Foundation vibration isolation and structural vibration isolation are the most widely used and effective energy dissipation and vibration reduction technologies. Among them, foundation vibration isolation is active vibration isolation, and structural vibration isolation is passive vibration isolation. Structural energy dissipation and shock absorption technology belongs to passive control in structural shock absorption control.
1 foundation vibration isolation technology
1. 1 hydraulic quality (HMS) control system. The application scope of the system is flexible buildings on the ground floor. Although the flexible building on the ground floor can meet the requirements of large space on the ground floor, its seismic performance is poor because of the large deformation of the flexible building on the ground floor. Therefore, the structural control method is proposed to improve the seismic performance of this kind of buildings. HMS system is mainly composed of hydraulic cylinder, piston and pipeline, which is installed on a single-layer frame, as shown in figure 1. As can be seen from Figure 1, when the frame vibrates due to ground movement, the liquid is pushed by the piston, which makes the liquid and mass in the pipeline vibrate, and part of the vibration energy of the frame is transferred to the liquid and mass, thus reducing the vibration of the frame structure. The compressibility of liquid in HMS system must be considered, and the "elasticity" calculation and analysis model of HMS system considering liquid compressibility is established. Starting from the "elastic" model, we can get a new seismic building control system composed of structure and HMS system.
1.2 base isolation with laminated rubber bearings. The commonly used mechanical models for seismic response analysis of base-isolated buildings with laminated rubber bearings include inter-story shear model, inter-story shear-bending model, inter-story torsion model and spatial bar system model, among which inter-story shear model is the most widely used. When the story shear model is used to analyze the dynamic response of base-isolated buildings, it is necessary to simplify the complex hysteretic characteristics of flexible isolation layers into a restoring force model that can be used for numerical analysis.
2 structural energy dissipation technology [1]
2. 1 Friction damper. Friction energy dissipator is a damping device with good energy dissipation performance, simple structure, low cost and convenient manufacture. As shown in Figure 2, the common friction energy dissipator consumes energy through the friction movement of the middle steel plate with long and narrow grooves relative to the upper and lower copper pads, and the sliding friction can be changed by adjusting the fastening force of bolts. The test results show that the sliding friction is proportional to the bolt fastening force. There is little difference between the maximum static friction and sliding friction, but the sliding friction is greatly attenuated, reaching 30%, which is caused by bolt looseness. Hysteretic curves show good rigid-plastic characteristics.
Friction sliding joints are composed of steel plates connected by high-strength bolts, and the sliding force of energy dissipator is controlled by friction between joint plates. Friction materials can be sandwiched between steel plates or the contact surface can be treated to adjust the friction coefficient, and the connecting bolts can be loosened to adjust the friction between steel plates, and the surrounding chain bars play the role of connecting and coordinating deformation. When the supporting external force cannot overcome the maximum static friction, the energy dissipator will not slide; When the external force can overcome the maximum static friction, the energy dissipator slides and consumes energy through friction. The test results show that Pall friction energy dissipator has stable working performance and strong energy dissipation ability.
2.2 Low carbon steel damper. Mild steel damper is a kind of energy dissipation device in passive control of structures. During earthquake or wind vibration, the energy input to the structure is dissipated through the plastic yield hysteretic deformation of low carbon steel, so as to achieve the purpose of shock absorption. An unbonded sliding interface is formed between the inner steel brace and the outer cladding (steel tube, reinforced concrete or concrete filled steel tube) to prevent the inner steel brace from buckling under compression, thus obtaining a complete hysteretic curve. The damper has the characteristics of convenience, durability and good hysteretic energy dissipation, and is gradually widely recognized by the engineering community.
2.3 lead damper. The structure of lead-rubber composite damper is mainly composed of thin steel plate, rubber, lead, extrusion head, connecting plate and protective layer. The steel sheet, rubber and connecting plate are vulcanized into a whole by high temperature and high pressure, and circular holes are left in the centers of the steel sheet, rubber and connecting plate. After vulcanization, lead is poured into the reserved holes by extrusion. Thin steel plates can be specially treated to improve damping force and post-yield stiffness.
2.4 Viscoelastic damper [2]. The energy dissipation structure with viscoelastic dampers plays an important role in engineering earthquake resistance. Due to the addition of additional damping, the total damping of the structural system no longer meets the orthogonality of the regular modes, which makes the motion equations involved coupled with each other and cannot be solved analytically by solving the general dynamic equations. Foss first put forward the theory of complex modal analysis method. Through the Foss transformation of the original coupling equation, the decoupled motion equation is obtained, and the response of the structure under earthquake is obtained. The complex modal theory is used to decouple the motion equation of base-isolated structure, and the response under earthquake is analyzed.
2.5 tuned liquid damper (TLD). Tuned liquid damper (TLD)[3] is a kind of water tank, which is mainly used for vibration control of high-rise buildings and towering structures. It uses the inertia and viscosity of the liquid in the container with fixed structure to reduce the vibration of the structure, and it is a passive control device. In this paper, the vibration control of seismic response of high-rise buildings is studied by TLD. In order to make TLD play a better vibration reduction effect, it is necessary to shake the water in the water tank as much as possible, and the shaking frequency of the water in the water tank is required to be equal to the natural vibration frequency of the structure, and the effect is the best.
2.6 tuned mass damper (TMD). TMD is a simple control structure device, which is easy to install, maintain and replace. Theoretical analysis shows that for general multi-storey buildings, the maximum displacement of the structure relative to the ground under earthquake excitation occurs at the top floor. At the same time, the results also show that the damping ratio of TMD is in the range of (0.05~0. 1), and the damping effect is good, but when it exceeds 0.2, the damping effect is not obvious; When the TMD mass ratio is less than 0.0 1, the vibration reduction effect is not obvious. With the increase of TMD mass ratio, the control effect becomes better and better, but when U is greater than a certain value (greater than 3%), the vibration reduction effect is not obvious. When the frequency ratio of TMD to the original structure is about 0.95, the control effect is good.
3 Conclusion
How to choose the damper reasonably depends on the actual situation of the project [4]. The technology of energy dissipation and shock absorption is simple in concept, convenient to manufacture, clear in shock absorption mechanism and wide in application. However, there are still some problems to be studied in order to make the energy dissipation technology more widely used: ① Further research on energy dissipation system and its effect: the position of energy dissipation components is sensitive to the damping effect of structures, so how to improve the damping effect and improve the economic and technical indicators of energy dissipation system should be the future research direction. ② Further development of energy dissipation components: At present, there are many types of energy dissipation components, but attention should be paid to the study of their practicability, economy and support connection forms. ③ Research on design calculation method and software of energy dissipation and shock absorption system: Only by providing designers with practical, simple and consistent design methods and software can the energy dissipation and shock absorption system be further popularized and applied.
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