A key issue in the design and construction of glass curtain wall is the rational selection of glass.

Glass is a very brittle material, so there can be no absolute safety glass. The use of glass in the building is bound to have a certain risk. Safety glass is only a man-made name, generally refers to the relatively small risk of personal injury to the glass (usually refers to tempered glass and laminated glass). There are also countries that have not adopted the sensitive name of safety glass.

As there is no absolute safety glass, glass safety can only be relative, so it should be based on the functional requirements of the different parts of the curtain wall, reasonable selection of glass, and strive to limit the use of safety, so that the risk of personal and property damage is minimized.

Generalized provisions of the curtain wall must use safety glass is not necessarily appropriate. Curtain wall situation is ever-changing, not a simple sentence, one size fits all. Some parts of the curtain wall with a single piece of tempered glass is more dangerous; in some cases, all the curtain wall with laminated glass will become a fire when the flames of the cage.

In fact, in recent years, injuries occurring in the destruction of the accident glass are almost all belong to the "safety glass" monolithic tempered glass; and included in the non-safety glass semi-tempered glass curtain wall has not been reported on the safety of the accident. Even in the overwhelming use of float glass with ordinary glass windows, have not heard as tempered glass so some sensational accident reports. Safety or insecurity, I am afraid to reconsider.

Second, tempered glass

(a) In recent years, tempered glass led to frequent accidents in the curtain wall

Into the twenty-first century, due to various reasons, the glass curtain wall has become a dominant world of tempered glass, "where the curtain wall glass is tempered" into the mainstream of public opinion in the last century, the eighth century, Nineties widely used semi-tempered glass out of the history stage. It seems that toughened almighty, from now on, "nothing happens".

However, in recent years, the frequent occurrence of tempered glass accidents, resulting in many personal injuries and property damage, but the facts ruthlessly negate the "tempered is safe" point of view. Known as non-safety glass, semi-tempered glass is not an accident, known as safety glass, tempered glass but frequent problems with the facts, can not help but cause people to reflect.

In August 2003, a commercial building in Tianjin, a 2m2 piece of tempered glass on the 5th floor of the sudden self-detonation, smashed a music teacher's left hand, disabled and can not play again, compensation of 6600 yuan.

In July 2006, Shanghai Jiangning Road, a building on the 36th floor of the tempered glass explosion, a couple was smashed and injured, but also smashed a moving Toyota car.

In May 2007, Jinan, a hotel glass explosion, hail-like broken particles flying out of the level of six, seven meters. Just a few minutes earlier, members of the national junior table tennis team had passed through, which was a great blessing in disguise.

In 2005, Nanning, a convention and exhibition center tempered glass has exploded more than fifty pieces, some from the center of the venue more than twenty meters in the air over the flowering. At that time, the ASEAN Expo is about to open, the heads of state gathered. In order to achieve absolute safety requirements, had to be a high cost of all affixed with special explosion-proof film. Its cost far exceeded the original proposal to use laminated glass.

In 2006, a newly built museum sightseeing elevator glass explosion in the air, the following cafe glass table smashed to pieces, fortunately, the incident occurred at 6:00 pm, the closing time has passed, otherwise the results are difficult to predict. Now have to change all the glass to aluminum, sightseeing elevator is no longer sightseeing.

In 2007, Beijing's so-and-so plaza, a number of pieces of glass from the explosion, flew out six or seven meters after the injury to three people, but also smashed the glass roof of the city railway station.

2006-2007, Shandong, an airport tempered glass has exploded 29 pieces.

In 2005, just built in Jinan, Shandong, a company office building since the explosion of more than ten pieces of glass, but also smashed a handful of BMW car.

2004 to date, Shenzhen has an office building tempered glass to 40 pieces per year at the rate of self-explosion, the first half of 2007 burst more than 20 pieces, but also injured people, and still in the self-explosion.

No need to list more examples, on the contrary, from the nineties to start using the semi-tempered glass, although not safety glass, but so far have not heard of cases of accidents. Doesn't the comparison between the two make you reflect?

(B) tempered glass explosion is inevitable

Self-bleeding is a characteristic of tempered glass, unavoidable, this is the industry's **** knowledge. In order to reduce the self-explosion rate, can only be preferred glass piece and secondary heat treatment. Even so, 1 ‰ burst rate is already the limit, can not be reduced. One thousand, two of the self-explosion rate has been a quality product, which means that a project burst a few pieces, a dozen pieces is a completely normal phenomenon, we will not find it strange.

But even if a piece of glass burst, there will be the possibility of injury and destruction, with serious consequences. Not to mention that people outside the industry do not know that this is the normal situation, it will make a big fuss, the media will be everywhere speculation, small things into a big, making it difficult for curtain wall manufacturers to fight.

Self-bleeding glass must be replaced, but the cost of replacement is far more than the glass itself, in the ultra-high-rise curtain wall and shaped curtain wall replacement, is even more difficult and dangerous.

What's more, once a blowout occurs, it means that similar events may occur in the future, when and where, but it is not known, so that people lose their sense of security. Every time the accident analysis, the owners are always worried and ask: "still blow up?" , we can only helplessly answer: "still possible, not yet up to standard."

(C) public **** building to be careful with tempered glass

The facts over the past few years have shown that: tempered glass as a "safety glass" used in crowded public **** building, there is a great security risks, so that the owners and visitors, are in an unsafe feeling. Because I do not know at what time, I do not know which piece of glass will suddenly explode, down a glass hail, splitting head and face, injuring and destroying things.

So in the crowded public **** building, had to use a single tempered glass, must be careful, take the necessary security measures:

1. Tempered glass to carry out the second heat treatment.

2. Curtain wall below the isolation zone, do not arrange to attract pedestrians and spectators to stay in the facilities. Indoors against the wall is not set up exhibits, catering, vending position. Outdoor parking space to leave the root of the wall, the root of the wall arranged green or pool.

3. Entrance and exit canopies.

4. Arrangement of metal security over the flow of people.

5. Stick the explosion-proof film.

(D) reduce the surface stress of tempered glass

The greater the surface stress of tempered glass, the deeper the degree of toughening, the more prone to self-explosion. Tempered glass surface stress is now stipulated not less than 90N/mm2, the purpose of which is to reduce the size of broken glass size, thereby reducing the risk of injury.

But the high stress accompanied by a high rate of self-explosion, stress greater than 90N/mm2, the risk of self-detonation greatly increased. And in fact, as long as the explosion, the danger already exists, the glass slag is a little smaller than the role of the decision.

Can we change the way of thinking: first to avoid or reduce the risk of self-explosion occurs, and then talk about the size of the glass slag. As long as it does not blow up, there is no question of large or small.

The current glass standard avoids this problem. Surface stress greater than 90N/mm2 glass is tempered glass, in line with current standards; surface stress less than 69N/mm2 glass is semi-tempered glass, also in line with current standards. However, glass with a surface stress of 69N/mm2 to 90N/mm2 is nothing and is not allowed to be used. In fact, the stress is lower than 90N/mm2 of the glass self-explosion rate is lower, less dangerous, what is wrong with it? As for these glass called what is not an important issue, can also be called "quasi-tempered glass", as long as the actual safety benefits can be let go of the use of the use of further experience in the use.

Third, semi-tempered glass

(a) the characteristics of semi-tempered glass

Semi-tempered glass heat treatment is similar to tempered glass, but the degree of tempering is low, the control of its surface stress is not greater than 69N/mm2. semi-tempered glass does not belong to the current definition of the "safety glass".

Semi-tempered glass surface stress is low, so there is no danger of self-explosion, no external influence, it will never explode, so in this sense, it is safer than tempered glass. Even if it breaks under external force, the fragments formed by the radial cracks will not fall down easily due to the adhesive seams and grooves around the perimeter. There can be time for removal and replacement.

Semi-tempered glass surface is relatively flat, small image distortion, more beautiful.

(ii) semi-tempered glass has a long experience in the application

Because of the above advantages of semi-tempered glass, so in Hong Kong, Macao and foreign glass curtain wall has a long history of application, many projects are still in the application. Domestically, during the period of 1990 to 2000, a number of projects using semi-tempered glass, so far in good condition.

The Mayor's Building in Guangzhou, completed in 1996, the outer piece of insulating glass is made of Belgian 6mm golden-colored coated semi-tempered glass, and the inner piece is made of 6mm float glass from NGL; the Guangdong Public Security Command Center, completed in 1997, is 110m high, and it is made of 6mm silver-gray coated monolithic semi-tempered glass from the U.S. The Qingdao Everbright Bank, completed in 1999, is made of semi-tempered insulating glass, and the outer piece is made of 6mm American silver-gray coated glass. 6mm silver gray coated glass from the United States. The author of the above handled several projects, so far ten years past, did not occur glass broken safety incidents.

The nineties built in Beijing, the new Dong'an market light roof, the use of semi-tempered laminated (body green glass and white glass), so far not found to have broken the plate.

Semi-tempered glass is relatively high security.

(C) large-scale curtain wall have used half-tempered glass

Moscow, Russian Federation Building roof height of 341m, for the European building, designed by the United States, China Construction Company general contracting, Shenyang Yuanda to undertake glass curtain wall project. Considering that the project is located thousands of miles away, once the glass burst, replacement, maintenance costs are extremely expensive, so decided to use all the project half tempered glass. Among them, the translucent part is laminated hollow (6mm+1.14PVB+6mm)+16Ar+8mm, and the three pieces of glass are semi-tempered; the opaque part is 8mm blue sky and white cloud color glaze printing monolithic glass, which is also semi-tempered.

Currently under construction, Guangzhou TV Tower is the world's independent tower. Total height of 620m, curtain wall height of 430m, curtain wall total area of 32,000 square meters, consisting of more than 5,000 pieces of triangular panels, the use of double laminated hollow: (8mm +1.52SGP + 8mmLow-E) + 12A + (8mm +1.52SGP + 8mm). The tower is thicker at the top and bottom, smaller in the center, and the shape is hyperbolic paraboloid. Considering the many types of glass, it is extremely difficult to replace the glass at high altitude, and all the glass is semi-tempered.

Another project under construction in Guangzhou - Guangzhou Zhujiang New City West Tower, for the height of 432m comprehensive building, facade bi-directional curved. Comparison of tempered glass and semi-tempered glass two programs. Replacement of glass at high altitude is extremely difficult to prevent self-explosion is the primary consideration, after demonstration decided to use (8mm +1.52PVB +8mm) +12A +10mm laminated insulating glass, three pieces of glass are semi-tempered.

Fourth, the load-bearing glass structure using monolithic tempered glass to fill the weight

Although the monolithic tempered glass is called safety glass, but it has two fatal flaws, so that it is not suitable for use in load-bearing glass structure:

1. no external causes of self-detonation;

2. self-detonation after the flyaway, instantaneous loss of all bearing capacity or produce people, things fall danger.

(a) load-bearing glass beams, glass columns

Full glass curtain wall load-bearing glass ribs (glass columns), glass beams on the top of the light is the supporting structure of the surface glass, once the glass beams, columns of spontaneous detonation, fly apart, the panel loses its support, the curtain wall or the top of the light will collapse, resulting in serious consequences. Beijing has occurred as a result of the glass rib explosion led to the collapse of the lobby all-glass curtain wall accident.

Glass beams, ribs and other appropriate use of laminated glass. Point support is appropriate to use tempered laminated glass; calculated by the support point stress permit, you can also use semi-tempered laminated glass. If the height of the full glass curtain wall is greater than 8m, the use of laminated glass is difficult, prefer to use float glass ribs. Although the float glass rib is not safety glass, can not guarantee absolute safety, but at least will not suddenly self-detonation. And even if it is ruptured under the action of external factors, it will not suddenly fly apart and disappear, it will be broken in place, temporarily support the panel, in order to repair, not to the collapse of the panel of major accidents.

(B) glass floor, glass stair treads, glass balustrades

These parts do not use a single piece of tempered glass is to prevent self-explosion, anti-flying dispersion, anti-personnel fall. At present, many public **** building balustrades are still using monolithic tempered glass, this balustrade has also occurred after a number of self-blown injury. When the railing can not not use a single piece of tempered glass, its thickness should not be less than 10mm, and check at any time, once the spontaneous explosion, to repair and replace in a timely manner.

Fifth, the roof of the light glass

The roof of the light with a single tempered glass or laminated glass is currently controversial, the reason is that these two types of glass used in the roof of the light, can not guarantee absolute safety. Monolithic tempered glass will explode, fly apart, injuring and destroying things; but tempered laminated glass will deflect after the explosion, will fall as a whole, but also very dangerous, two types of accidents have occurred in the country.

The two types of glass are not ideal, only in the two to seek a lighter danger. 5m height can be used below the single tempered glass. Other cases or laminated glass is good. In order to prevent the laminated glass as a whole fall, the glass compartment should not be greater than 1.6m × 1.6m; glass into the groove depth should not be less than 22mm. for the frame support glass, it is advisable to give preference to float glass and semi-tempered glass made of laminated glass, because it can be exempted from self-explosion to replace the glass of the trouble, and they rupture into a large piece of debris with a certain amount of residual capacity and residual stiffness, will not be easy to sagging, pulled out, fall, relatively safer.

Six, do not let the house become a cage of fire

Due to the "curtain wall to use safety glass" is not a comprehensive understanding of the content of some projects, some of the entire housing curtain wall all using laminated glass. Laminated glass is not afraid of strong impact, broken and not broken, will not fly apart, can be called safety glass, but if the entire building's exterior walls are laminated glass, and not set up enough evacuation routes and automatic firefighting equipment, in case of fire, there will be doors and windows closed, no door to escape the dangerous situation.

In particular, the main reliance on external fire public **** places and low-rise office, residential buildings, if all the use of laminated glass, once the fire, firefighters can not break the glass for rescue, inside the trapped people can not break the window to escape, safety glass has become a major security problem. Therefore, the curtain wall of these buildings must be part of the use of monolithic glass as an emergency exit, and make obvious markings.

Seven, point bearing glass

Point bearing glass in the bearing point (including steel claw bearing and plywood bearing) will produce a great deal of local stress, float glass is low-strength, difficult to bear, it is desirable to use high-strength tempered glass and its products. Priority is given to the use of tempered laminated glass and tempered insulating laminated glass. Of course, after calculation, if the stress at the bearing point is small, the choice of semi-tempered laminated glass is more favorable.

The laminated glass in the insulating glass should be placed on the indoor side.

The use of point bearing monolithic tempered glass should also pay attention to its self-explosion.

Eight, fire glass

The fire glass used in glass curtain walls and light roofs should be monolithic cesium potassium glass. It is mainly used for:

1. There are light transmission requirements of the horizontal firewall between the layers (high 800mm) and the floor of the firewall on the left and right sides of the firewall transparent vertical firewall (left and right width of 1.0m).

2. Smoke blocking between floors with beautiful and transparent requirements.

3. Transparent firewall in the floor dividing two fire protection zones.

4. Fireproof sealing around the indoor patio of the continuous floor.

The fireproof cesium-potassium glass can have a fire resistance of 1.0 hour to 2.5 hours, while the aluminum profile has a low melting point, poor fire resistance, and can not be used as a fireproof glass support structure, fireproof glass is usually supported by the steel structure, and if necessary, the steel structure is also attached to the fireproof coating.

Shenzhen TV center lens type white glass exterior curtain wall, in order to achieve the effect of full transparency, the interlayer smoke blocking without rock wool, replaced by 8mm thick cesium potassium fire glass.

Beijing Television Center has a central 31m × 36m, nearly 200m high large patio, due to fire safety requirements, surrounded by fireproof glass wall encapsulation, the large patio becomes an independent fire partition. In the construction of the West Tower of Guangzhou (430m high) also has a triangle with a large patio, part of which is also to be encapsulated with fire-resistant glass.

Nine, take design and construction measures to reduce glass rupture

Currently, a large number of glass broken in the project, there are due to glass self-destruction, there are due to temperature changes, and really damaged by strong winds and earthquakes and not much. A large number of breakage can be reduced through design and construction measures.

(a) design reasons

1. glass support point is too much. As the building requires a large area of glass, using six points, eight points or four points, six points plus a pair of side support. So many bearing points uneven force, it is easy to make the glass crack.

2. Support at the constraints are too strong, point support head without hinges, glass into the slot card is too tight, the glass plate rotation difficulties.

3. The plate seam is too small, the top of the glass expansion dead. I recently saw an office building in Linzhi, Tibet, a single glass hidden frame curtain wall, more than 30% of the glass cracks, many cracks parallel to the plate seam, the glass is squeezed outward arch. This is due to the width of the plate seam less than 8mm, Tibet, a large temperature difference between day and night, the daytime sunlight glass expansion, the plate seam is narrow, the embedded adhesive and hardening, the glass in-plane deformation is limited, only the outer arch rupture.

(B) construction reasons

1. edge processing. Some of the glass is not fine edge grinding, not chamfered; even some glass is not ground at all, crashing edge, crashing angle is not dealt with, which is prone to spontaneous explosion or rupture.

2. Forced installation. Glass is not flat after tempering, multi-point support is not level, high and low, can not be installed hard installation, installation of the initial stress is too great, resulting in a large number of glass self-explosion or rupture.

3. Installation of glass metal groove is too narrow, concrete, granite surface close to the surface of the glass, glass deformation is limited.

4. Glass gasket is too thin, some even only 2mm, glass expansion on the top of the bottom of the slot.

5. Caulking adhesive is unqualified, hardening without elasticity.　

X. Conclusion

There is no absolute meaning of safety glass, the use of glass have a certain risk. Through the reasonable choice of glass type, coupled with the necessary design and construction measures to achieve the glass limit the use of safety.