 was 19.5 million yuan, including a net profit of 230000 yuan and a total debt of 6.86 million yuan. In 2022, the revenue was 28.67 million yuan, including a net profit of 726000 yuan and a total debt of 750000 yuan.
According to the National Public Resource Trading Platform, Heilongjiang Jiamei Construction Co., Ltd. has won a total of 17 bidding projects in the past three years, including 10 government procurement projects and 7 engineering construction projects. The maximum winning bid amount is 32.9596 million yuan, which is the newly built affiliated comprehensive building project of the 34th Middle School campus.
Further search revealed that in the past three years, the company has participated in nearly 20 bidding projects related to schools, including sports field renovation, cafeteria construction, and maintenance and renovation of teaching building ceilings.
