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Overview of vibration control

토목환경공학개론 :. Overview of vibration control. 건설 · 환경공학과 구조동역학 및 진동제어 연구실. Structural Dynamics & Vibration Control Lab. 1. Introduction 1.1 Background 1.2 Recent international developments 1.3 Scope 1.4 Definitions 2. Passive energy dissipation

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Overview of vibration control

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

  2. 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 목차

  3. Motive Evolution of structural control in the u.s Evolution of structural control in the world Distinctive features of structural control 1.1 Background 1. Introduction

  4. 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 Motive Motive

  5. 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 Evolution of structural control in the U.S Evolution of structural control in the U.S

  6. 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. Evolution of structural control in the U.S

  7. Yao’s concept of structural control Feed back control Open & closed loop control

  8. 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 2s Induces large amplitude motion Evolution of structural control in the world Evolution of structural control in the world

  9. 1972 ~ Active structural control (concepts form Yao 1972) Hybrid structural control Semiactive structural control Evolution of structural control in the world

  10. 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 Distinctive features of structural control Distinctive features of structural control

  11. 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 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 1.2 Recent International Developments 1.2 Recent International Developments

  12. 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. 1.3 Scope 1.3 Scope

  13. 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. 1.4 Definitions 1.4 Defintions

  14. 1.4 Definitions - active control ex 1) Location : Kao Hsiung, Taiwan Size : 150m x 60m at Base, 85-story Fuction of building : Multi-purpose Control system : Multi-staged tuned active damper

  15. 1.4 Definitions - passive contol ex 1)

  16. 1.4 Definitions - passive contol ex 2)

  17. 1.4 Definitions - passive contol ex 3)

  18. 1.4 Definitions - passive contol ex 4)

  19. 1.4 Definitions - passive contol ex 5)

  20. 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. 1.4 Definitions

  21. 1.4 Definitions - hybrid control ex 1)

  22. 1.4 Definitions - hybrid control ex 1)

  23. 1.4 Definitions - semi active control ex 1)

  24. Structural health monitoring Detect changes that may include damage or degradation. In-situ, nondestructive sensing and analysis of structural characteristics including structural response. 1.4 Definitions

  25. 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. 2. Passive energy dissipation

  26. 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

  27. 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. Metallic yield dampers 2.1 Metallic yield dampers

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

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

  30. 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, long-term 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) Metallic yield dampers

  31. Metallic yield dampers

  32. Metallic yield dampers

  33. 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) Metallic yield dampers

  34. 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) Metallic yield dampers

  35. 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. Metallic yield dampers

  36. 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. Friction dampers 2.2 Friction dampers

  37. Friction dampers

  38. Friction dampers

  39. 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. Friction dampers

  40. 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) Friction dampers

  41. 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, 1994a,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) Friction dampers

  42. 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) Metallic yield dampers

  43. 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 Viscoelastic dampers 2.3 Viscoelastic dampers(vd)

  44. <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 Viscoelastic dampers 2. Typical viscoelastic damper (by the 3M company inc.) by shen and soong(1995)

  45. : Shear strain : Loss factor : shear stress : Shear storage modulus : Shear loss modulus Under a sinusoidal load with frequency  → , → 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) Viscoelastic dampers 3. Basic principles (Zhang et al,1989)

  46. 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) Viscoelastic dampers 4. Characteristics

  47. 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 Viscoelastic dampers

  48. 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 Viscoelastic dampers 5. Research development

  49. 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 Viscoelastic dampers

  50. 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 3M Company, St.Paul,MN ) → 10,000 VDs in each tower (distributed from 10th to 110th floor) Viscoelastic dampers 6. Application to civil engineering structures

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