Based on their connectivity, network glasses can be classified as flexible, stressed–rigid, or isostatic, if the number of topological constraints is lower, larger, or equal to the number of atomic degrees of freedom, respectively. Thanks to the absence of any stoichiometric requirement, the rigidity of glasses can be continuously tuned (e.g., from flexible to stressed–rigid) by changing their chemical composition. Interestingly, optimally-constrained isostatic glasses have been noted to exhibit unusual properties (e.g., nearly-reversible glass transition, low relaxation, desirable mechanical properties, etc.). Especially, the non-aging intermediate state features an almost vanished endotherm between the first and second heat scan across glass transition, providing a pathway for phase change material optimization in the application of non-volatile rewriteable media. However, the physical origin of the unusual behaviors and properties of isostatic glasses remain unclear.This thesis begins with investigating how the flexible-to-rigid transition in network glasses is encoded in their energy landscape based on molecular dynamics simulations. To this end, we introduce a simplified, yet realistic model of network glasses with varying connectivity. We characterize the topography of these glasses by adopting the activation-relaxation technique (ART), which enables a systematic search of saddle points and transition pathways in the energy landscape surface. We then demonstrate that the flexible-to-rigid transition arises from an interplay between low-energy saddle points (in flexible glasses) and topological frustration (in stressed–rigid glasses). Also, by utilizing the ring structure, we expand the transition correlation with ring size distribution. Meanwhile, we highlight the local heterogeneity with all the energy landscape features by dicing the model into small cubes. Comparing within a single glass helps exclude the effect of different configurations, further consolidating our conclusion on the physical origin of rigidity transition. Finally, to explore the role of chemistry effect in rigidity transition, we compare the behavior of the simple connectivity model with a realistic GexSe1-x model. With the similar shape of enthalpic differences, the realistic model could reveal the effect of glass-forming ability with experimental results where the simple model fails. Overall, we have a clear pathway towards understanding the physical origin of rigidity transition of GexSe1-x glass.

This dissertation addresses a wide spectrum of topics associated with resilience-based seismic evaluation and design of reinforced concrete structures. First, a comprehensive framework was developed enabling users to select, scale, and modify mainshock and aftershock ground motions (GMs) based on a set of different criteria. Various hazard-consistent target intensity measure metrics were utilized based on a set of conditioning criteria (IMi's). Then, a statistical approach was utilized to pull realization samples from a multivariate distribution of multiple intensity measures (IMi's) using both Monte-Carlo (MC) and Latin Hypercube Sampling (LHS) techniques. A comprehensive database of seismic records—namely, the PEER NGA-WEST2 database—was utilized to select those records whose IMi' s match the conditioning targets by assigning a different set of weights to different IMi's in a least-squares sense.

The effects of different GM selection strategies on a range of engineering demand parameters (EDPs) were investigated for a pair of 4-, 8- and 12-story ductile and non-ductile reinforced concrete (RC) buildings. In such studies, a very large number of nonlinear response history analyses (NRHAs) is unavoidable. Therefore, the analyses were performed using a parallel computing approach, which was specifically designed for the task at hand and carried out at the Texas Advanced Computing Center’s “Stampede2” supercomputer.

Another topic that was addressed in this dissertation has been the development of a novel framework to select earthquake records based on a spectral shape matching approach. The effects of different GM selection strategies based on a pre-existing spectral shape matching approach—namely, the response spectrum matching method—versus the newer approach developed in the present study was studied. The same ductile and non-ductile RC buildings mentioned above were utilized for this task and a variety of damage limit states (including the collapse) were used for comparison of fragility functions obtained using the two approaches.

Finally, an optimization framework was developed to reduce the effects of epistemic uncertainties associated with wide range of structural modeling parameters, on the probabilistic seismic responses of RC structures. To this end, a non-dominated sorting genetic algorithm (NSGA-II) was integrated with OpenSeesMP to determine optimal values of several design variables that minimize the median peak inter-story drift ratios (IDRs) at two different performance levels—namely, Immediate Occupancy (IO) and Collapse Prevention (CP)—simultaneously.

Seismic isolation systems are becoming more common in the construction of a variety of critical buildings/facilities, such as hospitals and data centers, that require more stringent seismic performance levels. The Triple Friction Pendulum (TFP) isolation bearing systems offer arguably the highest performance among seismic hazard mitigation devices/solutions. TFP bearings, which exhibit highly nonlinear and history-dependent responses, dissipate the seismic energy through friction. While there are numerous models available to simulate the cyclic responses of TFP bearings, most either lack several key features, such as coupled biaxial or triaxial reactions or account for these effects in a phenomenological manner. The present study tackles these issues by implementing a physics-based, extendable, and numerically robust model, which is packaged into a novel macroelement that can be used in nonlinear time-history analyses that are required for performance-based seismic assessment and design.

The aforementioned macroelement model is based on a mechanically consistent multi-surface plasticity approach that can simulate the triaxial hysteretic responses of TFP bearings. The macroelement model is developed and implemented in ABAQUS as a User-defined ELement (UEL). It is validated using experimental data from component-scale laboratory and full-scale shake table tests carried out at the E-Defense facility.

The experimentally validated biaxial and triaxial TFP models are then used in performance-based seismic assessment of a prototypical base-isolated braced frame building to examine the effects of modeling errors on the estimated seismic losses. While the scope of this case study was limited to one building, findings indicated that differences between the basic (i.e., uncoupled biaxial) and the more advanced (i.e., coupled biaxial and triaxial) approaches are non-negligible, warranting their use in practice as well as future studies.