What’s the progress in handling the vibration incident of "5 18" SEG Plaza Building? Responsible persons and experts of relevant units in Shenzhen answered questions from reporters.
On May 18, 2021, the SEG Plaza Building experienced a sense of vibration, and Shenzhen immediately launched an emergency response. The Municipal Emergency Bureau and Futian District Government organized the property management party to immediately evacuate the people in the building, implement closed management of the building, and carry out necessary traffic control on the surrounding areas. Every day, the SEG Plaza Building’s monitoring data such as vibration, tilt and settlement were released through official channels such as "Shenzhen Release", and the Municipal Housing and Construction Bureau organized academicians and authoritative technical teams to conduct structural safety and safety monitoring of the building.
How is the incident handling going, whether the building structure is safe, whether the cause of vibration is found out, and how to resettle the merchants … Recently, the responsible persons and experts of relevant units were interviewed by the media and answered questions from reporters on issues of public concern.
Is the building safe?
Authoritative experts determined that the building structure was safe.
Can continue to use
The person in charge of the Municipal Bureau of Housing and Urban-Rural Development responded that the bureau organized various forces to do a good job in technical disposal in accordance with the principle of "scientific, accurate, serious and safe".
First, an expert group composed of five academicians of the Academy of Engineering, including Yue Qingrui, Zhou Fulin, Nie Jianguo, Chen Zhengqing and Chen Xiangsheng, was set up to take charge of overall technical planning, and the professional fields covered engineering diagnosis and treatment, vibration control, composite structure, wind engineering and geotechnical engineering.
Second, Shenzhen Urban Public Safety Technology Research Institute, as the lead technical unit, organized China Metallurgical Architecture Research Institute and Shenzhen Housing Safety and Construction Engineering Quality Inspection and Appraisal Center to carry out back-to-back inspection and appraisal, while China Research Institute of Building Science and Guangdong Research Institute of Building Science provided advice on relevant schemes and technical achievements respectively, and 16 scientific research teams including Tsinghua University, Guangzhou University, Harbin Institute of Technology (Shenzhen), Hunan University, Tongji University and Shenzhen University provided technical support to carry out professional argumentation and analysis.
Third, the original design unit, the third-party authoritative organization and the expert team will conduct a triple review of the safety demonstration and cause analysis results.
The response of the expert group: First, Huayi Design Company, the original design unit, checked the structural safety of the building according to the original design code and the current design code, and it was reviewed and approved by the Guangdong Provincial overrun Committee;
Second, China Metallurgical Architecture Research Institute and Shenzhen Housing Safety and Construction Engineering Quality Inspection and Appraisal Center have systematically tested the building’s structural dynamic performance, and adopted technologies including laser Doppler vibration measurement, ultrasonic phased array test and audio acceleration test to comprehensively test and analyze the building’s structural structure, structural damage, material performance, joint connection, shear wall and core tube arrangement, etc. According to the test data, they are checked, analyzed and evaluated independently according to the original design code and the current design code.
Third, the China Institute of Building Science issued an opinion on the design review and inspection and appraisal.
Since May 18th, the third-party authoritative testing organization has continuously monitored the vibration, inclination, settlement and other indicators of SEG Plaza Building in real time: the maximum acceleration is 0.067m/s2, which is less than the relevant provisions of the national Technical Specification for Concrete Structures of High-rise Buildings -JGJ3-2010, which is the peak wind-induced acceleration limit of 0.25m/s2; The inclination rate is between 0.00% and 0.05%, which is less than the allowable value of 0.2% in the code; The daily settlement variation is between-0.45 mm and 0.42 mm, and the cumulative settlement is between-0.62 mm and 0.42 mm, so the building settlement is stable.
Expert group’s opinion: Through a large number of above tests, monitoring, tests, analysis and demonstration, and through multi-party review and appraisal, the main structure of SEG Plaza Building is safe within the design load range and under normal use, and can continue to be used.
Why does the building vibrate?
Wind-induced vortex-induced resonance of mast is the direct cause.
Through technical investigation, environmental and equipment operation investigation and test, the expert group ruled out the influencing factors such as subway operation, surrounding engineering construction or blasting, and air conditioning unit operation.
Through the key analysis of wind-induced vibration and structural cumulative damage, the expert group believes that:The coupling of wind-induced vortex-induced resonance of mast and the change of dynamic characteristics of building and mast has caused the induced vibration of SEG Plaza building.
1. Wind-induced vortex-induced resonance of mast is the main external cause of induced vibration of building.
The first is to carry out special dynamic performance test and analysis of the mast. Doppler laser vibration measurement and vibration video image recognition are adopted. The results show that 21 asymmetric wind-induced vortex-induced resonances occurred on the mast from May 18th to 20th, with the frequency of 2.12Hz.
The second is to carry out continuous dynamic performance monitoring and analysis of the building. The acceleration and other real-time monitoring are carried out from the basement of the building to the top mast, and various dynamic parameters such as vibration shape, frequency and damping ratio are measured, and the main vibration modes under various vibration conditions of the first 20 orders are obtained.
The results show that the induced vibration of the building on May 18 -20 is a high-order bending-torsion combined mode, which is 2.12Hz with the mast vibration frequency.
Thirdly, the excitation test verifies that the vibration of the mast can drive the building to vibrate. The excitation tests of the mast and the building were carried out in 26 working conditions and 63 groups in different positions, directions and frequencies. The results show that at the frequency of 2.12Hz, the fourth-order asymmetric vibration of the mast can drive the building to have high-order combined bending and torsion vibration.
To sum up, under the specific wind field condition of steady state and lasting for a certain period of time, the fourth-order reverse asymmetric vortex-induced resonance with the frequency of 2.12Hz was generated in the mast of the building, which excited the high-order bending-torsion combined mode of the main structure of the building with the frequency of 2.12Hz, and then caused the main structure of the building to feel vibration.
2. The change of the dynamic characteristics of the building and mast is the main internal cause of the induced vibration of the building after more than 20 years.
After the building has been used for more than 20 years, the cumulative damage of profiled steel composite floor slab and mast connection point in some floors has changed the structural frequency, damping ratio and other dynamic characteristics, and the mast and the main structure of the building have a common vibration frequency of 2.12Hz, forming a necessary condition for resonance. The above-mentioned local cumulative damage only affects the dynamic characteristics of the structure and does not affect the safety of the main structure.
How to solve the problem of building induced vibration?
Carry out mast demolition project
Repair local cumulative damage of structure
The expert group believes that dismantling the mast can effectively solve the problem of induced vibration of the building.The original lightning protection and navigation mark functions of the mast can be rearranged on the roof after the mast is dismantled.
The person in charge of the Municipal Housing and Construction Bureau responded: The mast demolition construction plan organized by the bureau has gone through three checks:
First, the original design unit rechecked the influence of demolition construction on the safety of the main structure;
Second, according to the advice provided by Guangdong Academy of Building Science on the construction scheme, the demolition scheme was further improved;
Third, the demolition plan was demonstrated by an expert group composed of experts recommended by the Ministry of Housing and Urban-Rural Development, the Provincial Housing and Urban-Rural Development Department and well-known experts from Shenzhen.
The demolition project will be carried out in the near future, and the damage repair project will be carried out simultaneously, with an effective construction period of about 32 days. If affected by extreme weather such as rainstorm, typhoon and high temperature, the construction work will be stopped in due course and the construction period will be postponed.
In order to ensure the safety of people’s lives and property, strict protection measures will be taken during the demolition period, and the Seg Plaza Building and some surrounding roads will be closed for management.
How to resettle merchants?
Provide temporary business space
Solve the appeal according to the law and regulations
According to the person in charge of the Municipal Emergency Bureau, the provincial party committee and government, the municipal party committee and municipal government and the relevant departments at higher levels attach great importance to the emergency handling of incidents. In accordance with the requirements of "life first, safety first", the municipal party committee and municipal government set up a special class at the municipal level to co-ordinate the disposal work, and the municipal emergency, housing construction, publicity, public security and Futian District units formed the on-site headquarters to analyze and judge risks daily, study and solve disposal-related matters in time, and respond to social concerns.
The person in charge of the Futian District Government introduced that since the incident, Futian District has coordinated business spaces such as shops and underground shopping malls through multiple channels to provide convenient conditions for merchants’ production and operation. In order to properly solve the reasonable demands of the masses, Futian District set up a communication platform, set up a consultation point for receiving visits, and set up a temporary party branch, 28 party member volunteer pioneers and 6 work teams to sink into the front line, thus solving the practical problem of a group of people’s "urgent difficulties and worries".
The person in charge of Futian District Government said,We will continue to provide temporary business premises for the majority of merchants. Merchants with temporary business needs can apply to the SEG Plaza Building Management Office.In line with the principle of "helping each other in the same boat, helping each other", we will guide all parties to negotiate according to the law and regulations, and properly solve the demands of merchants. After the mast removal project and the cumulative damage repair project are completed, the merchants and tenants will be organized to move back and resume the normal operation of the building as soon as possible.
The head of Fangseg Group, the owner of the building, said that after the building is restored to use, the property management of the building will be further strengthened to provide better services for merchants.
Source: Shenzhen Special Zone Daily (author Dou Yanwen)
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