BUILDING MOTION CONTROL: SUPPLEMENTARY DAMPING …

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)

Established in 1972

450+ employees

Global presence

In Indonesia since 90’s

Three Practice Areas:• Climate Engineering• Building Performance• Environmental

Engineering

RWDI – Company background

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

Vibration Overview

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?

WHY DOES IT HAPPEN?What causes vibration in tall & slender buildings?

• Wind

• Earthquakes

• Pedestrian Loading

Across-Wind Loading (Vortex Shedding)

wind

Directions of fluctuating force

Wind velocity

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ssw

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Vortex shedding

No vortex shedding

- Sometimes vortex shedding affects serviceability design only

- Requires additional structure or supplementary damping to satisfy serviceability demands

Vibration in Tall Buildings, Sights and Sounds

Sample acceleration predictions for a high-rise building

How much is too much?

Damping

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

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

Damping in Structures

Inherent Damping

Supplemental Damping

Overall Structural Damping

+

=

Supplementary Damping Systems

• 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

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

Wind-Induced Responses -Comparison

Without Damper With Damper

TMD Examples: Taipei 101

Pinnacle Dampers

Main Tower Damper

Pendulum length based on:

Also add space above & below for hardware

Simple Pendulum TMDs

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

Height requirement approx. ½ of simple pendulum configuration, plus a little more

Often still too space-consuming (vertically)

Alternative: Dual-stage Pendulum TMD

Trump Tower, New York City

• 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

Bloomberg Tower, New York

Animation demonstrating motion of TMD55 floor mixed use Tower

Bloomberg Tower, New York

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

TLCD Example: Random House, New York

Animation demonstrating motion of TLCD48 floor mixed-use Tower

57 floor mixed-use Tower

TLCD Example: Comcast Tower, Philadelphia

Tuned Sloshing Damper (TSD)

Tuned Sloshing Damper: Scale Model Testing

Un-tuned response

Resonant response

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

Most components can be assembled and tested in the factory before shipping to building for installation

Factory Acceptance Testing

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

THANK YOU

[email protected]: (+65) 9853 6712

www.rwdi.com