토목환경공학개론 Overview of vibration control 건설 환경공학과 구조동역학 및

토목환경공학개론: Overview of vibration control 건설·환경공학과 구조동역학 및 진동제어 연구실 Structural Dynamics & Vibration Control Lab.

목차 1. Introduction 1. 1 Background 1. 2 Recent international developments 1. 3 Scope 1. 4 Definitions 2. Passive energy dissipation 2. 1 Metal yield dampers 2. 2 Friction dampers 2. 3 Viscoelastic dampers 2. 4 Viscous fluid dampers 2. 4 Tuned mass dampers 2. 5 Tuned liquid dampers 2. 6 Other energy dissipators 2. 7 Code development and concluding remarks Structural Dynamics & Vibration Control Lab. 2

1. Introduction 1. 1 Background • Motive • Evolution of structural control in the u. s • Evolution of structural control in the world • Distinctive features of structural control Structural Dynamics & Vibration Control Lab. 3

Motive • Increased flexibility – The trend toward taller, longer and more flexible structures • Increased safety levels – Higher safety level demands : tall structures, nuclear power plants • Increased stringent performance requirements – Strict performance guide lines : radar tracking stations, radio telescope structures, aerospace structures • Better utilization of materials and lower cost – Economic considerations : savings in materials, weight and costs Structural Dynamics & Vibration Control Lab. 4

Evolution of structural control in the U. S • Roots primarily in the aerospace-related problems – Tracking, pointing, flexible space structure – The protection of buildings and bridges – For extreme loads of earthquakes and wind • Conceptual study by Yao in 1972 – Open loop control, closed loop contol, feedback structural control • The first world conference on structural control in 1994 Structural Dynamics & Vibration Control Lab. 5

Evolution of structural control in the U. S • International association for structural control in 1994 • ASCE became a member of Amerian Automatic Control Council(AACC) in 1995. • Passive base isolation system become an accepted design strategy. Structural Dynamics & Vibration Control Lab. 6

Yao’s concept of structural control Feed back control Open & closed loop control Structural Dynamics & Vibration Control Lab. 7

Evolution of structural control in the world • More than 100 years ago. – Wood house placed on ball bearings (Jone Milne, P. F. of engineering in Japan) • 1950’s – Linear system theory application to the structural dynamics – Developed from internal combustion engine • 1960’s – Base isolation for low-rise and medium-rise structures and bridges – Characteristics of base isolation • Filters high frequencies of the ground acceleration • Lengthens the natural period of vibration to about 2 s • Induces large amplitude motion Structural Dynamics & Vibration Control Lab. 8

Evolution of structural control in the world • 1972 ~ – Active structural control (concepts form Yao 1972) – Hybrid structural control – Semiactive structural control Structural Dynamics & Vibration Control Lab. 9

Distinctive features of structural control • Civil engineering structures are statically stable – The addition of purely active control force can cause destabilization – In contrast to aerospace structures which requires active control for stability • Loads are highly uncertain – Earthquake and wind loads have no definite magnitude and arrival time. – Mechanical loads are fairly well documented. • Erformance requirements are generally coarse Structural Dynamics & Vibration Control Lab. 10

1. 2 Recent International Developments • • 1990 - The U. S. National Workshop on Structural Control 1992 - The Japan National Workshop on Structural Control 1992 - The U. S. - Italy Workshop on Structural Control 1992 - The Tenth World Conference on Earthquake Engineering in Madrid, Spain • 1993 - International Workshop on Structural Control in Hawaii • 1994 - The Formation of IASC – International Association for Structural Control • 1995 - First European Conference on Structural Control • 1996 - The Second IASC in Hong Kong • 1998 - The Third IASC in Tokyo Structural Dynamics & Vibration Control Lab. 11

1. 3 Scope • The current state of the art in the control and monitoring Of civil engineering structures • A link between structural control and other fields of control theory • Future research needs and application efforts. Structural Dynamics & Vibration Control Lab. 12

1. 4 Definitions 1. 4 Defintions • Active control – External source powers control actuators – Actuators apply forces to the structure in a prescribed manner. – These forces can be used to both add and dissipate energy. – Type : open-loop control, closed-loop control • Passive control – Does not require an external power source. – Impart forces that are developed in response to the motion of the structure. – The energy in the passively controlled system can not be increased. Structural Dynamics & Vibration Control Lab. 13

1. 4 Definitions - active control ex 1) Location : Kao Hsiung, Taiwan Size : 150 m x 60 m at Base, 85 -story Fuction of building : Multi-purpose Control system : Multi-staged tuned active damper Structural Dynamics & Vibration Control Lab. 14

1. 4 Definitions - passive contol ex 1) Structural Dynamics & Vibration Control Lab. 15

1. 4 Definitions - passive contol ex 2) Structural Dynamics & Vibration Control Lab. 16

1. 4 Definitions - passive contol ex 3) Structural Dynamics & Vibration Control Lab. 17

1. 4 Definitions - passive contol ex 4) Structural Dynamics & Vibration Control Lab. 18

1. 4 Definitions - passive contol ex 5) Structural Dynamics & Vibration Control Lab. 19

1. 4 Definitions • Hybrid control – The combined use of active and control systems – Ex 1) viscoelastic damping + active mass damper – Ex 2) base isolation + actuator • Semiactive control – External energy requirements are smaller than active control system. – Do not add mechanical energy to the structural system. – Often viewed as controllable passive devices. Structural Dynamics & Vibration Control Lab. 20

1. 4 Definitions - hybrid control ex 1) Structural Dynamics & Vibration Control Lab. 21

1. 4 Definitions - hybrid control ex 1) Structural Dynamics & Vibration Control Lab. 22

1. 4 Definitions - semi active control ex 1) Structural Dynamics & Vibration Control Lab. 23

1. 4 Definitions • Structural health monitoring – Detect changes that may include damage or degradation. – In-situ, nondestructive sensing and analysis of structural characteristics including structural response. Structural Dynamics & Vibration Control Lab. 24

2. Passive energy dissipation • All vibrating structures dissipate energy – Due to internal stressing, rubbing, cracking, plastic deformation, and so on • Methods of increasing the energy dissipation capacity are very effective in reducing the amplitudes of vibration. • This may achieved by conversion of kinetic energy to heat, or by transferring of energy among vibrating modes. Structural Dynamics & Vibration Control Lab. 25

• Conversion of kinetic energy to heat – Devices that operate on principles such as frictional sliding, yielding of metal, phase transformation in metal. • Transferring of energy among vibrating modes – Supplemental oscillators, which act as dynamic vibration absorbers Structural Dynamics & Vibration Control Lab. 26

Metallic yield dampers 2. 1 Metallic yield dampers • Inelastic deformation of metals. – Very effective for the dissipation of energy input structure from an earthquake • The idea of utilizing added metallic energy dissipators (kelly, 1972; Skinner, 1975) • Many devices use mild steel plates with triangular or hourglass shapes so that yielding is spread almost uniformly throughout the material. Structural Dynamics & Vibration Control Lab. 27

Metallic yield dampers ADAS : A typical X-shaped plate damper or added damping and stiffness

Metallic yield dampers The area within the hysteresis loops measures the amount of dissipated energy.

Metallic yield dampers • Other materials, such as lead and shaped-memory alloys, have been evaluated. (Sakurai, 1992; Aiken and kelly, 1992) • Some particularly desirable features of these devices – Stable hysteretic behavior, low-cycle fatigue property, longterm reliability, relative insensitive to environmental temperature • An inelastic constitutive model for the material of metallic yield dampers is developed. (Dargush and soong, 1995) • A finite-element formulation for the tapered-plate energy dissipator is developed. (Tsai, 1995) Structural Dynamics & Vibration Control Lab. 30

Metallic yield dampers

Metallic yield dampers • The result shows that the proposed model effectively predicts the device behavior under wind and earthquake loading. • The direct use of experimental data – The hysteretic model is first selected. – The model parameters are determined. – The relationships between the model parameters and the size and material parameters of the device are established. • By employing a bilinear model, the relationships between the model parameters and the size and material parameters are established. (Ou and Wu, 1995) Structural Dynamics & Vibration Control Lab. 33

Metallic yield dampers • Utilize metallic dampers within a structural system – Formulate design guidelines and procedures based on knowledge gained from theoretical and experimental study. • Key parameters in reducing seismic response – B/d (ratio of bracing stiffness to device stiffness) – SR (brace-device assemblage stiffness to that of corresponding structural story) – (Yielding displacement of the device) (Xia, 1990; Xia and hanson, 1992; Tsai, 1993; Pong, 1994) Structural Dynamics & Vibration Control Lab. 34

Metallic yield dampers • Applications – The earliest applications of metallic dampers to the structural systems occurred in New Zealand. (Skinner, 1980) – ADAS devices have been installed in a 29 -story steel-frame building in Nalpes, Italy. (Ciampi, 1991) – In a two-story nonductile reinforced concrete building in San Francisco as a part of seismic retrofit. (Perry, 1993) – In three reinforced concrete buildings in Mexico City as a part of seismic retrofit. (Martinez-Romero, 1993) – In Japan, lead extrusion devices and metallic yield dampers have been installed in a number of buildings. Structural Dynamics & Vibration Control Lab. 35

Friction dampers 2. 2 Friction dampers • Friction provides another excellent mechanism for energy dissipation. • It is important to minimize stick-slip phenomena to avoid introducing high-frequency excitation. • Compatible materials must be employed to maintain a consistent coefficient of friction over the intended life of device. Structural Dynamics & Vibration Control Lab. 36

Friction dampers

Friction dampers • The dampers are not to slip during wind storms or moderate earthquake. • However, under severe loading conditions, the devices slip before yielding occurs in primary structural member. • These device not significantly affected by loading amplitude, frequency, the number of loading cycles. Structural Dynamics & Vibration Control Lab. 39

Friction dampers • Composition of the interface – Steel to steel, brass to steel, graphite impregnated bronze on stainness steel – Great importance for insuring longevity of operation of the devices • Most friction dampers used coulomb friction with a constant coefficient of friction. • Key parameters in reducing seismic response – YSR (ratio of initial slip load to yielding force of corresponding structural story) – SR (ratio of bracing stiffness to stiffness of corresponding structural story) (Nims, 1993; Scholl, 1993) Structural Dynamics & Vibration Control Lab. 40

Friction dampers • A combination mechanism – A friction damping device for control of structural damage due to severe earthquake motion – A viscoelastic damping device for control of low energy excitation – (Tsiatas and Olson, 1998; Pong, 1994 a, b; Tsiatas and Daly, 1994) • A bidirectional friction device – Consist of stack of sliders that are alternately flat and convex – Provide a nearly circular distribution of clamping pressure over the contact area – (Dorka, 1992) Structural Dynamics & Vibration Control Lab. 41

Metallic yield dampers • Applications – Pall friction devices have been installed in canada – Sumitomo friction dampers have been installed in a 31 -story steel-frame sonic office building in japan. (Aiken and kelly, 1990) – Pall x-braced friction devices and their variations have been installed in several buildings as a retrofit and new facility. (Pall, 1993, 1996) Structural Dynamics & Vibration Control Lab. 42

Viscoelastic dampers 2. 3 Viscoelastic dampers(vd) 1. Viscoelastic materials ① Characteristic 1) Rate dependent behavior (viscous) 2) Elastic behavior (elastic) 3) Store and dissipate energy at all deformation levels ② Kind 1) Polymeric materials : <fig 2. 3. 1 -1 Typical polymeric structure network> 2) Glassy materials : <fig 2. 3. 1 -2 Typical glass structure (sodium-silicate glass)> ③ Application : both wind and seismic protection Structural Dynamics & Vibration Control Lab. 43

Viscoelastic dampers 2. Typical viscoelastic damper (by the 3 M company inc. ) by shen and soong(1995) <Fig 2. 3. 2 -1 Viscoelastic damper > < fig 2. 3. 2 -2 Typical hesteretic loops > ▶ Viscoelastic dampers dissipate enegy through shear deformation of the viscoelastic layers Structural Dynamics & Vibration Control Lab. 44

Viscoelastic dampers 3. Basic principles (Zhang et al, 1989) : Shear strain : shear stress : Shear storage modulus : Shear loss modulus Under a sinusoidal load with frequency → , → : Loss factor where , Using → ------------------------------ (1) ▶ First term : in-phase portion with representing the elastic modulus Second term : out-of-phase portion represents the energy dissipation component ▶ , : Analytical expressions obtained Using experimental results (Chang et al, 1993) Using the Boltzmann’s superposition principles(Shen and Shoon, 1995) Structural Dynamics & Vibration Control Lab. 45

Viscoelastic dampers 4. Characteristics ① Force-displacement relationship ------------------------- (2) Where A : Total shear area , : Total thickness ▶ A linear structural system with added viscoelastic dampers remains linear with the dampers → A significant simplification in analysis of viscoelastically damped systems (Zhang et al. 1989 ; Zhang and Soong. 1992) ② Response analysis for linear system ▶ SDOF : Using eqs. (1) and (2) ▶ MDOF : Using the modal strain energy method (← Finite element analysis) (Soong and Lai. 1991 , Chang et al. 1993) Structural Dynamics & Vibration Control Lab. 46

Viscoelastic dampers ③ Temperature effect on the behavior of viscoelastic materials → Investigated and quantified (Chang et al. 1992 ; Shen and Soong. 1995) → Natural period varies moderately under varying temperatures → If the damper is designed as a stiff device, the damping ratio is almost unchanged when the temperature changes ( Kasai et al. 1994) → If the temperature is constant, the viscoelastic material is linear over a wide range of strain → At large strains : considerable self-heating due to the large amount of energy dissipated ↓ change the mechanical properties of material ↓ the overall behavior is nonlinear → Heating-softening effect is present even linear response : linear analysis can only be for approximation of the response the frequency domain approach is not suitable for seismic applications when large strains are most likely experienced Structural Dynamics & Vibration Control Lab. 47

Viscoelastic dampers 5. Research development ① Makris(1994) → Present a complex-parameter Kelvin model → Parameters are complex-valued but frequency-independent Applicable for nonlinear systems ② Makris and Dargush(1994) → Present a boundary-element formulation for the dynamic analysis of generalized viscoelastic materials ③ Blondet(1993) → Two full-scale dampers were dynamically tested ④ Nielsen(1994) → Six smaller dampers were tested to failure : The failure occurred at very large strain levels Structural Dynamics & Vibration Control Lab. 48

Viscoelastic dampers ⑤ Chang(1993), Lai(1995) → Full-scale prototype structure incorporated with VD was tested ⑥ Chang(1994) → Experimental and analytical studies on the inelastic seismic behavior of two 2/5 -scale steel movement restoring frames with and without VD ⑦ Recent experimental and analytical studies ( Foutch(1993) ; Lobo(1993) ; Chang(1994, 1995) ; Shen(1995)) → Apply to steel as well as reinforced concrete structures under a wide range of intensities of earthquakes ▶ Note : steel structure → seismic response is elastic reinforced concrete structure → seismic response is inelastic ↓ permanent deformation and damage ↓ addition of VD can reduce the development of damage Structural Dynamics & Vibration Control Lab. 49

Viscoelastic dampers 6. Application to civil engineering structures ① World Trade Center in New York (1969) (a) The World Trade Center (b) Damper installation <Fig 2. 3. 6 -1 Damper installation in the World Trade Center, New York> ( Courtesy of the 3 M Company, St. Paul, MN ) → 10, 000 VDs in each tower (distributed from 10 th to 110 th floor) Structural Dynamics & Vibration Control Lab. 50

Viscoelastic dampers ② The Columbia Sea. First Building in Seattle (1982) (a) The Columbia Sea. First Building (b) Damper installation <Fig 2. 3. 6 -2 Damper installation in the Columbia Sea. First Building, Seattle> (Courtesy of the 3 M Company, St. Paul, MN) → 260 VDs → To reduce wind-induced vibration Structural Dynamics & Vibration Control Lab. 51

Viscoelastic dampers ③ The Two Union Square Building in Seattle (1988) (a) The Two Union Square Building (b) Damper installation <Fig 2. 3. 6 -3 Damper Installation in the Two Union Square Building, Seattle> (Courtesy of the 3 M Company, St. Paul, MN) → 16 large VDs were installed parallel to four columns in one floor → To reduce wind-induced vibration Structural Dynamics & Vibration Control Lab. 52

Viscoelastic dampers ④ The 13 -story steel frame Santa Clara Country Building in San Jose, Calif (1994) → Use viscoelastic dampers to reduce seismic response ⑤ The Chien-Tan railroad station roof in Taipei, Taiwan (1994) → Utilized the dampers to reduce wind-induced vibrations ⑥ A navy-owned three-story lightly reinforced concrete building in San Diego (1997) Structural Dynamics & Vibration Control Lab. 53

Viscous fluid dampers 2. 4 viscous fluid dampers (VFD) 1. Fluids can be used to dissipate energy 2. Application scopes of VFD : arerospace Military applications Structural application 3. Characteristic : ① Linear viscous response over a broad frequency range ② Insensitivity to temperature ③ Compactness in comparison to stroke and output force ▶Study of the seismic retrofit of reinforced concrete structures (reinhorn, 1995) → Results : reduce inelastic deformation demand Reduce damage quantified by an index monitoring permanent deformation Structural Dynamics & Vibration Control Lab. 54

Viscous fluid dampers 4. Several kinds of VFD ① Cylindrical pot fluid dampers <Fig 2. 4. 4 -1 Cylindrical pot GERB damper > ( Makris and Constantinou, 1991) ② Viscous damping walls <Fig 2. 4. 4 -2 Viscous damping wall > (Miyazaki and Mitsusaka, 1992) ③ Orificed fluid dampers <Fig 2. 4. 4 -3 Schematic of fluidic orfice design> (Constantinou and Symans, 1993) Structural Dynamics & Vibration Control Lab. 55

Viscous fluid dampers 5. Typical damper <Fig 2. 4. 5 Taylor devices fluid damper (Constantinou et al. 1993) > ▶ It dissipates energy through movement of the piston in the highly viscous fluid ▶ Over a large frequency range ⇒ viscoelastic fluid behavior ▶ For Newtonian fluid (purely viscous fluid) ⇒ The output force is proportional to velocity of the piston Structural Dynamics & Vibration Control Lab. 56

Viscous fluid dampers 6. General Maxwell model (Makris and Constrantinou) X : Displacement of the piston F : Output force : Material constant ← Obtained through damper tests (Constantinou and Symans , 1992) : Fractional derivative ▶ For r=q=1 → Maxwell Model ( : Relaxation time, : Damping constant ) ▶ For model of the damper below the cut-off frequency about 4 Hz → Structural Dynamics & Vibration Control Lab. 57

Viscous fluid dampers ▶ Most VFDs in current applications → • Obtained by special design of the orifices • Advantages : the force tends to flatten out at higher velocities 7. Application of VFDs to civil engineering structures ① Two residential buildings in Los Angeles (Huffmann, 1985) → Isolation systems with helical steel springs and viscous dampers → Earthquake protection <Fig 2. 4. 7 -1 Base isolation system with helical springs and cylindrical pot fluid dampers (Huffmann, 1985)> Structural Dynamics & Vibration Control Lab. 58

Viscous fluid dampers ② 1 -km bridge weighing 25, 000 tons in Italy (1991) → Protected by viscous silicon gel dampers at each abutment ( weigh : 2 ton , length : 2 m , stroke : 500 mm ) ③ 78. 6 m high, 14 -story building at the center of Shizouka City, Japan → Viscous walls have been used <Fig 2. 4. 7 -2 SUT-Building in Shizuka city, Japan> < Fig 2. 4. 7 -3 VDW locations in SUT-Building> (Courtesy of Sumitomo Construction Co. , Ltd. , Tokyo, Japan) ( Miyazaki and Mitsusaka, 1992) Structural Dynamics & Vibration Control Lab. 59

Viscous fluid dampers ④ Five buildings of the new San Bernardino Medical Center (1994) → base isolation system with viscous fluid dampers → 233 dampers ( each damper : output force = 320, 000 lbs energy dissipation level = 3, 000 HP (at 60 in/s) ) ⑤ Boiler frame in Japan (1994) → results : seismic displacement response of the boiler frame with dampers is reduced to 50 -60% of the response without the dampers ⑥ 3 -Story Pacific Bell North Area Operations Center (1995) → 62 Dampers ( each damper : capacity = 130 k. N , stroke=50 mm) (a) Under construction (b) Damper installation <Fig 2. 4. 7 -4 Pacific Bell North Area Operations Center> (Courtesy of Taylor Devices, Inc. , N. Tonawanda, NY) Structural Dynamics & Vibration Control Lab. 60

Tuned mass dampers 2. 5 Tuned mass dampers (TMD) 1. Basic principle <Fig 2. 5. 1 Models of SDOF structure and TMD> Total effective damping ceq = We can reduce the response of structure system by adding tmd Structural Dynamics & Vibration Control Lab. 61

Tuned mass dampers 2. Practical considerations ① The amount of added mass ② TMD travel relative to the structure ③ Sensitivity to low levels of excitation 3. Research development ▶ As of today, most TMD applications have been made toward mitigation of wind-induced motion ▶ The seismic effectiveness of TMDs remains an important issue ① Den Hartog (1947) → Secondary mass with tuned spring and damping elements → Increase damping in the primary structure ② Clark (1988) → Propose the concept of MTMDs together with an optimization procedure Note : MTMD is to overcome the frequency-related limitations of TMDs Structural Dynamics & Vibration Control Lab. 62

Tuned mass dampers ③ Xu and Igusa (1992) ; Yamaguchi and Harnpornchai (1993) → Study on the behavior of MTMDs connected in parallel to the main system ④ Setareh (1994) → Propose DTMD consisting of two masses connected in series to the structure → Analytical Results ▶ DTMDs are more efficient than the conventional single mass TMDs over the whole range of total mass ratios ▶ DTMDs are only slightly more efficient than TMDs over the practical range of mass ratio (0. 01 -0. 05) ⑤ Matsuhisa et al (1994) → Compare the effectiveness of TMDs of the spring-mass type the pendulum type the circular track type → Optimal TMD configurations is quite different Structural Dynamics & Vibration Control Lab. 63

Tuned mass dampers ⑥ Li et al (1994) → Studied the effectiveness of a ring-type pendulum TMD on reducing seismic response of tall chimneys ⑦ Villaverde (1994) Numerical and experimental results on reducing the response of structure during different earthquakes → Some cases give good performance → Some have little or even no effect → Dependency on the characteristics of ground motion ▶ Response reduction is large for resonant ground motion ▶ Response reduction diminishes as the dominent frequency of the ground motion get futher away from the structure’s natural frequency Structural Dynamics & Vibration Control Lab. 64

Tuned mass dampers 4. Application to civil engineering structure ① The Centerpoint Tower in Sydney, Australia (ENR, 1971 ; Kwok and Mac. Donald, 1987) (a) Centerpoint Tower (b) Water Tank TMD <Fig 2. 5. 4 -1 TMD in Centepoint Tower (Kwok and Mac. Donald, 1987)> Structural Dynamics & Vibration Control Lab. 65

Tuned mass dampers ② Citicorp Center in New York and John Hancock Tower in Boston (a) Citicorp Center (b) TMD in Citicorp Center (Petersen, 1980; 1981) <Fig 2. 5. 4 -2 TMD in Citicorp Center> Structural Dynamics & Vibration Control Lab. 66

2. 6 Tuned liquid dampers ( TLD ) • TLD – Viscous action of fluid and wave breaking – Liquid sloshing Structural Dynamics & Vibration Control Lab. 67

Structural Dynamics & Vibration Control Lab. 68

2. 6 Tuned liquid dampers • TLCD – – Tube filled with water Passage of liquid through an orfice Fundamental frequency Length of column of water Dissipation term Nonlinear & depend on head loss Structural Dynamics & Vibration Control Lab. 69

• TLD • TMD – Activation mechanism No activation mechanism – Problem of inadequate setting Maintenance cost All time active The involved theory Complicated Hardware requirement & installation Simple At larger amplitude Not sensitive to actual frequency ratio between primary & secondary systems – Drawback Small error ( measuring the still-water level ) Not significant during the strong vibration – – – Structural Dynamics & Vibration Control Lab. 70

2. 6 Tuned liquid dampers • History of TLD – Sun(1991) : TLD ( SDOF with sinusoidal excitation) – Wakahara(1989) – Welt & Modi(1989 a) – Fujino et al(1988) : Wind-induced vibration : Building (wind & earthquake) : Behavior (rectangular & circular container ) Structural Dynamics & Vibration Control Lab. 71

2. 6 Tuned Liquid Dampers • Experiments ( test the validity ) – Small amplitude Experiments Theory – Welt & Modi (1989 b)’s experiments • Shape : partially filled torus shaped dampers in wind tunnel • Results : Damping ratio is sensitive to frequency ratio Amplitude Damping max at about 1. 0 – Fujino (1988) • Shape : cylindrical shaped container on a steel platform • Results : At small amplitude the added damping is highly depend on the ratio of structure to sloshing frequency ( maximum when the ratio 1) At larger amplitude any frequency ratio the added damping is reduced and almost constant for Structural Dynamics & Vibration Control Lab. 72

2. 6 Tuned liquid dampers – Sun (1989) • Shaking table test on rectangular TLD • Verify the accuracy of the simplified theory – Chaiseri et al (1989) • Rectangular container on a SDOF platform • First part Varying the water depth at constant amplitude • Second part • Result Significant Minimum at tuned case Varying the excitation frequency Minimum at tuned case Initial condition on structures and waves are not Structural Dynamics & Vibration Control Lab. 73

2. 6 Tuned liquid dampers • Application – Steel frame tower at Nagasaki Airport • 25 tuned sloshing damper • • • 50 in height tank 7 layers - 7 cm height Water depth 4. 8 cm Tank diameter 38 cm Mass of water 1. 6% of effective mass in fundamental mode 0. 59% of total mass of structure – Result • Critical damping ratio 4. 7% with damper (5 times of without damper) Structural Dynamics & Vibration Control Lab. 74

2. 6 Tuned liquid dampers – Yokohama Marine Tower Case • 39 tuned sloshing damper • • 50 cm height cylinder container 10 layers of 5 cm with water height 2. 1 cm Tank diameter 49 cm Total mass of water/tank 1% of effective modal mass 0. 3% of total mass of structure Structural Dynamics & Vibration Control Lab. 75

2. 7 Other energy dissipators • Vibration suppression method – Use – Shape : bridge cable (aerodynamic vibration) : cut as V and U stripes (protection tube surface of cable ) – Wind test result • Reynold’s number of cable aerodynamic vibration • Connecting two adjacent structures – Use earthquake – Method at roofs : controlling high-rise building during strong : connecting two adjacent structures with dampers – Requirement • Different dynamic properties Structural Dynamics & Vibration Control Lab. 76

2. 7 Other energy dissipators • High damping rubber – Properties : low stiffness & high energy absorption ability Similar with viscoelastic damper – Material : unvulcanized rubber ( LRB use vulcanized rubber) • Rubber composite damper – Use – Shape : cable-stayed bridges : rubber washer + cable sleeve • Impact damper – Use : highway light poles ( reduce wind vortex-induced oscillations) – Application : particle damper ( consist of four edged brackets ) Structural Dynamics & Vibration Control Lab. 77

2. 8 Code development and concluding remarks • Tentative requirement – The energy dissipation working group (EDWG) • The base isolation subcommittee of the structural engineers association of northern california (SEAONC) • Design guide line for wide range of system hardware (metallic, frictional, viscoelastic, and viscous devices except TMD, TLD) – General concept • Energy dissipators • Main structures Inelastic deformation Elastic deformation Conservative Structural Dynamics & Vibration Control Lab. 78

2. 8 Code development and concluding remarks • The april 1993 version of tentative requirement – Structures + Energy dissipation devices – Rate dependent device Dynamic analysis Response spectrum analysis (Viscoelastic & viscous dampers) – All rate-independent devices (metallic damper & friction dampers) Nolinear time history analysis – Inelastic stuructures – Prototype test – General statement about environmental factors • Such as temperature, moisture and creep Structural Dynamics & Vibration Control Lab. 79

2. 8 Code development and concluding remarks • A second document – By BSSC (Building Seismic Safety Council ) – Pronvisions = SEAONC ( in scope & concept ) • ATC ( Applied Technology Council) – Developing guidelines – Commentary for seismic isolation & energy dissipation systems Structural Dynamics & Vibration Control Lab. 80

2. 6 Tuned liquid dampers Structural Dynamics & Vibration Control Lab. 81

2. 6 Tuned liquid dampers Structural Dynamics & Vibration Control Lab. 82