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1. Abdallah, Ayman Ahmed. Dynamic substructuring by the boundary flexibility vector method of component mode synthesis.

Degree: PhD, Civil Engineering, 1990, Case Western Reserve University

► Component mode synthesis (CMS) is a method of dynamic analysis, for structures… (more)

▼ Component mode synthesis (CMS) is a method of dynamic analysis, for structures having a large number of degrees of freedom (D.O. F.). These structures often required lengthy computer CPU time and large computer memory resources, if solved directly by the finite-element method (FEM). In CMS, the structure is divided into independent components in which the D.O.F. are defined by a set of generalized coordinates defined by displacement shapes. The number of the generalized coordinates are much less than the original number of physical D.O.F., in the component. The displacement shapes are used to transform the component property matrices and any applied external loads, to a reduced system of coordinates. Reduced system property matrices are assembled, and any type of dynamic analysis is carried out in the reduced coordinate system. Any obtained results are back transformed to the original component coordinate systems. In all conventional methods of CMS, the mode shapes used for components, are dynamic mode shapes, supplemented by static deflected shapes. Historically, all the dynamic mode shapes used in conventional CMS are the natural modes (eigenvectors) of components. This work presents a new method of CMS, namely the boundary flexibility vector method of CMS. The method provides for the incorporation of a set of static Ritz vectors, referred to as boundary flexibility vectors, as a replacement and/or supplement to conventional eigenvectors, as displacement shapes for components. The generation of these vectors does not require the solution of a costly eigenvalue problem, as in the case of natural modes in conventional CMS, and hence a substantial saving in CPU time can be achieved. The boundary flexibility vectors are generated from flexibility (or stiffness) properties of components. The formulation presented is for both free and fixed-interface components, and for both the free and forced vibration problems. Free and forced vibration numerical examples are presented to verify the accuracy of the method and the saving in CPU time. Compared to conventional methods of CMS, the results indicate that by using the new method, more accurate results can be obtained with a substantial saving in CPU time. Advisors/Committee Members: Huckelbridge, Arthur A.

Keywords: Dynamic substructuring boundary flexibility vector component mode synthesis

2. Acosta, Jesus-Adolfo. Pavement surface distress evaluation using video image analysis.

Degree: PhD, Civil Engineering, 1994, Case Western Reserve University

► Maintenance and repair of the highway network accounts for one of the… (more)

▼ Maintenance and repair of the highway network accounts for one of the major expenses in the federal and state budget. Pavement Management Systems (PMS) have been implemented by Departments of Transportation and other transportation agencies to optimize the allocation of these funds. One of the most important inputs to a PMS is the pavement surface evaluation. Rating systems where pavement distress is measured by type, extent and severity, have been used extensively in order to quantify pavement surface condition. In most instances, these systems are both tedious and time consuming. Distress measurement is also subjective, which affects the precision of the rating. Identification and quantification of distress types are possible by automatic analysis of images captured by a microcomputer from video or film recordings. The present research describes the implementation of the PCR-Video System, which allows the identification and classification of most common pavement distress types. Depth and distance measurement devices were installed in a survey vehicle and connected to an on board microcomputer to determine the distance traveled and to allow the identification and quantification of depth related distress types. A bar color code method was developed to inscribe distance and depth readings onto the video S-VHS tape player, an image capturing board and a workstation was assembled. A set of images is digitized by the image capturing board and stored in main memory to remove overlapping areas present in consecutive frames. The Vertical and Horizontal Region Segmentation method was developed to eliminate the drawbacks found in conventional image segmentation approaches. A logic-based classification approach was also developed for cluster classification. The system when combined with a rating procedure, such as the PCR produces a quantitative measurement of pavement condition. Finally, the pavement inventory data file can be updated with the new pavement ratings. The system was validated by rating four roadway sections, previously inspected manually. The automated results showed very good correlation with the visually obtained ratings. Advisors/Committee Members: Figueroa, J. Ludwig.

Subjects: Engineering, Civil

Keywords: Pavement surface; distress evaluation; video image analysis

3. CHEN, LI. A BIOINSPIRED MICRO-COMPOSITE STRUCTURE.

Degree: PhD, Civil Engineering, 2005, Case Western Reserve University

► This thesis involves the design, fabrication and mechanical testing of a bioinspired… (more)

▼ This thesis involves the design, fabrication and mechanical testing of a bioinspired composite structure with characteristic dimensions of the order of tens of microns. The particular microarchitecture, designed and fabricated using microelectromechanical systems (MEMS) technology, involves two distinct length scales and represents a first attempt at mimicking the crossed-lamellar microstructure of the shell of the Giant Queen Conch Strombus gigas, which contains features the dimensions of which span five distinct length scales. After giving a review of the mechanical properties of mollusks, the detailed design of a microstructure, which approximates the crossed-lamellar arrangement of Strombus gigas, is presented. Fabrication of the microstructure using multi-microfabrication methods is conducted in terms of the designed fabrication flow. The problems encountered during the processes are discussed. The measurements of the strength, stiffness and work of fracture of the fabricated microstructure are conducted using a commercially available nanoindenter. Testing results are discussed and conclusions about the mechanical behaviors of the microstructure are drawn to summarize the achievement of this thesis. Finally, future work is outlined to point out the possible directions for improving the mechanical performance of the bioinspired composite. In parallel with my thesis research, I have developed a theoretical model for the experimentally observed cyclic loading-induced strengthening in MEMS polycrystalline silicon. The model relies on atomistic calculations that predict plastic-like behavior of amorphous silicon, which depending on initial density, is associated with dilatancy or compaction. The amorphous silicon is approximated as a Drucker-Prager plastic material, whose parameters are chosen to match the predictions of the atomistic calculations. The constitutive model is used to simulate the mechanical response to cyclic loads of notched polysilicon MEMS specimens containing deforming amorphous grain boundaries. The results demonstrate that certain combinations of mean stress and alternating stress produce plastic deformation and significant residual compressive stresses at the root of the notch, and in turn an increase in nominal strength. This work is presented in Chapter 6. Advisors/Committee Members: Ballarini, Roberto.

Keywords: Photoresist; silicon; Sputtered silicon; Etching; silicon film

4. Cleary, John. FORENSIC INVESTIGATIONS OF THE INNERBELT BRIDGE (CUY-90-1524) IN CLEVELAND, OHIO.

Degree: PhD, Civil Engineering, 2011, Case Western Reserve University

► The Innerbelt Bridge (CUY-90-1524) carries Interstate Route 90 over the Cuyahoga River… (more)

Subjects: Civil Engineering

Keywords: GIRDER; Truss; EXPANSION JOINT; pier; strain; L300-L301

5. Dai, Huiguang. Dynamic Behavior of Maglev Vehicle/Guideway System with Control.

Degree: PhD, Civil Engineering, 2005, Case Western Reserve University

► Magnetic levitation (Maglev) is an innovative transportation technology. A high speed maglev… (more)

Subjects: Engineering, Civil

Keywords: Maglev,Dynamics,Guideway

6. Eitel, Amy Katherine. PERFORMANCE OF A GFRP REINFORCED CONCRETE BRIDGE DECK.

Degree: PhD, Civil Engineering, 2005, Case Western Reserve University

► The corrosion resistance of fiber-reinforced polymers in addition to their high-strength and… (more)

Subjects: Engineering, Civil

Keywords: FRP composites; GFRP; FRP reinforcement; bridge performance; bridge monitoring

7. Fu, Lei. Application of Piezoelectric Sensors in Soil Property Determination.

Degree: PhD, Civil Engineering, 2004, Case Western Reserve University

► Piezoceramic as a smart or adaptive material has been widely used in… (more)

▼ Piezoceramic as a smart or adaptive material has been widely used in engineering measurement and control. When used in soil testing, the material can work as a wave transmitter or a wave receiver. Among the piezoelectric sensors, the bender element and the extender element are the most widely used. While the bender element is used to generate and receive shear waves, the extender element is used to produce and detect P-waves. One application of piezoelectric sensors is to measure shear wave velocities in centrifuge tests. Measurement techniques for both dry and saturated specimens were developed. A series of centrifuge model tests were performed. Bender element tests were carried out during the spin-up, spin-down, and in-flight stages of a centrifuge. Dynamic centrifuge tests were conducted on both dry and saturated models to investigate the influence of earthquake motions. Shear wave traveling times, accelerations, and pore water pressures were monitored during the tests. Based on the test results presented in this study, the current shear wave velocity-based liquefaction evaluation criteria were examined. Piezoelectric sensors were also used to develop a new piezo cone penetrometer. The piezo cone penetrometer is equipped with one set of bender elements and one set of extender elements. The equipment is designed for the purposes of measuring stiffness of the subgrade and the sublayer of a pavement in the field. Compared to the conventional CBR test, this method is quick and simple as well as being theoretically sound. The results in the laboratory have shown it to be a promising tool.Finally, a large odometer was developed for testing gravelly materials. The advantages of the device include that it can measure the stiffness of a soil with large grain sizes and can measure moduli in different planes. In conclusion, measurement of soil properties using piezoelectric sensors is direct and accurate. The technique is theoretically sound. The application of the technique is limited to low strain levels, which are in the elastic range of soil deformations. Advisors/Committee Members: Zeng, Xiangwu.

Subjects: Engineering, Civil

Keywords: Shear Wave; Bender Elements; SOIL; Centrifuge; Shear; Bender; Earthquake

8. Gang, Liu. VERIFICATION OF SHEAR WAVE VELOCITY BASED LIQUEFACTION CRITERIA USING CENTRIFUGE MODEL.

Degree: PhD, Civil Engineering, 2008, Case Western Reserve University

► The simplified procedure developed by Seed and Idriss (1971) for evaluating liquefaction… (more)

▼ The simplified procedure developed by Seed and Idriss (1971) for evaluating liquefaction potential of soils has become a standard procedure throughout North American and much of the world. Field tests, such as SPT, CPT and, have been widely used to determine the cyclic resistance ratio (CRR) in order to avoid the difficulties associated with sampling and laboratory testing. Although the in-situ case history–based liquefaction criteria have gained common usage in the field, their limitations, uncertainties and possible errors make it necessary to be validated/calibrated. Centrifuge model is an ideal tool to measure shear wave velocity and to validate/calibrate the shear wave velocity based liquefaction criteria. The principle of this research is to conduct dynamic centrifuge tests to model field soil layer response during earthquakes, while, before and after the earthquake test, the profile of the shear wave velocities of the model is measured by bender element tests. According to the measured shear wave velocities and observed model performances, conclusions about the liquefaction resistance of the model can be drawn, which can be further used to examine the field data based criteria. A series of centrifuge test were conducted on Nevada sand with different fine contents to determine the liquefaction resistance of soils. A new liquefaction criterion was developed based on the centrifuge test results by following the general format of the SPT based simplified procedure. Liquefaction resistance curves were established by modifying the relationship suggested by Dobry based on constant average cyclic shear strain theory. The new CRR curves were compared with some previous proposed liquefaction curves based on case history data. Also all the mentioned curves were examined by actual observation data during past earthquakes. The new criteria will provide an additional tool for practitioners and researchers to predict liquefaction occurrence. Advisors/Committee Members: Zeng, Xiangwu.

Keywords: LIQUEFACTION; Earthquake; CENTRIFUGE; Soils; SHEAR WAVE; Vs1; SHEAR

9. Ghiocel, Dan Mircea. Nonlinear dynamic response of a cable system to additive and parametric random excitations.

Degree: PhD, Civil Engineering, 1993, Case Western Reserve University

► The work presented herein investigates the behavior of a geometrically nonlinear cable… (more)

Subjects: Engineering, Civil

Keywords: Nonlinear cable system; Random excitations

10. He, Chunmei. GEOTECHNICAL CHARACTERIZATION OF LUNAR REGOLITH SIMULANTS.

Degree: PhD, Civil Engineering, 2010, Case Western Reserve University

► Many of the essential materials needed for the construction of permanent lunar… (more)

Subjects: Civil engineering

Keywords: Moon, Lunar Regolith, Simulant, JSC-1A, NU-LHT-2M, GRC-3, Geotechnical Characterization, Shear Strength

11. Hill, Daniel R. Bioasphalt and Biochar from Pyrolysis of Urban Yard Waste.

Degree: MS, Civil Engineering, 2012, Case Western Reserve University

► Pyrolysis is proposed as an alternative management method to composting for urban… (more)

Subjects: Environmental Engineering

Keywords: pyrolysis; carbonization; yard waste; waste management; bioasphalt; biochar; bio-oil; composting

12. Kurniawan, Antonius S. Generalized Eulerian-Lagrangian finite element methods for nonlinear dynamic problems.

Degree: PhD, Civil Engineering, 1990, Case Western Reserve University

► A Generalized Eulerian-Lagrangian formulation for Non-Linear Dynamic problems is developed for solid… (more)

Subjects: Engineering, Civil

Keywords: Eulerian-Lagrangian finite element nonlinear dynamic

13. Liang, Liqun. Development of an energy method for evaluating the liquefaction potential of a soil deposit.

Degree: PhD, Civil Engineering, 1995, Case Western Reserve University

► Liquefaction occurs in loose and saturated cohesionless soils subjected to strong ground… (more)

▼ Liquefaction occurs in loose and saturated cohesionless soils subjected to strong ground motion caused by earthquakes, machine vibrations, ocean waves, blasting, etc. It is a source of major damage to various types of structures. Under cyclic loading the pore water pressure in loose to medium dense, saturated cohesionless soils increases and the effective stress decreases, leading to a degradation of the shear strength and of the stiffness. It appears as if some damage occurs in the material. Recently, it was found that the level of energy dissipated into the soil can better represent this damage. To fully develop the energy approach for design purposes, a combination of experimental, analytical and numerical studies are needed. A total of 74 tests were conducted on hollow cylinder of soils under undrained conditions and torsional shear loading. The effects of factors such as: amplitude of shear strain, confining pressure, relative density, soil type, loading pattern and application of static shear, on the liquefaction characteristics and on energy dissipation were studied. Statistical analyses were conducted to obtain relationships between the energy dissipated and some of these important parameters. It is shown that the use o f the amount of dissipated energy per unit volume in the evaluation of the liquefaction potential has the advantage over conventional methods since the amount of dissipated energy per unit volume required for liquefaction is independent of the loading pattern. Based on observation and experimental results, models for the degradation of the maximum shear modulus and of the shear strength as a function of the energy were developed and used with a hyperbolic stress-strain relationship to provide a very effective numerical procedure that can be used to calculate the seismic response and the energy dissipation of a soil deposit. This procedure was incorporated into the program ELFS which was applied to solve a variety of problems, and predicts the seismic response of a horizontal deposit and its energy dissipation in a very satisfactory way. Finally, a formal procedure using the energy method to evaluate the liquefaction potential of a soil deposit is proposed Advisors/Committee Members: Figueroa, J. Ludwig.

Subjects: Engineering, Civil

Keywords: Soil liquefaction potential evaluation

14. Li, Bo. EFFECT OF FABRIC ANISOTROPY ON THE DYNAMIC MECHANICAL BEHAVIOR OF GRANULAR MATERIALS.

Degree: PhD, Civil Engineering, 2011, Case Western Reserve University

► The behavior of granular material primarily depends on the nature and arrangement… (more)

▼ The behavior of granular material primarily depends on the nature and arrangement of constituent particles (e.g., particle size and shape [roundness and angularity]), which, in turn, affect fabric anisotropy. Previous research has shown that the fabric of granular materials affects its overall mechanical properties, especially in particles with long axes and high angularity. Because micro-fabric reflects the geological and stress history of a deposit, the depositional environment, and weathering history, understanding such anisotropic behavior in granular materials is particularly important. However, most research has been conducted in laboratory environments using tri-axial and resonant column tests equipped by bender element to measure the fabric anisotropy under isotropic confining pressure, which does not necessarily reflect the actual response in the field. In this research, we investigate the effect of fabric anisotropy in granular materials on the seismic response of structures. We found that the deposition angle of granular materials can affect the dynamic responses of structures, such as sheet pile walls and strip foundations. In addition, fabric anisotropy influences liquefaction resistance, which is consistent with case reports from some earthquakes. This study focuses on the relationship between deposition methods and dynamic mechanical properties of granular materials. The geotechnical centrifuge at Case Western Reserve University was used to simulate seismic events. Scaled models of sheet pile walls and strip foundations were used in the model tests. A specially designed container was used to prepare models of various deposition angles. The test program was divided in two groups: dry conditions and saturated conditions. Measurements of deformation, pore pressure, and acceleration were taken to show the effect of fabric anisotropy. The response that was observed during the tests indicated the significant influence of fabric anisotropy on the soil structure during seismic events. A supplemental investigation of the effect of fabric anisotropy on small strain elastic properties was also carried out in a specially designed cubic container. The samples were prepared with 0°, 45° and 90° deposition angle and tested under K0 condition. The evaluation has been expressed in terms of fabric indices and degree of anisotropy obtained through the appropriate installation of piezo-electric sensors. The results of the tests were used to validate a micromechanical model, which could reasonably reflect the evolution of the internal structure of granular materials. Advisors/Committee Members: Zeng, Xiangwu.

Subjects: Civil Engineering

Keywords: FABRIC ANISOTROPY; Deposition Angle; Soil; Sands; Bender Element

15. Liu, Yan. Innovative Non-destructive Testing Technologies for QA/QC of Fresh and Early Stage Concrete.

Degree: PhD, Civil Engineering, 2011, Case Western Reserve University

► The dissertation describes the development and validation of a new instrument based… (more)

Subjects: Civil Engineering

Keywords: Concrete, Non-destructive Testing, Time Domain Reflectometry, Freeze-thaw Damage, Fresh Concrete, Early Stage Concrete

16. MA, JUN. Risk Assessment and Sequestered Contamination Evaluation for Legacy Heavy Metal Contaminants in Cleveland Area Brownfields.

Degree: PhD, Civil Engineering, 2005, Case Western Reserve University

► Brownfields are real estate properties for which the expansion, redevelopment, or reuse… (more)

▼ Brownfields are real estate properties for which the expansion, redevelopment, or reuse may be complicated by the presence or potential presence of a hazardous substance, pollutant, or contaminant. In old industrial cities such as Cleveland, brownfields can often be associated with legacy heavy metal contaminants. This dissertation presents the results of a series of brownfield surveys conducted in Greater Cleveland area. The heavy metal burdens (Cd, Cr, Cu, Ni, Pb and Zn) in soils are examined for fifty-three brownfields identified. Results demonstrate that most of these brownfield soils have heavy metal soil burdens well above background levels, seven of them contain lead concentrations in excess of Ohio’s industrial remediation criteria. Risk assessment of the heavy metals is presented for these brownfields using state guidance values. Results demonstrate an unexpected degree of variability in guidance values for different states, and this often affects dramatically the cumulative hazard quotient posed by heavy metals for the same site using different states’ criteria. The results of different soil extractions suggest that for lead the pH is perhaps the most important factor in its removal from soils, but chromium recovery is dependent on its speciation in the soil. Brownfield soils that have been contaminated for a long time often sequester contaminants deep within the soil particles. The sequestered contamination is difficult to remove. Heavy metal extractions are usually found to achieve improved results after soil pulverization, which exposes more of soil’s internal bulk volume to extraction and provides shorter diffusion pathways for the sequestered contaminants to be released. The results of sequestering quantification using this pulverization technique are presented. Heavy metal sequestering has been found to be a common property in brownfield soils analyzed. The mass transport mechanisms of sequestered contamination are modeled, solid-state diffusion is one possible explanation for sequestering, but a micropore structure with sufficient internal acid neutralization capacity that resists pore acidification and solubization of sorbed metals on pore walls can also sequester heavy metals. Electrokinetically enhanced mass transport of sequestered heavy metals is modeled, and the results indicate a significantly accelerated mass transport after the use of direct electric field. Advisors/Committee Members: Jennings, Aaron A.

Subjects: Engineering, Civil

Keywords: Sequestered Contamination, Heavy Metals, Electrokinetics, Brownfields

17. Oravec, Heather Ann. Understanding Mechanical Behavior of Lunar Soils for the Study of Vehicle Mobility.

Degree: PhD, Civil Engineering, 2009, Case Western Reserve University

► The mechanical properties of the lunar regolith are critical parameters in predicting… (more)

Subjects: Civil engineering

Keywords: bevameter; cone penetrometer; lunar soil simulant; shear strength; stress-strain characteristics; triaxial test

18. Othman, Ayman Mahmoud. Mechanical performance and fatigue crack growth behavior of polymer-modified asphalt concrete mixtures.

Degree: PhD, Civil Engineering, 1995, Case Western Reserve University

► The mechanical performance and fatigue crack growth behavior of SBS modified asphalt… (more)

▼ The mechanical performance and fatigue crack growth behavior of SBS modified asphalt concrete mixtures subjected to varying loading and environmental conditions were studied. Paris' and the Modified Crack Layer (MCL) models have been used to characterize the resistance of asphalt concrete mixtures to fatigue crack propagation. Both models successfully discriminate the effect of processing conditions on the fracture resistance of the AC-20 asphalt concrete mixtures as well as the effect of SBS content on the fracture resistance of the modified AC-5 mixture. SEM examination of the fracture surface of the SBS modified mixtures revealed ridge formation in binder rich areas which increases in intensity with the SBS percent in the mixture. Using AC-20 asphalt concrete mixture, the current study demonstrates the dependency of the Paris' and the MCL models parameters on the level of stress during fatigue loading. Fatigue crack growth analysis of SBS modified mixtures at various temperatures also revealed that Paris' model parameters (C* and m*) are both independent of temperature. However, the MCL model indicates only the consistency of the specific energy of damage γ′ with temperature, while the dissipative coefficient β′ showed d ependency on the temperature. The accumulated dissipated energy through fatigue failure which is introduced in this research as a fracture criteria, was correlated to fatigue life through temperature independent parameters. A cyclic thermal aging program was performed in an environmental chamber between 0° F and 70° F for five different numbers of cycles. The current investigation revealed that the SBS modifier helps maintain a constant fatigue resistance of the mixture over a moderate number of low temperature thermal cycles. A decrease in the fatigue resistance was observed at higher number of thermal cycles. The fatigue performance of the mixtures as predicted from Paris' and the MCL models was found to be consistent with what was predicted from the conventional indirect tensile strength and the critical energy release rate (J1c). Advisors/Committee Members: Figueroa, J. Ludwig.

Subjects: Engineering, Civil

Keywords: Polymer asphalt concrete, mechanical performance and crack growth

19. Panneerselvam, Dinesh. Mechanics of Asphalt Concrete: Analytical and Computational Studies.

Degree: PhD, Civil Engineering, 2005, Case Western Reserve University

► Permanent deformation under repeated loading (rutting) is the most prominent distress mechanism… (more)

▼ Permanent deformation under repeated loading (rutting) is the most prominent distress mechanism in pavements. In properly compacted pavements shear flow is considered to be the primary rutting mechanism. Also the mix exhibits volumetric/deviatoric coupling behavior which is observed when the mix dilates under shear loading. A new multi-dimensional hyperelastic-viscoelastic-viscoplastic-damage model is developed to describe the permanent deformations and coupling behavior of asphalt concrete. The elastic component of the asphalt concrete response is modeled by a second order hyperelastic model. Asphalt concrete mix exhibits volumetric/deviatoric coupling behavior even at very small strain values and hence an elastic model is used to capture this phenomenon. The viscoelastic model developed in this study is based on a new viscoelastic model which has been recently developed by Panoskaltsis and co-workers (Panoskaltsis, V.P., et al. “The Generalized Kuhn model of Viscoelasticity”, submitted for Publication). In the work presented here, the Generalized Kuhn model is applied for the description and prediction of asphalt behavior. The response of the material for frequency sweep test is captured and the model predicts the loss tangent for asphalt concrete very well. Furthermore, the model has been appropriately modified in order that the important asphalt temperature effects are taken into account through time temperature superposition principle. The viscoplastic component captures the rate dependent behavior and is based on Perzyna’s theory of viscoplasticity. This theory is used to model the ratcheting behavior exhibited by the mix and also the evolution of the permanent strain with number of loading cycles is captured. The loading surface used in this model is based on Vermeer loading surface, which was used successfully for soils. A nonassociative flow rule for the plastic strains as well as an evolution equation for the hardening parameter is given. This model takes into account the anisotropy in the material and also isotropic damage based on effective stress theories is included in the model. Numerical implementation and algorithmic aspects of the multi- dimensional hyperelastic-viscoplastic-damage model are presented. A robust integration algorithm for the nonlinear differential equations is described; also the algorithmic (consistent) tangent moduli are derived. The model is implemented into the finite element environment ABAQUS to study boundary value problems. Triaxial and Repeated simple shear tests at constant height (RSST-CH) are studied as boundary value problems and results are compared to experiments. Finally, a section of the pavement is studied as a boundary value problem to asses the capability of the model to predict rutting in the pavement. Advisors/Committee Members: Panoskaltsis, Vassilis.

Keywords: ASPHALT; ASPHALT CONCRETE; Pavements; Viscoplastic

20. Petrou, Michael Frixos. Fatigue performance of AASHTO and Ontario design for non-composite reinforced concrete bridge decks.

Degree: PhD, Civil Engineering, 1993, Case Western Reserve University

► Tests were conducted under a concentrated static, stationary pulsating and moving constant… (more)

▼ Tests were conducted under a concentrated static, stationary pulsating and moving constant wheel-load on 1/3-scale (P-Series) and 1/6.6-scale (B-Series) physical models of concrete bridge decks of a simply supported non-composite 50-ft long bridge with an 8.5-in. thick concrete deck supported on four steel girders spaced at 7 and 10 ft. Three deck designs are studied: (a) AASHTO "orthotropic" steel reinforcement, (b) Ontario "isotropic" steel reinforcement, and (c) "isotropic" minimum steel reinforcement. The presence of membrane compressive forces (arching action) in the deck enhances its static ultimate strength. Static ultimate strength values for the decks, P u, up to about three times the Johansen load are measured. The predicted critical deflections at instability of a 2-D 3-hinge compressive strut model (snap-through mechanism) restrained at the pinned supports by a horizontal elastic spring, and subjected at the crown to a concentrated vertical load correlate well with the measured ultimate deck deflections. The type of applied fatigue loading has a profound influence on the fatigue behavior of the decks. Under a moving constant wheel-load, the initial two-way deck slab action changes to a one-way slab action as failure is approached. The bridge decks subjected to a stationary pulsating load exhibited a flexural radial cracking, while those under a moving constant wheel-load exhibited a flexural grid-like pattern similar to the grid of the bottom steel layer. For a given applied fatigue load level, the decks subjected to a stationary pulsating loading regime exhibited higher fatigue life than those subjected to a moving load. Based on an exponential curve fit of the fatigue data in this study (log P/P u vs. logN cf or logN pf), while the 2.5 × 106 load cycle fatigue strength of the deck models under a stationary pulsating load ranges between 0.47 and 0.54 P u (safety factor 5 ÷ 12), at 2.5 × 106 wheel-load passages under a moving wheel-load is estimated to be at 0.21 to 0.28 P u (safety factor 2 ÷ 4). The fatigue strength of the bridge decks under a moving constant wheel-load is in the same range as the cracking load level while the fatigue strength under a stationary pulsating load is similar to the yielding load level for the steel reinforcement. (Abstract shortened by UMI.) Advisors/Committee Members: Perdikaris, Philip C.

Subjects: Engineering, Civil

Keywords: Concrete bridge decks; Fatigue performance

21. POWERS, LYNN MARIE. Mechanical Behavior of Ceramics at High Temperatures: Constitutive Modeling and Numerical Implementation.

Degree: PhD, Civil Engineering, 2006, Case Western Reserve University

► High-temperature creep behavior of ceramics is characterized by nonlinear time-dependent responses, asymmetric… (more)

▼ High-temperature creep behavior of ceramics is characterized by nonlinear time-dependent responses, asymmetric behavior in tension and compression, temperature dependent, and nucleation and coalescence of voids leading to creep rupture. Moreover, creep rupture experiments show considerable scatter or randomness in fatigue lives of nominally equal specimens. Failure is caused by the nucleation and growth of voids at the grain boundaries. To capture the nonlinear, asymmetric, time-dependent behavior, the standard linear viscoelastic solid model is modified. Nonlinearity and asymmetry are introduced in the volumetric components by using a nonlinear function similar to a hyperbolic sine function but modified to model asymmetry. Temperature is accounted for in the model through temperature-dependent parameters. The nonlinear viscoelastic model is implemented in an ABAQUS user material subroutine. Damage is modeled using two scalar internal variables, one for the deviatoric component and the other for the volumetric component. Each damage internal variable is assumed to be governed by a nonlinear, first order ODE that is a function of stress and two parameters. Each element is assigned damage parameters sampled from a lognormal distribution. An element is deleted when damage is equal to one. Temporal increases in strains produce a sequential loss of elements (a model for void nucleation and growth), which in turn leads to failure. Nonlinear viscoelastic model parameters are determined from uniaxial tensile and compressive creep experiments on silicon nitride. The model is then used to predict the deformation of four-point bending and ball-on-ring specimens. Simulation is used to predict statistical moments of creep rupture lives. Numerical simulation results compare well with results of experiments of four-point bending specimens. A Voronoi simulation of a tensile creep test is used to study the effects of temperature, stress and damage and to evaluate model predictions. A preliminary simulation of a two-phase material is presented. Advisors/Committee Members: Panoskaltsis, Vassilis P.

Subjects: Engineering, Civil

Keywords: Nonlinear Viscoelasticity; Ceramics; Creep; Damage; Randomness

22. Riggenbach, Kane Ryan. Finite Geometry Correction Factors for the Stress Field and Stress Intensities at Transverse Fillet Welds.

Degree: MS, Civil Engineering, 2012, Case Western Reserve University

► This study presents the numerical development of corrections factors for finite geometry… (more)

Subjects: Civil Engineering; Mechanical Engineering

Keywords: Stress Intensity Factor; Correction Factors; Williams Eigenvalue Series; Finite Dimension; Transverse Attachment; Stiffener; Cover Plate

23. Romeo, Alberto. On a crack tip interacting with a bimaterial interface.

Degree: PhD, Civil Engineering, 1995, Case Western Reserve University

► Because of its relevance to fracture of composite materials, the problem of… (more)

▼ Because of its relevance to fracture of composite materials, the problem of calculating the stress field at the tip of a crack perpendicular to the perfectly bonded interface between two isotropic half-planes has been addressed by several authors. However, to date a sound propagation criterion for cracks terminating at a bimaterial interface has not been proposed. The main purpose of this work is to provide such propagation criterion in terms of the physical parameters that control the inelastic deformation near the crack tip (critical crack tip opening displacement, ηc, and yield stress, σo). The plane elastostatics analysis of a crack tip impinging on the interface is presented first. This fundamental problem is used as a reference configuration for the analysis of a crack tip very close to the interface. The stress intensity factor (s.i.f.) and crack opening displacement (COD) of a semi-infinite crack approaching or penetrating the interface are calculated by means of a singular integral equation formulation as functions of the distance of the crack tip to the interface, δ, the Dundurs parameters α and β, and the s.i.f., k, associated with the reference problem of the same crack touching the interface. The calculated universal results provide a powerful tool for the asymptotic analysis of the s.i.f. and COD of cracks of finite length 2l with one tip at a distance δll l from the interface. Results for a crack loaded by a uniform far-field tension in each half-plane show that as δ → 0 the s.i.f. approaches its limits (zero or infinity, depending on the relative stiffness of the bonded materials) at a relatively slow rate. The problem of a crack terminating at the interface between an elastic and a yielding material is addressed next. A first estimate of the location of the elastic-plastic boundary in the ductile component of the bimaterial system is obtained by means of the Von Mises yield criterion applied to the elastic asymptotic stress field. These results show qualitatively that the size of the yielded region is a strong function of the elastic mismatch. A cohesive crack model is then proposed, which provides a general propagation criterion for both small and large crack tip deformation in terms of the non-dimensional ratio ρ2/L, where the parameter ρ2 is proportional to the small scale yielding (SSY) critical cohesive zone length and L is a characteristic length of the problem. This criterion, which represents a generalization of the Dugdale-Barenblatt model for a homogeneous medium, is used to analyze the effective toughening resulting from the presence of the interface in selected material combinations. It is shown that the critical stress at incipient crack propagation does not change significantly for a relatively wide range of α-β and ρ2/L combinations Advisors/Committee Members: Ballarini, Roberto.

Subjects: Engineering, Civil

Keywords: Crack, tip; Bimaterial interface

24. Verma, Dhirendra. Stochastic modeling of fatigue crack growth.

Degree: PhD, Civil Engineering, 1990, Case Western Reserve University

► Fatigue of metals has been recognized as an important cause of failure… (more)

Subjects: Engineering, Civil

Keywords: Stochastic modeling fatigue crack growth

25. Yu, Xinbao. Experimental Study of an Innovative Bridge Scour Sensor.

Degree: PhD, Civil Engineering, 2009, Case Western Reserve University

► Scour is a major threat to the safety of bridges. Instruments for… (more)

Subjects: Civil engineering

Keywords: Bridge scour; Sensor; Time Domain Reflectometry (TDR); Turbulent flow; Sediment

26. Zalewski, Bartlomiej Franciszek. UNCERTAINTIES IN THE SOLUTIONS TO BOUNDARY ELEMENT METHOD: AN INTERVAL APPROACH.

Degree: PhD, Civil Engineering, 2008, Case Western Reserve University

► Interval boundary element method (IBEM) is developed allowing computation of the worst… (more)

Subjects: Civil engineering

Keywords: boundary element method, discretization error, interval boundary element method, error analysis, interval analysis

27. Zhang, Bin. FUSION OF SENSOR TECHNOLOGY AND MULTI-PHYSICS SIMULATION OF CEMENT HYDRATION KINETICS.

Degree: PhD, Civil Engineering, 2012, Case Western Reserve University

► This dissertation explored the development of several innovative guided radar technologies to… (more)

Subjects: Civil Engineering

28. Zhang, Fangmei. DISTRIBUTION OF METABOLIC CHARACTERISTICS AMONG AEROBIC SOIL BACTERIA AND IMPLICATIONS FOR BIOTRANSFORMATION OF ORGANIC AND METALLIC WASTES.

Degree: PhD, Civil Engineering, 2007, Case Western Reserve University

► Comingled organic and metallic pollutants challenge soil remediation efforts because of their… (more)

▼ Comingled organic and metallic pollutants challenge soil remediation efforts because of their distinct chemical and biological transformation behavior. Bioremediation of such wastes depends upon pollutant types, remediation endpoints, and microbial metabolism and habitat. This research examined relationships between habitat, cell physiology, and aerobic biotransformation of chromium and organics. It was hypothesized that the degree of soil attachment by culturable heterotrophic bacterial communities in the vadose zone correlates to chromium biosorption, reduction, and tolerance; cell surface properties; growth rate; and substrate affinity. Compared to weakly soil-associated communities, strongly-associated communities were expected to have slower growth and greater substrate affinity, hydrophobicity, and chromium tolerance. Community-level relationships were not expected to hold true at the population level, however. Instead, bacterial isolates were anticipated to exhibit cell surface properties and biotransformation behavior not necessarily linked to their original soil association or community. The research sought to identify the biotransformation potential of often-overlooked soil microorganisms and to assess their use in achieving low residual contaminant concentrations in comingled chromium wastes. Serial elution was used to extract two variably-attached bacterial communities from noncontaminated vadose zone soil. Five microbial isolates were cultured from these consortia. Consortia and isolates were characterized with respect to: 1. cell surface hydrophobicity and charge, using solvent-, resin-, and titration-based tests; 2. the rate and extent of growth on yeast extract and salicylic acid, a model organic pollutant; 3. chromium toxicity under variable substrate conditions; 4. chromium reduction, measured via x-ray spectroscopy; and 5. the kinetics and extent of chromium biosorption. As hypothesized, the easily-detached bacterial community (F1) was less hydrophobic than its counterpart (F3), but its isolates varied unpredictably in hydrophobicity. Furthermore, F1 exhibited faster Monod-type growth but lower affinity for yeast extract (µmax=0.35 1/hr, Ks=36.6 mg/L) than F3 (µmax=0.30 1/hr, Ks=12.2 mg/L), whereas its isolates showed growth variability. Salicylic acid generally produced non-Monod growth and increased apparent chromium toxicity. All isolates and consortia were able to sorb and reduce chromium, regardless of cell surface properties or original attachment. Chromium resistance was negatively correlated to substrate (yeast extract) affinity among isolates, positively correlated to the substrate affinity of consortia (as hypothesized), and independent of cell surface properties. Advisors/Committee Members: Skubal, Karen L.

Subjects: Engineering, Environmental

Keywords: biotransformation; co-contaminants; microbial habitat; bacterial attachment; bioremediation

29. Zou, Yunyi. FRP Reinforced Concrete and Its Application in Bridge Slab Design.

Degree: PhD, Civil Engineering, 2005, Case Western Reserve University

► For decades, bridge slabs have been troubled by the corrosion of steel… (more)

▼ For decades, bridge slabs have been troubled by the corrosion of steel reinforcements. The unique corrosion resistance of FRP (Fiber-Reinforced Polymers) bars makes them a promising alternative to steel bars. Because of the relatively low elastic modulus of FRP reinforcement, the post-cracking serviceability often is the controlling factor in the flexural design of FRP reinforced concrete. Since bridge deck slabs are under repeated traffic loads, it is the post-cracking serviceability under cyclic loads that becomes vital in the design and maintenance decision-making process. Experiments have been conducted to investigate the post-cracking flexural performance of FRP RC (reinforced concrete) under constant amplitude cyclic loading. Each specimen tested was a beam with a single FRP bar at the bottom. Two different types of FRP bars were used. The crack opening was monitored for specimens of different size. Up to 2 million cycles of cyclic loads have been applied at 100% service load levels. It has been found that there are two stages in the crack growth of FRP reinforced concrete. The first stage is early growth, which is characterized by increasing crack mouth opening displacement (CMOD). The second stage is the stabilization of CMOD and crack length. No fatigue failure was encountered in the testing under service loading and moderate overloads. The effects of moderate overload on observed crack growth were also investigated. The performances of two different FRP bars were compared. A model was proposed to predict long term crack growth in FRP R/C under cyclic loading, based on the Paris equation. Two FE (finite element) crack representations were examined. One was a debonded length representation. In this model it was assumed that there was a debonded length around each crack, within which there was no tangential interaction between concrete and reinforcement. Beyond the debonded length, the interface between concrete and reinforcement was tied with no relative movement. The other representation examined was a fictitious material crack representation. A fictitious material was placed in a triangular crack cross section, with a maximum width of 2.5mm (0.1 in). Then, the modulus of elasticity of the fictitious material was calibrated, based on the observed testing results, after crack growth had stabilized. Both representations have been used to analyze bridge slabs. Finally, an empirical slab design was discussed. Advisors/Committee Members: Huckelbridge, Arthur.

Subjects: Engineering, Civil

Keywords: FRP; reinforced concrete bridge slab; crack; crack growth; arching effect; bridge slab empirical design