Ph.D. - Civil and Environmental Engineering

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    A Statistical Dynamic Modulus Model of Hot Mix Asphalt Using Joint Estimation and Mixed-Effects Accounting for Effects of Confinement, Moisture and Additives
    ([Honolulu] : [University of Hawaii at Manoa], [December 2016], 2016-12) Corrales, Jose
    With the implementation of mechanistic-empirical pavement design methods, dynamic modulus (|E*|) has become the predominant characteristic of Hot Mix Asphalt (HMA) used as the elastic modulus in the computation of stresses and strains in pavement structures. The predictions of |E*| obtained with the Witczak models currently used in the Mechanistic Empirical Pavement Design Guide (MEPDG) do not account for some HMA characteristics such as polymer modified binders, fibers, confinement and aging effects related to climatic conditions. Therefore, development of models more representative of local materials and conditions are desirable. In this study, a predictive model for dynamic modulus of HMA was developed taking into consideration several HMA characteristics and testing conditions. 6821 observations of 257 mix specimens from three different laboratory datasets, two from Hawaii and one from Costa Rica, were used to estimate the model parameters. All three data sets contain information about some variables in common such as air voids, binder content, and gradation; however, some datasets contain mix characteristics and testing conditions not available in other datasets such as confinement level, available only in the Hawaiian datasets, and the number of freeze-thaw cycles, available only in the Costa Rican dataset. Important characteristics observed from these datasets include confinement, number of freeze-thaw cycles, binder modifiers (SBS polymers) and mixture additives (e.g. fibers and anti-stripping agents), all of which together with other commonly used variables were found to have statistically significant effects. The model was developed by using joint estimation and mixed-effects techniques. Joint estimation allowed the identification of model parameters available from only some of the databases and the determination of bias parameters. It also resulted in more efficient parameter estimates. The mixed-effects approach was used to account for unobserved heterogeneities between samples. Using these approaches, together with proper consideration of heteroscedasticity, allowed the estimation of a comprehensive statistical predictive model that satisfies closely all the regression assumptions and that provides accurate values of |E*| for Hawaiian and Costa Rican conditions for any combination of temperature and frequency. These can be used to generate the |E*| inputs that the MEPDG needs to compute |E*| master curves.
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    Harvesting Energy from Ambient Vibrations
    ([Honolulu] : [University of Hawaii at Manoa], [August 2016], 2016-08) Zhang, Hui
    In vibratory energy harvesting, the energy flow generally goes through three stages: the external vibration energy is firstly coupled into the device as kinetic energy, which is partially converted to electricity through electromechanical conversion unit (such as electromagnetic, piezoelectric, and electrostatic), then the generated electricity is applied to the electrical load circuit. The process of such energy flow indicates that the energy coupled in the first stage determines the maximum available energy converted to electricity, while the electricity delivered to the load depends on the characteristics of electrical load circuits. Note that the first stage for coupling energy is achieved by device dynamics. To best understand vibratory energy harvesting, the effects of device dynamics and electrical load circuits on energy harvesting performance are investigated in this dissertation. For the effects of device dynamics, we do the study from four areas: parametric oscillator/device, global resonance, the roles of excitation, and dynamics outside the potential well. At first, we investigate the potential of using a nonlinear parametric oscillator/device to harvest energy. In such device, the excitation appears as a parameter of the dynamical system. Such parameterization of the excitation provides a cross-frequency energy transfer in the excitation, resulting in modifying the frequency content of the excitation, i.e. modulation of the excitation, which enables the device into the orbits of higher-order subharmonic oscillations more easily. A device with a pendulum-type architecture is proposed and used as an illustrative example. The further investigation in device dynamics has proved that for a nonlinear device, there exists a generalized, global resonance condition which requires matching of all of the frequencies between the device and the excitation. Under global resonance, the device performance is optimized with the maximum energy harvesting efficiency, but its corresponding displacement is not the largest because the amplitude of global resonance response is strongly correlated with the fundamental frequency supported by a nonlinear potential well (e.g. potential function). Such results suggest that traditionally relying only on increasing the device response in nonlinear systems can be misleading. The global resonance condition also shows that damping of the device and modulation of the excitation play critical roles in facilitating the frequency match required for resonance. According to the global resonance condition, it is revealed that the potential of nonlinear device in harvesting energy from multi-frequency vibrations benefits from multiple frequency match, not from the wider bandwidth obtained from single-frequency response. To harvest energy from multi-frequency vibration using non- linear devices, a device-design concept based on global resonance is thus proposed. When the global resonance condition is satisfied, the instantaneous power of the excitation is always non-negative, resulting in the maximum device performance. Conversely, when the condition is not satisfied, the excitation does negative work for a duration per cycle, leading to the reduction of the energy harvested. During such duration, the excitation actually takes energy back from the device, acting as a sink. The extent to which the excitation behaves as a sink determines the energy harvesting performance. We find that instantaneously changing device response to ensure the velocity in phase with the excitation can reduce the behavior of the excitation as a sink, resulting in dramatic increase of the energy harvested. Based on our findings, it has shown that an active method based on manipulating the roles of excitation would be more promising in bringing vibration energy harvesting to fruition. Although the responses of a device are usually constrained by its potential well, it is possible for the dynamics of a pendulum-type device to escape from the potential well. Here, we also investigated the possibility of utilizing the dynamics outside the potential well of a device for harvesting energy from vibrations. A pendulum-type device is used as an example. Results show that when the device dynamics is outside the potential well and stays in stable orbits of period-one rotations, the harvested energy is proportional to the energy level of the orbit, neither depending on the natural frequency of the device nor on the intensity of the excitation. For the effects of electrical load circuits, we consider three types of non-resistive loads, such as a resistive load with a rectifier, a resistive load with a rectifier and a regulating capacitor, and a simple charging circuit consisting of a rectifier and a storing capacitor. Numerical results suggest that when the harvested energy is to be stored in capacitors, the ultimate voltages across capacitors are the same as the open- circuit voltage of the device minus the rectifier drop. For charging loads, therefore, the amount of stored energy is determined by the capacitance and the device performance under open circuit. Moreover, a larger capacitor is beneficial for an electromagnetic harvester, but not for a piezoelectrical harvester.
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    HCM Analysis of the Potential Impacts of Driverless Vehicles on the Quality of Flow of Freeways and Intersections
    ([Honolulu] : [University of Hawaii at Manoa], [May 2016], 2016-05) Shi, Liang
    Autonomous or self-driving vehicles, popularly called “driverless cars” (DLC), are capable of navigating themselves through freeways and intersections without any human intervention. It is believed that DLC can bring about tremendous changes to our daily life, including safety, traffic efficiency, environment and community. By 2020 various companies will release their DLC models designed with different levels of automation. Traffic will be mixed with vehicles driven by human drivers and DLC, which cause uncertainties in the magnitude of impacts of DLC and their traffic shares. The Highway Capacity Manual (HCM) was modified to analyze the future impact of DLC on traffic flow operations. A review of the HCM parameters that might be directly affected by DLC is presented in this study. These parameters were modified to include the features of DLC: the technical capability which is quantified by the car-following headway of DLC, and the proportion of DLC in the traffic stream. Case studies were conducted to estimate the effects of DLC on the quality of traffic flow on a basic freeway segment, freeway weaving segment, signalized intersection, all-way stop-controlled intersection and roundabouts. For each case study, a sensitivity analysis was provided to evaluate the potential impacts of DLC with different technological capabilities under various traffic demands and proportions. The results from all case studies reflect the commonality of DLC impacts. DLC are able to maintain constant speed at a shorter car-following distance, which can smooth the traffic flow. For DLC that are connected with infrastructure and other DLC, the car-following distance will become shorter. With more connectivity built between DLC and infrastructure, the road space and delay will be saved by platooning. If in the future all vehicles are driverless cars, capacity of the road will be doubled or tripled. This means every road lane is capable of serving twice as many vehicles at no cost to the city. But if in the future there is only 1% of DLC in traffic, traffic flow will not improve. If the portion of DLC reaches 5%, congestion will improve by 5% if they are regular DLC, or by 12% if they are connected DLC. In the latter scenario, traffic flow can begin to improve in a noticeable way. However, if DLC are designed to drive conservatively, they will cause more delays than humans do.
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    Evaluation of the SRICOS-EFA Method for Predicting Scour in Hawaiian Rivers
    ([Honolulu] : [University of Hawaii at Manoa], [May 2016], 2016-05) Rahimnejad, Reza
    Nearly 60% of bridge failures in the country are due to scour. The Hawai‘i Department of Transportation (HDOT) has a vested interest in the integrity of bridges and their foundations during heavy floods. It is known that many of the older existing bridges in Hawai‘i were not designed for scour. Therefore, it is critical to have an accurate assessment of their scour potential. In addition, it is also critical to obtain accurate scour predictions when designing new bridges. An underestimate of the scour depth could lead to potential risk of bridge failure while an overestimate can increase the cost of the new bridge construction unnecessarily. In Hawai‘i, scour calculations are traditionally performed based on the Richardson and Davis equation (1995) where the only soil parameter required is the mean particle size, D50. Using this method for cohesive soils is known to lead to overestimated scour depths since the scour depth is inversely proportional to D50, and cohesive soils have very small particle size. Inter-particle electrical forces exist in cohesive soils which cause cohesive soils to erode slower than granular soils. The SRICOS (Scour Rate In COhesive Soils) method accounts for the time-dependent nature of scour in silts and clays. It requires erodibility testing on soil samples using an Erosion Function Apparatus (EFA) and will generally result in smaller scour depths that can lead to savings in bridge construction. The main objectives of this research were to: (1) Obtain undisturbed soil samples from 5 water channels on the island of Oahu to perform EFA and soil testing; (2) Propose a method to define the critical shear stress and evaluate factors affecting its magnitude; (3) Develop a model to predict an EFA curve for a cohesive soil in Hawai‘i based on some common soil parameters; and (4) Examine the applicability of the Pocket Erodometer Test (PET) to Hawai‘ian cohesive soils. The main contributions from this research are summarized as follows: A cohesive soil was reconstituted in the laboratory under 4 different consolidation pressures resulting in 4 different water contents, void ratios, unit weights and consolidation stresses and then tested using the EFA. It was found that the critical shear stress increased with decreasing water content, decreasing void ratio, increasing unit weight and increasing consolidation stress. That the soils can be considered normally consolidated also suggests that the critical shear stress increases with undrained shear strength. The mathematical properties of the EFA curves for 33 cohesive soil samples were studied. Based on these curves, it was found that by plotting the log of the shear stress versus the scour rate, the curves approximate a hyperbola very closely. It is also proposed that the critical shear stress be estimated as the intercept of the hyperbola on the shear stress axis with some constraints. A model was developed to predict an EFA curve using common soil parameters and the hyperbolic model. Three parameters are needed to fully define this hyperbola. Four explanatory variables (soil parameters) are required to define the three hyperbolic model parameters. They include water content, liquid limit, plasticity index and activity, all of which are easily measured in the laboratory. Use of this model in the SRICOS EFA method to estimate scour depth can result in less scour and in significant foundation cost savings. Scour depths at five water channel sites were estimated using HEC-18 and the SRICOS EFA method. It was found that the SRICOS method always resulted in lower scour depths than HEC-18. The PET was used to derive the erosion categories for 33 cohesive soil samples from the five water channel locations and then compared to those from the EFA. It was found that the current PET erosion criterion that separates the medium and high erodibility categories should be increased from 15 to 28 mm to increase the reliability of the method. With this revised criterion, the reliability of the PET for Hawai‘i soils and for soils that were used to develop this criterion improved. It was also found that Briaud et al.’s (2012) erodibility criteria based on soil classification is not very reliable.
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    Implementation of Structural Health Monitoring System to Indirectly Recover Building and Bridge Displacements
    ([Honolulu] : [University of Hawaii at Manoa], [May 2016], 2016-05) Bell, Michael
    An internal model based method is used to estimate the structural displacements under ambient excitation using only acceleration measurements. Strain measurements are incorporated to expand the method to single span concrete bridges subjected to moving vehicle loads. The structural response is assumed to remain the linear range for the duration of the loading. The excitation is assumed to be with zero mean and relatively broad bandwidth such that at least one of the fundamental modes of the structure is excited and dominates in the response. Using the structural modal parameters and partial knowledge of the load, their respective internal models can be established. These internal models can then be used to form an autonomous state-space representation of the system. It is shown that structural displacements, velocities, and accelerations are the states of such a system, and it is fully observable when the measured output contains structural accelerations only. Reliable estimates of structural displacements are obtained using the standard Kalman filtering technique. These displacement estimates can be used to determine the moment demand and provide insight into whether this demand is exceeding the capacity of the bridge. The effectiveness and robustness of the proposed method has been demonstrated and evaluated via numerical simulations of an eight-story lumped mass model along with a simply supported single span concrete bridge subjected to a moving traffic load. Experimental data of a three-story frame excited by ground accelerations from an actual earthquake record is also used. Lastly, field data from an inverted arch concrete bridge is analyzed as proof of concept for deployment of a structural health monitoring system for the purpose of displacement estimations.