Recognizing that soil-structure interaction affects appreciably the earthquake response of highway overcrossings, this paper compares approximate analytical solutions and finite element results to conclude on a simple procedure that allows for the estimation of the kinematic response functions and dynamic stiffnesses of approach embankments. It is shown that the shear-wedge model yields realistic estimates for the amplification functions of typical embankments and reveals the appropriate levels of dynamic strains which are subsequently used to estimate the stiffness and damping coefficients of embankments. The shear-wedge model is extended to a two-dimensional model in order to calculate the transverse static stiffness of an approach embankment loaded at one end. The formulation leads to a sound closed-form expression for the critical length, , that is the ratio of the transverse static stiffness of an approach embankment and the transverse static stiffness of a unit-width wedge. It is shown through two case studies that the transverse dynamic stiffness (“spring” and “dashpot”) of the approach embankment can be estimated with confidence by multiplying the dynamic stiffness of the unit-width wedge with the critical length, . The paper concludes that the values obtained for the transverse kinematic response function and dynamic stiffness can also be used with confidence to represent the longitudinal kinematic response function and dynamic stiffness respectively.

This paper examines the transient rocking response of anchored blocks subjected to physically realizable horizontal pulse-type motion. Restrainers with elastic-brittle and elastic-plastic behavior are considered. Under one-sine pulse anchored blocks can overturn with two distinct modes of overturning: (1) by exhibiting one impact; and (1) without exhibiting any impact. It is found that restrainers are more efficient in preventing overturning of small slender blocks subjected to low frequency pulses. The study uncovers that while for most of the frequency range anchored blocks survive higher accelerations than free-standing blocks, there is a finite frequency range where the opposite happens. The paper examines this counterintuitive behavior and explains the destructive effect that increased strength and increased ductility of restrainers have on the rocking stability of rigid structures when excited by certain ground motions. KEY WORDS: rocking, anchored, pulse-type motions, ductility.

This dissertation systematically addresses the modeling, quantifying, and protection of highway bridges against earthquake hazards. Firstly, the research substantially improves the p-y spring based simulation method to predict the seismic responses of highway bridges that accounts for various soil-structure interaction effects. Closed-form formulae are provided for the p-y spring input parameters to capture the bridge-embankment interaction effects, based on which an integrated step-by-step modeling procedure is developed. The procedure is applied to simulate the seismic responses of a well instrumented highway overcrossing and validated against the recorded responses during the 1992 Petrolia earthquake.

Secondly, the study derives a response modification factor to quantify the relative impact of liquefaction induced lateral spreading with respect to seismic shaking on column drifts for highway bridges. The column drift response under lateral spreading is correlated to the crust layer energy imposed on the pile foundation at bridge piers. Under seismic shaking, the column drift ratio is directly related to the peak ground acceleration. By normalizing the column drift under the lateral spreading to that of under the seismic shaking, the proposed modification factor captures key features of how columns respond under both lateral spreading and seismic shaking, and offers reliable column drift demand predictions.

Thirdly, this study investigates the effectiveness and optimal design of seismic protective devices for highway bridges. Component-level fragility functions are developed by using the probabilistic seismic demand analysis. To transparently quantify the bridge performance at the system level, seismic repair cost ratios are derived to combine damage probabilities, damage ratios and replacement costs of critical bridge components. Thereafter, a multi-objective genetic optimization method with the Pareto optimal concept is employed to identify the optimal design parameters of protective devices.

Subsequently, the research derives a consistent performance index to facilitate the performance-based design and optimization of seismic protective devices. By converting the system-level repair cost ratio to be a function of median-level engineering demand parameters, a uniform design surface is generated for various protection designs. The derived surface can be easily implemented in the performance-based seismic protection design and optimization without iteratively updating the design goal when a new group of design parameters are considered. The robustness of the proposed method is examined in a case study to identify the optimal protection designs by using a genetic optimization scheme.

Lastly, the study derives the seismic demand models for bridge rocking columns with foundation on rigid supports when subject to horizontal near-fault strong motions. The system equations of motion are derived and solved to incorporate the column flexibility and the rocking impact mechanism. By representing the near-fault ground motions with corresponding pulses, dimensional analyses are carried out to regress the closed-form expressions of system’s drift and uplift demands. A rigorous validation process is implemented to demonstrate that the proposed models can be used with confidence to predict the seismic demands of the rocking system directly from structural and ground motion characteristics.

This paper presents a systematic procedure for the seismic response analysis of highway overcrossings. The study employs an elementary stick model and a more sophisticated finite element formulation to compute response quantities. All dynamic stiffnesses of approach embankments and pile groups are approximated with frequency-independent springs and dashpots that have been established elsewhere. A real eigenvalue analysis confirms the one-to-one correspondence between modal characteristics obtained with the three-dimensional finite element solutions and the result of the simpler stick-model idealization. A complex eigenvalue analysis reveals modal damping values in the first six modes of interest and shows that realistic damping ratios assume values much higher than those used by Caltrans. The efficiency of the proposed method is validated by comparing the computed time response quantities with records from the Meloland Road and Painter Street overcrossings located in southern and northern California respectively. The proposed procedure allows for inexpensive parametric analysis that examines the importance of considering soil-structure interaction at the end abutments and center bent. Results and recommendations presented by past investigations are revisited and integrated in comprehensive tables that improve our understanding on the dynamic characteristics and behavior of freeway overcrossings. The study concludes with a step-by-step methodology that allows for a simple, yet dependable dynamic analysis of freeway overcrossings, that involves a stick model and frequency-independent springs and dashpots.

This paper examines in depth the transient rocking response of free-standing rigid blocks subjected to physically realizable trigonometric pulses. First, the expressions for the dynamic horizontal and vertical reactions at the pivot point of a rocking block are derived and it is shown that the coefficient of friction needed to sustain pure rocking motion is in general an increasing function of the acceleration level of the pulse. Subsequently, the paper shows that under cycloidal pulses a free-standing block can overturn with two distinct modes: (1) by exhibiting one or more impacts; and (2) without exhibiting any impact. The existence of the second mode results to a safe region that is located on the acceleration-frequency plane above the minimum overturning acceleration spectrum. The shape of this region depends on the coefficient of restitution and is sensitive to the nonlinear nature of the problem. The paper concludes that the sensitive nonlinear nature of the problem in association with the presence of the safe region that embraces the minimum overturning acceleration spectrum complicates further the task of estimating peak ground acceleration by only examining the geometry of free-standing objects that either overturned or survived a ground shaking.

This paper investigates the dynamic response of shallow foundations on linear and nonlinear soil medium using finite element method. The study was motivated by the need to develop macroscopic foundation models that can realistically capture the nonlinear behavior and energy dissipation mechanism of shallow foundations. An infinitely long strip foundation resting on soil half-space is analyzed in depth to evaluate the dependence of its dynamic responses on various parameters, e.g. foundation width, material properties, input motion amplitude and frequency etc. Special attentions are paid to choose appropriate domain scale, mesh size and boundary conditions so as to minimize the often observed numerical oscillations when the outgoing waves are contaminated by the reflecting waves at boundaries. Such judicious choice results in an excellent agreement between the finite element analysis and the analytical solution of strip foundation on linear soil half-space. Closed-form formulas are developed to describe the frequency-dependent linear dynamic stiffness of strip foundation along both horizontal and vertical directions. Various nonlinear constitutive models of soil, which exhibit the yielding and kinematic hardening behavior of soil, are implemented in this study to evaluate the dynamic stiffness of strip foundation sitting on nonlinear soil medium. The finite element analyses reveal the strong dependency of response on input motion amplitude, frequency and yielding of soil. A nonlinearity indicator is developed to incorporate the combined effects of initial elastic stiffness, yielding stress and excitation amplitude. The numerical analyses presented here provide improved understanding on the nonlinear behavior and energy dissipation mechanism of shallow foundations under dynamic loads.

Recent earthquake disasters have demonstrated the seismic vulnerability of highway bridge systems. Rapid seismic assessment of regional highway bridges is critical to help reduce severe loss of life and property. However, measurement of the regional scale system performance faces the challenge of dealing with the large uncertainty in structural properties and spatial characteristics. Traditionally, the numerical modeling approaches are established to simulate nonlinear response for each highway bridge across a regional portfolio. This process is largely limited by accuracy of model and computational effort. Especially some key structural component parameters are almost impossible to be retrieved for some ancient bridges. An alternative data-driven framework is developed to predict seismic responses or damage level of bridges using machine learning techniques. The proposed hierarchically structured framework enables a customized application in different scenarios. Firstly, the typical modeling technique for reinforcement concrete highway bridges is introduced using specific elements for different components. However, the modeling procedures are material-level parameter dependent and time consuming. The nonlinear analysis convergence is also a frustrating problem for numerical simulations. Due to these realistic limitations, a simple, fast and robust numerical model which can be developed with only component-level information needs to be adopted. It’s shown that the bridge bent representation can be simplified as a single degree of freedom system. The force-displacement relationship of the bridge can be roughly approximated by a bilinear curve. So a simplified 2D bilinear model is adopted for highway bridges throughout the study. Secondly, the statistical distributions for selected bridge input parameters can be derived based on the regional bridge inventory. Then an iterative process by sampling and filtering input parameters can be used to generate as many bridges as possible candidates for a specific region. The proposed bridge models and selected historical ground motions will be utilized to develop a seismic response prediction model using machine learning for instrumented highway bridges. This study investigates the optimal features to represent the highway bridge and ground motion. Different regression models are applied for near-fault motions and far-field motions and similar performance can be achieved, which significantly outperformed the traditional methods. Finally, to predict the seismic response of the non-instrumented highway bridges whose ground motion information is missing, the kriging interpolation model is implemented first. Then graph network is exploited to improve the performance. Different rules are evaluated for constructing an undirected graph for the highway bridges in an active seismic region. Subsequently, the Node2vec model is conducted to extract the embedding for each node and a graph neural network is implemented to predict the seismic response. Furthermore, vast amounts of text description data from online social platforms can be used to help detect the potential severely damaged bridges rapidly once an earthquake happens. A Convolution Neural Network classification model is implemented to evaluate the overall damage level distribution based on the collected text data. GloVe model is used to generate the word vector as its distributed representation.

To understand the baseline performance of lithium (Li) anode in liquid electrolytes, the electrochemical and physical properties of Li anode are studied with realistic parameters including: thin thickness (50 µm), practical areal capacity (1 to 4 mAh cm-2), practical areal current (0.5 to 2 mA cm-2), and low electrolyte/capacity ratio. Two different Li salts, lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI), are used to probe the effects of the electrolyte chemistry and concentration. The cycling of Li/Li symmetric cells, combined with investigation using the scanning electron microscope, demonstrates that the soft-short of Li/Li cells is induced by the continuous volume expansion of Li electrodes during cycling instead of dendrites. The volume change of a Li electrode is dictated by the depth of deposition and stripping (i.e., areal capacity) and the electrolyte/capacity ratio, with no strong correlation with the type of Li salt and concentration. On the other hand, the average coulombic efficiency (CE) measurement demonstrates inherent correlation with the type of Li salt and its concentration in the electrolyte. Li electrode surface chemical analysis indicates that the fluoride-rich surface layer formed in the LiPF6 electrolyte can be detrimental to both CE and Li deposition-stripping overpotential.We report acrylonitrile (AN) as an effective additive in carbonate-based electrolytes to enable uniform and dense lithium (Li) deposition and to improve the coulombic efficiency of Li metal anode. Our electrochemical, spectroscopic, and theoretical study reveal that AN is cathodically electropolymerized on the Li surface prior to the electrochemical decomposition of the electrolyte during Li deposition. The resultant polyacrylonitrile artificial solid electrolyte interphase enables uniform nucleation and growth of Li deposition with significantly reduced side reactions. The effectiveness of the AN additive is demonstrated in 0.4 Ah Li||LiNi0.6Mn0.2Co0.2O2 pouch cells (using 50-μm Li anode, 3 mAh cm-2 cathode areal capacity, and 4g Ah-1 electrolyte) with excellent cycle stability under realistic charge-discharge condition. The hydrofluoric acid (HF) based side reaction in lithium (Li) hexafluorophosphate (LiPF6) electrolyte system hindered the direct application of LiPF6 electrolyte (in organic carbonate solvents) for Li metal batteries. In this study, we report phosphorus pentoxide (P2O5) as an effective additive in LiPF6 based electrolyte not only enable uniform and dense Li deposition but also mitigate the transition metal (TM) dissolution and cracking problems of LiNi0.6Mn0.2Co0.2O2 (NMC622) particle. The poor Li metal deposition behavior and the increasingly growth of cathode impendence caused the poor cycle life of the Li||NMC622 pouch cell in 1M LiPF6 electrolyte. The cycle life of the pouch cell in 1M LiPF6 electrolyte with P2O5 additive was greatly enhanced from 30 cycles to more than 230 cycles, with the capacity retention: 87.7% (230 cycles).

The paper evaluates the radiation damping associated with shallow foundations sitting on linear or nonlinear soil medium. The study was motivated by the need to develop macroscopic foundation models that can realistically capture the nonlinear behaviour and energy dissipation mechanism of shallow foundations. Such model is essential to simulate the complex behaviour of structure components (e.g. shear walls, columns etc.) sitting on flexible foundations due to soil-structure interaction effects. In this study, the dynamic response of an infinitely long strip foundation resting on an elastic and inelastic half-space is investigated. The numerical analysis results presented here reveal that dynamic responses of shallow foundations strongly depend on amplitude and frequency of the input motion. In particular, the radiation damping of the system is affected by soil nonlinearity, foundation geometry and excitation frequency. The yielding of soil reduces the energy dissipation through the out going waves. As a result, the radiation damping of nonlinear soil medium is significantly lower than the elastic soil counterpart. The effects of initial elastic stiffness, yielding stress and excitation amplitude are incorporated in a nonlinearity indicator, which has shown strong correspondence to the radiation damping of the system.