Du Jiyu Talks about "The Existing Curtain Wall Security Status and Countermeasures"

[China Aluminum Industry Network] 1. Existing curtain wall and its formation

The existing curtain wall usually refers to the building curtain wall that has been completed and delivered for use. Therefore, the appearance of the existing curtain wall is formed along with the production and use of the building curtain wall. From the structure and manifestation of a similar architectural curtain wall, the existence of existing curtain walls can be traced back to the church lighting windows and various types of glass domes constructed using art glass before the nineteenth century (Figure 1). The first curtain wall with the form of a building curtain wall structure should be the “Crystal Palace” constructed by the London Industrial Exhibition in 1851, and the glass curtain wall of the Haridad Tower built in San Francisco, USA in 1917 (Figure 2), and 381 meters high in New York in 1831. The stone walls of the Empire State Building, the New York Liwa Building and the United Nations Building built in the early 1950s. Therefore, the existence of the existing curtain wall in the world is more than a hundred years old. However, with the New York Lihua Building and the United Nations Building as the real architectural curtain walls, the existing curtain wall in the world is already far more than half. century.

With the development of China's reform and opening up, in the early 1980s, China began to build glass curtain walls. The glass curtain wall completed by the Guangzhou Trade Fair in 1981, the glass curtain wall of the Great Wall Hotel in Beijing built in 1984, and the Shenzhen Development Center building of the previous full-hidden frame glass curtain wall constructed in 1986, have been over 30 years old. . Therefore, in our country, both curtain walls have formed and existed for quite a long time.

2. The State of Existing Curtain Walls in China

The development and status quo of China's existing curtain wall have basically coincided with the speed and status of China's economic development. Since the early 1980s, it has demonstrated the momentum of rapid development, and its current basic status and characteristics can be summarized by the fact that it has a large stock, aging, and security issues.

2.1 Existing huge curtain wall

China's curtain wall industry started from 1983 and entered a period of rapid development in the 1990s. After nearly 30 years of development, it has now become the world's leading producer of curtain wall production and use of large countries, and is gradually becoming a world-class curtain wall power. According to statistics of industry data carried out by the Aluminum Doors, Windows, Doors, and Curtain Wall Committee of the China Construction Metal Structure Association, the annual output of building curtain walls in China is only 150,000 m2 from the end of the “Sixth Five-Year Plan” period (1985), and 1.05 million m2 in 1990. In the final period (2000), the construction volume reached 10 million m2, an increase of 70 times in 15 years and an average annual increase of 5 times. The area of ​​the building curtain wall to be completed during construction should be between 78.9 million square meters. From 2003 to 2013, the total output value of building curtain walls was 1,0288.7 million yuan. If the average price was 1,100 yuan per square meter, the area of ​​curtain walls completed during this period should be around 945 million square meters. Since 2014, with the deepening of China's economic transition, the decrease in GDP growth rate and the annual completion area and production of building curtain walls have declined, but they have basically remained at about 100 million square meters, with an output value of about 150 billion yuan. If we remember from 1983, the building curtain walls that have been built in China for more than 30 years, that is, the existing existing curtain walls, should exceed 1.2 billion square meters, and their stock is huge.

2.2 The aging facade of existing walls

The curtain wall of the building belongs to the external maintenance structure of the building and is based on the stipulation of China's "Unified Standard of Structural Design Reliability" GB50068-2001. Its design service life is 25 years (Figure 3). According to this standard, the curtain wall of buildings built before 1990 in China has exceeded the scope of the design life of the building. According to the statistical results of the existing curtain wall stock, the area should be more than 10 million square meters. For example, from the viewpoint of the aging of certain materials and the degradation of mechanical properties, most of the curtain walls before 2000 had already experienced the phenomenon of aging, and their area was even greater. It can be seen that with the passage of time, there will be more and more curtain walls in China that have reached the age of design and ageing, and that there is an aging phenomenon. This is an irreversible trend.

2.3 Security has been concerned about the existing curtain wall

Due to the huge stock of existing curtain walls and the increasingly aging trend, and occasional incidents in which the tempered glass blew up and fall from time to time in recent years, the safety of the existing curtain wall is extremely high for the entire society including the top leaders and departments of the country. Pay attention. According to the incomplete statistics of our country's news reports in the past decade or more, the most serious accidents in China's existing curtain walls are the loss and fall of the opening curtains of glass curtain walls. The most common safety accident is the explosion of glass particles caused by the explosion of tempered glass. The damage and damage caused. Table 1 shows statistics of glass curtain wall accidents that occurred in China in the past decade based on incomplete relevant news reports.

Table 1

However, the problems with glass curtain walls do not represent all the problems with existing curtain walls, especially the problem of self-detonation of tempered glass. It more reflects the defects of tempered glass itself and does not fully represent the safety issues of existing curtain walls. . Over time, the unreasonable management of existing curtain walls, the aging of materials, the wear and tear of machinery, the corrosion of metals, and the repetitive effects of long-term loads have caused the existence of many uncertain potential factors for the safety of existing curtain walls. s concern.

3, existing curtain wall security status

Our country has both the security status of curtain walls, the use and trials under natural environmental conditions for 30 years, and the safety investigations conducted in different regions. It shows that there are no collapses of existing curtain wall structures. Several times have passed in China in recent years. In the earthquake, the seismic performance and safety of the existing curtain wall also performed well. It can be seen from this that China's existing curtain walls are basically reliable in terms of safety performance. At the same time, we should also be soberly aware that China's building curtain walls have grown from scratch, never standardized to standardized, and have experienced different stages of development. Some of the existing curtain walls now exceed the service life of the building design. Different parts and materials of the curtain wall are different. The degree of aging, fatigue, wear and corrosion, etc., all have an impact on the safety and reliability of the existing curtain wall.

3.1 Turn off the fan

The opening of the curtain wall lighting and ventilation is an integral part of the curtain wall. From the atypical pneumonia epidemic caused by the SARS virus infection in 2003, and the need for green building design, people are increasingly vocal in raising the ventilation capacity of the building curtain wall, and the proportion of the curtain wall opening area occupied by the curtain wall is increasing. Large, some local standards have even made it mandatory. However, from the perspective of security, the openable part of the curtain wall, especially the openable fan that can be opened, is a weak link in the curtain wall security. From the recent investigation of the existing curtain wall security conditions in Shenzhen for more than 25 years, it was found that almost 30% of the curtain walls had fallen off as a whole. Especially in the typhoon season, the phenomenon was more serious, and some curtain walls were almost every year. Both have the phenomenon of turning off the fan. The reason is that in addition to unreasonable structural design, excessive sash size, mismatched hardware components, or poor quality, improper operation and use, the safety accident caused by the lack of normal maintenance of the opening fan is particularly prominent. This phenomenon is more common in residential buildings and is extremely dangerous. Figure 4 shows the damaged glass curtain opening fan and it has not been able to get timely maintenance and repair.

3.2 Structural sealant aging

Hidden frame glass curtain wall is the use of silicone structural sealant to bond the glass to the supporting structure of the curtain wall, and the load of the glass panel is transmitted to the building main structure through the connecting piece. Due to the special assembly structure, the ability of the hidden glass curtain wall to reduce the stress damage and earthquake resistance caused by the glass mosaic structure is higher than that of other types of glass curtain walls. Hidden frame glass curtain walls that are manufactured and installed in strict accordance with the specifications have good safety performance and usage records. Because the hidden frame glass curtain wall is structurally assembled with a silicone structural sealant and the structural sealant bears the load transmission, the mechanical properties and aging resistance of the silicone structural sealant have an important influence on the safety performance of the hidden frame glass curtain wall. Therefore, the mechanical properties and aging resistance of silicone structural sealants have attracted attention from all walks of life. In particular, the performance of silicone structural sealants that have been in place for more than a decade and their impact on the safety performance of glass curtain walls has received more attention.

Silicone structural sealant is a kind of polymer material with good aging resistance. In the early 1970s, foreign countries began to use silicone structural sealant to manufacture and install hidden glass curtain walls. It has been nearly half a century. In China, it has also been 30 years since the mid-1980s. The testing data from the production date (1997) of a certain silicone sealant manufacturer in China from its production date (1997) to the aging resistance test after 10 years (2007) and 15 years (2012) The corresponding verification can be obtained, see Table 2. From Table 2, it can be seen that after 10 years, the elasticity of the silicone structural sealant has dropped by 25%, and after 15 years it has dropped by 35%, but the tensile strength has not declined yet.

Table 2

Closer to the need for engineering reconstruction in a shutdown project in Shenzhen, on-site sampling and testing of silicone structural sealants (foreign products) that have been in use for 20 years and found that although their elasticity has decreased, they may have affected the Normal use, but there is no obvious drop in its adhesive force, there is no defect that affects the structural sealant bearing capacity, see Table 3.

table 3

Silicone structural sealant as a polymer material, from the above test results can be seen that it has a very good anti-aging properties. But for its true service life limit, so far, there is no accurate answer worldwide. In engineering applications, current material suppliers generally only provide a commercial quality assurance period of 10 years, but this does not mean that silicone structural sealants have only 10 years of normal use performance, and silicone structural sealants 10 years later. There is always a misconception that there will be danger and no security guarantees. China has recently completed the compilation of the product standards for the construction industry of JGT 475-2015, “Structural Sealant for Building Curtain Walls”. The silicone structural sealant used for building curtain wall projects has been designed for a useful life of no less than 25 years. That is, the service life of the silicone structural sealant should be more than 25 years. It can also prove that the service life of silicone structural sealant controlled and tested through strict production process should be more than 25 years, not the current 10-year shelf life. The existing large number of existing hidden frame glass curtain walls that are still used for more than 30 years are the result of natural aging resistance for a long time, which can reflect that the real aging resistance of silicone structural sealants can reach 25 years or the above.

In 2016, the Shenzhen Municipal Bureau of Housing and Urban-Rural Development organized a curtain wall expert to conduct a survey on the safety of 16 curtain wall projects that have been completed in Shenzhen for more than 20 years (before 2000). Among them, 10 projects are hidden frames and semi-hidden frame glass curtain walls, all of which are made of silicone structural sealant. So far, no safety accidents have occurred due to aging problems of structural sealants. Through on-site key observations and manual inspections, it can be found that most of the structural sealants that have hidden glass curtain walls have signs of aging such as colloidal hardening and surface pulverization. In particular, structural sealant aging phenomena that are more than 25 years old are more evident. However, it has not been observed that colloids that pose a danger to the curtain wall itself are cracked, or that there is degumming and cracking on the adhesive surface. For these projects, the structure sealant can still be used for a long time. How big the potential safety problem is, it needs constant attention and safety inspections, and scientific judgments can be made by adopting multiple test methods to verify the test.

3.3 corrosion of metal components

The aging of sealing materials such as sealants and sealants, and the structural displacements that cause leakage of existing curtain walls, causing serious corrosion to the existing curtain wall metal support components, are another issue that poses a potential safety issue for existing curtain walls. Since most of the supporting members and connecting members of the existing curtain wall are basically concealed, it is difficult to find the corrosion problems caused by the rainwater leakage under normal circumstances, but there is certainly a corrosion of metal materials at the locations where rainwater leaks. And in China's existing curtain wall should be ubiquitous (Figure 5). In addition to the corrosion of metal components caused by the leakage of rainwater, the corrosion caused by the contact interface of different metals is also quite serious. This occurs mainly at the connection sites of the connectors.

3.4 Glass panel damage

The damage to the glass façade panel, especially the damage caused by the explosion of the tempered glass, has been a major cause of the security of the existing curtain wall in China. After 20 years of use, some glass curtain walls have continued to suffer the problem of self-detonation of glass; some also have glass. The curtain wall had just been built but it could not be completed and delivered due to the large amount of glass blew. The on-site safety inspection showed that under the correct design conditions, the main cause of glass breakage was the type of glass and the quality of the glass itself. In the investigation and inspection of existing curtain wall safety conducted in Shenzhen, all projects using tempered glass have self-detonation problems, and some of them have a far greater rate of self-detonation than normal blebbing rates. However, some tempered glass has almost no self-explosion, and the product quality is very good. Among all the projects using semi-tempered glass, including the glass curtain walls that have reached the design age limit, no self-explosion has occurred. Even if other factors cause the glass to break, it will not cause the problem of falling. Fig. 6 shows that the semi-tempered glass still has no peeling after being damaged.

3.5 panel and panel connector aging

Separation of ribs on the back side of the sheet, looseness of the connection between the panel and the supporting member, etc. all affect the appearance and safety performance of the aluminum panel curtain wall. In recent years, in Hainan, Fujian, and Guangdong, there have been aluminum panel curtain walls due to the unreliable connection and the aluminum panel curtain wall panels have been opened by the wind. The phenomenon that the stone curtain wall plate falls off is also a relatively common phenomenon. The reason is that the plate is exposed to the natural environment for a long time and is affected by wind, rain, sunlight and high and low temperatures, and the weathering, cracking of the panel, loosening of connecting pieces, and so on. Some of the more loose stones, such as marble, sandstone, and limestone, are particularly serious (Figure 8).

3.6 Fire Prevention of Existing Curtain Walls

China has the problem of fire protection of curtain walls. Due to the intervention of the external insulation system of the external wall, the fire safety problem is extremely severe. Even if the newly implemented “Code for Fire Protection in Architectural Design” GB makes specific provisions, it has not been able to It is also difficult to completely avoid the curtain wall system involving the outer side due to the fire in the inner external wall insulation system. Because of the passage between the curtain wall and the external wall insulation system, the combustion temperature can reach 1,000 degrees, enough to destroy all the components of the curtain wall, especially the non-transparent curtain wall, such as metal plate curtain wall, stone curtain wall, artificial board curtain wall and so on. Figure 9 shows that the base wall has an insulating material, and the outer layer is the temperature curve between the channels recorded when the aluminum-plastic panel curtain wall is in the fire test.

At the same time, there are many problems in the construction quality of the fire prevention between the layers of the curtain wall. The fireproof materials do not meet the design requirements, the plugging is not complete, and the sealing position is incorrect. Some projects deal with curtain wall interlayer sealing as a decorative component. The sealing layer can be seen from the top of the building to the bottom layer (Figure 10). This plugging effect will pose a serious threat to the lives of people in the construction of a fire.

3.7 Potential hazards caused by non-standard design and construction

Since the end of the 1990s, with the dramatic increase in the construction volume of curtain walls, the number of companies involved in the construction of curtain wall projects has increased substantially. The situation that the design did not meet the requirements of the regulations, the materials were fake and inferior, and the construction quality was not strictly regulated and irregular occurred from time to time, resulting in the existence of some curtain wall projects that did not meet the requirements of the design and construction specifications and had quality defects or safety problems. The phenomena listed below are only indicative of many potential hazards.

1) Improperly designed glass opening fan

There are hidden frame glass opening fans, including hidden frame glass curtain walls and concealed frame opening fans for conventional doors and windows. A considerable part of the glass does not support the lower end of the frame (Figure 11); the use of hollow glass opening fan, there is insulating glass The problem of non-overlapping of structural sealants bonded with structural sealants and insulating glass and sash frames (Fig. 12); excessive opening of open sashes is also a common offense design (Fig. 13). The normal use of the opening fan poses a potential danger.

2) Replace structural sealants with other types of adhesives

Hidden frame glass curtain wall is a kind of glass curtain wall that adopts architectural structure sealant for structural assembly. Qualified hidden frame glass curtain wall usually cannot have the safety problem of falling glass. Due to manual operation and environmental factors, or through the use of fire and other high-temperature applications, the glass bonding performance of hidden glass curtain walls often fails to achieve good design performance, but usually does not affect the normal use of glass curtain walls. One of the main reasons that may cause the glass of the hidden frame curtain wall to fall off is that the construction unit and the insulating glass manufacturer use the unqualified silicone structural sealant or non-structural sealant (generally sealant) when making the hidden frame glass curtain wall. Polysulfide rubber is structurally bonded to the glass, resulting in shedding and falling of the entire glass of the hidden frame glass curtain wall (Fig. 14); secondly, the construction unit did not strictly follow the requirements of “Glass Curtain Wall Engineering Technical Specification” JGJ-102. And installation of hidden glass curtain wall, auxiliary material and silicone structural sealant are incompatible, and the surface treatment of the substrate is not correct.

3) No anti-fall measures for out-popping glass or inverted stone

Outlier glass curtain wall glass designs do not use laminated glass, and there are a large number of early building curtain walls, and some are still in use (Figure 15). Inverted stone design did not take anti-fall measures, and some even have serious rain leakage phenomenon, the safety hazard is extremely serious (Figure 16)

3.8 The lack of curtain wall maintenance and repair

In the large number of existing curtain wall projects in China, most of the projects do not have a clear responsibility for curtain wall safety management. There are widespread incomplete preservation of engineering and technical data, and the lack of use of curtain wall maintenance and maintenance systems and normal safety inspections. Problems such as the failure to carry out regular safety appraisal and the insufficiency of funds for maintenance and repair of curtain walls have caused great harm to the normal operation of existing curtain walls.

4. Countermeasures

4.1 Strict implementation and continued safety inspection of existing curtain walls

The previous regulation on the safety management of existing building curtain walls by the Ministry of Construction was issued on September 1, 2006 by the Department of Engineering Quality and Safety Supervision and Industry Development of the Ministry of Construction. Notification of Remedial Work> (Qualification Quality Letter [2006] No. 109). The "Notice" requires all localities to earnestly strengthen the use of existing building curtain wall safety management, and actively organize and carry out special rectification of existing building curtain walls in the region, timely investigation of quality and safety hazards, and strengthen the supervision and management of the existing building curtain wall security maintenance. On December 5, 2006, the Ministry of Construction issued the Notice on Printing and Distributing the Measures for the Administration of the Safety and Maintenance of Existing Curtain Walls (Qian Jian [2006] No. 291). On March 1, 2012, the Ministry of Housing and Urban-Rural Development issued the "Notice on Organizing and Conducting a National Safety Inspection of Existing Glass Curtain Walls" (Quality [2012] No. 29). This is an existing nationwide glass curtain wall organized by ministries and commissions. Safe troubleshooting. On March 4, 2015, the Ministry of Housing and Construction and the State Administration of Safety Supervision issued the Notice on Further Strengthening the Safety Protection of Glass Curtain Walls (Jianbiao [2015] No. 38). The documents require that the competent department of urban and rural housing construction at all levels use The existing glass curtain wall must carry out a comprehensive safety survey, establish an existing information database for curtain wall, establish a sound safety supervision mechanism, further increase inspections, and investigate and deal with violations of law and regulations in accordance with the law.

For the safety inspection and management of existing curtain walls, the competent provincial and municipal governments in various parts of the country have issued corresponding management regulations and implementation rules, among which Shanghai has taken a comprehensive approach to the safety management of existing curtain walls, while other regions There is still a considerable gap. Both the safety management and inspection of the curtain wall have not been fully implemented or are in a form of failure and have not been implemented. In order to ensure the safety of existing curtain walls, we must have a high level of awareness of the importance of conducting safety inspections and maintenance of existing curtain walls. We must strictly implement the responsibility for the existing curtain wall safety management, and improve the existing curtain wall safety management organizations and operating mechanisms. To explore and implement the existing sources of funds for the maintenance and repair of existing curtain walls, to cultivate and improve the technical level of existing curtain wall inspectors, and to maintain the ongoing curtain wall security and maintenance work as a routine normative work.

4.2 Establishing an Existing Curtain Wall Inspection Agency and R&D Site Inspection Technologies

The safety inspection and appraisal of the existing curtain wall is different from the general performance testing of the curtain wall. It cannot simply use the existing curtain wall inspection agency as an existing curtain wall safety inspection and appraisal agency. The safety inspection, identification and treatment of existing curtain walls are similar to the case where a patient is ill and goes to a hospital for treatment. The affected person first needs to be examined by a doctor, and if necessary, the doctor can arrange for the examination of various organs of the body, such as blood tests, ultrasound, and CT and so on, pending the results of the examination, the doctor will then make a comprehensive judgment based on the results of the instrument examination and propose a treatment plan, and treat the disease with the right medicine. It can be seen that the inspection of existing curtain walls requires professional and high-level and experienced building curtain wall employees, including senior professionals who have long been engaged in the design, construction, and management of curtain walls, and can fully master and familiarize themselves with the specifications and testing methods of curtain walls. People come to play. According to the inspection procedures and inspection contents, they carry out on-site inspection of the existing problems of the curtain wall and verification of the project files, and according to different inspection results, propose further performance requirements for curtain wall testing, including testing items, testing plans and testing methods. Through special inspections, the existing problems of the existing curtain wall are determined based on the detected results, and a reliability appraisal report and the maintenance, repair, or reconstruction plan of the existing curtain wall are made. At present, there are not many curtain wall inspection agencies with such capabilities. We should promptly establish professional inspection agencies with curtain walls to cope with the increasing number of existing curtain wall inspections.

As the safety inspection of existing curtain walls is basically on-site, especially for on-site inspections of concealed works and structural sealants, there is currently no better detection method. In order to adapt to the characteristics of the existing curtain wall inspection, we must further research and develop new detection technologies, such as on-site non-destructive testing technology, that can not only find the existing problems of the curtain wall, but also maintain the integrity of the existing curtain wall.

4.3 Formulate and improve the existing curtain wall standard system

China has not yet completed the establishment of relevant standards for the reliability evaluation of existing curtain walls and the maintenance and repair of existing curtain walls. The national industry standard "Regulations for the reliability evaluation and reinforcement of existing curtain walls" is being submitted for approval and has not yet been implemented. There are also local standards in various provinces and cities have been completed and in implementation, such as Shanghai, Guangdong and Shenzhen. However, as a standard system to measure is not perfect, especially for the evaluation criteria index values ​​and detection methods of existing security defects existing in existing curtain walls, it is not yet systematic, accurate and unified. For example, the aging degree and the service life of structural sealants that have a significant impact on the safety of hidden glass curtain walls, it is difficult to have effective quantifiable index values ​​and detection methods for accurate assessment. With this kind of problem, we should step up technical research and join related companies to conduct in-depth research on detection methods, criteria, and criteria. We should seek a practical method for detection and determination so that we can detect and deal with the aging of structural sealants as early as possible. Security risks.

The maintenance and renovation technologies of existing curtain wall projects are not exactly equivalent to those of newly-built curtain walls. Their design and construction are more difficult than the design and construction of new curtain walls. Especially for the calculation and determination of the reliability and bearing capacity of the original building structure and the original building curtain wall components, the construction technology and safety management need to have special engineering design standards to standardize and implement.

4.4 Implementation of a New Screen Design Scheme Review System

At present, China still has a large number of new construction curtain walls put into use every year. To ensure the safety and reliability of existing curtain walls and prevent new curtain walls from entering the existing curtain wall with potential dangers, we should strengthen the management of curtain wall design and establish new constructions. The construction curtain wall implements a design scheme review system, which controls the possible safety problems of the building curtain wall at the stage of the plan and stops it to improve the safety and reliability of the existing curtain wall. China's current "Technical Specifications for Glass Curtain Wall Projects" JGJ102-2003 and "Technical Specifications for Metal and Stone Curtain Wall Engineering" JGJ133-2001 have been implemented for more than ten years. As some of the regulations and basic requirements put forward by the national industry standards, are increasing. Some of the safety requirements are no longer adapted. In addition to the current architectural design of the exterior design of the building, the novel and complex facade design, the design of the oversized panel section, and the appearance of new building materials raise many new challenges for the design of the building curtain wall, exceeding and breaking through the existing design specifications. There are many stipulated designs and there are potentially more risk factors. According to the current design specifications, the establishment and implementation of more stringent local standards and regulations in accordance with the conditions of different regions, and the review of the design of the building curtain wall will greatly reduce the safety risks of the new construction curtain wall. Shanghai, Zhejiang, and Shenzhen have begun to implement this system and are worth exploring and promoting. Fig. 17 and Fig. 18 show that some new large-faced glass curtain walls in China have not been used yet, and they need to be reconstructed due to the large area of ​​glass self-detonation.

5 Conclusion

In order to improve the status quo of existing curtain walls in China, and improve the safety of existing curtain walls in China, we should start with strengthening safety supervision, establish a standardized and legal market order and concept of building curtain walls, and strictly implement the existing curtain wall safety management responsibility system and safety inspection. The system explores and ensures the source of the funds for the maintenance and repair of existing curtain walls, strengthens the safety management and supervision of all parties involved in the design, production, construction, and use of curtain walls, and completes the formulation and implementation of relevant standards and standards for existing curtain walls as soon as possible. In the course of the safety renovation of the existing curtain wall, we still need to combine the needs of the development of China's green building, vigorously develop the technology of building energy saving and indoor environment transformation with the existing curtain wall, and comprehensively upgrade the performance of the existing curtain wall in China.

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