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Item CCEER 23-01: Guidelines For Circular Rebar Cage Assembly With U-BOLT Connectors(2023-10) Vahedi, Masood; Ebrahimian, Hamed; M. Itani, AhmadThis guideline presents a systematic fabrication and design approach for rebar cages using mechanical U-bolt connectors to ensure their stability and safety during the lifting process. The purpose of this guideline is to provide a straightforward tool for determining the layout of U-bolts and lifting points, and to quickly estimate rebar cage deflection during lifting. The guideline is based on a comprehensive experimental and analytical research campaign that investigated the behavior of rebar cages reinforced with U-bolt connectors. The research aimed to promote the adoption of U-bolt connectors as a viable solution to improve the overall safety of rebar cages not only during lifting, but in the future for all phases of construction.Item CCEER-22-01: Nonlinear Analysis of Near-Fault Structures Using Physics-Based Simulated Earthquake Ground Motions(2022-01) Kenawy, Maha; McCallen, DavidThis report presents the results of several studies on the use of physics-based earthquake simula- tions in engineering analysis of building structures. Three-dimensional physics-based simulations offer new opportunities to advance our understanding of the impacts of fault rupture characteristics, seismic wave propagation patterns and site conditions on the dynamic response of civil structures to strong ground shaking, especially at short distances from active faults. In pursuit of this goal, we study the characteristics of broadband simulated ground motions in the near-fault region where field recordings are typically sparse, propose procedures to incorporate those simulations into en- gineering analysis, and assess their impacts on structures at the regional scale. The first chapter of this report focuses on the characteristics of near-fault ground motion char- acterized by strong velocity pulses, known as pulse-type records. Over the past two decades, seismic performance assessment methods have incorporated pulse-type records into the analysis of near-fault structures in several ways. We examine the assumptions associated with the empirical classification of ground velocity records as pulse-type or non-pulse, and show that this type of classification may be deficient in representing the potential impacts of ground motion records on building structures. We systematically study the differences between the characteristics of records classified as pulse or non-pulse using over 23,000 simulated records, and identify several inten- sity measures that may be suited for selecting representative records for the analysis of near-fault structures, without distinction between pulse-type and non-pulse ground motions. In the second chapter, we propose a procedure for selecting simulated earthquake records for performance-based seismic design of buildings. We design a deterministic framework to assess the bias associated with employing different intensity measures and selection criteria, and put forth recommended best practices to reduce the bias associated with predicting the seismic demands on structures using a relatively small number of curated records from a large database of simulated ground motions. We conclude that restricting the source distance characteristics associated with the underlying pool of candidate records is the most effective strategy to reduce the bias, assuming the candidate pool is sufficiently large and diverse, and may eliminate reliance on the empirical classification procedures of near-fault records. In the final chapter, we present a case study that involves predicting the regional-scale impacts of a magnitude 7.0 rupture of the Hayward fault on buildings across the San Francisco Bay Area using two fault rupture realizations in a domain representative of the region’s geological character- istics. We examine the effects of increasing the highest resolved frequency in the simulations, and reducing the minimum shear wave speed represented in the domain on the demands on low-, mid- and high-rise buildings. We discuss the important interactions between the site representation and forward directivity effects near the fault, and show that low-rise buildings may be more sensitive to the geological properties than high-rise buildings.Item CCEER-22-02: Response And Behavior Of Mechanical Connectors For Application In Rebar Cages: An Experimental Study(2022-02) Vahedi, Masood; Ebrahimian, Hamed; Itani, Ahmad M.Collapse of rebar cages often leads to construction schedule delays, added costs, and sometimes injuries and fatalities. These cages are commonly used for the construction of reinforced concrete structures. They consist of longitudinal and transverse reinforcing bars connected by tie-wires. Analytical and experimental investigations showed that the lateral strength and stability of these cages depend on the tie wire connections. The experimental testing of tie wire connections showed they are weak and flexible, thus causing the poor lateral strength and stiffness of rebar cages. Mechanical connectors, such as U-bolt or clamps, can replace tie-wire connections by joining the longitudinal and transverse rebar. These connectors can be used at selected locations along the cage to improve the cage strength and stability. This report presents the results of experimental tests conducted on various types of mechanical connectors to determine their force-deformation response for different degrees of freedom. The tests utilized ribbed and plain rebars with various sizes of transverse bars. The force-deformation responses were idealized with bilinear models to be used in computational models to investigate the system-level behavior of rebar cages. Test results showed that the mechanical connectors are twenty times stronger and provide larger stiffness when compared to tie wire connections. This significant increase in strength and stiffness shows great potential in using mechanical connectors to improve the lateral stability of rebar cages.Item CCEER-20-08: Seismic Response Of Precast Columns With Non-Proprietary UHPC-Filled Ducts Abc Connections(2021-08) Aboukifa, Mahmoud; Moustafa, Mohamed A.; Saiidi, M. SaiidAccelerated bridge construction (ABC) has several advantages, such as reducing onsite construction time, reducing the traffic congestion around construction sites, and improving the quality of the prefabricated elements for both new bridges or rehabilitation or replacement of old bridges. ABC is considered a good and efficient candidate to replace the cast-in-place (CIP) conventional on-site construction techniques. ABC has been widely used in low seismic regions mostly in the superstructure elements. However, ABC is not widely implemented in the substructure elements such as column-base connections, especially in moderate and high seismic regions due to the uncertainty in the seismic performance of the substructure connections. Few ABC seismic connections were developed and have been demonstrated for potential use in high seismic regions. Among these is ultra-high performance concrete (UHPC) filled grouted-duct connection. The use of proprietary UHPC poses another challenge for wider implementation of this type of connection. The overall goal of this study was to develop non-proprietary, feasible alternative for the grouted-duct ABC seismic connection for precast bridge columns that can emulate the seismic performance of conventional CIP connections. Reducing the costs and using non-proprietary materials was the focus of this study to establish a less expensive, less restrictive alternative for UHPC-filled grouted-duct connections and avoid sole-source specification. In the first phase of this project and a companion study (Subedi et al. 2019), several non-proprietary UHPC mixes were developed and two were selected at the University of Nevada, Reno. They were used in 22 large scale pullout specimens to determine the bond behavior of UHPC-filled duct systems. Given their observed satisfactory performance, one of the non-proprietary UHPC mixes was further used and incorporated into UHPC-filled duct connections of two 42%-scale column models to connect the precast columns to footings. Both column models were tested to failure under combined axial and cyclic lateral loading to investigate their seismic performance and evaluate their ability to emulate the seismic performance of the CIP system. Moreover, analytical investigation for each column model was conducted to simulate the global response of the column models. The analytical studies were conducted using finite element computer program OpenSEES. Specific modeling assumptions for these connections that include the bond-slip effects in bars and ducts and bar debonding effects were validated for future implementation and further use in the design of this connection in actual bridges. Overall, non-proprietary UHPC-filled duct connections were successfully demonstrated to have acceptable seismic performance and are, in turn, recommended as suitable precast column-to-footing or column-to-cap beam connections for moderate and high seismic regions. Using such connection with the proposed UHPC mix can assure the formation of full plastic moment in columns without any connection damage.Item CCEER-20-07: Regional-Scale Seismic Risk To Reinforced Concrete Buildings Based On Physics-based Earthquake Ground Motion Simulations(2021-07) Kenawy, Maha; McCallen, DavidThis document reports the development and findings of a computational study which examines the regional-scale variability of seismic risk to reinforced concrete (RC) buildings using physics- based earthquake simulations. The development of the structural simulation models is presented first, followed by a description of the study components, and discussion of its findings as they relate to the seismic risk to RC buildings. Finally, the implications of the study findings on the performance and design of RC buildings near active earthquake faults are summarized, and the study limitations are reported. This report is divided into three parts: In part I, the simulation framework for RC moment frames is described. The framework rests upon the theory of lumped plasticity (LP) models, which is described in the first chapter. The second chapter outlines a program, the RC Structural Model Generator, which calibrates the LP component parameters and generates structural analysis scripts of RC frames with any number of stories/bays. The program is intergated into a regional-scale workflow to allow for expedient simulation of the nonlinear response of RC buildings to earthquake ground motions over large computational domains. The program performance is assessed using several static and dynamic verification problems that are described in the following chapter. In part II, broadband physics-based earthquake simulations are utilized to characterize the regional-scale risk to modern RC buildings using the workflow described in part I. Dense datasets of high-resolution simulated ground motions were generated using kinematic fault rupture mod- els with varying rupture characteristics to represent shallow crustal earthquakes, and resolved up to frequencies of 5 Hz. Over forty thousand nonlinear time history simulations of modern short- and mid-rise RC special moment frame buildings were conducted. The spatial variability of the structural risk within a single earthquake scenario and between different rupture scenarios was examined, and the impact of the geologic and rupture characteristics on the structural response quantities was characterized. In addition, the relationship between the structural demands near the fault and the stiffness and ductility characteristics of the buildings was investigated. The study reveals that the structural demands on RC buildings due to a M7 strike-slip earthquake may vary by a factor of up to 8.0 at very short distances from the fault, and the dispersion in the demands is found to depend on the frequency content of the buildings. The interstory drift and member rotation demands are substantially impacted by important features of the geological structure and the characteristics of the rupture scenarios, particularly the presence of localized high-slip regions along the fault plane. Flexible buildings exhibit higher sensitivity to the presence of strong veloc- ity pulses near the fault, as compared to stiffer buildings. Comparison of the characteristics of the simulated ground motions against real earthquake records suggests that the simulated motions, par- ticularly using the hybrid rupture scenarios, may offer reasonable risk estimates for low-frequency structures, and conservative estimates for high-frequency structures. Part III of this report presents some computational and theoretical supplements to the study, including the software tool which was created to aid the design of modern RC moment frame buildings.