1. Structural Control: Overview and Fundamentals
Akira Nishitani
Vice President & Professor　　　　　　　　　WASEDA University, Tokyo, Japan

2. Outline 1. Introduction for WASEDA and Myself
2. Introduction for Structural Control
3. Some keywords for structural control
4. Brief view of active structural control
5. Components of control system
6. Semiactive structural control
7. Smart damping or smart dampers
Continued

3. Outline (Cont’d)
8. Significance of nonlinearity or artificially-added nonlinearity in structural control
9. Semiactive variable slip-force level dampers
10. Future directions
Appendix LQ control and LQG control

4. ■ 1. Introduction for:
Waseda Univ. and myself

5. About Waseda Univ.

6. Waseda University since 1882　　

7. Waseda University since 1882　　早稲田大学

8. Waseda University: - 125th Anniversary in 2007.
- Second oldest private university in Japan, founded in 1882.
- 125th Anniversary in 2007.
- the first private university in Japan that established engineering school.
- Waseda Department of Architecture is the second oldest in Japan.

9. Data of Waseda University:
- Number of students: 50,000
- Number of students in School of Science and Engineering: 7,000
- More than 100,000 application forms submitted to the Admission Center every year

11. About myself.

12. Myself : - Vice-President, Waseda Univ. since 2006.
- PhD at Columbia, 1980
- Vice-President, Waseda Univ since 2006.
- Professor of Structural Engineering in Dept. of Architecture, since 1993.

13. Myself (Cont’d) :
- Have been doing researches related to smart structures technology including active/semiactive structural control for nearly 20 years.
- Have been involved to the activity of IASCM [ International Association for Structural Control and Monitoring ] since its establishment in 1994.

14. Myself (Cont’d) :
- Have been the Chairperson of the JSPS [Japan Society for Promotion of Science] 157th Committee on Structural Response Control since April Currently, Vice-President, JAEE [Japan Association of Earthquake Engineering].

15. ■ 2. Introduction for:
Structural Control

16. Structural Control:
▲ Active control ▲ Passive control

17. Structural Control: ▲ Active control ▲ Passive control
With or without Energy supply
With or without Control computer

18. Structural Control: ▲ Active control ▲ Passive control
With Energy supply
With Control computer

19. Structural Control: ▲ Active control ▲ Passive control
Without Energy supply
Without Control computer

20. Structural Control:
▲ Active control - Full-active control - Semi-active or Semiactive control - Hybrid control ▲ Passive control - Base Isolation - Passive damper-based control

21. Structural Control:
▲ The idea of seismic structural control: not a totally new idea. ▲ The basic principles for seismic response control: presented in Japan in 1960.

22. Seismic Response Control Principles:
Reduce the effect of seismic excitation.
2. Prevent a structure from exhibiting the resonance vibration.
3. Transfer the vibration energy of a main structure to the secondary oscillator.
4. Put additional damping effect to a structure.
5. Add a control force to a structure.

23. These ideas were proposed by Kobori and Minai in 1960.

24. Professor Takuji Kobori

25. They proposed the idea of: Seismic-Response-Controlled Structures or 制震構造.

26. Seismic-response-controlled structure
Building
Nonlinear mechanism
Nonlinear mechanism
Nonlinear mechanism
Nonlinear mechanism

27. Seismic Response Control Principles:
Reduce the effect of seismic excitation.
Base Isolation
2. Prevent a structure from exhibiting the resonance vibration.
3. Transfer the vibration energy of a structure to the secondary oscillator.
TMD Control
4. Put additional damping effect to a structure.
Passive damper control
5. Add a control force to a plant. AMD Control

28. Japan has been leading the world in terms of the practical applications of structural control schemes.

29. Practical Applications in Japan:
# of Buildings:
Base isolation: over 2,000
Passive dampers: over 300
Active control: over 40

30. ■ Keywords for structural control.

31. - TMD - AMD - Smart damper - Semiactive damper - Controllable damper - LQ control - LQG control - Feedback control - Feed-forward control

32. - TMD: Tuned Mass Damper - AMD: Active Mass Damper - Smart damper - Semiactive damper - Controllable damper - LQ control - LQG control - Feedback control - Feed-forward control

33. - TMD: Tuned Mass Damper - AMD: Active Mass Damper - Smart damper - Semiactive damper - Controllable damper - LQ control - LQG control - Feedback control - Feed-forward control

34. ‘smart’ expressions such as ‘smart’ cars,
There are many kinds of
‘smart’ expressions such as
‘smart’ cars,
‘smart’ dampers,
‘smart’ structures,
‘smart’ medicine, etc.

35. Indeed,
“The Merriam-Webster
Paperback Dictionary”
gives a modern interpretation
of ‘smart.’

36. Containing a microprocessor of limited calculating capability.

37. With the names such as ‘smart structures,’
‘intelligent structures,’
‘dynamic intelligent buildings,’ etc.,
civil structures have been getting more and more human beings-like characteristics.

38. ■ 4. Overview of active structural control:

39. - In 1989,
a real building with active control technology applied was completed in Tokyo, Japan. - This was the first full scale implementation of active or computer-based response control in the world.

40. Professor Takuji Kobori

41. The name of the building:
Kyobashi Seiwa Building
(Currently,
Kyobashi Center Building)

43. Kyobashi Center Building

44. - This building employed an AMD system.
- AMD is one of the typical active control devices or actuators for buildings.

45. AMD
AMD

46. which is manipulated by a control computer based on the response data.
- AMD is a mass of weight installed into the top floor or near top floor,
which is manipulated by a control computer based on the response data.

47. The inertial force resulting from AMD movement
Control force
Structure
responding to
Seismic or wind excitation

48. AMD
Driving Force
AMD
Building

49. AMD
Driving Force u
Mass of AMD m
AMD
Building
Mass of Building M

50. x
AMD xa k X
building or main structure K xg

51. The equation of motion of a structural system with AMD integrated is:

52. The equation of motion of a structural system with AMD integrated:
(1)

53. The equation of motion of a structural system with AMD integrated:

54. AMD xa x xg

55. As a result,
since the birth of the world’s first active-controlled building, now more than 40 buildings in Japan have installed a variety of active control schemes.

56. Full-scale active control implementations:
Kyobashi Seiwa Bldg., 1989
Bidg. #21, Kajima Technical Research Institute, 1990
Sendagaya INTES, 1992
Applause Tower, 1992
Osaka ORC 200, 1992
Kansai Airport Control Tower, 1992
Long Term Credit Bank, 1993
Ando Nishikicho Bldg., 1993
Porte Kanazawa, 1994
Shinjuku Park Tower, 1994
RIHGA Royal Hotel, 1994
MHI Yokohama Bldg., 1994
Hikarigaoka J City, 1994
Hamamatsu ACT City, 1994
Riverside Sumida, 1994
Hotel Ocean 45, 1994
Osaka WTC Bldg., 1995

57. Full-scale active control implementations(cont.):
Dowa Kasai Phoenix Tower, 1995
Rinku Gate Tower, 1995
Hirobe Miyake Bldg, 1995
Plaza Ichihara, 1995
HERBIS Osaka, 1997
Nisseki Yokohama Bldg., 1997
Itoyama Tower, 1997
Otis Elevator Test Tower, 1998
Bunka Gakuen, 1998
Oita Oasis Hiroba 21, 1998
Odakyu Southern Tower, 1998
Kajima Shizuoka Bldg., 1998
Sotetsu Bldg., 1998
Century Park Tower, 1999
Sosokan, Keio Univ., 2000
Gifu Regional Office, Chubu Power Electric Company, 2001

58. However,
most of these implementations were mainly aimed at the response control against small/moderate seismic or strong wind excitation.

59. The ultimate goal of active control:  To enhance the structural safety against severe seismic events.  Need to establish such a control scheme as to achieve the final goal of active structural control.

60. Reference: A. Nishitani and Y. Inoue (2001).
　“Overview of the application of active/semiactive control in Japan,”
　Earthquake Engineering & Structural Dynamics, Vol. 30(11), pp

61. Active structural control:
- The full-scale active control implementation to a civil structure has opened the door to ‘modern’ earthquake engineering or ‘modern’ structural engineering.
- Structural engineering is now integrating more and more modern, advanced and IT-related technologies.

62. ■ 5. Components of Control System:
- How is a control system composed?

63. From the point of view of system control engineering, …..

64. Control System: Plant structure whose responses are controlled Sensors
- Control computer (Controller)
- Control actuator

65. Control System: Plant Sensors Actuator Controller Seismic Input
Control Input
Plant
Sensors
Actuator
Controller

66. Seismic Structural Control:
Reduce the effect of seismic excitation which a plant is subjected to.
Prevent a plant from exhibiting the resonance vibration.
Transfer the vibration energy of a plant to a control-actuator.
Put additional damping effect to a plant.
Add a control force to a plant through an actuator or actuators.

67. Passive Control System:✓
■ Plant structure whose
responses are controlled
■ Sensors
■ Control computer (Controller)
■ Control actuator ✓

68. Base Isolation: ✓ ■ Plant structure whose responses are controlled
■ Sensors
■ Control computer (Controller)
■ Control actuator ✓

69. Passive Damper Control:
Reduce the effect of seismic excitation.
Prevent a plant from exhibiting the resonance vibration.
Transfer the vibration energy of a plant to a control-actuator.
Put additional damping effect to a plant.
Add a control force to a plant.

70. TMD Control: Reduce the effect of seismic excitation.
Prevent a plant from exhibiting the resonance vibration.
Transfer the vibration energy of a plant to a control-actuator.
Put additional damping effect to a plant.
Add a control force to a plant.

71. Base Isolation: Reduce the effect of seismic excitation.
Prevent a plant from exhibiting the resonance vibration.
Transfer the vibration energy of a plant to a control-actuator.
Put additional damping effect to a plant.
Add a control force to a plant.

72. Active Control System:✓
■ Plant structure whose
responses are controlled
■ Sensors
■ Control computer (Controller)
■ Control actuator ✓ ✓ ✓

73. AMD Control: Reduce the effect of seismic excitation.
Prevent a plant from exhibiting the resonance vibration.
Transfer the vibration energy of a plant to a secondary vibration system.
Put additional damping effect to a plant.
Add a control force to a plant.

74. Theoretically,
There are two kinds of active control schemes: ……..

75. There are two kinds of active control schemes:
Theoretically,
There are two kinds of active control schemes:
Feedback control
and
Feed-forward control.

76. Plant Sensors Actuator Controller Control Input Output
External input such as seismic excitation
Plant
Sensors
Control Input
Output
Actuator
Controller

77. Plant Feedback Control Sensors Actuator Controller Control Input
External input such as seismic excitation
Plant
Sensors
Control Input
Output
Actuator
Controller
Feedback Control

78. Plant Feedback Control Sensors Controller+Actuator Control Input
External input such as seismic excitation
Plant
Sensors
Control Input
Output
Controller+Actuator
Feedback Control

79. Plant Feedback Control Controller Response Control Input
External input such as seismic excitation
Plant
Response
Control Input
Controller
Feedback Control

80. External input excitation
H(s)
Response
Control Input
G(s)
Feedback Control

81. External input excitation
Plant transfer function
H(s)
Response
Control Input
Feedback gain
G(s)
Feedback Control

82. External input excitation
Plant transfer function
H(s)
Response
Control Input
Feedback gain
G(s)
Feedback Control

83. Plant Controller+Actuator Sensors Response Control Input
External input such as seismic excitation
Plant
Response

84. G(s)
Control Input
H(s)
External input excitation
Response

85. G(s) H(s) Feed-forward Control Response Control Input
External input excitation
Response
Feed-forward Control

86. ■ 6. Semiactive Structural Control:
- What is semiactive control?
- How is semiactive control conducted?

87. Semiactive control:
Combines the beneficial features of both of passive and active control systems.

88. No energy supply to a control actuator needed. Active control:
Semiactive control:
Passive control:
No energy supply to a control actuator needed.
Active control:
Flexibility, Adaptability,
Efficient performance.

89. Semiactive control: - Less energy - More efficiency
- Better performance

90. Control System: Plant structure whose responses are controlled Sensors
- Control computer (Controller)
- Control actuator

91. Control System:
Seismic Input
Plant
Sensors
Actuator
Controller

92. Semiactive control:
There are two major ways defining or characterizing semiactive control concept.

93. The most general definition:
Semiactive control is ……

94. The most general definition:
Semiactive control is conducted by changing or controlling a part of charactersitics of control actuator only at appropriate time instants.

95. The most general definition:
Semiactive control is conducted by changing or controlling a part of charactersitics of control actuator only at appropriate time instants.
 Adaptive characteristics.

96. This definition leads to:
- Large power not needed.
- Required power not dependent
of the magnitude of
seismic excitation.

97. The second significant point:
Semiactive control operation does not inject mechanical energy into a plant structure or control device or actuator. 

98. The second significant point:
Semiactive control operation does not inject mechanical energy into a plant structure or control device or actuator.
 It has much less potential to destabilize the structure.

99. In typical semiactive control:
Actuator: Damper Controlled characteristics such as the damping coefficient, the magnitude of relief load, etc., of the damper are controlled. This kind of dampers are ……..

100. Typical semiactive control:
Actuator: Damper Ccontrolled characteristics such as the damping coefficient, the magnitude of relief load, etc. of the damper are controlled. This kind of dampers are called ‘controllable’ dampers.

101. Then, for example,
consider a type of semiactive control in which the damping coefficients of installed viscous dampers are controlled.

102. Then, for example,
consider a type of semiactive control in which the damping coefficients of installed viscous dampers are controlled.
 This change would not have any effect on the structure which is not subject to any other external input excitation.

103. On the contrary,
the movement of AMD could make an entire structure vibrate even in case of no other external input excitation.

104. On the contrary,
the movement of AMD would make an entire structure vibrate even in case of no other external input excitation.
 This is very significant difference between full-active and semi-active control.

105. AMD
Power
AMD
Building

106. One of smart control schemes
Controlled dampers
 Smart dampers
One of smart control schemes
 Control scheme based on “smart” or “controlled” dampers

107. ■ 7. Smart damping or Smart Dampers

108. Vibration Control
- Buildings
- Motor vehicle suspensions

109. z
Car Body or
Building　
Spring xg
Damper

110. Computer control of
of suspension systems
in 1980s.
Computer control
of buildings in 1989.

112. z
Car Body
Spring xg
Damper

113. - Ride Comfort  Absolute movement of car body = 0 - Driving Stability
= Movement of ground

114. Trade-off between 　　　 ride comfort and driving stability
Spring
Damper
Variable

115. Transfer function
from xg to z

116. Low damping
High damping

117. For better ride comfort, smaller absolute accelerations.
 High damping is not appropriate
for the high-frequency region.
 Constant damping is not appropriate.

118. Skyhook damper z xg

119. Skyhook damper
Csh z C xg

120. Skyhook damper
Csh z C xg . . .
C (z-xg) = Csh z

121. Csh z xg C C (z-xg) = Csh z C = Csh [z / (z-xg)] Skyhook damper . . .

122. Pioneering Implementations of Smart Damping:
Kajima Shizuoka Building
Keio University Soso-kan Building
Chubu Electric Power (CEP) 　　　 Gifu Regional Office Building

123. Kajima Shizuoka Building

124. - Kajima Shizuoka Building
The World’s first smart damping
or semiactive variable damping
implementation to a building.

125. Variable damping system in Kajima Shizuoka Bldg.:
The damping coefficients
of oil-dampers is controlled
so that LQG-based optimal control
force should be provided
in terms of damping force.

127. Keio Univ. Soso-kan Building

128. - Keio Univ. Soso-kan Building
The world’s first smart base-
isolated building or
building with base isolation
integrating semiactively-controlled
variable damping system.

129. CEP Gifu Regional Office Building

130. - CEP Gifu Regional Office Building： The world’s first building
employing
an autonomous-decentralized
semiactive smart damping system.

131. Autonomous-decentralized control system

132. A-D Control System: Plant Seismic Input Act. Sensors Act. Act.
Controller
Controller
Sensors
Controller
Sensors

133. Autonomous-Decentralized Control System:
- Each of distributed control systems is autonomously controlled by its own local, decentralized controller, not by only one center controller.　　　　　　

134. Autonomous-decentralized control system (AD control system)
Height of a huge, high-rise building
Width of a huge building with very wide floors
One central control computer does not seem appropriate.
Autonomous-decentralized control system (AD control system)

137. A-D Semiactive Damper

138. Switching Oil Damper with Built-in Controller

139. “Switching oil damper with built-in controller”
-The ‘damper’ is a Maxwell type of system consisting of a stiffness element (spring) and a controllable oil damper element.

140. Damper
Spring

141. Cmax
Cmin K +
Vel
Disp
By properly choosing the damping coefficient,

142. 2
Cmax
Cmin 1 3
Cmin
Cmax
Passive Damper Hysteresis 4

143. Cmax
Cmax
Cmax
Cmax

144. ② ① ① ③ ④ ② ②

145. ③ ③ ④ ④

146. - Each damper autonomously controlled by its own decentralized controller
 Autonomous-decentralized control system

147. Several newly constructed buildings in Japan have installed this type of semiactive damper systems.
“Switching oil damper with built-in controller”

149. The Shi’odome District

150. The Shi’odome Kajima Tower

151. The Shi’odome Kajima Tower

152. Roppongi Tower

153. Autonomous-decentralized control system
- Control operation could be conducted based upon the response information only in the neighborhood of each control devise.

154. Autonomous-decentralized control
+ Artificial Nonlinearity concept
seems appropriate or fitted to structural control against severe seismic excitations.

155. - Basic concept - Control effect - Oil hydraulic dampers
■ 8. Significance of nonlinearity 　or artificially-added nonlinearity in structural control
- Basic concept - Control effect - Oil hydraulic dampers

156. tan-1βK tan-1αK tan-1αK tan-1(α+β)K Linear structure
Bi-linear subsystem
tan-1βK
tan-1αK
tan-1αK
tan-1(α+β)K

157. γ＝α/（α＋β）

158. tan-1 γK
tan-1 K

159. W ΔW
Damping Coefficient =　　
　ΔW/W/(4π)

160. tan-1γK
tan-1 K
Equivalent viscous damping ratio
= (1-γ)/((1+γ)π)

162. α=0.7
α=0.8
α=0.9
α=1.0 β

163. What would happen to a SDOF
structure subjected to seismic excitation with this algorithm?　　　　　

164. Case 1: α=β=0.5 Case 2: α<β α= 0.3; β= 0.7
　 α= 0.3; β= 0.7　　　　
El Centro 1940 earthquake NS component with 2 m/sec2　　　　　　

165. Response Accelerations
α=β= 　①
α=0.3, β= 0.7

166. Response Displacement
α=β=
α= 0.3, β=

167. Damper hystereses
α= β=
α=0.3, β= 0.7

168. As an AD semiactive control system integrating artificial nonlinearity philosophy,

169. Variable slip-force level dampers

170. ■ 9. Semiactive Variable Slip-force Level Dampers
- Basic concept - Control effect - Oil hydraulic dampers

171. - Basic concept:
- Semiactive control - Utilizing artificial nonlinearity - Autonomous-decentralized system

172. 図7　完全弾塑性型

173. A damper is controlled
so that it begins to slip at the occurrence of peak velocity.  - No need for modeling. - Only local response information needed.

175. Damper ductility factor = 2

176. The effectiveness of this scheme:
is analytically measured in terms of equivalent viscous damping ratio.　　

177. Damper+Structure
tan-1 αK
tan-1(α+β)K

178. What would happen to a SDOF
structure subjected to seismic excitation with this algorithm?　　　　　

179. Case 1: α=β=0.5 Case 2: α<β α= 0.3; β= 0.7
　 α= 0.3; β= 0.7　　　　
El Centro 1940 earthquake NS component with 2 m/sec2　　　　　　

180. Response Accelerations
α=β= 　①
α=0.3, β=

181. Response Displacement
α=β=
α= 0.3, β=

182. Damper hystereses
α= β=
α= 0.3, β=

183. Case 1: α=β= 0.5 Estimated damping coefficient = 0.087

184. Acceleration Response Spectrum

185. Simulation for a 20-storie high-rise building:
- Steel structural model accounting for shear and bending deformations.　　　　　　

186. Natural Period of original structural model:
1st Mode: 1.78 sec
2nd Mode: sec
3rd Mode: sec

187. Dampers are installed on every floor.
Each damper is controlled only based upon the interstory drift response velocity.  Autonomous-decentralized control.
Damper is effective only on shear deformation.　　　　　　

188. Autonomous-Decentralized Control System:
- Each of distributed control systems is autonomously controlled by its own local, decentralized controller, not by only one center controller.　　　　　　

189. Building 1: α=β= 0.7
Building 2: α=β= 1.0

190. (a) Accelerations
(b) displacements
　Maximum resoponses

191. The presented concept can be put into practice utilizing an oil-hydraulic damper-based device.
- A damper containing an electromagnetic relief valve is utilized.

192. The presented concept can be put into practice utilizing an oil-hydraulic damper-based device.
- A damper containing an electromagnetic relief valve is utilized.  This is a kind of variable-orifice damper.　

193. 図13　オイルダンパ

194. Experimental model of semiactive variable slip-force level damper

195. Relationship between damper velocity
and electric voltage given to the valve

196. Experimental results responding to sinusoidal excitation with increasing amplitudes
Constant
slip-force
level
shear force (kN)
Variable
slip-force
level
shear force (kN)
Displacement (mm)

197. Reference:
A. Nishitani, Y. Nitta and Y. Ikeda (2003). “Semiactive structural-control based on variable slip-force level dampers,” J. of Structural Engineering, ASCE, Vol. 129(7), pp

198. ■
- Semiactive and smart concept based schemes have been presented for structural control of buildings as well as the full scale implementations of some of such schemes in Japan. -

199. ■
- The concept of semiactive variable slip-force level dampers has been presented.

200. ■ 10. Future directions:
- Semiactive and smart strategies, or smart passive strategies, are expected to play more and more significant role in the future stage of structural engineering, integrating the autonomous-decentralized concept. -

201. ■ Optimal control: LQ control & LQG control:
LQ: Linear, Quadratic LQG: Linear, Quadratic and Gaussian -

202. ■ LQ control & LQG control:
Two schemes for optimal control:
Response: whether probabilistic
or deterministic?
If the response is probabilistic, then the control input will be probabilistic.
 LQG control. -

203. ■ LQ control & LQG control:
In the case where the response and control input are stationary, Gaussian random processes,  LQG control. -

204. The equation of motion of a structural system with control input:

205. The state equation:

206. The state equation:
LQG control

210. LQG control:
LQG control statistically satisfies the samllest value of E[J].

211. Little people discuss other people. Average people discuss events.
Epigram:
Little people discuss other people.
Average people discuss events.
Big people discuss ideas.
(M.S. Grewal, A.P. Andrews Kalman Filtering: Theory and Practice Using MATLAB [Second Edition], John Wiley, 2001)

212. Thanks for your attention.