Dangers in production and construction of stone curtain wall
Tie-back method: four annular grooves are drilled on the back of the slate, and four metal steel bars are inserted into the annular grooves for connection, so that the heavy slate is fixed in the air. The upper two steel pins bear the full weight of the slate, and the lower two steel pins bear the wind pressure. This is a kind of weak connection, the load is easy to concentrate on the edge of the cave, wear the stone, and the notch is enlarged, which makes the steel pin easily separated from the stone. The surface of the slate is subjected to different positive or negative pressures every second, and the slate is in long-term vibration. The higher the floor, the more obvious the vibration. The round hole behind the stone is easy to wear and expand, especially in high-rise buildings, it is very dangerous to use slate.
Slotted connection on the slate: there are long or short slots at the upper and lower ends or the left and right ends of the slate, and there is a slot in the middle of the edge of the slate. Slate is generally 25-30 mm thick and 7-8 mm wide, which can be divided into short and long grooves. When installing, insert the stainless steel plate into the groove. In order to reduce the hard friction between stainless steel and stone, epoxy resin is usually injected between grooves. In fact, epoxy resin itself is also hard. The stainless steel plate handle is fixed on the metal structure frame with bolts.
Generally speaking, there are many ways to make stainless steel plates. Some of them are divided into two pieces in the middle of one end of the steel plate, and bent 90 degrees left and right, so that the stainless steel bent part with handle is inserted into the groove of the left and right slate, and the left and right slate are hung; Some use the short side of T-shaped stainless steel plate to insert into the slate groove up and down respectively, and the long side is used as the fixed handle; Some don't use stainless steel plate, but use ordinary steel plate for zinc plating (easy to rust), and some use short-side steel plate to weld at the end of long-side steel plate instead of T-type stainless steel. Can the welding quality of hundreds of steel plates be detected? If the weld is not full and there is space inside, the strength will be obviously reduced, the steel plate will break, and the slate weighing 75 kg (1 m2) will fall with it, which is very dangerous.
What's more, using 6063 aluminum alloy profile instead of stainless steel, I don't know that the strength of 6063 aluminum alloy is far from that of stainless steel, and the strength is very different. To achieve the strength of stainless steel, the brand of aluminum alloy should be 7074 or 7075, which is completely different from the composition of 6063 aluminum alloy. What is even more deceptive is that it actually patented 6063 aluminum alloy instead of stainless steel.
A high-rise stone curtain wall should use at least hundreds of stone slabs. It is inevitable that so many stone slabs are slotted and the two sides of the slot deviate from the center line. Due to the uneven thickness of the two sides of the groove, the thin edge is easy to break, which leads to the slab falling from the tall building.
High-rise stone curtain wall can also be bonded by composite method, that is, dry hanging and then using structural adhesive. It is difficult to bond stones. There are three disadvantages in using structural adhesive to bond stone, that is, the porosity, dust and unevenness of natural stone make it difficult to clean the stone surface, which makes the direct bonding performance between stone and structural adhesive poor. Unlike some standards that simply say that the stone surface should be cleaned before bonding. How can I clean it? Anyway, can you clean it up? At the same time, structural adhesive is difficult to meet the uncontrollable natural stone factors and variables, so it is very dangerous to rely solely on bonding.
The stone slabs on both sides of the four corners of the high-rise stone curtain wall are under positive and negative pressure every second. The windward side is subjected to positive pressure and the crosswind side is subjected to negative pressure. The vibration frequency of the two slabs at the corner joint is the largest, and the displacement of the slab joint is obvious. The four corners are the weak points of the slate curtain wall, so it is easy to unhook from this corner first. However, in general construction, the four corners are still constructed by general dry hanging method, and a firmer fixing method is rarely adopted.
With the development of high-rise buildings, people hope that the heavy cement concrete and red bricks will be replaced by light materials for the exterior walls. The weight of stone curtain wall is very heavy, which not only aggravates the foundation, but also runs counter to the lightweight wall of high-rise buildings.
Danger in reality
Bidding in the construction industry has not been fully standardized. Many stone curtain wall projects are the lowest cost bids, and some are subcontracted. Therefore, in order not to lose money, we must cut corners. High-rise (50 ~ 100 meters high) stone curtain wall 200 yuan 100 square meters of low-grade granite is indeed quite a lot, isn't it dangerous?
Many design institutes are not familiar with curtain walls, so draw a range on the drawings and indicate what curtain walls are. Stone curtain wall is no exception. The winning curtain wall company designed it by itself. Some design institutes invite architects to examine them carefully, but most of them have gone through formal examination, so isn't it dangerous that the design can't be controlled?
In all construction projects, the state requires the supervision company to be responsible for the quality, which is completely correct and necessary, and is the key to ensure the quality of the project. Unfortunately, many supervision engineers are civil engineers and don't understand curtain walls, let alone stone curtain walls. This is because there is a lack of curtain wall teaching materials in supervision training materials, and many supervisors are retired technicians. How to ensure the final quality without training and understanding of curtain wall supervision? Due to the lack of learning new technology, construction quality inspection stations all over the country often encounter various difficulties in quality acceptance.
The fire resistance of stone curtain wall is very poor, especially in high-rise buildings, where fires are usually lit indoors. The fire in the building will raise the temperature of the stainless steel plate and metal structure that hangs the slate, soften the steel and lose its strength. Tall buildings will fall off slates, which will not only cause danger to pedestrians, but also make it difficult to put out the fire. This is like the World Trade Center in the United States, because the World Trade Center is all steel structures, steel loses its strength when it softens at high temperature, and the World Trade Center collapses from top to bottom.
During 1998 and 2000, the glass curtain walls in many provinces and cities in China were inspected. The inspection results show that there are unqualified curtain walls in all provinces and cities, and the unqualified curtain walls in some provinces reach 30% ~ 50%. Generally, glass curtain walls are less dangerous than stone curtain walls. If 10% of the stone curtain wall is unqualified, the consequences will be unimaginable, not to mention 40%.
Stone curtain wall has poor seismic performance. In the event of a major earthquake, the slate hook will fall, and the slate in the high-rise stone curtain wall will fall from the sky!
some advice
1. There are four countries in the world that can produce ultra-thin stone honeycomb panels, namely France, America, Italy and Germany. Sino-French joint venture established ultra-thin stone honeycomb panel production line in Changzhou to process natural stone into stone industrial products, which is a new product to replace heavy stone.
Generally, the thinnest granite in China can be sawed by 9mm, and it will be broken if it is thinner. By high-tech method, the large granite with a width of 1.2m and a length of 2.4m is sawn into a thickness of 3 ~ 4mm, and can be compounded with aluminum honeycomb to make ultra-thin stone honeycomb panels. The maximum board surface can reach 1.2m× 2.4m, and can be sawed into various specifications according to the requirements of curtain wall. The impact strength is increased by 10 times compared with the original wood board, and the bending strength is increased by more times. Its advantages are light weight, simple installation, safety, reliability and long service life.
2. As can be seen from the above, it is too dangerous for high-rise buildings to use real stone curtain walls, and the standard can be set at 100 meters. In the event of an accident, this standard does not assume any responsibility. Need to find out the cause of the accident from the local building, design institute, raw materials, construction supervision, quality inspection station and other design departments. The state expressly stipulates that the construction project should implement the "lifelong responsibility system". Even if you have retired, if you have an accident, you should be held accountable. Therefore, from the local building authorities and design institutes, it is necessary to explain to users that high-rise buildings should try not to use real granite stone as curtain walls, and must use ultra-thin stone honeycomb panels to achieve the same effect as real stone.
The detailed information of "Safe Application of Stone Curtain Wall" can be found in the link of Zhong Da Consulting Design, and all relevant building construction information you want is available.
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