First of all, let's take a look at SEG Building, with a total height of 355.8 meters, 79 floors, 75 floors above ground and 4 floors underground, with a total construction area of 654.38+0.7 million square meters. It is the tallest concrete filled steel tube building in the world at present.
Seg Building is a concrete-filled steel tube structure, which is a composite structural material formed by filling concrete in thin-walled circular steel tubes. It is a special form of hoop concrete. The basic principle of concrete filled steel tube is to make the core concrete in a three-dimensional compression state with the help of the hoop constraint of circular steel tube, so that the core concrete has high compressive strength and compressive deformation ability. Concrete-filled steel tube not only has excellent mechanical properties such as high strength, light weight, good ductility, fatigue resistance and impact resistance, but also has excellent construction properties such as saving labor and materials, easy erection and fast construction.
Concrete filled steel tube (CFST) is one of the most effective and economical structural forms to apply high-strength concrete to high-rise buildings and long-span bridges. This is because: (1) steel pipe has a ferrule effect on core concrete, which can effectively overcome the brittleness of high strength concrete; (2) There is no steel skeleton in the steel pipe, which is convenient for pouring high-strength concrete, and because of the separation of the steel pipe, it does not interfere with the ordinary concrete of the beam-slab structure outside the pipe, and there is no trouble of staggered pouring; (3) There is no concrete protective layer outside the steel pipe, which can give full play to the bearing capacity of high-strength concrete.
Shenzhen SEG Plaza Building is a super-high-rise building with steel structure system designed and built by China itself, which was of milestone significance at that time. The fabrication of the steel pipe column of SEG Plaza Building was entrusted to Guangzhou Guangzhou Shipbuilding International Co., Ltd. in accordance with the corresponding engineering standards in GB 50205-95 "Verticality of Head and Tail Pipe Axis d/500". The tower structure is a frame tube composed of concrete filled steel tubular columns and solid web steel beams. There are four reinforced concrete shear walls in the tube and 16 concrete filled steel tubular columns around the tower. The strengthening layer consists of steel structure rigid arms and surrounding trusses. The floor is composed of cast-in-place concrete slabs with profiled steel plates and steel beams.
However, the bedrock distribution in the construction site of SEG Building fluctuates greatly, with deep northeast and shallow southwest. The minimum burial depth of Yanshanian weathered granite bedrock is about 45 meters. There are no major faults and fault zones at the site. The groundwater level is about 0.5 ~ 2.0m (below the natural ground).
All foundations adopt pile foundation (hand-dug cast-in-place pile), and the pile end of the main tower falls on weathered bedrock, with a buried depth of 0.5m; The pile end of the bearing platform falls on the moderately weathered bedrock, with a buried depth of 0.5m ..
It can be said that the site selection, design, materials and construction of SEG Building are in strict accordance with national requirements. Without quality problems and natural disasters, the possibility of the collapse of SEG Building is almost zero. Experts also confirmed that although the SEG building was shaking, no abnormal safety situation was found in the main structure and surrounding environment of the building, no cracks were found in the surrounding ground, and the indoor steel structure and decorative surface were in normal condition.
Then why is the SEG building shaking? The shaking of SEG Building should be a * * * vibration problem. Every object has one or more * * * vibration frequencies. If the external frequency is the same as the * * * vibration frequency of the object, it will cause the object to vibrate, and the vibration amplitude is the largest.
Generally speaking, there are many reasons for the * * * vibration of bridges or buildings, such as the * * * vibration energy conversion when the frequency of abnormal wind rotation matches the frequency of the building itself, or the huge force generated by eddy current in fluid mechanics. We can find in the past news that some buildings are shaking for these reasons, so there will be carefully designed devices in the new buildings to avoid the frequency matching between the buildings and the external wind field.
But there are also many reasons, which can be said to be unexpected. For example, on July 5, 201/year, a shopping mall in Seoul, South Korea suddenly shook for about 10 minutes. Everyone thought that an earthquake was coming and fled. After investigation, the conclusion is very surprising: there is a gym on the 12 floor of this building. At that time, someone was practicing aerobics, which caused the whole building to shake!
What's the situation of SEG Building? According to the official preliminary investigation results and the specific situation of the building, it should be the damper problem of the building, which led to the shaking of the building.
Seg Tower is 355.8 meters high. According to the whip tip effect, the higher the building, the more obvious the shaking. Low-rise buildings are mainly affected by gravity. As the building gets higher and higher, it will be more affected by crosswind than by gravity. So in general, high-rise buildings will use dampers. What is damping? Various frictional forces and other obstacles that attenuate free vibration are called damping. The "special" components placed on the structural system can provide motion resistance and reduce motion energy, and are called dampers. Simply put, the role of dampers is to reduce the impact of vibration on buildings.
Since 1970s, dampers (or shock absorbers) have been used in buildings, bridges, railways and other structural projects to reduce vibration and dissipate energy.
According to the investigation, the SEG building is not equipped with baffles, so it will shake due to the influence of wind, subway operation and temperature. Next, the SEG building installed dampers to improve the wind and earthquake resistance and comfort.
Of course, a more in-depth and specific investigation will be based on a comprehensive analysis of the building and its surrounding areas. After the shaking of the SEG building, China evacuated the crowd in time and made a comprehensive physical examination of the building, so we don't need to worry, just wait for the result.