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TRB’s National Cooperative Highway Research Program (NCHRP) Report 698: Application of Accelerated Bridge Construction Connections in Moderate-to-High Seismic Regions evaluates the performance of connection details for bridge members in accelerated bridge construction in medium-to-high seismic regions and offers suggestions for further research.
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.
The traveling public has no patience for prolonged, high cost construction projects. This puts highway construction contractors under intense pressure to minimize traffic disruptions and construction cost. Actively promoted by the Federal Highway Administration, there are hundreds of accelerated bridge construction (ABC) construction programs in the United States, Europe and Japan. Accelerated Bridge Construction: Best Practices and Techniques provides a wide range of construction techniques, processes and technologies designed to maximize bridge construction or reconstruction operations while minimizing project delays and community disruption. - Describes design methods for accelerated bridge substructure construction; reducing foundation construction time and methods by using pile bents - Explains applications to steel bridges, temporary bridges in place of detours using quick erection and demolition - Covers design-build systems' boon to ABC; development of software; use of fiber reinforced polymer (FRP) - Includes applications to glulam and sawn lumber bridges, precast concrete bridges, precast joints details; use of lightweight aggregate concrete, aluminum and high-performance steel
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.
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.
Accelerated bridge construction (ABC) utilizes rigorous planning, new technologies, and improved methods to expedite construction. Prefabricated columns and their connections to adjoining bridge members (cap beams, footings, pile caps, and pile shafts) are the most critical components of ABC in moderate- and high-seismic regions. The TRB National Cooperative Highway Research Program's NCHRP Research Report 935: Proposed AASHTO Seismic Specifications for ABC Column Connections develops AASHTO specifications for three types of precast column connections to facilitate ABC implementation in moderate- and high-seismic regions.
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