published_or_final_version / abstract / Civil Engineering / Doctoral / Doctor of Philosophy

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While site effects are accounted for in most modern U.S. seismic design codes for building structures, there exist no standardized procedures for the computationally efficient integration of nonlinear ground response analyses in broadband ground motion simulations. In turn, the lack of a unified methodology affects the prediction accuracy of site-specific ground motion intensity measures, the evaluation of site amplification factors when broadband simulations are used for the development of hybrid attenuation relations and the estimation of inelastic structural performance when strong motion records are used as input in aseismic structural design procedures. In this study, a set of criteria is established, which quantifies how strong nonlinear effects are anticipated to manifest at a site by investigating the empirical relation between nonlinear soil response, soil properties, and ground motion characteristics. More specifically, the modeling variability and parametric uncertainty of nonlinear soil response predictions are studied, along with the uncertainty propagation of site response analyses to the estimation of inelastic structural performance. Due to the scarcity of design level ground motion recording, the geotechnical information at 24 downhole arrays is used and the profiles are subjected to broadband ground motion synthetics. For the modeling variability study, the site response models are validated against available downhole array observations. The site and ground motion parameters that govern the intensity of nonlinear effects are next identified, and an empirical relationship is established, which may be used to estimate to a first approximation the error introduced in ground motion predictions if nonlinear effects are not accounted for. The soil parameter uncertainty in site response predictions is next evaluated as a function of the same measures of soil properties and ground motion characteristics. It is shown that the effects of nonlinear soil property uncertainties on the ground-motion variability strongly depend on the seismic motion intensity, and this dependency is more pronounced for soft soil profiles. By contrast, the effects of velocity profile uncertainties are less intensity dependent and more sensitive to the velocity impedance in the near surface that governs the maximum site amplification. Finally, a series of bilinear single degree of freedom oscillators are subjected to the synthetic ground motions computed using the alternative soil models, and evaluate the consequent variability in structural response. Results show high bias and uncertainty of the inelastic structural displacement ratio predicted using the linear site response model for periods close to the fundamental period of the soil profile. The amount of bias and the period range where the structural performance uncertainty manifests are shown to be a function of both input motion and site parameters.

Container cranes represent one of the most critical components of ports worldwide. Despite their importance to port operations, the seismic behavior of cranes has been largely ignored. Since the 1960s, industry experts have recommended allowing cranes to uplift, believing that it would limit the amount of seismic loading. However, modern cranes have become larger and more stable, and the industry experts are now questioning the seismic performance of modern jumbo cranes. The main goal of this research was to experimentally investigate the seismic behavior of container cranes from the general elastic behavior through collapse, including non-linear behavior such as buckling and cross section yielding, utilizing the 6 degree-of-freedom shake tables at the University at Buffalo. The testing was divided into two phases. The first phase of testing was conducted on a 1/20th scale model. The second phase of testing was conducted on a 1/10th scale model, which was designed such that no inelastic action would develop prior to uplift (as is the common design practice). In support of the experiments, finite element models were created to determine what simplifications could be made to the structure to aid in testing. The data collected from the testing has been used to validate finite element models, to give a better understanding of the behavior of container cranes under seismic excitations, validate fragility models, and to develop recommendations and guidelines for the design and testing of container cranes.

Quantitative and qualitative assessment of the seismic risk to highway bridges is crucial in pre-earthquake planning, and post-earthquake response of transportation systems. Such assessments provide valuable knowledge about a number of principal effects of earthquakes such as traffic disruption of the overall highway system, impact on the regions' economy and post-earthquake response and recovery, and more recently serve as measures to quantify resilience. Unlike previous work, this study captures unique bridge design attributes specific to California bridge classes along with their evolution over three significant design eras, separated by the historic 1971 San Fernando and 1989 Loma Prieta earthquakes (these events affected changes in bridge seismic design philosophy). This research developed next-generation fragility curves for four multispan concrete bridge classes by synthesizing new knowledge and emerging modeling capabilities, and by closely coordinating new and ongoing national research initiatives with expertise from bridge designers. A multi-phase framework was developed for generating fragility curves, which provides decision makers with essential tools for emergency response, design, planning, policy support, and maximizing investments in bridge retrofit. This framework encompasses generational changes in bridge design and construction details. Parameterized high-fidelity three-dimensional nonlinear analytical models are developed for the portfolios of bridge classes within different design eras. These models incorporate a wide range of geometric and material uncertainties, and their responses are characterized under seismic loadings. Fragility curves were then developed considering the vulnerability of multiple components and thereby help to quantify the performance of highway bridge networks and to study the impact of seismic design principles on the performance within a bridge class. This not only leads to the development of fragility relations that are unique and better suited for bridges in California, but also leads to the creation of better bridge classes and sub-bins that have more consistent performance characteristics than those currently provided by the National Bridge Inventory. Another important feature of this research is associated with the development of damage state definitions and grouping of bridge components in a way that they have similar consequences in terms of repair and traffic implications following a seismic event. These definitions are in alignment with the California Department of Transportation's design and operational experience, thereby enabling better performance assessment, emergency response, and management in the aftermath of a seismic event. The fragility curves developed as a part of this research will be employed in ShakeCast, a web-based post-earthquake situational awareness application that automatically retrieves earthquake shaking data and generates potential damage assessment notifications for emergency managers and responders. / Errata added at request of advisor and approved by Graduate Office, March 15 2016.

Past earthquake events have shown that seismic damage to electrical power systems in commercial buildings, hospitals, and other systems such as public service facilities can cause serious economic losses as well as operational problems. A methodology for evaluation of the seismic vulnerability of electrical power systems is needed and all essential components of the system must be included. A key system component is the switchboard cabinet which houses many different elements which control and monitor electrical power usage and distribution within a building. Switchboard cabinets vary in size and complexity and are manufactured by a number of different suppliers; a typical cabinet design was chosen for detailed evaluation in this investigation. This study presents a comprehensive framework for the evaluation of the seismic performance of electrical switchboard cabinets. This framework begins with the introduction and description of the essential equipment in building electrical power systems and explains possible seismic damage to this equipment. The shortcomings of previous studies are highlighted and advanced finite element models are developed to aid in their vulnerability estimation. Unlike previous research in this area, this study proposes practical, computationally efficient, and versatile numerical models, which can capture the critical nonlinear behavior of switchboard cabinets subjected to seismic excitations. A major goal of the current study was the development of nonlinear numerical models that can accommodate various support boundary conditions ranging from fixed, elasto-plastic to free. Using both linear and nonlinear dynamic analyses, this study presents an enhanced evaluation of the seismic behavior of switchboard cabinets. First the dynamic characteristics of switchboard cabinets are determined and then their seismic performance is assessed through nonlinear time history analysis using an expanded suite of ground motions. The seismic responses and associated ground motions are described and analyzed using probabilistic seismic demand models (PSDMs). Based on the PSDMs, the effectiveness and practicality of common intensity measures are discussed for different components. Correlation of intensity measures and seismic responses are then estimated for each component, and their seismic performance and uncertainties are quantified in terms of engineering demand parameters. The results of this study are intended for use in the seismic vulnerability assessment of essential electrical equipment in order to achieve more reliable electrical power systems resulting in reduced overall risk of both physical and operational failures of this important class of nonstructural components.

This research investigated the behavior of nonseismically detailed reinforced concrete exterior beam-column joints subjected to bidirectional lateral cyclic loading using nonlinear finite element analysis (NLFEA). Beam-column joints constitute a critical component in the load path of reinforced concrete buildings due to their fundamental role in integrating the overall structural system. Earthquake reconnaissance reports reveal that failure of joints has contributed to partial or complete collapse of reinforced concrete buildings designed without consideration for large lateral loads, resulting in significant economic impact and loss of life. Such infrastructure exists throughout seismically active regions worldwide, and the large-scale risk associated with such deficiencies is not fully known. Computational strategies provide a useful complement to the existing experimental literature on joint behavior and are needed to more fully characterize the failure processes in seismically deficient beam-column joints subjected to realistic failure conditions. Prior to this study, vulnerable reinforced concrete corner beam-column joints including the slab had not been analyzed using nonlinear finite element analysis and compared with experimental results. The first part of this research focused on identification and validation of a constitutive modeling strategy capable of simulating the behaviors known to dominate failure of beam-column joints under cyclic lateral load using NLFEA. This prototype model was formulated by combining a rotating smeared crack concrete constitutive model with a reinforcing bar plasticity model and nonlinear bond-slip formulation. This model was systematically validated against experimental data, and parametric studies were conducted to determine the sensitivity of the response to various material properties. The prototype model was then used to simulate the cyclic response of four seismically deficient beam-column joints which had been previously evaluated experimentally. The simulated joints included: a one-way exterior joint, a two-way beam-column exterior corner joint, and a series of two-way beam-column-slab exterior corner joints with varying degrees of seismic vulnerability. The two-way corner joint specimens were evaluated under simultaneous cyclic bidirectional lateral and cyclic column axial loading. For each specimen, the ability of the prototype model to capture the strength, stiffness degradation, energy dissipation, joint shear strength, and progressive failure mechanisms (e.g. cracking) was demonstrated.

Fires following earthquake (FFE) have historically produced enormous post-earthquake damage and losses in terms of lives, buildings and economic costs, like the San Francisco earthquake (1906), the Kobe earthquake (1995), the Turkey earthquake (2011), the Tohoku earthquake (2011) and the Christchurch earthquakes (2011). The structural fire performance can worsen significantly because the fire acts on a structure damaged by the seismic event. On these premises, the purpose of this work is the investigation of the experimental and numerical response of structural and non-structural components of steel structures subjected to fire following earthquake (FFE) to increase the knowledge and provide a robust framework for hybrid fire testing and hybrid fire following earthquake testing. A partitioned algorithm to test a real case study with substructuring techniques was developed. The framework is developed in MATLAB and it is also based on the implementation of nonlinear finite elements to model the effects of earthquake forces and post-earthquake effects such as fire and thermal loads on structures. These elements should be able to capture geometrical and mechanical non-linearities to deal with large displacements. Two numerical validation procedures of the partitioned algorithm simulating two virtual hybrid fire testing and one virtual hybrid seismic testing were carried out. Two sets of experimental tests in two different laboratories were performed to provide valuable data for the calibration and comparison of numerical finite element case studies reproducing the conditions used in the tests. Another goal of this thesis is to develop a fire following earthquake numerical framework based on a modified version of the OpenSees software and several scripts developed in MATLAB to perform probabilistic analyses of structures subjected to FFE. A new material class, namely SteelFFEThermal, was implemented to simulate the steel behaviour subjected to FFE events.