STRUCTURAL DESIGN FOR VIBRATION-SENSITIVE …
Transcript of STRUCTURAL DESIGN FOR VIBRATION-SENSITIVE …
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STRUCTURAL DESIGN FOR VIBRATION-SENSITIVE ENVIRONMENTS
Brad Pridham, Ph.D., P.Eng.Principal, Acoustics Noise & Vibration
November 11, 2020
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Learning Objectives
1. Understanding of the nature and significance of commonly encountered sources of vibration in sensitive environments;
2. Understanding criteria for the vibration design of sensitive environments;
3. Refresher on dynamics of structural systems;
4. Understanding of the significance of the vibration path and how strategic siting and layouts can reduce the cost of vibration control; and,
5. Identify some of the implications of vibration control on structural design.
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Agenda
• Fundamental Concepts• Source, path, receiver• Key issues for building environments• Vibration criteria• Fundamentals of Linear Structural Dynamics
• Concepts & Control Measures• Environmental Vibration• Floor Vibration
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Image obtained from: Dynamics of structures, Ray W. Clough and Joseph Penzien, McGraw-Hill, 1975.
• Mechanical equipment• Footfalls• Process tools & equipment• Stamping
• Road & Rail vehicles• Process tools & equipment
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Source – Path - Receiver
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• Imaging
• Microscopy
• Micro-surgery etc.
Vibration effects on image quality
Low Vibration Environments
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• Work environments
• Patient care floors
Occupant Comfort Tactile Vibrations
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Occupant Comfort
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• Research/medical equipment
• Building services
Noise Control
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1 4 8 80
0.05
0.1
0.5
RM
S A
ccel
erat
ion
(%g)
Frequency (Hz)
Vibration Criteria
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1 4 8 80
0.05
0.1
0.5
RM
S A
ccel
erat
ion
(%g)
Frequency (Hz)
• 1x, ISO-OpOperating theaters
• 2x, ISO-ResResidences
• 4x, ISO-OfficeOffices
• 8x, ISO-WorkshopWorkshops
8 ×
4 ×
2 ×
1 ×
Human Comfort Criteria
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1 4 8 80
0.05
0.1
0.5
RM
S A
ccel
erat
ion
(%g)
Frequency (Hz)1 4 8 80
4000
RM
S V
eloc
ity (µ
in/s
)
Frequency (Hz)
�̇�𝑦 =�̈�𝑦
2𝜋𝜋𝜋𝜋
Acceleration Velocity
Sensitive Equipment Criteriaintegration
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• 1/2x, Class ALow res microscopy
• 1/4x, Class BCT scanners
• 1/8x, Class CHigh res microscopy
• 1/16x – 1/32x, Class D/EMRI, SEM, NMR 1 4 8 80
125
250
500
1000
2000
4000
RM
S V
eloc
ity (µ
in/s
)Frequency (Hz)
1 ×
12
×
14
×
18
×
116
×
132
×
A
B
C
D
E
ISO-Op
Sensitive Equipment Criteria
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Criteria SummaryStructural damage concerns ~30x ISO-Workshop
Threshold of perception
Low sensitivity
Offices, residences, microscopy (<40x)
Moderately sensitive
Microscopy (100x – 400x), vivaria, surgery, CT
Ultra-sensitive
Imaging (SEM, TEM), MRI, NMR
Design may be governed by Serviceability
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Vendor Criteria
MRI Electron Microscopy
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Additional Comments - Criteria
• Manufacturer’s criteria should always be used when available
• Measurement data processing must be consistent with methods used to formulate criteria -> frequency resolution, integration window
• Discuss detailed requirements with end users
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FUNAMENTALS OF LINEAR DYNAMICSSDOF & MDOF Linear Systems
Modal parameters Response evaluation Continuous systems
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Fundamentals of Linear Dynamics
System Parameters
Frequency of Oscillation
Damping Ratio
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Dynamic Amplification Factor (DAF)
Frequency Ratio
Fundamentals of Linear Dynamics
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Response to Harmonic Loading
Fundamentals of Linear Dynamics
Dynamic Amplification Factor
Newton’s 1st Law Sinusoid
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Response to Transient Loading
Fundamentals of Linear Dynamics
Newton’s 1st Law
Exponentially Decaying Sinusoid
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Continuous Systems and Modal Analysis
Fundamentals of Linear Dynamics
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Generalized Coordinates – “Modes of Vibration”
Fundamentals of Linear Dynamics
• Each mode can be examined separately to establish response contribution and evaluate control measures
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Mode Shape - φ
Fundamentals of Linear Dynamics
input
mass
response
SDOF
𝐹𝐹𝑛𝑛 = 𝜑𝜑𝑇𝑇𝐹𝐹
𝑚𝑚𝑛𝑛 = 𝜑𝜑𝑇𝑇𝑀𝑀𝜑𝜑
�̈�𝑈𝑛𝑛 = 𝜑𝜑𝑇𝑇�̈�𝑦𝑛𝑛
• Vector of spatial distribution of motion (dynamic deflection)
for mode n
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Response of Linear MDOF Systems – Mode Superposition
Fundamentals of Linear Dynamics
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Linear Dynamics - Key Takeaways
Fundamentals of Linear Dynamics
1. Increasing mass:i. Reduced response by way of Newton’s 1st Lawii. Reduced system frequency – how does it affect r ?
2. Increasing stiffness increases the system frequency – how does it affect r?
3. Increasing damping is only affective at resonance
4. Continuous linear systems can be decoupled into a series of SDOFs
5. The spatial distribution of mass, stiffness, damping, and externally applied forces are important to the design for vibration control
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ENVIRONMENTAL VIBRATIONConcepts & Control Measures
Equipment and procedures Slab-on-grade design Ground-borne noise Occupant comfort
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Environmental Vibration Control
Sources
• Cars, trucks, buses• Railway• Activity from neighboring buildings
(MEP, heavy equipment, etc.)
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Environmental Vibration Control
Forces from Road Vehicles
• Axel hop• Body bounce
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Environmental Vibration Control
Example: Measured Road Vibrations
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Environmental Vibration Control
Forces from Rail Vehicles
Narrow-band random process
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Commuter Rail (DMU), Tie-on-ballast
Light Rail, Embedded Track
Environmental Vibration Control
Example: Measured Rail Vibrations
Freight, Tie-on-ballast
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Environmental Vibration Control
Example: Measured Stamping Vibrations
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Control Measures
• Source: establish the nature and relevance of sources (spatial and temporal)
• Path: strategic layouts, structural isolation joints, wave barriers
• Receiver: foundation design, equipment/room isolation and control
Control of the path and receiver are most effective
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Environmental Vibration – SOURCE Control
Source Characterization – Temporal Statistics
• 20-hours of road traffic data collected next to a highway
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Environmental Vibration – SOURCE Control
Source Characterization – Site Mapping
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Environmental Vibration – PATH Control
Modifying the Transmission Path: Wave Barriers
Example: Effectiveness of Wave Barriers
• Target: 25% reduction in vibration level• Concrete barrier in clay (Vs = 600 ft/s)• What size barrier is needed?
Source Source Frequency (Hz)
Barrier Dimension (ft)
Width Depth
Freight Train 4 16 131
Truck 15 7 23
LRT 40 3 7
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Environmental Vibration – PATH Control
Foundation Attenuation (Coupling Loss)
Wave Scattering
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Environmental Vibration – PATH Control
Slab “Isolation”
Perimeter isolation joint
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Environmental Vibration – PATH Control
Example: Isolated slabs
Vibration data collection
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Environmental Vibration – PATH Control
Example: Isolated slabs
Ambient vibration
0 50 100 150 200 250 30010
-14
10-12
10-10
10-8
10-6
0 50 100 150 200 250 30010
-14
10-12
10-10
10-8
10-6
Frequency (Hz)
PS
D (g
2 /Hz)
Vertical Axis
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0 10 20 30 40100
101
102
103
0 10 20 30 40100
101
102
103
Time (s)
Acce
lera
tion
(g x
10-3
)
Impact hammer on floor
Environmental Vibration – PATH Control
Example: Isolated slabs
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Impact hammer on floor
0 50 100 150 200 250 30010
-14
10-12
10-10
10-8
10-6
0 50 100 150 200 250 30010
-14
10-12
10-10
10-8
10-6
Vertical Axis
Frequency (Hz)
Mea
n P
SD
(g2 /H
z)
Environmental Vibration – PATH Control
Example: Isolated slabs
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Environmental Vibration – RECEIVER Control
Equipment Isolation
Ground motion
Isolator
Tool
Interaction Force
• System is designed to behave as an SDOF• “Isolator” can be passive or active• Isolator selection is based on:
– Source characteristics– Cost– Durability and robustness
• Base structure designed to be very stiff(~ 3x106 – 6x106 lb/in)
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Environmental Vibration – RECEIVER Control
Transmissibility – Mechanical Springs and Elastomers
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Environmental Vibration – RECEIVER Control
Passive Control Systems
Rubber mounts
Pneumatic springs
Optical tables
Negative Stiffness Isolators
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Environmental Vibration – RECEIVER Control
Active Control Systems
SEM Base Active Table Supports Active Plinths/Platforms
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Environmental Vibration – RECEIVER Control
Transmissibility – Precision Control
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Environmental Vibration – RECEIVER Control
Quiet Room Design Concept
• Plinth mass 3x – 5x equipment mass• Acoustic enclosure (typically masonry) supported on
base structure not floating slab• Provide space for access to isolators• Thickened room slabs for control of local disturbances
– 8” – 12” slab in surrounding areas
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FLOOR VIBRATIONConcepts & Control Measures
Occupant comfort Sensitive equipment Specialty surgical suites
Multiple sources of vibration to consider
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Control Measures
• Source: strategic layouts of corridors and “source areas” – Response Mapping
• Path: optimizing mass and stiffness, partitions
• Receiver: strategic layouts, isolated structure, equipment isolation
Successful designs incorporate a combination of source, path, and receiver control
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Floor Vibration – SOURCE Control
Space Layouts – Response Mapping
Walking path
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Floor Vibration – SOURCE Control
Space Layouts – Response Mapping
Walking path
‘quiet’zone
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Floor Vibration – PATH Control
Optimizing Design for Serviceability
• Example – footfall response of a laboratory floor
A
B
• Target criteria:
Room A VC-C, 500 µin/sRoom B VC-B, 1000 µin/s
• Response simulation for walker in corridor
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Floor Vibration – PATH Control
Optimizing Design for Serviceability
• Framing – base caseBeams: W14x22
Girders: W21x44
Slab: 3.5” conc. 1.5” deck
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Floor Vibration – PATH Control
Optimizing Design for Serviceability
Resp
onse
Lev
el
ISO-Workshop32,000 µin/s, 800 µm/s
ISO-Office16,000 µin/s, 400 µm/s
ISO-Residential8,000 µin/s, 200 µm/s
ISO-Operating Theatre4,000 µin/s, 100 µm/s
Class A2,000 µin/s, 50 µm/s
Class B1,000 µin/s, 25 µm/s
Class C500 µin/s, 12.5 µm/s
Class D250 µin/s, 6.25 µm/s
Class E125 µin/s, 3.125 µm/s
A
B
• Target criteria exceeded in both bays
Room A ISO-Op, 4000 µin/s
Room BISO-Res, 8000 µin/s
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Floor Vibration – PATH Control
Optimizing Design for Serviceability
• Identify the problem zones & associated mode(s) of vibration
Mode 1: 7.5 Hz
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Floor Vibration – PATH Control
Optimizing Design for Serviceability
• Framing revisions
Mode 1: 7.5 Hz
Beams:W14x22 → W18x60Girder:W21x44 → W24x103
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Floor Vibration – PATH Control
Optimizing Design for Serviceability
Resp
onse
Lev
el
ISO-Workshop32,000 µin/s, 800 µm/s
ISO-Office16,000 µin/s, 400 µm/s
ISO-Residential8,000 µin/s, 200 µm/s
ISO-Operating Theatre4,000 µin/s, 100 µm/s
Class A2,000 µin/s, 50 µm/s
Class B1,000 µin/s, 25 µm/s
Class C500 µin/s, 12.5 µm/s
Class D250 µin/s, 6.25 µm/s
Class E125 µin/s, 3.125 µm/s
A
B
• Target criteria satisfied in both bays
Room A VC-C, 500 µin/s
Room BVC-B, 1000 µin/s
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Floor Vibration – PATH Control
Optimizing Design for Serviceability
FEM
Modal Parameters
Simulation
Assessment
Mitigation
Optimization
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Integration with Revit
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Floor Vibration – PATH Control
Optimizing Design for Serviceability – Partition Effects
• Example: pre- and post-fit-out measurements
Floor Plan
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Floor Vibration – PATH Control
Optimizing Design for Serviceability – Partition Effects
• Slab-to-slab partitions run below
Floor Plan
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Floor Vibration – PATH Control
Optimizing Design for Serviceability – Partition Effects
• Free decay floor response at mid-span – no significant change in damping
0 0.2 0.4 0.6 0.8 1-0.02
-0.01
0
0.01
0.02
Time (s)
Acce
lera
tion
(g)
0 0.2 0.4 0.6 0.8 1Time (s)
Pre Fit-Out Post Fit-Out
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Floor Vibration – PATH Control
Optimizing Design for Serviceability – Partition Effects
• Change to bay frequency
0 5 10 15 200
0.05
0.1
0.15
0.2
Acce
lera
tion
(%g)
Frequency (Hz)
Pre Fit-Out: 8 Hz
Post Fit-Out: 9.5 Hz
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Floor Vibration – PATH Control
Optimizing Design for Serviceability – Partition Effects
-500
0
500
Velo
city
(µm
/s)
4 6 8 10 12 14 16 18 20
-500
0
500
Time (s)
Pre Fit-Out
Post Fit-Out
• Footfall responses
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Floor Vibration – PATH Control
Optimizing Design for Serviceability – Modelling Partition Effects
• k = 2 kip/in/ft
Linear springs at stud wall locations
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Floor Vibration – RECEIVER Control
Supplemental Damping
Tuned mass dampers, viscous dampers Active mass dampers
19” (h) x 20”m (L) x 14” (W)
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Floor Vibration – PATH Control
Supplemental Damping – TMD vs. AMD
• AMD requires 1/10th the mass and achieves better control
• Power and maintenance issues in development
• Product release coming soon
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Summary
• Generic vibration criteria are derived from the ISO Base Curve (threshold of human perception)
• Most problems encountered can be examined using the SDOF model
• Critical sources to consider for structural design of sensitive environments:– Environmental sources: road and rail traffic, nearby industrial sources– Floor vibration: occupant activity, building services, environmental sources
• Remember: Source – Path – Receiver control paths– Source: layouts and source characterization;– Path: layouts, isolation joints, barriers, optimization of structural dynamics– Receiver: layouts, tool isolation, supplemental damping(?)
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HOW A VIBRATION CONSULTANT CAN HELP
Reduce uncertainty associated with vibration design elements
Experience-based guidance related to: criteria integration of vibration design with other disciplines feasibility of various solutions implementation
“Insurance check” for design team
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TYPCIAL SCOPE OF WORK
Site investigation Existing installations, new sites
Design analysis/technical assessments Dynamic modelling (FEA, empirical models etc.) Isolation system design
Performance specifications for controls Coordination with vendors Monitoring and performance testing Peer reviews
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THANK YOU!
Brad PridhamPrincipal, Technical Director – SLR Consulting
226 706 8080 [email protected]