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This study presents an innovative bridge column technology for application in seismic regions. The proposed technology combines a precast post-tensioned composite steel-concrete hollow-core column with supplemental energy dissipation, in a way to reduce on-site construction burdens and minimize earthquake-induced residual deformations, damage, and associated repair costs. The column consists of two steel cylindrical shells, with high-performance concrete cast in between. Both shells act as permanent formwork; the outer shell substitutes the longitudinal and transverse reinforcement, as it works in composite action with the concrete, whereas the inner shell removes unnecessary concrete volume from the column, prevents concrete implosion, and prevents buckling of energy dissipating dowels when embedded in the concrete. Large inelastic rotations can be accommodated at the end joints with minimal structural damage, since gaps are allowed to open at these locations and to close upon load reversal. Longitudinal post-tensioned high-strength steel threaded bars, designed to respond elastically, in combination with gravity forces ensure self-centering behavior. Internal or external steel devices provide energy dissipation by axial yielding. This dissertation reviews the main principles and requirements for the design of these columns. The experimental findings from two quasi-static reversed cyclic tests are then presented, and numerical simulations of the experimental response are proposed.
Longitudinal bar debonding allowed spread of yielding and prevented premature failure of reinforcements in UHPC-filled duct connections and grouted coupler column pedestal. The SMA-reinforced ECC column showed superior seismic performance compared to a conventional column in which the plastic hinge damage was limited to only ECC cover spalling even under 12% drift ratio cycles. The column residual displacements were 79% lower than CIP residual displacements on average due to the superelastic NiTi SMA longitudinal reinforcement, and higher base shear capacity and higher displacement capacity were observed. The analytical modeling methods were simple and sufficiently accurate for general design and analyses of precast components proposed in the present study. The proposed symmetrical material model for reinforcing NiTi superelastic SMA was found to be a viable alternative to the more complex asymmetrical model.
Traditional cast-in-place, concrete bridge construction is often a lengthy undertaking, which is burdensome to the motoring public because of the traffic delays that it causes. Precast construction can accelerate the process by moving fabrication offsite, and then rapidly erecting and connecting bridge components onsite. However, designing connections that are both easy to complete and are robust under seismic loading is challenging. This thesis describes a connection that is intended to meet those criteria, and builds on previous work to do so. Experimental, precast, pre-tensioned specimens developed by Davis et al. (2012) showed good seismic performance, but had significant damage at low drift levels. Adding experimental, ductile materials resulted in less structural damage (Finnsson, 2013), but required unconventional construction materials and awkward fabrication. A new precast, pre-tensioned, column-to-cap beam connection has been developed. The design utilizes (1) unbonded prestressing strands to help the column re-center, (2) bonded reinforcing bars to dissipate energy, (3) a baseplate to permit rigid-body, rocking behavior of the column, and (4) a steel tube to confine the column concrete at the rocking interface. The strands are pre-tensioned when the column is cast, so the connection can be completed without any onsite stressing operations. The connection's seismic performance was evaluated with pseudo-static, cyclic testing of one subassembly. The test results showed that the specimen was stiff at low loads, re-centered well, dissipated energy, and was ductile and durable. Damage to the concrete was negligible and the peak moment strength was measured at drifts exceeding 10%. The system offers a method for achieving accelerated bridge construction that also provides excellent seismic performance and uses only conventional construction materials.
Accelerated bridge construction (ABC) has become increasingly popular in the eyes of state and federal transportation agencies because of its numerous advantages. To effectively execute ABC projects, designers utilize prefabricated structural elements that can be quickly assembled to form functional structural systems. It is advantageous to the bridge designer if these systems emulate the design and behavior of conventional cast-in-place systems. If this can be achieved, typical analysis and design procedures can be used. The difficulty with developing emulative systems is usually encountered in the design and detailing of connections. Substructure connections are particularly critical in seismic zones because they must dissipate energy through significant cyclic nonlinear deformations while maintaining their capacity and the integrity of the structural system. The research presented in this dissertation focused on developing and evaluating earthquake resistant connections for use in accelerated bridge construction. The project was comprised of three main components; testing of five large-scale precast reinforced concrete column models, a series of individual component tests on mechanical reinforcing bar splices, and extensive analytical studies. Column studies included the design and construction of five half-scale bridge column models that were tested under reversed slow cyclic loading. Four new moment connections for precast column-footing joints were developed each utilizing mechanical reinforcing bar splices to create connectivity with reinforcing bars in a cast-in-place footing. Two different mechanical splices were studied: an upset headed coupler and grout-filled sleeve coupler. Along with the splice type, the location of splices within the plastic hinge zone was also a test variable. All column models were designed to emulate conventional cast-in-place construction thus were compared to a conventional cast-in-place test model. Results indicate that the new connections are promising and duplicate the behavior of conventional cast-in-place construction with respect to key response parameters. However, it was discovered that the plastic hinge mechanism can be significantly affected by the presence of splices and result in reduced displacement ductility capacity. In order to better understand the behavior of mechanical splices, a series of uniaxial tests were completed on mechanically-spliced reinforcing bars under different loading configurations: monotonic static tension, dynamic tension, and slow cyclic loading. Results from this portion of the project also aided the development of analytical models for the half- and prototype-scale column models. Results indicated that, regardless of loading configuration, specimens failed by bar rupture without damage to the splice itself. The analytical studies conducted using OpenSEES included development of microscope models for the two mechanical reinforcing bars splices and full analytical models of the five half-scale columns, which were both compared with respective experimental results to validate the modeling procedures and assumptions. Prototype-scale analytical models were also developed to conduct parametric studies investigating the sensitivity of the newly developed ABC connections to changes in design details. In general, the results of this study indicate that the newly develop ABC connections, which utilize mechanically-spliced connections, are suitable for moderate and high seismic regions. However, emulative design approaches are not suitable for all of the connections develop. A set of design recommendations are provided to guide bridge engineers in the analysis and design of these new connections.
"This report presents the behavior of hollow-core fiber reinforced polymer-concrete-steel columns (HC-FCS) under axial, combined axial-flexural, and vehicle collision loading" (page ii).
Nearly all bridge bents (intermediate supports) are constructed of cast-in-place reinforced concrete. Such bridges have served the nation well in the past, but to meet current design expectations, they need to be improved in three areas: 1) speed of construction, 2) seismic resiliency, and 3) durability. Building on previous research at the University of Washington (Hieber et al. 2005, Wacker et al. 2005, Pang et al. 2010, and Haraldsson et al. 2013), a new pre-tensioned bent system has been developed to address these needs. The system consists of 1) precast technology that reduces construction time, 2) unbonded pre-tensioning that minimizes post-earthquake displacements, and 3) high-performance materials that extend the bridge's life-span. Davis et al. (2012) tested a version of the system using conventional concrete in the plastic hinge regions. They found that pre-tensioning improved the system's re-centering capabilities but led to earlier bar buckling and bar fracture than in previously tested RC columns. In order to delay bar buckling and bar fracture, the system was modified to include Hybrid Fiber Reinforced Concrete (HyFRC) in the plastic hinge regions. This composite concrete has been shown to exhibit superior durability and cracking resistance (Ostertag et al. 2007). The effect of the HyFRC on the pre-tensioned bent system was investigated both with quasi-static and dynamic tests. The quasi-static tests showed that using HyFRC in the plastic hinge region increased column ductility; in all cases the column maintained more than 80% of its strength up to a drift ratio of 10%. The HyFRC also delayed spalling of the concrete, but it did not significantly increase the drift ratios at the onset of bar buckling and bar fracture. The shake-table tests of a cantilever column, which was designed to re-center up to a drift ratio of 3.0%, showed that the new system had lower expected residual drifts than columns constructed with conventional cast-in place methods. The pre-tensioned column had a residual drift of 0.23% after experiencing a peak drift ratio of 5.5%. In contrast, the companion reference column, constructed using cast-in-place technology, had a residual drift ratio of 0.83% after experiencing a peak drift ratio of 5.7%. A numerical model in OpenSees was developed and calibrated with a set of 34 RC quasi-static, cyclic tests. This model was calibrated using a concrete constitutive model that takes into account concrete early reloading, developed as part of this research, and used commonly used steel constitutive models; Giuffre-Menegotto-Pinto's (Steel02) model, and Moehle and Kunnath's (ReinforcingSteel) model. The simulations showed improved accuracy in comparison to previous research (e.g., Berry and Eberhard 2007), and showed that the response of the system was affected more by the chosen steel model than by the concrete model. The results of these simulations were used to make predictions of the response of five columns tested on the UC Berkeley shake table. These simulations showed that models built using the proposed strategy predict peak displacements quite accurately, especially at the yield and design level, but do not accurately capture residual displacements.