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Author: William Dean Trono
Publisher:
ISBN:
Category :
Languages : en
Pages : 199
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Book Description
Modern reinforced concrete bridges are designed to avoid collapse and to prevent loss of life during earthquakes. To meet these objectives, bridge columns are typically detailed to form ductile plastic hinges when large displacements occur. California seismic design criteria acknowledges that damage such as concrete cover spalling and reinforcing bar yielding may occur in columns during a design-level earthquake. The seismic resilience of bridge columns can be improved through the use of a damage resistant hybrid fiber reinforced concrete (HyFRC). Fibers delay crack propagation and prevent spalling under extreme loading conditions, and the material resists many typical concrete deterioration mechanisms through multi-scale crack control. Little is known about the response of the material when combined with conventional reinforcing bars. Therefore, experimental testing was conducted to evaluate such behaviors. One area of focus was the compression response of HyFRC when confined by steel spirals. A second focus was the tensile response of rebar embedded in HyFRC. Bridge columns built with HyFRC would be expected to experience both of these loading conditions during earthquakes. The third focus of this dissertation was the design, modeling, and testing of an innovative damage resistant HyFRC bridge column. The column was designed to rock about its foundation during earthquakes and to return to its original position thereafter. In addition to HyFRC, it was designed with unbonded post-tensioning, unbonded rebar, and headed rebar which terminated at the rocking plane. Because of these novel details, the column was not expected to incur damage or residual displacements under earthquake demands exceeding the design level for ordinary California bridges. A sequence of scaled, three dimensional ground motion records was applied to the damage resistant column on a shaking table. An equal scale reinforced concrete reference column with conventional design details was subjected to the same motions for direct comparison. Compression tests showed that the ductility of HyFRC is superior to concrete in the post-peak softening branch of the response. HyFRC achieved a stable softening response and had significant residual load capacity even without spiral confinement. Concrete required the highest tested levels of confinement to achieved comparable post-peak ductility. Tension tests showed that HyFRC provides a substantial strength enhancement to rebar well beyond their yield point. Interesting crack localization behavior was observed in HyFRC specimens and appeared to be dependent on the volumetric ratio of rebar. The damage resistant HyFRC bridge column attained its design objectives during experimental testing. It exhibited pronounced reentering behavior with only light damage under earthquake demands 1.5 to 2.0 times the design level. It accumulated only 0.4% residual drift ratio after seven successive ground motions which caused a peak drift ratio of 8.0%. The conventional reinforced concrete column experienced flexural plastic hinging with extensive spalling during the same seven motions. It accumulated 6.8% residual drift ratio after enduring a peak drift ratio of 10.8%.
Author: William Dean Trono
Publisher:
ISBN:
Category :
Languages : en
Pages : 199
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Book Description
Modern reinforced concrete bridges are designed to avoid collapse and to prevent loss of life during earthquakes. To meet these objectives, bridge columns are typically detailed to form ductile plastic hinges when large displacements occur. California seismic design criteria acknowledges that damage such as concrete cover spalling and reinforcing bar yielding may occur in columns during a design-level earthquake. The seismic resilience of bridge columns can be improved through the use of a damage resistant hybrid fiber reinforced concrete (HyFRC). Fibers delay crack propagation and prevent spalling under extreme loading conditions, and the material resists many typical concrete deterioration mechanisms through multi-scale crack control. Little is known about the response of the material when combined with conventional reinforcing bars. Therefore, experimental testing was conducted to evaluate such behaviors. One area of focus was the compression response of HyFRC when confined by steel spirals. A second focus was the tensile response of rebar embedded in HyFRC. Bridge columns built with HyFRC would be expected to experience both of these loading conditions during earthquakes. The third focus of this dissertation was the design, modeling, and testing of an innovative damage resistant HyFRC bridge column. The column was designed to rock about its foundation during earthquakes and to return to its original position thereafter. In addition to HyFRC, it was designed with unbonded post-tensioning, unbonded rebar, and headed rebar which terminated at the rocking plane. Because of these novel details, the column was not expected to incur damage or residual displacements under earthquake demands exceeding the design level for ordinary California bridges. A sequence of scaled, three dimensional ground motion records was applied to the damage resistant column on a shaking table. An equal scale reinforced concrete reference column with conventional design details was subjected to the same motions for direct comparison. Compression tests showed that the ductility of HyFRC is superior to concrete in the post-peak softening branch of the response. HyFRC achieved a stable softening response and had significant residual load capacity even without spiral confinement. Concrete required the highest tested levels of confinement to achieved comparable post-peak ductility. Tension tests showed that HyFRC provides a substantial strength enhancement to rebar well beyond their yield point. Interesting crack localization behavior was observed in HyFRC specimens and appeared to be dependent on the volumetric ratio of rebar. The damage resistant HyFRC bridge column attained its design objectives during experimental testing. It exhibited pronounced reentering behavior with only light damage under earthquake demands 1.5 to 2.0 times the design level. It accumulated only 0.4% residual drift ratio after seven successive ground motions which caused a peak drift ratio of 8.0%. The conventional reinforced concrete column experienced flexural plastic hinging with extensive spalling during the same seven motions. It accumulated 6.8% residual drift ratio after enduring a peak drift ratio of 10.8%.
Author: Pardeep Kumar
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 110
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Book Description
Author: Wilson Nguyen
Publisher:
ISBN:
Category : Bridges
Languages : en
Pages : 50
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Book Description
Author: Pardeep Kumar
Publisher:
ISBN:
Category :
Languages : en
Pages : 187
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Book Description
After an earthquake event it is the responsibility of the engineers to decide if the bridge structure is safe for the traffic flow, requires repair or needs to be replaced completely depending on the damage level. Effective, economical and timely repair of Reinforced Concrete (RC) bridges after a seismic event is crucial to avoid traffic congestion and lengthy detours. Fiber Reinforced Polymer (FRP) composite laminates are one of few options with several advantages. Use of FRP jackets in structural engineering is gaining interest in applications such as strengthening weak structural elements, improving the existing structure capacity to resist increased loads due to change in use of structure and retrofitting structural elements for seismic upgrades. The study presents shaking table experimental investigation to evaluate the use of FRP for repairing RC bridge columns with circular cross-sections. Two 1/4-scale RC columns were tested in as-built configuration. Both tests had identical geometry and reinforcement details except for the spacing of the transverse reinforcing bars. One column had closely spaced hoops satisfying code requirements and the other had larger spacing, representing a shear-critical column. The test specimens were subjected to a series of horizontal and vertical excitations on a shaking table and experienced moderate to high damage. The damaged columns were subsequently repaired with unidirectional FRP composite laminates and subjected to the same set of earthquake excitations. The obtained experimental data showed that the repaired columns achieved higher strength and ductility with lower residual displacements compared to the as-built ones contributing to the resiliency of the bridge system. A three-dimensional (3D) Finite Element (FE) model was developed and calibrated using the experimental test results. A bilinear confined concrete model was adopted to model the constitutive relationship of the FRP confined concrete without explicitly modeling the FRP composite jacket. Due to variability of the material properties, several calibration parameters were studied to develop a reliable FE model. The results of the dynamic FE analysis showed great potential for 3D modeling of the repaired test specimens. From this study, it is concluded that the used FRP composite laminates represent a viable solution for the effective and rapid repair of damaged RC bridge columns. A parametric study was conducted to evaluate the horizontal force, deformation, and confining strain response of the retrofitted RC bridge columns using the computational model. The response of the FE models with different number of FRP plies in the jacket was investigated. The analytical results suggested that increasing the number of FRP plies in the jacket significantly changed the confining strains response of the confined cross-section but the global force-deformation was not significantly affected.
Author: Gunnsteinn Finnsson
Publisher:
ISBN:
Category : Columns, Concrete
Languages : en
Pages : 156
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Book Description
Many bridges in the United States are getting old and will need to be replaced in the near future. If these bridges are constructed with conventional cast-in-place methods, this construction will cause traffic congestion, which is a costly problem. Furthermore, these cast-in-place systems are susceptible to earthquake-induced damage, such as bar buckling, bar fracture and residual displacements. A new pre-tensioned precast bent system has been developed to meet these challenges. The system consists of precast technology to accelerate the bridge construction, unbonded pre-tensioning to minimize residual displacements, and high-performance materials that extend the bridge durability. Davis et al. (2012) tested the new system using only conventional concrete. They found out that pre-tensioning improves system's re-centering capabilities, but it results in earlier bar buckling and bar fracture than in previously tested reinforced concrete columns (Pang et al. 2008, Haraldsson et al. 2012). Two columns were designed and tested in the University of Washington Structural Laboratory. In the plastic-hinge region of the columns a very ductile concrete shell was added. The shell was made of a hybrid fiber reinforced concrete (HyFRC, developed by Prof. Ostertag at U.C. Berkeley) containing both polymer and steel fibers. The main goal of adding the shell was to delay spalling and buckling of the longitudinal reinforcement bars. One of the columns was the same as one of the columns tested by Davis with only the addition of HyFRC shell. The other column had a HyFRC shell in the plastic hinge region and stainless steel reinforcement bars as longitudinal reinforcement instead of regular black steel rebars. The addition of the stainless steel rebar was expected to increase the ductility of the system and minimize the corrosion susceptibility. The tests showed that the HyFRC delayed the concrete spalling, and to a limited extent, the buckling of the longitudinal bars. The main benefits of having the HyFRC shell was that the columns kept 80% of its strength at 10% drift ratio, which was much higher than the conventional concrete specimens tested by Davis et al. (2012). The response of the stainless steel column was comparable to the black steel column, the main difference being that the stainless steel column was stronger, because the stainless steel was stronger than the black steel.
Author: Sebastián Varela Fontecha
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 1706
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Book Description
Ordinary reinforced concrete (RC) highway bridges complying with current seismic design provisions are expected to be severely damaged during a strong earthquake. Previous earthquakes have shown that closing a bridge for repair or having to replace the bridge because of extensive damage and permanent tilting of the structure can be very costly and detrimental to the transportation in major urban areas. When RC bridges reach their useful life, only a small portion of the concrete and steel debris from demolition is recycled, while the rest goes to landfills. This is not the ideal end-of-life for construction materials because their extraction and manufacturing emits greenhouse gases, consumes energy, and depletes natural resources, all of which are negatively affecting the environment. In an attempt to link seismic resistance and resiliency with sustainability in bridge engineering, a new generation of earthquake-resistant and resilient highway bridges designed for disassembly (DfD) was developed in this study for the first time. The global objective of developing these bridges is to (1) minimize the economic impact of losing bridge functionality after strong earthquakes, and (2) reduce the environmental impact of producing new construction materials. The new bridge concept first involved the development and shake-table testing of three 1/4-scale deconstructible column models under simulated strong near-fault motions from the 1994, Northridge, California earthquake. The models were then disassembled and inspected, and subsequently reassembled and retested. Three replaceable plastic hinge elements and connections were developed incorporating advanced materials such as engineered cementitious composite (ECC), shimmed flexural rubber bearings, Nickel-Titanium (NiTi) and Copper-Aluminum-Manganese (CAM) super elastic shape memory alloy (SMA) bars, and prefabricated fiber-reinforced polymer (FRP) tubes were integrated in the column models. An additional cast-in-place column combining ECC and CAM SMA was designed and tested to develop an insight into the behavior of large-scale CAM-reinforced members under seismic loading before this type of SMA was adopted in the replaceable plastic hinge elements. The tests confirmed the feasibility of DfD columns. The experimental investigation was then complemented by analytical studies in OpenSees, in which analytical models were developed to replicate the measured response of the column models. To determine the feasibility of the columns within a bridge system, a 1/4-scale, three-bent, two-span bridge model was designed, constructed and tested under simulated near-fault earthquakes on three shake-tables. Upon successful performance of the original bridge, the bridge model was disassembled, all the components were inspected, and the bridge was subsequently reassembled and retested. Extensive evaluations of the behavior of the columns, connections, plastic hinges, as well as the entire system were made during the experimental investigation. The performance of the reassembled bridge demonstrated the feasibility of the proposed elements in a bridge system. Analytical studies using OpenSees were also conducted to develop a baseline for future studies.
Author: Nasi Zhang
Publisher:
ISBN:
Category :
Languages : en
Pages : 394
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Book Description
In this dissertation, the application of steel fiber reinforced self-consolidating concrete (SFRSCC) to precast unbonded post-tensioned segmental bridge columns in moderate-to-high seismic regions is evaluated numerically and experimentally. Drop weight impact tests are first conducted on plain concrete and steel fiber reinforced concrete (SFRC). The standard drop test recommended by the American Concrete Institute (ACI) is first conducted and a modification to this standard ACI, which involves visual inspection of first cracking and ultimate failure, is then developed. The Kolmogorov-Smirnov (K-S) test along with fitted normal and lognormal distributions are used to examine the distribution of the number of blows required to cause first cracking and ultimate failure of the concrete. The minimum sample size required to calculate the impact strength of SFRC is determined using equations available in the literature. This sample size is used in the subsequent impact study on SFRSCC specimens. The static and dynamic properties of ten groups of SFRSCC, including one group of self-consolidating concrete (SCC) without steel fibers, are studied and compared. Dramix℗ʼ ZP305, RC-65/35-BN, and RC-80/30-BP steel fiber (glued and hooked end) at a volume of 0. 25%, 0. 5% and 1% are considered in the study. The static properties are calculated using compression tests, split-tension tests and flexural beam tests. The dynamic properties are determined using the modified ACI impact test. A dynamic load sensor is installed underneath the base plate of the impact test machine to measure the relative reaction force history. The recorded reaction forces are used to develop an automated impact test method, which can circumvent visual inspections. Two large-scale (1:3. 37), precast, unbonded and post-tensioned segmental columns, one constructed with SCC and one constructed with SFRSCC (with 0. 5% of ZP305 steel fiber by volume), are tested under cyclic loading. These segmental columns incorporate shear keys at the joints. The backbone force-displacement relationships of the segmental columns are calculated from a pushover model available in the literature. The hysteretic behavior of the segmental columns under cyclic loading is also simulated by a numerical model developed on the OpenSEES platform. A single span, large-scale (1:3. 37) bridge model incorporating SFRSCC segmental columns (with 0. 5% of ZP305 steel fiber by volume) is tested on a shake table. Two types of cap beam-to-superstructure connections are considered for the bridge model: a connection using non-seismic rubber bearing and a fixed connection. The bridge model is tested for far field and near field ground motions along various directions and with increasing peak ground accelerations (PGAs). The evolution of the cumulative damage to the bridge model after each seismic test is evaluated through a system identification involving white noise excitation. A flag-shaped hysteretic model is proposed and validated through the cyclic test results obtained in this research and those available in the literature. The proposed flag-shaped model is used to predict the seismic response of the bridge model. Adding steel fibers to concrete significantly improves its impact strength and ductility. The SFRSCC segmental columns suffered less damage than the SCC columns for the same level of drift. The large-scale bridge model incorporating SFRSCC segmental columns sustained high intensity far field and near field ground motions with limited damage. The proposed flag-shaped hysteretic model can be used to simulate the cyclic behavior of segmental columns, and to provide reasonable estimates of their seismic response under strong ground motions.
Author: Ashkan Vosooghi
Publisher:
ISBN: 9781124404332
Category : Carbon fiber-reinforced plastics
Languages : en
Pages : 742
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Book Description
The main objective of the study was to develop a rapid and effective repair method using carbon fiber reinforced polymer (CFRP) materials for earthquake-damaged reinforced concrete bridge columns. This study consisted of three main phases. In the first phase, a data base of 33 test columns was developed and analyzed and five distinct apparent seismic damage states were defined. The damage states were correlated to measured seismic response parameters in terms of drift, frequency, strains, and yield and ultimate displacements. Fragility curves were developed and applied for two case studies in performance-based design (PBD) and performance-based assessment (PBA) of bridge columns. Comprehensive experimental and analytical studies were conducted in the second phase of the study. Two standard single columns, one standard two-column bent, and two substandard columns were tested on a shake table, repaired using CFRP fabrics, and retested on the shake table to evaluate the proposed repair procedure. The measured data were extensively analyzed to investigate the performance of the repaired columns compared to the original column responses. It was concluded that the strength and ductility of the standard columns were successfully restored and those of sub-standard columns were upgraded to the current seismic standards after the repair. However, the stiffness was not restored due to material degradation during the original column tests. Even though the repair process was done rapidly and was treated as "emergency" repair with implication that it was a temporary measure, it can be treated as a permanent repair as long as the stiffness of repaired columns is sufficient for non-seismic loading. In the analytical studies, extensive static and dynamic nonlinear analyses were performed on the column models and a simple analytical method was developed for the repaired columns to account for stiffness degradation. Based on the results from the experimental and analytical studies, repair design recommendations were developed in the third phase to aid bridge engineers in quickly designing the number of layers of CFRP layers based on the apparent damage and basic information about the column fixity, size, and reinforcement.
Author: Islam Mohamed Mantawy
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 946
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Book Description
The seismic performance of a new bridge system is studied, tested and improved. The new bridge system: 1) reduces onsite construction time by using precast components, 2) eliminates major earthquake damage by utilizing rocking column and confinement of the column ends with a steel tube, and 3) maintains the system functionality after a strong earthquake by minimizing residual drift through the use of prestressing strands in the columns. Furthermore, it uses only conventional materials. The shaking table performance of a quarter-scale, two-span bridge constructed using the new system was compared with that of a conventional cast-in-place bridge with similar geometry tested in 2005. The new bridge system was constructed in about 20% of the time needed for the conventional cast-in-place system. In the tests, the conventional bridge suffered major concrete cracking and spalling, whereas in the new system, damage to the concrete was only cosmetic. In the conventional bridge, the longitudinal bars buckled and both the longitudinal and spiral reinforcement fractured, whereas in the new system the damage to the reinforcement was limited to longitudinal bar fracture, and that occurred only under excitations larger than the design level motion. The residual drift of the new system was essentially zero for all motions, whereas one of the exterior bents of the conventional bridge was so badly damaged and out of plumb that some of the supplemental mass on the bridge had to be removed and testing was stopped shortly thereafter. The only substantial damage that the new bridge system experienced was longitudinal reinforcing fracture. Therefore, ways to delay fracture were developed analytically. Reinforcement fractures were audible during the shaking table tests of the pretensioned rocking system. Reinforcement fractures were estimated in three ways using: 1) audio recorded during each test, 2) measured rotations at column ends and 3) analytical models, which included a fatigue material. This analytical model was then used to explore methods to improve the performance of the system by delaying reinforcement fracture. The analytical parametric studies on the scaled model showed that increasing the bar size and the locally debonded length of the reinforcement were both effective strategies to reduce and delay bar fractures. For the shaking table experimental model configuration, the analytical model showed that increasing the longitudinal bars by one size and increasing the debonded length by 44% would delay bar fracture until an excitation 67% larger than the excitation where reinforcing bars first fractured in the physical experiment. The parametric study also was conducted for a prototype bent; this recommended values for longitudinal bar size, debonded lengths for longitudinal bars and effective prestressing for prestressing strands to delay the fracture of the longitudinal bars and the yielding of the prestressing strands until after the 150% design level motion.
Author: Hiroshi Yokota
Publisher: CRC Press
ISBN: 100017381X
Category : Technology & Engineering
Languages : en
Pages : 8732
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Book Description
Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations contains lectures and papers presented at the Tenth International Conference on Bridge Maintenance, Safety and Management (IABMAS 2020), held in Sapporo, Hokkaido, Japan, April 11–15, 2021. This volume consists of a book of extended abstracts and a USB card containing the full papers of 571 contributions presented at IABMAS 2020, including the T.Y. Lin Lecture, 9 Keynote Lectures, and 561 technical papers from 40 countries. The contributions presented at IABMAS 2020 deal with the state of the art as well as emerging concepts and innovative applications related to the main aspects of maintenance, safety, management, life-cycle sustainability and technological innovations of bridges. Major topics include: advanced bridge design, construction and maintenance approaches, safety, reliability and risk evaluation, life-cycle management, life-cycle sustainability, standardization, analytical models, bridge management systems, service life prediction, maintenance and management strategies, structural health monitoring, non-destructive testing and field testing, safety, resilience, robustness and redundancy, durability enhancement, repair and rehabilitation, fatigue and corrosion, extreme loads, and application of information and computer technology and artificial intelligence for bridges, among others. This volume provides both an up-to-date overview of the field of bridge engineering and significant contributions to the process of making more rational decisions on maintenance, safety, management, life-cycle sustainability and technological innovations of bridges for the purpose of enhancing the welfare of society. The Editors hope that these Proceedings will serve as a valuable reference to all concerned with bridge structure and infrastructure systems, including engineers, researchers, academics and students from all areas of bridge engineering.
