building motion control: supplementary damping …
TRANSCRIPT
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BUILDING MOTION CONTROL: SUPPLEMENTARY DAMPING SYSTEMS FOR TALL & SLENDER BUILDINGS
Sudeesh Kala, M.A.Sc., B.E. (Hons), P.Eng.
Regional Manager | Associate
Rowan Williams Davies & Irwin Inc. (RWDI)
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Established in 1972
450+ employees
Global presence
In Indonesia since 90’s
Three Practice Areas:• Climate Engineering• Building Performance• Environmental
Engineering
RWDI – Company background
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Vibration Overview
Why are we concerned with vibration?
How much is too much?
How to control it?
Damping
Inherent structural damping
Uncertainty of as-built damping
Tall and slender buildings = low damping
Supplementary Damping Systems
Types and example installations
Design considerations
Factory acceptance testing, installation, & commissioning
Talk Overview
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Vibration Overview
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Vibration is a Serviceability Limit State
Like deflection or local deformation, vibration limits are not typically defined by any Building Code or regulatory agency
A building can be absolutely safe, yet still be unfit for its intended purpose
Excessive vibration can cause:
• Discomfort for occupants
• Structure-borne noise
• Cumulative damage (fatigue) to partitions, glazing
• Elevator cable collisions inside hoistway
What’s the big deal?
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WHY DOES IT HAPPEN?What causes vibration in tall & slender buildings?
• Wind
• Earthquakes
• Pedestrian Loading
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Across-Wind Loading (Vortex Shedding)
wind
Directions of fluctuating force
Wind velocity
Cro
ssw
ind
Re
spo
nse
Vortex shedding
No vortex shedding
- Sometimes vortex shedding affects serviceability design only
- Requires additional structure or supplementary damping to satisfy serviceability demands
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Vibration in Tall Buildings, Sights and Sounds
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Sample acceleration predictions for a high-rise building
How much is too much?
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Damping
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Damping in Structures
Internal External
Inherent Damping
Material Contact Areas
Internal friction
Cracking
Thermal effects
Joints
Connections
Bearings
Cladding
Partitions
Energy radiation to the soil
Flooring/Ceiling
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Considerable scatter in available data
Tall buildings certainly don’t seem predisposed to *high* levels of as-built inherent structural damping
Damping is often observed to be amplitude-dependent
Damping in Structures – How much?
Image Credit: Smith & Willford, Arup, “Damping in tall buildings –uncertainties and solutions”, 17th Congress of IABSE, 2008
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Damping in Structures
Inherent Damping
Supplemental Damping
Overall Structural Damping
+
=
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Supplementary Damping Systems
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• Distributed:
• Viscous Dampers
• Visco-Elastic Dampers
• Used extensively for control of
earthquake response in highly
active seismic regions
• Might not participate in
low-to-moderate wind events
• Inspection & Maintenance
Types of Supplemental Damping Systems
Image Credit: Tipping Mar
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Solid Mass Type:
• Tuned Mass Damper (TMD)• Various configurations possible
Water/Liquid Type:
• Tuned Liquid Column Damper (TLCD)
• Tuned Sloshing Damper (TSD)
Semi-Active Damper
Active Damper
Types of Supplemental Damping Systems
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Wind-Induced Responses -Comparison
Without Damper With Damper
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TMD Examples: Taipei 101
Pinnacle Dampers
Main Tower Damper
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Pendulum length based on:
Also add space above & below for hardware
Simple Pendulum TMDs
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If T = 5.5 seconds length = 25’ (7.5 m) plus
If T = 6.5 seconds length = 34’ (10.5 m) plus
If T = 8.0 seconds length = 52’ (16 m) plus
If T = 10.0 seconds length = 81’ (25 m) plus
Plus: Add 6.5’ (2 m) for cable supports, beams, etc
Can be very space-consuming (vertically)
Simple Pendulum TMDs, for assorted periods
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Height requirement approx. ½ of simple pendulum configuration, plus a little more
Often still too space-consuming (vertically)
Alternative: Dual-stage Pendulum TMD
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Trump Tower, New York City
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• Uses less space than other TMDs
• Accommodates wide tuning range for any building
frequency
• Can often be adapted into mechanical floors, with
footprint of e.g. 40’ x 40’ (12 m square)
• Height requirement from 18’ to 26’ (5.5 m to 8m) *each case requires design investigation
• Can practically expect 5% damping
Alternative TMD: Opposed Pendulums
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Bloomberg Tower, New York
Animation demonstrating motion of TMD55 floor mixed use Tower
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Bloomberg Tower, New York
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Same general principle as TMDs – a large body of mass oscillating out-of-phase with the primary structure, and dissipating precisely the right amount of energy per cycle
Liquid-based dampers
• TLCD
• TSD
• Other abbreviations are common:• Tunes Sloshing Water Damper (TSWD)• Tuned Liquid Damper (TLD)• Liquid Column Vibration Absorber (LCVA)
Liquid Instead of a Dense Solid
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TLCD Example: Random House, New York
Animation demonstrating motion of TLCD48 floor mixed-use Tower
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57 floor mixed-use Tower
TLCD Example: Comcast Tower, Philadelphia
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Tuned Sloshing Damper (TSD)
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Tuned Sloshing Damper: Scale Model Testing
Un-tuned response
Resonant response
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A TSD can be designed to work in both directions
Careful detailing is required to allow attainment of optimal tuning ratio and internal dissipation ratio in each perpendicular axis of as-built structure
Tuned Sloshing Damper: Bi-directional
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Most components can be assembled and tested in the factory before shipping to building for installation
Factory Acceptance Testing
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Benefits of Supplemental Damping Systems
• Can be used in combination with mass, stiffness, and/or
aerodynamic changes to improve/hone building
performance
• Very efficient means to absorb/resist wind energy
• Can help maximize leasable floor space
• Building comfort improvements
• Help reduce overall cost of structure
Conclusions