1. 1? Early stage of base isolation technology
The concept of base isolation was first put forward by Japanese scholar Hehe Haocang in 198 1. It is believed that several layers of logs are laid crisscross on the foundation, and then concrete foundation is built on the logs to weaken the energy transmitted by the earthquake.
1909, J.A. Calante Lentz of the United States proposed another seismic isolation scheme, that is, laying a layer of talc or mica between the foundation and the superstructure to make the building slip during the earthquake and achieve the purpose of seismic isolation.
192 1 year, when American engineer F.L. Wright designed Imperial Hotel in Tokyo, Japan, he deliberately used dense short piles to penetrate the surface hard soil, directly inserted into the bottom of soft soil, and used soft soil as isolation layer. 1923 Great Kanto Earthquake occurred, and similar buildings nearby were seriously damaged, but this building is still intact.
1924 Kenzaburo, a Japanese ghost head, put forward a seismic isolation scheme of inserting bearings between the column foot and foundation of the building. In 1927, Taro Nakamura of Japan discussed how to install dampers to absorb energy, and made a useful exploration in the theory of isolation.
At this stage, although there has been a clear concept of isolation and a certain theoretical basis for isolation, the application of base isolation technology has not been well studied and developed due to the level and conditions at that time.
1.2? Modern stage of base isolation technology
With the gradual establishment of earthquake engineering theory and the further inspection of structural engineering by actual earthquakes, especially in recent twenty or thirty years, people have accumulated quantitative experience on the performance of isolated and non-isolated structures, thus eliminating and sublimating some early isolation methods. Among them, the laminated rubber pad base isolation system is considered to be the most effective system in the practical application of isolation technology.
1984, New Zealand built the world's first four-story building with lead-core laminated rubber pads as isolation elements. 1985 The first four-story rubber cushion isolation building was built in California, USA? Ding Sheng Judicial Affairs Center. 1986 A five-story high-tech center building was built in Japan, with lead rubber mats. At present, more than 30 countries in the world are carrying out research in this field, and this technology has been applied to bridges, buildings and even nuclear facilities. Up to now, more than 3 100 base-isolated buildings have been built in the world, of which more than 80% are laminated structures.
Since 1980s, China began to attach importance to the research of base isolation, and many domestic scholars have made great progress in the research of internationally popular base isolation systems. At present, more than 2,000 buildings with various base isolation systems have been built in China, including laminated rubber cushion isolation system, sand cushion sliding friction system, graphite mortar sliding system and suspension isolation structure system. Most of them adopt bonded laminated rubber cushion isolation system. Modern isolation technology has been widely used for 30 years, and the application of isolation technology has become dominant in buildings in Japan and other countries. China will surpass Japan for the first time in 2007.
2? Isolation principle of laminated rubber cushion system
The principle of base isolation is illustrated by the seismic response spectrum of buildings, and its acceleration response spectrum and displacement response spectrum curves are shown in figure 1.
Figure 1? Structural response spectrum curve
As can be seen from the figure, there are two main factors that have an important influence on the seismic response of buildings: one is the period of the structure, and the other is the damping ratio. Low-rise buildings in ordinary non-isolated earthquakes have high stiffness and short period, and their basic period is just in the frequency band with the largest earthquake input energy. Therefore, the corresponding acceleration response is much larger than the ground motion, but the displacement response is smaller, as shown in point A in the figure. If the period of the building is prolonged and the damping is unchanged, the acceleration response is greatly reduced, but the displacement response is increased, as shown in point B in the figure. If the damping of the structure continues to increase, the acceleration response will continue to weaken, and the displacement response will also decrease obviously, as shown in point C in the figure. In other words, the acceleration response of the structure can be greatly reduced by prolonging the period of the structure and giving greater damping. At the same time, the large displacement of the structure can be provided by the isolation layer between the bottom of the superstructure and the top of the foundation, rather than by the relative displacement of the superstructure itself. In this way, the superstructure will move closer to translation during the earthquake, which greatly improves the safety of the superstructure.
The isolation layer of laminated rubber cushion base isolation system is composed of multiple isolators. Vibration isolators include laminated rubber pads and dampers, which are divided into ordinary laminated rubber pads, lead rubber pads and high damping rubber pads. The isolation system has long period, large damping ratio and obvious isolation effect. In particular, the latter two kinds of vibration isolators are adopted, and no additional dampers are needed, so the construction is convenient.
3? Performance evaluation of laminated rubber cushion base isolation system
In many base isolation systems, through a lot of experiments and research, according to the international evaluation standard of isolation systems, the laminated rubber pad isolation system has the following performance advantages:
1)? The vertical bearing capacity of the system is large. Generally, the design value of vertical bearing capacity of a single isolator can reach thousands of tons and the ultimate bearing capacity can reach tens of thousands of tons.
2)? The isolation layer of the system has a stable elastic reset function, which can be automatically reset instantly in many earthquakes, which is completely incomparable to the friction sliding isolation system.
3)? The isolator has good durability, low cycle fatigue resistance, hot air aging resistance, ozone aging resistance, acid resistance and water resistance. Through the performance tests of the product specimen, its service life is 60 ~ 80 years [2]. Recently, Japan has replaced the isolator in the laminated rubber cushion base-isolated building which has been used for 65,438+00 years. The results show that its indexes are different from those of 65,433.
4)? The isolation effect is obvious, and its acceleration response is much lower than that of non-isolated structures. The theoretical analysis results are in good agreement with the experimental results. M-high reinforced concrete base-isolated building, in February, 2007 1987+ 17, the measured ground acceleration was 43.8? Cm/s2, and the maximum acceleration of the roof is only 1 1.9? Cm/sec 2. In the research process of laminated rubber cushion base isolation system, through the analysis and calculation of four different types of structural isolation systems, it can be seen that in areas with seismic fortification intensity of 8 degrees, if laminated rubber cushion base isolation system is adopted, the fortification intensity of the upper structure can be reduced by 1 ~ 2 degrees, and there is a large safety reserve.
5)? Compared with other isolation systems, the uneven settlement of the foundation has no obvious influence on the isolator, and the structure is simple, the installation is convenient and the force transmission mode is simple and clear.
Although the laminated rubber cushion isolation structure has many obvious advantages, it is found that the dynamic performance requirements of the system are quite strict, and it is very different from the traditional non-isolation structure from design to construction. In order to ensure the reliability of the analysis and calculation results, the dynamic responses of four different structural systems are analyzed by four methods, and it is found that:
1)? The dynamic characteristics of laminated rubber cushion base-isolated structure not only vary with different structural system types, but also have a great relationship with different installation positions of isolators. Therefore, in the design, we should not only carry out special conceptual design, but also carry out dynamic analysis from multiple angles, so as to grasp its dynamic response reasonably and accurately and ensure the safety and reliability of the design.
2)? In the isolation structure, in order to really isolate the superstructure from the ground, we should pay attention to the structural treatment of some key parts, such as the isolation treatment of the bottom stairs from the main structure, and the flexibility of water, gas, heating and distribution pipelines when they pass through the isolation layer. On the one hand, negligence will bring great disaster in the earthquake.
3)? In addition, the isolation layer of laminated rubber cushion base isolation system has strict requirements for construction. The displacement of the isolation layer cannot be disturbed and constrained by any reason, and the isolator and its accessories cannot be damaged during construction. It is also required to place the isolator in a higher position to ensure that the seismic layer can be horizontally displaced and immediately reset after the earthquake.
4? conclusion
1)? Because the laminated rubber cushion isolation system has the performance advantages of large vertical bearing capacity, strong elastic reset function and obvious isolation effect, the height limit and safe distance of traditional buildings can be appropriately relaxed in the design.
2)? The research results show that the fortification intensity of the superstructure of the laminated rubber pad base isolation system can be reduced by 1 ~ 2 degrees, and there is still a large safety reserve.
3)? Although it seems that adding an isolation layer will increase the cost of the isolation system, the cost saved with the reduction of the fortification intensity of the superstructure can be used to build the isolation layer. Therefore, compared with similar non-isolated buildings, the engineering cost of the whole isolated building is basically the same or slightly lower. The economic and social benefits of the base isolation system are enormous if the losses caused by the destruction of the building structure, the loss of internal property, casualties and the shutdown caused by the destruction of the building are added up.
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Natural rubber isolation technology can resist earthquakes of magnitude 8.3 or above!
The Wenchuan earthquake in Sichuan changed life and death in an instant, and the most direct and serious harm came from the collapse of a large number of buildings lacking adequate earthquake prevention measures. If those buildings adopt the world-tested earthquake-resistant construction technology, the reality of a large number of casualties may be rewritten, and the fresh lives of tens of thousands of compatriots may not be so angry and helpless.
technical background
The Malaysian Rubber Committee (MRB) initiated the natural rubber isolation technology (RSIT) on 1976, and started the research and development of the natural rubber base isolation technology for buildings against earthquake disasters, and has been working closely with the Earthquake Engineering Research Center (EERC) of the University of California, Berkeley (now a colleague, Pacific Engineering Research Center).
Malaysia Rubber Research Institute (RRIM) and Abdul Razak Research Center (TARRC) in London, England are pioneers in product research and development of Malaysia Rubber Committee. The Malaysian Rubber Committee has made great contributions to the development of the world rubber industry in the past 70 years, especially in the basic research in the field of natural rubber. Hundreds of millions of ringgits have been spent on the research and development of natural rubber isolation technology (RSIT), and millions of ringgits have been continuously invested every year. The success of rubber isolation technology (RSIT) of Malaysian Rubber Committee (MRB) has saved millions of lives and billions of dollars worth of assets, and prevented them from being destroyed by global earthquake disasters.
Natural rubber base isolation system was first applied in the United States, Japan and Britain. Later, the cooperation between EERC and MRPRA promoted the support of the United Nations Industrial Development Organization (UNIDO) and helped developing countries with frequent earthquake disasters such as Indonesia, China, Chile and India to produce low-cost isolation system products. With the support of MRPRA, the research plan of EERC makes natural rubber base isolation system one of the most effective methods to resist natural earthquake disasters in the world today. ?
The scientific research results show that the natural rubber bearing with high damping will bounce some seismic waves back to the ground, and the other part will be absorbed, thus buffering the torsional force transmitted by seismic waves to buildings, reducing the direct impact damage of seismic waves to buildings, and finally ensuring the safety of life and property. At the same time, due to the application of high damping natural rubber bearings, the construction cost of traditional building structures and walls will be reduced by about 20%.
Application status
Public welfare facilities building
The legal and judicial center of the foothills community is located 20 kilometers (12 miles) away from the San Andreas fault in the United States. As one of the research projects developed by the EERC research and development plan, it is the first anti-seismic building public welfare facility in the world that has been proved to be able to withstand an earthquake with a magnitude of 8.3 on the Richter scale.
Construction of nuclear power plant facilities
Practice has proved that the seismic design of rubber isolation technology (RSIT) foundation greatly simplifies the cost of safety design, the consumption of construction time, standard equipment, piping system and earthquake load construction of nuclear power plants in the United States. In addition, with the discovery of nearby faults, the standard of seismic design will be improved. For example, a nuclear power plant does not need to be redesigned, but only needs to upgrade the base isolation system of the building facilities. ?
When designing isolation bearings, EERC only designed, manufactured and tested two liquid metal nuclear reactors. EERC designed, manufactured and tested two kinds of isolation bearings: the first one, named PRISM, was designed with high form factor and was only used to provide lateral isolation; The second type, called SAFR, adopts the design of isolation bearing with low form factor, which can provide both lateral and longitudinal isolation of the reactor. The test results also show that different shape factors can provide different isolation characteristics, which makes the research institute more aware of the characteristics of this material technology.
Hospital facilities building
At present, there is a great demand for basic isolation in hospitals, mainly to strengthen the protection of hospital facilities and patients. The main purpose of using base isolation is to set the dynamic characteristics of the building so that it will not be subjected to excessive vibration during the earthquake. There are several base isolation structures to choose from: high damping rubber base isolation, friction pendulum device, low damping rubber and additional damping device. Choosing the right system depends on the applicability, cost and special function requirements of the system. In recent years, the United States, Japan, Italy, New Zealand, Chile and India have used base isolation systems in most hospitals and completed nearly 1000 rebuilt earthquake-resistant building facilities.
Japan actively adopts base isolation technology.
Although it started late, the research and development of base isolation technology has developed rapidly in Japan. The first large-scale base-isolated building was completed in 1986. There are several reasons for the rapid development of base isolation in Japan. A large part of all construction expenditure must be budgeted for the research of base isolation design, and large construction companies are actively attacking this market. The approval procedure for building base-isolated buildings in Japan is very simple and standardized. As Japan is a country with a high incidence of earthquake crisis, Japanese people have an extraordinary demand to study the application of this technology in order to provide long-term security for Japanese citizens and society. Recently, the calculation center of Tohoku Electric Power Company in Miyako Province of Japan has also widely used high damping rubber isolation bearings in buildings.
At present, the largest base-isolated building in the world is the West Japan Post Computer Center located in Shenhu County. This six-story building covers an area of 47,000 square meters (500,000 square feet) and is supported by 120 rubber isolation bearings. It has an isolation period of 3.9 seconds and is located about 30 kilometers from the epicenter of the Kobe earthquake in 1995. 19 mile) the building experienced severe ground displacement. The peak ground displacement acceleration of the isolation bearing is 400 cm/s square (? 0.4 1g), but the isolation system will reduce the peak acceleration transmitted to the sixth floor to 127cm/s square (? 0. 13? g？ )。 The estimated displacement of the isolator is about 12 cm (4.8 inches). A fixed foundation building adjacent to the center suffered some damage, but it was not damaged at all because the center adopted base isolation. Base isolation system is used more and more in Japan, especially after Kobe earthquake. Due to the performance of West Japan Post Computer Center in this earthquake, more buildings, especially apartments, have increased the application of base isolation.
construction cost
The application and construction of building rubber isolation technology (RSIT) mainly includes the following three expenses:
1) Cost of evaluation of building load-bearing and seismic structure;
2) customized processing and production costs of natural rubber isolation bearings;
3) Installation and construction costs.
The above expenses account for about 5% of the total cost of building facilities.
Application summary
After more than 30 years of research and repeated tests, the stability of base isolation has been greatly improved. As for other problems, such as isolation displacement, failure, unexpected response, etc., have been greatly reduced. Moreover, the difficulty of making large isolators has been overcome, and isolators with a diameter of 60 inches (1.5 meters) can also be made with current technology. Located in Liuxi, California, USA? The 70 natural rubber bearing manufactured by King/C.R Diagnostic Trauma Center is the largest isolation bearing in the United States, and the diameter of the isolation bearing manufactured by them is 1.40 inch. At the same time, it is proved that using low coefficient rubber to make large bearings can provide a more reliable isolation system.
It is more convincing to install base isolation systems in several construction projects in the United States. 1989 After the Loma Prieta earthquake in California, a large-scale vibration isolator of10 was installed in the city hall of Oakland, USA. A new public safety building in Berkeley also uses isolation bearings. All Martin Luther King's entertainment centers are equipped with earthquake-proof facilities, and the Hearst Memorial Mining Building at the University of California, Berkeley is also equipped with isolators. In the process of installing the isolator, the classical architectural art facilities have never been affected, but the seismic index has been greatly improved.
Chengdu, Sichuan News Network, March 28th (Reporter Jiang Liang, Xia Yifan) How to improve the seismic fortification quality of houses in the reconstruction of Sichuan disaster area after Wenchuan earthquake? On March 28th, experts from Japanese universities who came to Rong to attend the seminar on concrete frontier technology at the invitation of China Construction Commercial Concrete Company pointed out that the practice of the earthquake in Japan proved that elastic buildings had remarkable disaster reduction effect, and the reconstruction of Sichuan disaster area could learn more from Japan's advanced experience in this respect.
After the Wenchuan earthquake, people in the industry are very concerned about the seismic and shockproof ability of buildings. Professor Guqiaogang of Japan University pointed out that the earthquake resistance of building structures can be achieved through earthquake resistance, earthquake suppression and isolation. Among them, earthquake resistance is mainly to resist the earthquake force by strengthening the columns, beams, walls and supports of the building, while earthquake control is to absorb the earthquake energy by installing dampers and other equipment inside the building, so as to achieve the purpose of protecting the building, while seismic isolation is to install isolators between the building and the ground to isolate the building from the earthquake force. "It has been proved that presetting isolators in buildings can effectively reduce the damage of buildings during earthquakes."
Professor Guqiaogang said that laminated rubber bearings, lead laminated rubber bearings and elastic sliding bearings are the most widely used in Japan at present. Among them, the use of rubber in high-rise buildings can effectively improve the seismic performance of buildings. "There is an earthquake-proof apartment in Tokyo, Japan, which is 93 meters high. The exterior of the building uses newly developed high-strength sixteen-layer rubber, and the central part of the building uses laminated rubber made of natural rubber. In the event of a magnitude 6 earthquake, these measures can reduce the stress of the building by half. "
When talking about what problems should be paid attention to in building reconstruction in Sichuan disaster area, Japanese experts suggested that more elastic buildings could be built. Professor Guqiaogang said that elastic buildings are very popular in Japan at present, and there are more than ten elastic buildings in Tokyo alone, which have withstood the test of the earthquake with a magnitude of 6.6 on the Richter scale, and the disaster reduction effect is remarkable. "This kind of elastic building is built on the isolator and consists of layered rubber, hard steel plates and dampers. The building structure is not in direct contact with the ground. Among them, the damper is composed of spiral steel plates, which can effectively slow down the ups and downs during the earthquake. "
Guqiaogang believes that although the use of isolation technology increases the construction cost, the building can be safe and sound under the intensity of 6 degrees. "If a skateboard is set between the ground and the building, no matter how the ground shakes, the building will hardly shake. The isolation technology is most suitable for middle and high-rise buildings, especially the general laminated rubber isolation bearing isolation structure, compared with the concrete structure with large mass and stiffness. "
Yoshio Arai, also from Japanese University, analyzed the reasons for the deterioration of reinforced concrete structures. He pointed out that the main reasons for the deterioration of reinforced concrete structure are not only salt damage, freezing damage and the harm caused by the reaction between acidic substances and alkali aggregate in reinforced concrete structure, but also the proportion of reinforced concrete structure, poor concrete construction and reinforcement, poor design and so on. "I hope that Sichuan will pay attention to these issues during post-disaster reconstruction."