From past research post-tensioned concrete masonry walls have performed well due to in-plane loading, yet despite the advantage of being more aesthetically pleasing, post-tensioned clay brick masonry walls have not been investigated under this loading. Five half scale structural specimens using this system were constructed and tested, and the results from these tests plus a proposed force-displacement analysis procedure are included herein. The results show that post-tensioned clay brick masonry walls are well suited for seismic regions when the walls are grouted and unbonded, and the presence of confinement plates in the compression region greatly enhances the overall performance of the wall. In addition, the force-displacement analysis shows that in order to account for the overall behavior of the wall, cyclic degradation characteristics must be included.

Fatigue performance modeling is one the major topics in asphalt concrete modeling work. Currently the only standard fatigue test available for asphalt concrete mixtures is the flexural bending fatigue test, AASHTO T-321. There are several issues associated with flexural fatigue testing, the most important of which are the stress state is not uniform but varies over the depth of the specimen and equipment for fabricating beam specimens is not widely available. Viscoelastic continuum damage (VECD) fatigue testing is a promising alternative to flexural fatigue testing. Different researchers have successfully applied the VECD model to asphalt concrete mixtures using constant crosshead rate direct tension test. However, due to the load level limitation of the new coming Asphalt Mixture Performance Tester (AMPT) testing equipment, there is an immediate need to develop a model that can characterize fatigue performance quickly using cyclic test data. In this study, a simplified viscoelastic continuum damage model developed at NCSU is applied to various North Carolina mixtures, which are used in the NCDOT HWY-2007-7 MEPDG local calibration project. It is shown that the simplified VECD model can predict fatigue tests fairly accurately under various temperature conditions and strain levels. It is also shown that the model can be further utilized to simulate both the strain controlled direct tension fatigue test and the traditional beam fatigue test. In this thesis, simulation results are presented. Conclusions regarding the applicability of the new model are advanced as well as suggestions for further work.

This research documents the findings from the study of failure mechanisms of fatigue cracking in asphalt pavements using the finite element program that employs the viscoelastic continuum damage model for asphalt layer and a nonlinear elastic model for unbound layers. Both bottom-up and top-down cracks are investigated by taking several important variables into account, such as asphalt layer thickness, layer stiffnesses, pressure distribution under loading, and load levels applied on the pavement surface. The crack initiations in different pavement structures under different loading conditions are studied by monitoring a damage contour. The developed finite element code, called VECD-FEP++, employs the viscoelastic continuum damage model as the constitutive model of asphalt concrete and the universal model (or so-called Uzan-Witczak resilient modulus model) for unbound materials. The finite element analysis of various pavement-load combinations showed significantly different failure mechanisms. Details on the VECD-FEP++ and the findings are given in the following chapters.

This thesis focuses on the behavior of clay masonry walls subjected to cyclic racking loading. It proposes that the seismic performance of clay masonry walls can be substantially improved if the section is adequately confined in the extreme compression zone at the toe of the wall to delay crushing of the masonry unit. This is accomplished by placing a 3.2mm thick galvanized steel plate in the mortar joint, of successive courses, in the plastic hinge region of the wall. The objective is investigated by conducting seven tests on full-scale clay masonry walls with various longitudinal and confining reinforcing ratios under seismic excitation. The results presented in this thesis show that adequately confining the grout of the clay masonry walls in the plastic hinge region may lead to substantially favorable seismic performance.

The bond performance of a unique type of reinforcing steel rebars, claimed to have high corrosion resistance as well as high tensile strength, with concrete was studied. The objective was to investigate the bond behavior of straight rebars made out of this steel, named MMFX, embedded in concrete flexural members and to examine the applicability of the current expressions for bond force to predict the bond capacity of the MMFX bars embedded in concrete. Two phases of experimental investigation was conducted. In the first phase, four beam end specimens were tested and in the second phase eight splice beams were studied. The bond behavior of the MMFX steel bars was found to be similar to that of carbon steel. The bond strength of the MMFX is significantly reduced as the tensile stresses developed in the bar went beyond the proportional limit. Both the ACI code 318-02 equation for bond force and the current equation proposed by the ACI committee 408 for bond force gave conservative prediction for bond force for low stress levels. However, at high stress levels, the prediction of the two equations went to the unconservative side. The non linear behavior of the MMFX stress-strain curve was the reason behind the unconservative prediction. The above two equations were modified to ensure conservative prediction at high stress levels. A second degree best fitting curve was found to be the best to describe the relationship between the splice length and the bond force capacity for both # 6 and # 8 MMFX bars.

The need to extend the applicability of the AASHTO LRFD Bridge Design Specifications to high-strength concrete is being addressed by a series of projects being sponsored by the National Cooperative Highway Research Program (NCHRP). Among these projects, NCHRP Project 12-64 is being carried out at North Carolina State University (NCSU) to expand the use of the design specifications to 18,000 psi (124 MPa) for reinforced and prestressed concrete members in flexure and compression. As a part of this project, specimens were tested to determine the material properties of three high-strength concrete mixtures having target compressive strengths of 10,000, 14,000, and 18,000 psi (69, 97, and 124 MPa). The effects of various curing methods were also studied. This study covers the compressive strength, elastic modulus, Poisson?s ratio, and modulus of rupture of high-strength concrete. The study showed that extended curing beyond 7 days resulted in little or no increase in compressive strength. For predicting the elastic modulus of high-strength concrete, the ACI 318-02 or AASHTO-LRFD equation over-estimates the actual modulus while the ACI 363R-92 equation adequately predicts the measured value. The modulus of rupture equation in ACI 318-02 or AASHTO-LRFD gives a good approximation of the modulus of rupture of high-strength concrete when 1-day heat curing and 7-day moist curing are used. The equation from ACI 363R-92 gives a good estimate of modulus of rupture values for continually moist-cured specimens. The Poisson?s ratio of high-strength concrete is generally within the range of that reported for normal-strength concrete.

The objective of the research presented is to develop an accurate and advanced material characterization procedure to be incorporated in the Superpave performance models system. The procedure includes the theoretical models and its supporting experimental testing protocols necessary for predicting responses of asphalt mixtures subjected to tension loading. The model encompasses the elastic, viscoelastic, plastic and viscoplastic components of asphalt concrete behavior. Addressed are the major factors affecting asphalt concrete response such as: rate of loading, temperature, stress state in addition to damage and healing. Modeling strategy is based on modeling strain components separately and then adding the resulting models to attain a final integrated ViscoElastoPlastic model. Viscoelastic response, including elastic component, is modeled based on Schapery?s continuum damage theory comprising of an elastic-viscoelastic correspondence principle and work potential theory. As for the viscoplastic response, which includes the plastic component, its characterization stems from Uzan?s strain hardening model. The testing program required for developing the models consists of complex modulus testing for determination of material response functions, constant crosshead rate testing at low temperatures for viscoelastic modeling, and repetitive creep and recovery testing for viscoplastic modeling. The developed model is successful in predicting responses up to localization when microcracks start to coalesce. After that, fracture process zone strains detected using Digital Image Correlation are used to extend the model?s ability in predicting responses in the post-localization stage. However, once major macrocracks develop, the currently developed model ceases to accurately predict responses. At that state, the theory of fracture mechanics needs to be integrated with the current continuum damage-based model.

Problems in fields ranging from geomechanics to biomechanics require response of saturated porous media subjected to dynamic loading. An engineering problem requiring the true behavior of saturated porous medium should consider the coupling of both fluid and solid phases yielding the simultaneous analysis of flow of pore fluid and deformation of solid skeleton. Depending on the nature of loading vis-à-vis the characteristics of the media, different formulations; fully-dynamic (FD), partially-dynamic (PD), quasi-static (QS) are possible. In this study, analytical solutions and numerical models are developed for the response of plane strain saturated porous media, and wave-induced response of seabed in free field and around a breakwater under pulsating/breaking waves. For each formulation, the results are presented with pore-pressure, shear and normal stress distributions within porous medium. The response is studied for various conditions and regions of applicability of formulations are identified in non-dimensional and actual parametric spaces. This can be used for a specific case with known loading and medium characteristics and may help engineers identify the necessary formulation to be used in a given problem. Effect of seabed-wave parameters and inertial terms on standing/breaking wave-induced pulsating/impact response of seabed-caisson system were investigated. The selection of the adequate formulation is decided depending upon the response variable and ranges of physical parameters. While FD formulation yields the minimum response in cyclic wave, for impacting wave it yields variable distributions in between the other two formulations. The areas of instantaneous liquefaction were identified inside the domain through contours of mean effective stress for both types of waves. Liquefied regions are concentrated at the front toe of rubble under cyclic wave which can initiate a vertical-horizontal movement and rotation towards the seabed causing structural failure. Liquefied areas in case of breaking waves are much larger compared to cyclic waves. Additional analyses made introducing a constitutive model for the inelastic behavior of soil to evaluate the nonlinear dynamic response of seabed reveal the importance of the inclusion of material nonlinearity effects.

Simulation models are important tools for managing water resources systems. An optimization method coupled with a simulation model can be used to identify effective decisions to efficiently manage a system. The value of a model in decision-making is degraded when that model is not able to accurately predict system response for new management decisions. Typically, calibration is used to improve the predictability of models to match more closely the system observations. Calibration is limited as it can only correct parameter error in a model. Models may also contain structural errors that arise from mis-specification of model equations. This research develops and presents a new model error correction procedure (MECP) to improve the predictive capabilities of a simulation model. MECP is able to simultaneously correct parameter error and structural error through the identification of suitable parameter values and a function to correct misspecifications in model equations. An evolutionary computation (EC)-based implementation of MECP builds upon and extends existing evolutionary algorithms to simultaneously conduct numeric and symbolic searches for the parameter values and the function, respectively. Non-uniqueness is an inherent issue in such system identification problems. One approach for addressing non-uniqueness is through the generation of a set of alternative solutions. EC-based techniques to generate alternative solutions for numeric and symbolic search problems are not readily available. New EC-based methods to generate alternatives for numeric and symbolic search problems are developed and investigated in this research. The alternatives generation procedures are then coupled with the model error correction procedure to improve the predictive capability of simulation models and to address the non-uniqueness issue. The methods developed in this research are tested and demonstrated for an array of illustrative applications.

Upstream piping configuration has been known to impact the UV reactor validation using biodosimetry tests. However, the influence of upstream configuration on the UV dose distribution has not been experimentally investigated. This research was performed to evaluate the UV reactor dose distribution under multiple upstream configurations using UV sensitive fluorescent microspheres. The upstream hydraulics configurations included two kinds of 90- degree bends and one straight pipe configuration. Experimental tests were performed at 51 gpm flow rate, 91% UV transmittance (UVT) on a single lamp low-pressure high-output (LPHO) UV reactor. The UV irradiation kinetics of the photo-chemically active fluorescent microspheres was performed with bench-scale collimated beam experiments. The correlation with microspheres fluorescence intensity distribution to UV fluence distribution was achieved by a statistical process involving Bayesian and Markov chain Monte Carlo integration technique. The results of this study showed that the straight pipe configuration produced a shift in UV fluence distribution to a higher UV fluence range compared to the two elbow configurations. No significant difference was formed between the two elbow configurations. The fluorescent microspheres Bayesian method can serve as an additional test to the traditional biodosimetry for UV reactor validation by providing sensitivity in detecting design parameter change and added confidence in the results by providing unbiased UV dose behavior.