Departmental Seminar
Spring 2007
2:30-3:30 pm (Thursday)
Inter-School Lab (705 CEPSR)
Announcements: a new home page about Professor Raymond D. Mindlin
Fourth Biot Conference on Poromechanics, 2009
Tenure-Track Position Available: Construction Engineering/Management
Past Seminars and Lectures



January 25, 2007
Engineering Models in Support of Regional Natural Disaster Risk Mitigation

Professor Rachel Davidson (host: Prof. George Deodatis)
School of Civil and Environmental Engineering
Cornell University

Despite impressive advances in the understanding of natural disaster risk and the development of technologies to reduce structural vulnerability, Hurricane Katrina and other recent events remind us that natural disaster risk remains significant. Engineering models can play an important role in supporting efforts to mitigate future losses. This presentation will describe two examples of mathematical models developed to support regional natural disaster risk mitigation. In the first, a simulation model was developed to estimate changes in regional hurricane risk (annual economic losses) over time. Most currently available loss estimation models use the present-day building inventory as input to estimate future hurricane losses. However, the number, locations, value, and vulnerability of buildings in a region vary with time, thus compromising the accuracy of loss estimates and the effectiveness of mitigation plans based on those estimates. The new method integrates four models—wind hazard, building inventory change, building vulnerability change, and economic change—in a simulation framework to compute changes in expected annual hurricane losses over time. A case study illustrates application of the method for residential woodframe buildings in selected counties in North Carolina. Case study results indicate the estimated rate of change of expected annual hurricane losses, the relative importance of different factors in causing that change, and the effects of different mitigation policies on the hurricane risk over time.

In the second project, a suite of optimization models are being developed to help communities at risk decide: (1) how much to spend on pre-earthquake mitigation that aims to reduce future losses versus waiting until after an event and paying for reconstruction, and (2) which of the many possible mitigation activities to fund. The models integrate information about the magnitude and character of the regional earthquake risk; the costs and benefits associated with each possible mitigation alternative; the available budget; and the specific regional objectives for risk management, which might include minimizing total costs, minimizing the possibility of a large loss, and ensuring that the risk is equitably distributed. Currently available loss estimation models provide increasingly comprehensive estimates of regional risk, but offer little guidance about how to use that information to make mitigation resource allocation decisions. Application of the optimization models is illustrated through case studies in Los Angeles County. Results suggest which buildings—by structural type, occupancy type, and census tract location—should be upgraded so as to satisfy different possible objectives. The impacts of both projects on regional policy-making and risk communication efforts will be discussed, as will plans for continuing work in this area.
February 8, 2007
Electromechanical Response of Smart Piezoelectric Materials

Prof. T. A. Venkatesh (host: Prof. Xi Chen)
Department of Mechanical Engineering, Tulane University

Piezoelectric materials, by virtue of their unique electromechanical characteristics, have been well recognized for their potential utility in many applications as sensors and actuators, from medical ultrasound devices, atomic force microscopes and sonar hydrophones to structural health monitoring and energy harvesting applications. Considerable research efforts in the past years have resulted in the development of several monolithic piezoelectric materials with enhanced properties. However, the sensing or actuating functionality of monolithic piezoelectric materials are generally limited. Hence, the composite approach to piezoelectric materials provides a unique opportunity to access a new design space with optimal mechanical and coupled characteristics, hitherto inaccessible through monolithic materials. A new analytical model is developed to predict the complete elastic, dielectric and piezoelectric constitutive properties of a piezoelectric composite system, where the constituent phases could in general be elastically anisotropic and piezoelectrically active. Furthermore, through finite-element modeling, a systematic methodology for predicting the complete set of piezoelectric properties as a function of the poling characteristics, size, shape, and distribution of the constituent phases is presented. Strategies for designing novel piezoelectric composites with enhanced sensitivities in multiple directions are also identified. Model predictions are compared with experimental results for select piezoelectric composites.


February 15, 2007
Some Recent Studies on the Mechanics of Carbon Nanotubes

Dr. Guoxin Cao (host: Prof. Xi Chen)
Columbia University

Carbon nanotubes (CNTs) have been subjected to intensive study since their discovery in 1991 due to their unique combinations of mechanical, electrical and chemical properties. The mechanical properties of CNTs must be fully understood in order to fulfill their promising applications. In this talk, the elastic properties of single-walled and multi-walled carbon nanotubes in the axial and radial directions are studied by using molecular dynamics (MD) simulations. New phenomenological continuum models and their effective elastic moduli are generalized from the MD
analyses.

Both MD and continuum approaches are then applied to explore the thermal vibration properties of CNTs, the lateral and radial vibration characteristics of CNTs under various loading modes, and the buckling behaviors of CNTs under bending, compression, and torsion, as well as nanoindentation. The numerical studies offer useful insights to apply CNTs as nanowires in nanoelectronics, nanostrain sensors, nanotransistors, nanovalves, nanocomposites and new methods of measuring the CNT elastic properties.

March 8, 2007
Water drop erosion on turbine blades

Prof. Qulan Zhou (host: Prof. Xi Chen)
Senior Visiting Scientist from Xi'an Jiaotong University

In the wet steam stage of a steam turbine, the erosion caused by high-speed impact of water drops is regarded as one of the primary reliability concerns and its mechanism must be sufficiently understood. The investigation of water drop erosion on turbine blade is a coupled solid-fluid mechanics problem, where an effective numerical framework is established. The flow field and movement of water drops in a whole stage of a steam turbine are simulated. The impact process of water drop on the metal blade surface is analyzed by a new nonlinear wave model that couples solid and fluid mechanics. After the impact stress field on the blade surface is obtained, the fatigue life of the blade can be estimated. A comprehensive numerical simulation framework is established to simulate the water drop erosion on metal blades, where key insights regarding the system reliability are obtained as the characteristics of water drops and working conditions of turbine are varied. The most dangerous erosion regions are predicted which agree well with experiments.
March 29, 2007
Uniqueness of indentation test

Mr. Manhong Zhao (host: Prof. Xi Chen)
Ph.D. candidate, Columbia University

Micro/nanoindentation is widely used to extract material elastoplastic properties from the measured force-displacement curves. One of the most well-established indentation techniques utilizes dual (or plural) sharp indenters (which have different apex angles) to deduce key parameters such as the elastic modulus, yield stress, and work-hardening exponent for materials that obey the power-law constitutive relationship; a number of groups have shown that the solution of such technique is unique. However, here we show the existence of “mystical materials”, which have distinct elastoplastic properties yet they yield almost identical indentation behaviors, even when the indenter angle is varied in a large range. These mystical materials are therefore indistinguishable by most existing indentation analyses unless extreme and impractical indenter angles are used. Explicit procedures of deriving these mystical materials are established, and the general characteristics of the mystical materials are discussed. In many cases, for a given indenter angle range, a material would have infinite numbers of mystical siblings, and the existence maps of the mystical materials are also obtained. Furthermore, we propose two alternative techniques to effectively distinguish these mystical materials. The study addresses the important question of the uniqueness of indentation test, as well as providing useful guidelines to properly use the indentation technique to measure material elastoplastic properties.

April 12, 2007

Vulnerability to Natural Hazards in Marginalized Communities: An Interdisciplinary Perspective

Dr. Rebekah Green (host: Prof. Deodatis)
Earth Institute of Columbia University

 

Decreasing structural vulnerability to natural hazards in marginalized communities is an interdisciplinary challenge – one that encompasses infrastructural fragility, risk perception, and politicized dimensions of pre-disaster planning and post-disaster recovery. This can be illustrated through two case studies.  The first study, a mixed qualitative and quantitative survey in four neighborhoods in Istanbul, Turkey, shows how rapid urbanization and widespread distrust of the formal construction industry have led residents to believe that unauthorized housing and informal inspection are the most effective means of reducing exposure to hazards. This risk perception has contributed to the continued production of poor quality construction vulnerable to seismic excitation. The second study focuses on the recovery of New Orleans’ heavily-flooded, low-income neighborhoods after Hurricane Katrina. A stratified damage and recoverability survey of 2569 residential structures found that over half were cost effective to repair. Analysis of repair costs indicates that current recovery policies will promote depopulation in low-income neighborhoods and may contribute to increased social and physical vulnerability in the future. Findings from both these studies have contributed to the tailoring of engineering assistance in marginalized communities affected by natural hazards. 

Dr. Green is a post-doctoral research fellow at the Earth Institute of Columbia University. She received her Ph.D. from Cornell University, where she combined structural engineering and cultural anthropology to study illegal construction in Istanbul, Turkey. She has worked with community-based organizations in several Asian countries and more recently in New Orleans to adapt engineering  vulnerability assessments to local disaster prevention planning and post-disaster recovery.
April 19, 2007

BOTDR Detection of Chemicals in Subsurface and Infrastructure

Prof. Sibel Pamukcu (host: Prof. Culligan)
Professor and Associate Chair
Department of Civil and Environmental Engineering
Lehigh University

 

This seminar will present the conceptualization and development of a chemical sensor capable of online detection of target liquid chemicals distributed over large areas in the subsurface or over infrastructure. The sensor assembly is based on coupling of a reactive polymer and standard optical fiber. The Brillouin scattering property of standard optical fibers makes it possible to obtain strain measurements at intermitted positions along a single fiber due to thermal or mechanical loading. The entire sensing fiber length can be in kilometers or meters with varying spatial resolution of measurement from a few centimeters to a meter. The distributed sensor in discussion is being developed to match the needs of large scale civil-infrastructure and facility testing and monitoring, such as underground or above ground geo-media, containment facilities, pipelines, structural components, or paved surfaces. The seminar will summarize results of current laboratory applications and discuss the implications of forward-looking concepts in sensing using the technology.

Seismic Responses of Subway Structures in Liquefiable Soils and the Mitigation: Experimental and Numerical Investigations (postponed)
  Huabei Liu (host: Prof. Ling)
Associate Professor, Department of Civil Engineering
Tsinghua University


The construction of subway or other tunnels in liquefiable soils sometimes is inevitable. Severe damages to the underground structure may occur during strong earthquake due to the excessive deformations of soils or even floatation of the underground structure itself. The seismic responses of subway structures in liquefiable soils and the possible damages were investigated using dynamic centrifuge tests and fully coupled Finite Element analysis. The possible mechanisms of the seismic responses were identified. Some possible mitigation schemes were studied and a simplified analysis method was also proposed for the in-plane response of subway structures. The necessary further research is finally discussed. 

Dr. Huabei Liu is an associate professor of Geotechnical Engineering in the Department of Civil Engineering at Tsinghua University. He obtained his Ph.D. in Geotechnical Engineering from the Department of Civil Engineering and Engineering Mechanics at Columbia University in December, 2002. Afterwards he firstly worked as a postdoc research scientist at Columbia for 7 months and then returned to China and became a faculty member at Tsinghua University in August, 2003. Dr. Liu works mainly in the field of geosynthetic-reinforced soil structures, soil liquefaction and constitutive modeling of geomaterials. He now serves as a member in the Technical Committee of Soil-Structure Interaction (TC 38) of the International Society of Soil Mechanics and Geotechnical Engineering (ISSGE).

April 26, 2007
Molecular Mechanics and Materials Monitoring in Civil Engineering
Prof. Masoud Ghandehari (host: Prof. Betti)
Associate Professor, Department of Civil and Environmental Engineering
Brooklyn Polytechnic University

Complementing current knowledge in materials performance and transport phenomena that are based on theoretical principles and historical patterns, real time in-situ chemical analysis promises to improve practices of health management in infrastructure materials and the geo-environment. This presentation outlines opportunities offered by embedded optical fiber probes for in in-situ, subsurface analysis in civil engineering. Target species include moisture, chlorides, products of materials dissolution, as well various classes of contaminants in the subsurface environment. Developments of near-infrared analysis for long term robust applications will be the specific focus of discussion. 

May 3, 2007

NOVEL GROUND MODIFICATION TECHNIQUES TO ADDRESS VOLUME CHANGE BEHAVIOR OF EXPANSIVE SOILS

Prof. Anand J. Puppala  (host: Prof. Culligan)
Professor, Department of Civil and Environmental Engineering
The University of Texas at Arlington

 
Expansive soils undergo large amounts of heaving and shrinking due to seasonal moisture changes. These movements lead to cracking of the infrastructure built on them and these distress problems have resulted in billions of dollars of repair costs annually. The US alone has spent more than five billion dollars to rehabilitate the foundations of residential buildings, lightly loaded structures, buried utilities, highways and airfield pavements, and embankments built on expansive soils. Chemical stabilization methods are most frequently used since they provide fast, efficient, repeatable and reliable improvements to expansive soil properties. However, most of these methods do not address shrinkage movements in dry environments and some do not provide effective treatment when soils contain large amounts of soluble sulfates. New methods are still needed to reduce volumetric strain related expansive soil movements. In this presentation, two novel methods using deep soil mixing technology and a compost soil amendment to mitigate volume changes of expansive soils will be covered. Both laboratory design and field studies on pilot scale structures built with comprehensive instrumentation will be presented. Findings, recommendations and current implementation status details will be provided.