BRIDGE ENGINEERING ASSOCIATION Informing …
Transcript of BRIDGE ENGINEERING ASSOCIATION Informing …
7th New York City Bridge Conference
August 26-27, 2013
BRIDGE ENGINEERING ASSOCIATION
Informing Infrastructure Decisions through Large-Amplitude Forced Vibration Testing
Nenad Gucunski, Franklin Moon, John DeVitis and Sharef Farrag
Civil and Environmental Engineering
Center for Advanced Infrastructure and Transportation (CAIT)
Brady Cox and Farnyuh Menq – NHERI, The University of Texas at Austin
NHERI@UTexas Structural Testing WorkshopNew Brunswick, NJ, August 3, 2017
Outline
• NSF EAGER Project – Objectives and general scope of activities
• Foundation dynamics and dynamic soil-foundation-structure interaction (DSFSI)
• Numerical simulation of the dynamic response of a bridge-soil system
• Field implementation using UTA NHERI mobile shakers
Informing Infrastructure Decisions through Large-Amplitude Forced Vibration Testing
Motivation - Civil Infrastructure Evaluation
Aging Infrastructures
– Need for the development of reliable safety assessment approaches
– Structural-Identification (St-Id) has evolved over the past few decades as a result of:
• Adoption of sensing technologies (global and local)
• Development of highly refined simulation models
• Development of model calibration techniques (both deterministic and probabilistic)
Motivation - Civil Infrastructure Evaluation
Current St-Id for Structure-Foundation Systems
– Based largely on the response data using various inputs (static loading, wind, temperature changes, pull-release, impact, shakers, etc.)
– Those low-level demand inputs are leading to responses similar to operational limit states =>the use of such responses to inform the safety assessment of systems under extreme events requires significant extrapolation
Motivation - Civil Infrastructure Evaluation
=> Large-amplitude mobile shakers offer significant potential to improve the reliability of St-Id by overcoming low-level mechanisms in a controlled manner
NH
ERI
Mobile
Shakers
NSF EAGER (Early-concept Grants for Exploratory Research) Project
Overarching Aim
– To explore and establish the ability of large-amplitude,
forced vibration testing to reveal the current performance
and forecast the future system performance of structures,
with the consideration of dynamic soil-foundation-structure
effects.
NSF EAGER (Early-concept Grants for Exploratory Research) Project
More Focused Objectives
– Develop, evaluate, and refine a series of:
1. Forced vibration testing and control strategies to capture response measurements indicative of key performance attributes of substructure/foundation and superstructure systems
2. Data interpretation frameworks for structural system identification and assessment
– Perform a validation of the testing/control strategies and data interpretation frameworks on an operating structure with known substructure, foundation, and soil characteristics.
Research Plan
• Development of Forced-Vibration Testing Strategies
– Parametric study to examine the correlation between certain measurable responses (both foundation and superstructure) and the foundation/substructure type/condition
• Development of Data Interpretation Frameworks
– Model-Free Frameworks - Methods based primarily on data processing, data visualization, and data fitting techniques
– Model-based Frameworks - Methods that update simulation models of the system being identified, and then employ these to examine behaviors that cannot be directly observed (St-Id)
Research Plan
• Field Implementation and Validation
– Field implementation of the most promising testing strategies and data interpretation frameworks
– Since the deployment of large shakers is the easiest to accomplish on bridges (A bridge in Hamilton, NJ was selected as the implementation structure)
– To be carried out with a UTA NHERI shaker (T-Rex) and dense instrumentation arrays
Envisioned Field Implementation
Foundation Dynamics and Dynamic Soil-Foundation-Structure Interaction (DSFSI)
Objective of Dynamic Soil-Foundation-Structure (DSFS) Interaction Analysis
The fundamental
objective of soil-
foundation-structure
interaction analysis is to
evaluate the dynamic
response by
encompassing the
radiation of energy of
the waves propagating
into the soil.
Effects of Soil and DSFSI on the Response
• Site amplification of ground motion (earthquake loading).
• Soil flexibility will effect the flexibility of the overall SFS (Soil-Foundation-Structure) system and, thus, reduce the fundamental frequency. (In comparison to a structure founded on rock.)
• Radiation of energy through soil will lead to a significantly higher damping. (Exceptions are shallow soil layers.)
• DSFSI (Dynamic SFS Interaction) increases as soil becomes softer, and the structure becomes more rigid. And vice versa.
• Generally, DSFSI gives smaller response amplitudes under earthquake and other dynamic loads than modeling on a rigid base. Displacements at the top of a structure may be larger due to rocking of the structure (foundation).
Modeling of DSFSI Problems - Direct and Substructure Methods
Direct Approach
Substructure Approach
Free Field Interaction
(after Wolf, 1985)
Impedance
Foundation Dynamics Problem – Impedance Functions
F
C Ku
𝒖 =𝑭
𝑲+ 𝒊𝝎𝑪
Rigid and massless foundation
Kvs - static stiffness
k - stiffness impedance coefficient
c - damping impedance coefficient
a0 - dimensionless frequency (wR/Vs)
Impedances are functions of frequency!
K K k ia cv vs ( )0 - vertical impedance
Response of Foundations to Vertical Loading
Factors Affecting Dynamic Response of Foundations
• Soil properties (primarily shear modulus, damping and Poisson’s ratio)
• Geometry (shape) of the foundation
• Depth of embedment of the foundation
• Presence of a rigid base
• Mode of vibrations (translation or rotation)
• Dynamics and frequency of loading
• Foundation flexibility (stiffness)
Modes of Vibrations
Sliding/SwayingSliding/
Swaying
RockingRocking
Twisting
Vertical
(from Fang, 1991)
Static Stiffness for a Rigid Circular Footing on an Elastic Half-Space
(from Gazetas, 1983)
Impedance Coefficients for a Circular Footing on an Elastic Half-Space - Vertical
a0a0
2 4 6 2 4 6
(Luco and Westman 1971, from Gazetas 1983)
Damping Ratio for Surface Foundations
(from Richart et al., 1970)
Some Elements Affecting Foundation Impedance Functions
• Embedment significantly increases the dynamic stiffness and equivalent damping ratio. => An effective way to reduce the anticipated high amplitudes of vibrations.
• For a foundation on a stratum, static stiffness in all modes increases (more for translational than rotational modes) with the relative radius to depth to bedrock ratio R/H.
• Impedance coefficients have undulations (instead of smooth functions for H-S) associated with natural frequencies of the stratum.
• Below the first resonant frequency of each mode of vibration, c is zero or negligible. (No surface waves to radiate energy, while bedrock prevents “vertical” radiation.) Vertical and sliding modes affected more.
• Foundation flexibility affects soil reaction and displacement distributions, and impedance coefficients.
Impedance Coefficients of a Rigid Circular Foundation on a Stratum - Vertical
2 4 6 a0 2 4 6 a0
(after Kausel and Ushijima, 1979)
Effect of Foundation Flexibility Expressed Through Stiffness Ratio on Soil Reaction Distribution
0 0.2 0.4 0.6 0.8 1 1.2-2.5
-2
-1.5
-1
-0.5
0N
orm
alli
ze
d s
oil
rea
ctio
n
REAL PART =0.0%
=0.35
a =2.69
0
=0.0
Normalized radius
s =0.008 s =0.125 s =1 s =8 s =125r r r r r
sE h
V Rr
p
s
3
1 1
2
0
3a
R
Vs
0
0w
0 0.2 0.4 0.6 0.8 1 1.2-0.2
-0.1
0
0.1
0.2N
orm
aliz
ed d
ispla
ce
me
nt
REAL PART
s =0.008 s =0.125 s =1 s =8 s =125r r r r r
=0.0%
=0.35
a =2.69
0
=0.0
Normalized radius
Effect of Stiffness Ratio on Displacement Distribution
0 1 2 3 4 5 6 7-2
-1.5
-1
-0.5
0
0.5
1
1.5
Dimensionless frequency, a 0
V
V
s1
s2
V =2
=0.35 =0.0 =0.0
R /d =10 1
s2
_
s =0.008 s =0.125 s =1 s =8 s =125r r r r r
Impedance c
oeff
icie
nt k
Effect of Stiffness Ratio on Impedance Functions
Numerical Model and Parametric Study of Dynamic Response of Bridge-Soil Systems
Parametric Study - 2D Model of Hypothetical Bridge
Variables
Vs: Soil S-Wave Velocity; 200-400 m/s
R: Footing Radius; 2-4 m
Hc: Column Height; 3-12 m
Constants
Wf: Footing Width; 1.3m
Tf: Footing Thickness; 0.5 m
Wc: Column Width; 0.5 m
Ts: Slab Thickness; 0.2 m
Fs: Half Column Spacing, 3 m
ρs: Soil Density; 1900 kg/m3
ν : Poisson’s ratio; 0.333
Foundation3 m 6 m 3 m
Bridge Swaying Response Under Horizontal Harmonic Loading
Sample Displacement Time Histories - Deck
-1.50E-04
-1.00E-04
-5.00E-05
0.00E+00
5.00E-05
1.00E-04
1.50E-04
2.00E-04
2.50E-04
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Ux
(m)
Time (s)
-3.00E-05
-2.00E-05
-1.00E-05
0.00E+00
1.00E-05
2.00E-05
3.00E-05
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Uy
(m)
Time (s)
Horizontal
Vertical
Sample Displacement Time Histories - Foundation
-1.50E-05
-1.00E-05
-5.00E-06
0.00E+00
5.00E-06
1.00E-05
1.50E-05
2.00E-05
2.50E-05
3.00E-05
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Ux
(m)
Time (s)
-0.005
-0.004
-0.003
-0.002
-0.001
0
0.001
0.002
0.003
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
Ro
tati
on
(ra
ds)
Time (s)
Horizontal
Rotation
0
2
4
6
8
10
12
0 0.5 1 1.5 2 2.5 3 3.5 4
Load
(kN
)
Frequency (Hz)
Sample Loading Spectrum
Sample Horizontal Displacement, Velocity and Acceleration Response Spectra
-0.01
-0.005
0
0.005
0.01
0 1 2 3 4 5
Dis
pla
cem
ent
(m)
Frequency (Hz)-0.00006
-0.00005
-0.00004
-0.00003
-0.00002
-0.00001
0
0.00001
0 1 2 3 4 5
Dis
pla
cem
ent
(m)
Frequency (Hz)
-0.0002
0
0.0002
0.0004
0.0006
0.0008
0.001
0.0012
0 1 2 3 4 5
Vel
oci
ty (
m/s
)
Frequency (Hz)-0.005
0
0.005
0.01
0.015
0.02
0 1 2 3 4 5
Vel
oci
ty (
m/s
)
Frequency (Hz)
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
2.5
0 1 2 3 4 5
Acc
ele
rati
on
(m
/s^2
)
Frequency (Hz)-0.005
0
0.005
0.01
0.015
0.02
0 1 2 3 4 5Acc
ele
rati
on
(m
/s^2
)
Frequency (Hz)
Real Part Imaginary Part
Sample Foundation Vertical Displacement and Rotation Response Spectra
Vertical Displacement
0.00E+00
2.00E-02
4.00E-02
6.00E-02
8.00E-02
1.00E-01
1.20E-01
1.40E-01
1.60E-01
0 0.5 1 1.5 2 2.5 3 3.5 4
Uy
(m)
Frequency (Hz)
0.00E+00
2.00E-04
4.00E-04
6.00E-04
8.00E-04
1.00E-03
1.20E-03
1.40E-03
1.60E-03
1.80E-03
2.00E-03
0 0.5 1 1.5 2 2.5 3 3.5 4
Ro
tati
on
(ra
ds)
Frequency (Hz)
Rotation
Fundamental Swaying Frequency Vs. Pier HeightRigid Base
Fundamental Swaying Frequency Vs. Pier HeightFlexible Base (R=2 m, Vs=200 m/s)
Fundamental Swaying Frequency Vs. Slenderness Ratio
0
0.5
1
1.5
2
2.5
3
0 0.5 1 1.5 2 2.5
Fre
qu
en
cy a
t p
eak
(H
z)
Slenderness Ratio
R=2, V=200
R=2, V=300
R=3, V=200
R=3, V=200
R=3, V=300
R=3, V=400
R=4, V=200
R=4, V=300
R=4, V=400
R=8, V=800
Finite Element Model of Hobson Avenue Bridge
Fundamental Swaying Mode for Rigid Base
Finite Element Model of Hobson Avenue Bridge
Fundamental Swaying Mode for Flexible Base
Field Implementation Using UTA NHERI Mobile Shakers
Field Implementation and Validation
• Objectives :
– To measure the response of all components: ground, foundation, substructure and superstructure in both vertical and horizontal directions, to infer the contributions of soil-foundation-substructure interaction on the overall response of the superstructure.
– To enable assessment of transmissibility (motion transfer) and force transfer between superstructure and foundation, and from the foundation to surrounding soil.
– To enable assessment of foundation impedance functions for both vertical and rocking motion.
• The results will be compared against the models within the parametric study to place the field test in context
• Secondary objective: The results obtained from the bridge excitation using a NHERI shaker (vertical mode only) and THMPER will be compared
Hobson Avenue Bridge over I-195, Hamilton, NJ
Hobson Avenue Bridge over I-195, Hamilton, NJ
Hobson Avenue Bridge over I-195, Hamilton, NJ
Hobson Avenue Bridge over I-195, Hamilton, NJ
Geophone Array
MASW (Multichannel Analysis of Surface Waves) Testing
MASW (Multichannel Analysis of Surface Waves) Testing
T-Rex positionDeck Triaxial AccelerometersSubstructure and Ground Triaxial GeophonesDeck Triaxial Geophones
Swaying Test – Center Pier
T-Rex positionDeck Triaxial AccelerometersSubstructure and Ground Triaxial GeophonesDeck Triaxial Geophones
Swaying Test – Middle of South Span
T-Rex positionDeck Triaxial AccelerometersSubstructure and Ground Triaxial GeophonesDeck Triaxial Geophones
Swaying Test – South Abutment
T-Rex Mobile Shaker
T-Rex in Position for Testing
T-Rex and THMPER
Geophones and Accelerometers on Bridge Deck
Central Pier
Sensors
Sensors
Ground Triaxial Geophone Array
What Are the Questions We Are Trying to Answer?
• Can we infer the contributions of soil-foundation-substructure interaction on the overall response of the superstructure?
• Can we develop data interpretation frameworks for structural system identification and assessment that will take into consideration DSFSI?
• Can large-amplitude, forced vibration testing using NHERI shakers (in a fully controlled manner) reveal the performance of structures beyond operational limit states? Are we entering a nonlinear range?
Acknowledgements
• NSF EAGER– Project support through Award Id. 1650170 (Program officer: Dr. Richard J. Fragaszy)
• NSF NHERI (Natural Hazards Engineering Research Infrastructure) – Provided access to UTA NHERI mobile shakers
• NJDOT – Support in bridge selection, and providing documentation and access to Hobson Avenue Bridge (Mr. Eddy Germain)
• UTA NHERI team
Thank You