Seminar on Design of Tall Buildings: Trends and Advancements for Structural Performance, November 2016

1. Dr. Naveed Anwar
Smart Systems for Structural
Response Control
Design of Tall Buildings: Trends and Achievements for
Structural Performance
Bangkok-Thailand
November 7-11, 2016
Naveed Anwar, PhD

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Everything is getting
smarter !
(We hope humans don’t fall behind)

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Smart Everything !
Smart Phone
Smart Car
Smart TV
Smart Home
Smart City

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•Smart
Cities
Smart
Buildings
Smart
Structures
Smart
Devices
Smart
Materials

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Why smart structures ?
• Excitation fluctuates so Demand fluctuates
• But Capacity is constant
• Therefore level of safety is not consistent

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Why smart structures ?
• Typically capacity is designed
based on “Peak” estimated
demand
• What if peak demand never
comes > Un-economical
• What if demand exceeds
estimated peak > Un-safe

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Simplest case – Restressed Beam
• PT is design to balance a specific load
value
• It does not work efficiently for any other
value of load pattern or value
• What if PT force could change with
load ?
• >> Smart PT Beam

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Key Fluctuating Excitations
•Wind
Earthquake
Vibrating loads
Others: Flood, Temperature, Settlement, Creep, …

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Response Indicators and Response Control
Deformation, Drift
Acceleration
Dissipated energy
Stresses and strains
•Stiffness Strength
Damping Ductility

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What a smart structure does?
Ability to change values of
response controllers
to modify the response
based on fluctuation of
excitement and demand

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Smart Structure

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Smart Structural System
ability to sense any change in external actions
diagnose any problem at critical locations
measure and process data
take appropriate actions to improve system performance
while preserving structural integrity, safety, and serviceability
1
2
3
4

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Smart Structure Devices
Energy
Dissipating
Systems
Active or
Passive
Control
Systems
Health
Monitoring
Systems
Data
Acquisition
System

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Applications for Smart Structure Devices
Structures subjected to extraordinary
vibrations
Important structures with critical
functionality and high safety requirements
Flexible structures with high serviceability
requirements
1
2
3

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Basic Control Principle

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Acknowledgment
• Some material and figures based on:
• Franklin Y. Cheng, Hongping Jiang and Kangyu Lou (2008) Smart
Structures – Innovative systems for seismic response control. CRC
Press, Taylor & Francis Group, LLC, ISBN-13: 978-0-8493-8532-2

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Equation of Motion
Equation of motion governing lateral response of linear SDF
𝑚 𝑢 𝑡 + 𝑐 𝑢 𝑡 + 𝑘𝑢 𝑡 = 𝑃(𝑡)
In terms of frequency of structure and damping ratio
𝑢 𝑡 + 2𝜉𝜔 𝑛 𝑢 𝑡 + 𝜔 𝑛
2 𝑢(𝑡) = − 𝑢 𝑔(𝑡)

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Reduction of Lateral Displacement
Increasing the damping of the system
Reducing the intensity of ground motion
experienced by the system
Increasing the difference between forcing
frequency and the natural frequency of system

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Equation of Motion Using Control System
With Control System
𝒎 + 𝒎 𝒄 𝒖 𝒕 + (𝒄 + 𝒄 𝒄) 𝒖 𝒕 + (𝒌 + 𝒌 𝒄)𝒖 𝒕 = −(𝒎 + 𝒎 𝒄) 𝒖 𝒈(𝒕)
Equation of motion
𝑚 𝑢 𝑡 + 𝑐 𝑢 𝑡 + 𝑘𝑢 𝑡 = 𝑃(𝑡)

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Damping Systems for Dynamic Response Control

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Damping Devices and Systems
Damping devices and systems applied to a lateral load-resisting system

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Damping Devices and Systems
Passive
Control
Systems
Semi-active
Control
Systems
Active
Control
Systems
Hybrid
Systems

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Passive Control Systems

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Passive Control Systems
 Use Various mechanical devices which reacts to structural vibrations
resulting in dissipating a portion of their kinetic energy.
 Requires no external power source and are capable of generating
large damping forces with increasing structural response

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Passive Control Systems
Tuned Mass
Dampers
(TMDs)
Tuned Liquid
Dampers
(TLDs)
Friction
Devices
Metallic Yield
Devices
Viscoelastic
Dampers (VE)
Fluid Viscous
Dampers
(FVDs)

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Tuned Mass Dampers (TMD)
𝑚
𝑚
𝑚
(a) (b) (c)
Working Mechanism:
Externally applied
force on main
structure can be
balanced with the
restoring force
developed in
additionally attached
mass-spring-dashpot
system

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Tuned Liquid Dampers (TLD)
Working Mechanism:
Same as TMD with a
difference that water or
any other liquid is used
as the mass and the
restoring force is
generated by weight of
sloshing liquid inside a
container
𝑚
Direction of Vibration
P
(a) (b)

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Friction Devices
Working Mechanism:
Conversion of kinetic
energy of moving bodies
in to heat energy.
In X-braced dampers,
slotted slip joints provide
force resistance through
friction by brake lining
pads installed between
the steel plates Directionof Vibration
Beam
Column
Brace
Friction
Damper
Hinges
Links
Moment
Connections to
Braces
Friction Damper
Slotted Slip
Joints

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Metallic Yielding Devices
Working Mechanism:
Seismic design of
conventional structures is
controlled by their expected
post-yield ductility which is a
measure of its energy-
dissipating capacity. This led
to the idea that additional
metallic devices capable of
exhibiting stable hysteretic
behavior can be used to
absorb energy of main
structure
Directionof Vibration
Beam
Column
Brace
Yielding
Damper
Rods
Rod Rings
Yielding Damper

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Viscoelastic Dampers
Working Mechanism
Viscoelastic (VE)
dampers are based on
the use of VE materials
which dissipate seismic
energy through their
shear deformation when
subjected to vibrations
Brace
VE
Damper
Pinned Connections

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Semi-active Control Systems

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Semi-active Control Systems
 Referred as controllable or intelligent
systems.
 Working principle is “computer processes
the vibration measurements coming from
sensors and generates the command for
control actuator to modify the properties
of passive damper according to
requirement”
Passive
Processor to change
properties
Semi Active

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Components of Semi-active Control System
Semi-
active
Control
System
Vibrating
Measuring
Sensors
Control
Computers
Control
Actuators
Passive
Damper

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Advantages & Limitations of Semi-active Control Systems
Advantages:
 Additional adaptive system which collects and process the information
about response of main structure and modifies the damper’s property
based on this information.
 Economically combine the advantage of both passive and active
control systems
Limitations:
 Control capacity is limited by the maximum capacity of their constituent
passive device

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Common Semi-active Control Systems
Semi-active
Tuned Mass
Dampers
Actuator
generates the
control force
which is required
to develop
optimum
amount of
damping in TMD
Semi-active
Tuned Liquid
Dampers
Semi-active
Friction Dampers
Semi-active
Vibration
Absorbers
Is based on
mechanism
responsible for
variable
adjustment and
tuning of the
liquid.
Electric motor is
used to operate the
actuator applying
compression force
to interface.
Efficient control
system us used to
adjust this force to
achieve
performance
Use variable
orifice valve
capable of
varying flow of
hydraulic damper.
Damping
capacity is
obtained from
viscous liquid.

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Common Semi-active Control Systems
Electrorheological
Dampers
Based on smart ER
fluids containing
dielectric particles. In
the presence of
electric fields,
dielectric materials
polarized and
increased resistance
to flow
Semi-active
Stiffness Control
Devices
Magnetorheological
Dampers
Semi-active Viscous
Fluid Damper
Consist of hydraulic
cylinder, double
acting piston rod,
solenoid control valve
and connecting tube.
Opening or closing of
control valve results
in system
optimization
Use smart MR fluids
and contain micron-
sized magnetically
polarizable particles
suspended in any
viscous liquid.
Magnetic field
controls particle
behaviour
Use the opening or
closing of a
solenoid valve to
regulate the
amount of the fluid
through a bypass
loop, according to
commands from
control algorithm

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Active Control Systems

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Active Control Systems
Use electrohydraulic actuators which generate optimum amount of
control force based on actual measured response of main structure
Effective
Control on
Structure
Response
Adaptability to
Ground
Motion
Characteristics
Suitability to
Use for any
Control
Objectives
Ability to
Suppress
Responses
Against Wide
Range of
Frequencies
Advantages

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Schematic Diagram of Active Control Systems
Measurements Controller Measurements
Sensors
Earthquake
Excitations
Structural
Response
Sensors
Control Signal
Actuators
Control Forces
Structure
Power
Supply

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Common Types of Active Control Systems
Active Mass Damper (AMD)
Active Tendon Systems
Active Brace Systems
Pulse Generation Systems

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Active Mass Dampers (AMD)
 Natural extensions of
TMDs with the addition of
an active control
mechanism.
 Motion of passive TMD is
now controlled by the
actuator to generate
control forces.
Comparison of Smart Structures with AMD and TMD

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Structure with AMD
Model & Free Body Diagram for Structures with AMD

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Active Tendons System
 Consist of a set of pre-stressed
tendons subjected to controllable
tensile forces.
 Under seismic excitation, inter-
story drifts are produced causing
the relative movement between
actuator piston and cylinder,
resulting in variable tensile forces
in pre-stressed tendons. Which
provides the desirable control
forces to achieve response
control
α
x(t)
ẍg (t)
u(t)
Active
tendon
Actuator
Schematic Diagram of Active Tendon System

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Active Braced Systems
 This system uses the existing
structural braces to
develop an active control
system by adding actuator
 Different types of bracing
systems (diagonal, K-
braces and X-braces) can
be used in conjunction with
hydraulic actuators
capable of generating a
large control force.
Active Bracing System with Hydraulic Actuator

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Limitations of Active Control Systems
Requires significant amount of
external power supply and complex
sensing and signal processing
Actuators capable of producing large
control forces is key requirement

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Hybrid Systems

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Common Hybrid Systems
Hybrid Mass Dampers
Hybrid Base-Isolation System
Hybrid Damper-Actuator Bracing Control
Intelligent Hybrid Control Systems

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Hybrid Mass Dampers (HMD’s)
 Combines passive TMD with
an active control actuator.
 The actuator generates a
control force which adjusts
the properties of TMD
resulting in an increase in
AMD’s efficiency
Hybrid Mass Damper

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Hybrid Base-Isolation System
 Combines base isolation
system with an active
control system.
 Active tendon system is
installed on a base-
isolated structure
Hybrid system with base isolation and actuators

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Hybrid Damper Actuator Bracing Control
Combines a hybrid
device with an actuator
resulting in increased
efficiency and control on
structural response

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Intelligent Hybrid Control Systems
Structure
Response > TR ?
Z (t) = 0
Or
Z˚ (t) = 0
Z (t) or Z˚(t)
Feedback Gain
Z(t)Excitations
No
Structure
Response > TR ?
Z (t) = 0
Or
Z˚ (t) = 0
Z (t) or Z˚(t)
Feedback Gain
Z(t)
No
Yes
+
-
Working Mechanism of Single Stage Intelligent Hybrid System

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Intelligent Hybrid Control Systems
Working Mechanism of Three Stage Intelligent Hybrid System
Structure
> Ist Threshold
Structure
> 2nd
Threshold
Structure
Damper Damper Actuator Damper Actuator
Ground Motion
Stage 1 Stage 2 Stage 3
Response Response
NoYesNo Yes
Will Adjusted feedback gain

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Base Isolation Systems for Seismic Response
Control

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Base Isolation Systems for Seismic Response Control
 Tend to reduce the energy transfer from ground acceleration to
structure.
Bearing
Elastomeric
Bearings
Sliding Type
Bearings
Most Important Component

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Common Types of Bearings
Elastomeric Bearings
Lead-Plug Bearings
High-Damper Rubber Bearings
Friction Pendulum Bearings
Pot-Type Bearings

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Types of Bearing
Elastomeric Bearings Lead-Plug Bearings

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Types of Bearing
Friction Pendulum Bearing Friction Pendulum Bearing
with Double Concave

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Types of Bearing
Piston with Teflon-Coated
Surface at the top
Elastomer Base Pot
Seal
Top Plate with Stainless Surface
Typical Plot Type Bearing

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Sensing and Data Acquisition Systems

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Components of Data Acquisition Systems
Data
Acquisition
System
Sensors
Signal
Conditioning
Unit
Control
Computer

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Schematic of Analog Sensing and Data Acquisition System
Smart Seismic
Structure
Sensors
Actuators
Signal
Conditioner
Analog Computer

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Schematic of Digital Sensing and Data Acquisition System
Smart Seismic
Structure
Sensors
Actuators
Signal
Conditioner
A/D
Boards
Digital
Controller
D/A
Boards

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Components of Data Acquisition and Digital Control Systems
Sensors
Actuator(s)
Amplifier
Filter
Multiplexer
Signal Conditioner
A/D
Observer
Controller
D/A
Data
Recorder
Display
Smart Structure
Control Computer

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Smart structures use smart devices and materials
to add some intelligence to adapt, react, adjust,
respond and handle multiple demands, and
levels as and when needed
Help to make the structures safer, specially for
earhquales and strong winds

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