Over the years, all walks of life also make great progress with rapidly economic development in China, in the meanwhile, rapid development also presents the increasing demand for resources and energy. So there are many environmental problems throughout the development. Of these problems, the earthquake is a relatively frequent natural disaster and has a extremely bad impact. During earthquake, lots of constructions would damage or even collapse which threatening people's personal and property safety, resulting in casualties. Therefore, it is a very urgent task to take effective measures to improve the seismic performance of construction projects.
1.Main Principle of Building Seismic Design
It is an effective measure to improve the seismic performance so as to reduce the damage of personal and property safety. The technicians have also been making tireless efforts in this area. In the long-term practical work, they also summed up a set of experience to improve the structure and seismic performance, and this theory is put into the actual construction and gets a very good result. However, the rapid development of science and technology requires the development of seismic performance to take an effective measure that seismic performance is very good and protect the building structure, and that measure is now widely used in basic isolation technology. The main way to build a seismic structure is to install a damper and place the isolation layer that is highly reliable and has a relatively small stiffness in the horizontal direction between the upper structure and the basic surface. This is able to effectively reduce the impact of the earthquake on the structure ensuring the safety and stability. But the seismic self-vibration period of the building with the isolation layer will be extended, so the structure will not produce a very intense acceleration response. Therefore, placing the isolation layer in the construction has a very positive significance. Only to scientifically determine the ratio to the stiffness and damping,
the seismic performance has improved significantly.
2.Problems on the Building Seismic Design
2.1.Principle of Building Isolation
The main seismic design is to build a isolation system between the upper and the lower structure that could form a isolation layer which can block the transmission of the force during the earthquakes and then reduce the vibration of the structure. A good seismic design not only can increase the service life of building, but also can reduce the adverse effects caused by earthquake in order to protect people’s safety. In general, the height of the building is directly proportional to the safety requirements of the building structure. Therefore, in some high-rise buildings, seismic design must be used. The application of building isolation technology affect the isolation effect. The general deformation of structure is concentrated in the isolation layer which belongs to the energy dissipation layer. The layer improves the energy dissipation effect of the damper and helps to reduce the reaction rate of earthquakes.
2.2.Requirements of Building Seismic Design
The stability of the construction can be greatly enhanced with seismic design. The design should consider the form of the construction, seismic intensity and construction targets to develop the most scientific seismic design, from which to choose the lowest cost and the best effects one. Furthermore, it is generally necessary to ensure that the target intensity of seismic design is higher than that of the building. Once a horizontal earthquake has occurred, the building's isolation structure will have a better safety stock and ensure that the structure is 1.5 times higher than the seismic precautionary intensity. Every parameters and performance should be checked to ensure the installation quality when determine the isolation components. Sampling detection combining with the parameters and types are used to compare with the elements. And the number of sampling detection is generally greater than three, all components are qualified when the test passed.
2.3. Type of Isolation Building
There are two main types of isolation building, one is base isolation, another is mid-story isolation. Both two types are affect the seismic performance. This article has simply analyzed and introduced the problems that should be noticed during the seismic design in the following parts.
2.3.1.Base Isolation(as shown in Figure 1)
It is necessary to install the isolation layer on the foundation of the building and the superstructure, but the height of the isolation layer can not be too high. And the isolation layer shall have a strong stability and reliability over a long-term usage to effectively reduce the harm caused by the earthquake and to absorb the energy generated by the earthquake to ensure the safe use of construction. In addition, a good base isolation could protect the internal equipment that can make sure the good performance of these devices and reduce the earthquake that the users feel to prevent the internal structure from secondary disasters.
Figure 1 Base Isolation
2.3.2.Mid-story Isolation(as shown in Figure 2)
There is a isolation layer setting in the middle floor above the foundation and the upper part of isolation layer directly contacts with the foundation like the ordinary building, so there is no problem existing between the bottom volume of the isolation building and the wall. However, seismic construction should be under the isolation layer. If the construction site is relatively narrow, it is best to set the isolation layer on the ground because deformation in the air is conducive to saving land and can effectively reduce excavation quantity.
Figure 2 Mid-story Isolation
3.Measurements of Isolation Building
The isolation space is generally divided into five parts and each parts has its own role. There is a brief introduction as following.
3.1.Measurements about the Upper Part
The upper part of isolation lawyer is at the top of the isolation space. When the earthquake happened, the upper part of the isolation lawyer would have a certain displacement which has a certain relationship with design and the direction of displacement is not fixed.The deformation produced by the upper part is large without large acceleration which ensure that the furniture wouldn’t turn over during the earthquake. You should do the following work to avoid deformation in the isolation lawyer.
- The obstacles shall be completely removed in the stairs, elevators and corridors.
- Install the seismic joint in the upper part.
- Between the seismic joint and the ground should have a horizontal isolated seams. If this construction is difficulty, you can add a horizontal slipping cushion.
3.2.Design of the Isolation Layer
Isolation lawyer, where installs the isolation components, is easy to deform between the upper and the lower parts, so it is really necessary to take seismic measures to prevent from deformation. In addition to setting the pipeline in the isolation lawyer, nothing else construction can be built, and after that sealed treatment can be done. Generally speaking, the outer parts of the isolation lawyer involve the protective equipment, for example, the rain-block components among which height is not in excess of 0.5m couldn’t be involved in the construction area. It is recommended that which height of the isolation layer is between 1. 8 and 2. 1 m only can be considered as height of the construction considering the planning and other factors.
3.3.Design of the Lower Part
The lower part is located below the isolation lawyer and play an important role in supporting. Only the most scientific construction methods and raw materials can improve the safety and the stability of the lower part. Multi-layer rubber bearings generally have lead core which has a two-lane structure featured with strong hysteresis. So the earthquake will increase the structural stiffness, and the intensity is also able to disperse energy. That is to say, this devise combines the advantages of isolators and dampers with simple operation. Therefore, the seismic design often chooses multi-layer rubber bearings.
Peripheral part is 40cm apart from the upper structure. Shielding cloth should be set to avoid the other people coming close. To prevent the upper structure from large deformation, a certain space is needed around the peripheral part.
Between two buildings usually need to leave some space as a venue. In addition, the upper structure will also have a strong shaking during earthquake, so we must make precautions so as to ensure that the earthquake won’t produce a great displacement.