Usage of energy dissipation technology in tall building strcuture
Reading Report of Tall Building Structure Major： Structural Engineering ID NO： 1130411 Name： 王瑞 1 Usage of Energy Dissipation Technology in Tall Building Structure 【 Abstract 】 With the developing of tall building structure theory and the application of new material and new technology, the height of high-rise building is increasing and the body type is becoming more complicated, which make it hard to satisfy the seismic requirements with regular structure system only. As a method that can solve the seismic problems properly, the energy dissipation technology has been widely used in design of high-rise building. A brief introduction of energy dissipation technology and the usage of it in tall building structures are given in this report. 【Keyword】seismic design, energy dissipation technology, tall building structure 1 Introduction of energy dissipation technology The theoretical basis of energy dissipation system will be introduced through an example of single-degree of freedom system. The system is composed by a concentrated mass m in the top, a frame without mass to provide the stiffness and a viscous damper to dissipate the seismic energy. Assuming there is no axial deformation in the beams and the columns. The system is presented in Fig.1. Fig.1 Single-degree of freedom system The differential equations of motion of this system under harmonic force is mu '' cu ' ku P0 sin wt The steady-state displacement response can be calculated as u (t ) u0 sin( wt ) (ust )0 Rd sin( wt ) The displacement reaction coefficient can be described as 2 Rd u0 (ust )0 1 2 1 ( / n ) 2 2 ( / n )2 2 From the equations above, the displacement reaction coefficient is becoming smaller with the increase of damping ratio or damp, which means smaller dynamic response amplitude. This is the theoretical basis of energy dissipation technology. We can take measures to increase the damp of the system to dissipate the seismic energy and thus reduce the dynamic response of structure [1]. The energy dissipation technology mainly includes energy dissipation devices like dampers and damping constructions like energy dissipation brace. These devices and constructions can provide additional stiffness and additional damp for the structure to dissipate the seismic energy and reduce the dynamic response under earthquake, which reduce the earthquake disaster effectively. These devices can provide high stiffness under the action of wind or small earthquakes. At the same time they can turn into inelastic or yield firstly under severe earthquakes to increase the damp and dissipate the energy [2]. 2 Energy dissipation devices The basic idea of energy dissipation devices is that these devices won’t undertake the load directly under normal circumstances but can share part of the load and dissipate the dynamic energy under certain vertical load, which can reduce the response of the structure [1]. The most common energy dissipation device in use is the damper (Fig.2). Dampers are usually installed in locations like braces, joints between beams and columns, joints between frames and shear walls, bottom chords of trusses and so on [3]. When earthquake happens, the damping force will do work under the relative motion caused by earthquake and dissipate the dynamic energy. This process can translate the kinetic energy into heat and reduce the earthquake response. The most prominent advantage of dampers is that it won’t change the original structure system [4]. This kind of energy dissipation devices has been widely used in seismic design in China. Fig.2 dampers in structure 3 3 Energy dissipation constructions Energy dissipation construction is a broad concept. The main measure is to improve the energy dissipation capability by certain construction design. To achieve this purpose, we usually prefer bending energy consumption to shear energy consumption or axial energy consumption because of its full hysteresis curve. We can also design to achieve the purpose that some components can enter plastic state to dissipate the dynamic energy thus protect the main structure. Energy dissipation braces, energy dissipation shear wall, energy dissipation joints and connections are main kinds of energy dissipation construction in use. 3.1 Energy dissipation braces (1) Cross energy dissipation brace This kind of brace is based on the theory of HADAS (one kind of hysteretic dampers). It can dissipate dynamic energy through the plastic deformation of steel frames located in the cross position of the brace. (2) Friction energy dissipation brace Friction dampers composed by high-strength bolts and steel plates are installed in this kind of brace. It can provide high stiffness without apparent slide under the action of wind or small earthquake. On the other hand it will slide under severe earthquake and reduce the stiffness of structure. The friction in brace can dissipate the energy and reduce seismic response of structure [5]. Fig.3 The computational model for friction energy dissipation brace (3) Eccentric energy dissipation brace This kind of brace is often used in steel frame structure. It can dissipate seismic energy through the plastic deformation of eccentric beam section. The eccentric beam 4 will not yield under the action of wind or small earthquake and can provide enough stiffness [6]. The brace will yield under big earthquake and dissipate energy. Fig.4 Regular eccentric brace system 3.2 Energy dissipation wall Energy dissipation wall is based on the theory of dampers or install them directly on shear walls or non-bearing walls. It mainly concentrated on the construction measures to deal with the connection parts between walls and frames or the gaps between walls and frames which can control the value of shear force acted on the wall and the deformation capability. These construction measures can help dissipating the dynamic energy [7]. Besides, buckling restrained brace is also one kind of energy dissipation constructions widely used. For traditional braces, the compression strength is much smaller than tensile strength and the buckling of braces can badly influence the stiffness, bearing capacity and the earthquake resistant behavior. Buckling restrained brace is composed of both steel and concrete to make sure that the braces will not buckle under compression force. So the compression strength is equal to the tensile strength. The ductility and hysteresis ability are also improved. This kind of braces can dissipate the dynamic energy through the yielding of steel in serious earthquake. 4 Energy dissipation structure systems Many kinds of new structure systems are designed to improve the energy dissipation capability in recent years. Some typical examples will be introduced in this part. 4.1 RC tube in tube structure with friction joints The friction joints in RC tube in tube structure is composed of frame tube, wall tube and the friction joint devices (Fig.5). Certain gaps are set up in the slabs connecting the frame tube and wall tube where friction joint devices are installed. Under severe earthquakes，the differential movement between the frame tube and the 5 wall tube causes hysteretic energy dissipation by the friction joints slipping [8]. Fig.5 Friction joints in RC tube in tube structure This kind of structure system can improve the seismic performance in two aspects. Firstly, the deformation modes of frame tube and wall tube are different under lateral loads. The deformation of frame tube is bending type and that of the wall tube is shearing type. The friction joints will do work caused by the different deformation of these two parts. Secondly, under severe earthquake, especially when the seismic predominant period is closed to the natural period of structure, resonance can be easy to happen in the structure. The friction joints can help to change the overall stiffness of structure and the natural period, which can avoid the resonance [9]. 4.2 Energy dissipation structure system with high-level transfer floor With the rapid development of high rise buildings in recent years，in order to meet the functional requirements，the lower part of many high rise buildings is always frame structure so that it can provide large space for commercial purpose，and the upper part is often used as residence or hotels which need relatively small space. Complex structural forms of high rise structure with high-level transfer floor are proposed and widely used in China. But a significant problem is that the vertical stiffness is not continuous that may causes damage concentrated in the parts near the transfer floor. The internal force and deformation of components on different sides of the transfer floor can also change suddenly which is dangerous in severe earthquakes. To solve these problems, experts propose to apply energy dissipation devices in the structures with high-level transfer floor. In this new structure system, damping devices like dampers or braces are installed in the lower part to the high-level transfer floor and replace some of the shear walls (Fig.6). These devices can act as subsidiary components under normal circumstances. Under severe earthquake, they will provide additional stiffness and damp to the structure and change the dynamic response to reduce damage to the main structure [10]. Energy dissipation devices can also be installed in the transfer floor thus won’t influence the functional requirements of architecture. 6 Fig.6 Energy dissipation structure system with high-level transfer floor 5 conclusion and advices The research of energy dissipation technology has developed rapidly in recent years in China. The technology has been applied in many tall building structures and improved the seismic performance of structures significantly. But there are still many problems to be solved. (1) More research about the durability and reliability of energy dissipation devices should be taken to improve the function of them. (2) More experiments are needed to test the seismic performance of structures with dampers or damping braces to get the detailed character. (3) Research about the design method and specialized code are needed to standardize the usage of energy dissipation technology. (4) Application of the energy dissipation technology in complicated structures is quite important and more work can be done to design new kinds of energy dissipation structure systems As a conclusion, energy dissipation technology is acting an important role in seismic design of tall building structures with a bright future in application. 7 References [1] 李宜．浅谈耗能减震技术[J]．现代科技，2009，8：68-70． [2] 刘宏昌．现代工程减震技术分析[J]．中国新技术新产品，2010，17：164-165． [3] 李嵩峰，张慧媛，薛茹．耗能减震技术的研究与进展[J]．焦作大学学报，2001，6(2)： 52-54． [4] 黄誉，彭伟．浅述结构消能减震控制技术的研究与应用[J]．四川建筑，2006，26(6)： 126-128． [5] 王春波．摩擦耗能支撑框架结构减震性能研究[D]．西安：西安建筑科技大学，2006． [6] 张磊．高层建筑偏心支撑钢框架抗震性能的研究[D]．西安：西南交通大学，2004． [7] 吕西林，孟良．一种新型抗震耗能剪力墙结构——结构的抗震性能研究[J]．世界地震 工程，1995，2：22-26． [8] 马文静，刘伟庆，王曙光．筒中筒结构内部摩擦连接消能减震体系的研究[J]．世界地 震工程，2008，24(3)：16-19． [9] 周云，邓雪松，吴从晓．高层建筑耗能减震新体系概念与实现[J]．工程抗震与加固改 造，2007，29(6)：1-7． [10] 冷加冰．高位转换短肢剪力墙结构耗能减震设计与分析[D]．哈尔滨：哈尔滨工程大学， 2006． 8
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