 Full-Scale Monitoring of Tall Buildings |
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The NatHaz Modeling Laboratory launched a full-scale monitoring project in collaboration with Skidmore Owings and Merrill in Chicago
and the Boundary Layer Wind Tunnel Laboratory at the University of Western Ontario. In this program, several tall buildings
in the city of Chicago were instrumented, using accelerometers, ultra-sonic amemometers and high precision
global positioning systems(GPS). These measurements form a necessary bridge between the predicted response of the buildings,
both via finite element analysis and wind tunnel testing performed as part of the design process.
Not only does this give valuable insight into the design community's current ability to estimate the dynamic properties and response
of a structure under the action of wind loads, but it also helps to discover the actual dynamic response of the building
under the wind action and to suggest modifications to current design approaches.
The project is widely recognized as the first of it's kind in the U.S which includes introduction of GPS monitoring
in an urban environment.
For this project, additional information is available in Dr. Tracy Kijewski-Correa's Dissertation
"Full-Scale Measurements And System Identification : A Time-Frequency Perspective".
Chicago Full-Scale Monitoring Project [WEB]
Full-Scale Measurements And System Identification: A Time-Frequency Perspective
- Tracy Kijewski-Correa's dissertation :
Volume 1 [PDF]
,
Volume 2 [PDF]
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| Aerodynamic Loads Database : An Interactive Database |
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Under the action of wind, tall buildings oscillate simultaneously in the alongwind, acrosswind and torsional directions.
While the alongwind loads have been successfully treated in terms of gust loading factors based on quasi-steady and strip theories,
the acrosswind and torsional loads cannot be treated in this manner, as these loads cannot be related in a straightforward manner
to fluctuations in the approach flow. As a result, most current codes and standards provide little guidance for the acrosswind
and torsional response.
In order to provide some guidance at the preliminary design stages of buildings, an interactive aerodynamic loads database
for assessing dynamic wind induced loads on a suite of generic isolated buildings is introduced.
The database consists of high frequency base balance measurements involving 7 rectangular building models,
with side ratio (D/B, where D is the depth of the building section along the oncoming wind direction) from 1/3 - 3,
three aspect ratios for each building model in two approach flows, namely, BL1 (α = 0.16) and BL2 (α = 0.35)
corresponding to an open and an urban environment. The data are accessible with a user-friendly Java-based applet
through the worldwide Internet community. Through the use of this interactive portal, users can select the geometry
and dimensions of a model building, from the available choices, and specify an urban or suburban condition.
Upon doing so, the aerodynamic load spectra for the alongwind, acrosswind or torsional directions is displayed with
a Java interface permitting users to specify a reduced frequency (building frequency x building dimension/wind velocity)
of interest and automatically obtain the corresponding spectral value. When coupled with the supporting web documentation,
examples and concise analysis procedure the database provides a comprehensive tool for computation of wind-induced response
of tall buildings, suitable as a design guide in the preliminary stages.
Aerodynamic Loads Database [WEB]
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| Aerodynamics of Tall Building and Long-Span Bridge |
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In the area of wind effects, investigations are being made encompassing both basic and applied aspects
that include topics such as the mapping and synthesis of random pressure fields over bluff bodies,
unsteady loads on buildings, limit states for serviceability of tall buildings
and the analysis of structural damage due to extreme winds.
Boundary layer wind tunnels are being utilized for the physical modeling of wind-structure interactions.
Aerodynamics of tall buildings and long-span bridges are two major areas of investigation.
These experimental results are being integrated with computational models to predict the structural response.
Flow field around obstacles and buildings is also being simulated by utilizing computational techniques.
For bridge aerodynamics, additional information is available in Dr. Fred Haan's Dissertation
"The Effects of Turbulence on the Aerodynamics of Long-Span Bridges".
Aerodynamics of Tall Building [WEB]
Long-Span Bridge [WEB]
Tall Buildings Forum, April 4~6, 2002 [WEB]
The Effects of Turbulence on the Aerodynamics of Long-Span Bridges [PDF]
- Fred Haan's dissertation
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| Wavelet Analysis / System Identification |
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Due to the presence of nonlinear and nonstationary characteristics in a variety of signals, traditional analysis tools like
Fourier Analysis are often incapable of capturing some of the salient features.
This research addresses this issue by introducing a comprehensive wavelet-based analysis framework tailored
to accommodate nonlinear and nonstationary features of Civil Engineering signals.
The wavelet framework introduced in this research, predicated on the properties of the Morlet Wavelet,
provides flexible criteria for the separation of closely-spaced modal contributions,
discretization of the time-frequency plane, and identification and melioration of end effects through a reflective padding scheme.
Within this framework, wavelets are demonstrated to be capable of revealing hidden characteristics in simulated and measured wind,
wave and earthquake data. In these discussions, the wavelet instantaneous bandwidth is introduced
as a means to track subcyclic nonlinear behavior in a manner comparable to the Hilbert Spectra.
Other wavelet applications in this research include its adaptation for identification of correlation
in time and frequency and its enhancement through smart thresholding schemes.
This framework also provides the backdrop for the extension of wavelets to the identification of frequency and damping
in Civil Engineering structures, for which a number of processing concerns become paramount.
For more information about Wavelet Analysis in Civil Engineering, please see Dr. Tracy Kijewski-Correa's dissertation
"Full-Scale Measurements and System Identification : A Time-Frequency Perspective"
Full-Scale Measurements And System Identification: A Time-Frequency Perspective
- Tracy Kijewski-Correa's dissertation :
Volume 1 [PDF]
,
Volume 2 [PDF]
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| Damping Systems : TLD and TLCD |
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Auxiliary damping systems have found useful applications in the control of wind-induced vibrations of tall buildings,
bridge towers, chimneys, etc. The next generation of Tuned Liquid Dampers (TLDs) and Tuned Liquid Column Dampers (TLCDs)
are being studied using prototype models. Modeling efforts for sloshing include Sloshing-Slamming (S
2) analogy for TLDs.
Semi-active strategies for TLCDs include gain-scheduling and clipped-optimal control laws.
For more information about TLC and TLCD in Civil Engineering, please see Dr. Swaroop Yalla's dissertation
"Liquid Dampers For Mitigation Of Structural Response : Theoretical Development And Experimental Validation".
Kareem, A., Kijewski, T. and Tamura, Y. (1999), "Mitigation of Motions of Tall Buildings
with Specific Examples of Recent Applications", Wind and Structures, Vol.2, No.3, pp.201-251.
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Submitted Paper [PDF]
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Published Paper [PDF]
Tuned Liquid Damper(TLD) and Tuned Liquid Column Damper(TLCD) [WEB]
Video of Resonant Sloshing (AVI format) : 1.5Mb
Liquid Dampers For Mitigation Of Structural Response [WEB]
- Swaroop Yalla's dissertation
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| Real-time Model Predictive Control(MPC) |
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In order to enhance structural performance during extreme events like earthquakes and strong winds,
semi-active control devices have gained popularity.
In this content, real-time Model Predictive Control (MPC) based schemes have been implemented in structures
to reduce the dynamic load effects and vibrations under these extreme events.
This includes one-line real-time feedforward-feedback control, earthquake and wind loads modeling,
constraints consideration, controller-structure interaction, system identification,
shaking table test and experimental verifications, etc. This study offers proof of the concept,
and facilitates in prototyping of this control strategy for full scale implementation
in our efforts to reduce damage caused by natural hazards.
For more information about Model Predictive Control schemes in structural control,
please see Dr. Mei's dissertation
"Model Predictive Control Schemes for the Mitigation of Natural Hazards: Theoretical and Experimental Studies"
Real-Time Model Predictive Control for Structural Engineering [WEB]
Model Predictive Control Schemes for the Mitigation of Natural Hazards [PDF]
- Gang Mei's dissertation
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| Design of Floating Offshore System : Tension Leg Platform(TLP) |
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The reliable design of floating offshore systems, e.g., tension leg platforms (TLPs) in deep water can only be ensured
through an enhanced response prediction capability with respect to the effects of environmental loads.
The dynamic behavior of TLPs is significantly different from conventional platforms.
Not only is the applied loading complex in nature due to the interaction between waves and oscillatory platforms,
but more importantly, second-order forces in random seas and the coupling of combined TLP-tether systems
preclude straightforward application of the numerical methods applied to conventional platforms.
The development of computational procedures for analyzing combined TLP-tether system response to the simultaneous action of wind,
waves, currents, and motion mitigation through passive and active systems is investigated.
Design of Floating Offshore Systems [WEB]
Stochastic Response of Offshore Compliant Systems to Environmental Loads
- X. Song's dissertation
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| Stochastic Dynamics / Simulation & Modeling |
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In the fields of earthquake engineering, stochastic dynamics and structural reliability,
studies on the numerical simulation of nonstationary space-time realizations of ground motion
and associated structural response, wind related processes, ARMA systems,
bispectral analysis in modeling nonlinear vibrations, dynamics of nonlinear dynamical systems are in progress.
Studies including time-frequency description of random processes using Fourier, Hilbert and Wavelet Transforms are in progress.
Another area of concentration involves simulation of non-Gaussian random fields to model stormy seas,
seismic acceleration and wind induced pressure fluctuations.
The large eddy simulation has been utilized to numerically generate flow around prismatic structures & evaluate attendant wind loads.
Modeling and Simulation of Non-Gaussian Processes [PDF]
- K. Gurley's dissertation
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| Dynamic Load Simulator / Hardware-in-the-Loop |
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In order to develop realistic test methods for evaluating the performance of building components,
connections and systems in severe wind events the next generation of wind test facilities are investigated.
This includes multifan and multi-actuator systems, termed as Dynamic Load Simulator (DLS),
with force-feedback control loop to generate loads on structures both aerodynamically and mechanically.
Such systems are also very attractive for the experimental testing of small scale models subjected to wind,
wave and earthquake loading.
Dynamic Load Simulator [PDF]
Hardware-in-the-Loop [PDF]
- Swaroop Yalla's dissertation : Chapter 6 (6.5 Hardware-in-the-loop Simulation)
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| Wind Load Effects in Gust Fronts |
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The built environment experiences forces of nature generated by a host of damaging atmospheric events,
including gust-fronts induced by downdrafts associated with thunderstorms. An accurate prediction of load effects
that result from the interaction of structures with these extreme events is a critical part of designing
and constructing the built environment and protecting its occupants.
The primary goal of this project is to better understand and quantify wind loads and their effects on buildings
under transient wind events, e.g., gust-fronts. To accomplish this goal, a systematic approach is proposed
that focuses on capturing salient characteristics of transient flows associated with gust-fronts
and attendant load effects on geometrically-scaled models of generic building shapes in a transient flow field simulator.
The significance of transient wind events and their load effects can be readily surmised from an analysis of thunderstorm databases
both in the U.S. and around the world, which suggest that these winds represent the design wind speed for many locations.
As a result, these wind speeds become the input to codified design procedures validated in traditional boundary layer wind tunnels.
However, the mechanics of gusts associated with convective gust-fronts differ significantly from conventional turbulence
both in its kinematics and dynamics, e.g. their contrasting velocity profile and their transient nature.
A Tribute to Jack E. Cermak in the Wind Engineer, AAWE, July 2003 [PDF]
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| Codes & Standards and Design Tools |
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Research is in progress to translate current research findings for design applications.
The development of these design tools is focused on capturing accurate description of wind load effects on structures
without added complexity which may deter application of these tools in day-to-day design practice.
In this context recent developments include formulation of a new gust loading factor,
equivalent static load formulations for uncoupled and coupled cases, mode shape corrections,
role of aeroelastic balance in design, velocity profiles, interactive database, guidance on selection of damping values
and natural periods of wind excited structures. Input is provided to ASCE7 for its scheduled revisions.
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