Author: Yuling Gao
Publisher:
ISBN:
Category :
Languages : en
Pages : 131
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Book Description
Earthquakes are one of the main natural hazards that have caused devastations to bridges around the world. Given the observations from past earthquakes, substantial analytical and experimental research work related to bridges has been undertaken in Canada and other countries. The analytical research is focussed primarily on the prediction of the seismic performance of existing bridges. It includes bridge-specific investigations which are mainly conducted using deterministic approach, and investigations of bridge portfolios which are based on probabilistic approach. In both cases, nonlinear time-history analyses are extensively used. To conduct analysis on a given bridge, analytical (i.e., computational) model of the bridge is required. It is known that the seismic response predictions depend greatly on the accuracy of the input of the modeling parameters (or components) considered in the bridge model. The objective of this study is to investigate the effects of the uncertainties of a number of modeling parameters on the seismic response of typical highway bridges. The parameters considered include the superstructure mass, concrete compressive strength, yield strength of the reinforcing steel, yield displacement of the bearing, post-yield stiffness of the bearing, plastic hinge length, and damping. For the purpose of examination, two typical reinforced concrete highway bridges located in Montreal were selected. Three-dimensional (3-D) nonlinear model the bridge was developed using SAP2000. The effects of the uncertainty of each parameter mentioned above were investigated by conducting time-history analyses on the bridge model. In total, 15 records from the earthquakes around the world were used in the time-history analysis. The response of the deck displacement, bearing displacement, column displacement, column curvature ductility, and moment at the base of the column was considered to assess the effect of the uncertainty of the modeling parameter on the seismic response of the bridge. Recommendations were made for the use of these modeling parameters on the evaluation of the seismic performance of bridges.
Author: Borislav Todorov
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Bridges play a key role in the transportation sector while serving as lifelines for the economy and safety of communities. The need for resilient bridges is especially important following natural disasters, where they serve as evacuation, aid, and supply routes to an affected area. Much of the earthquake engineering community is interested in improving the resiliency of bridges, and many contributions to the field have been made in the past decades, where a shift towards performancebased design (PBD) practices is underway. While the Canadian Highway Bridge Design Code (CHBDC) has implemented PBD as a requirement for the seismic design of lifeline and major route bridges, the nature of PBD techniques translate to a design process that is not universally compatible for all scenarios and hazards. Therefore, there is great benefit to be realised in the development of PBD guidelines for mainshock-aftershock seismic sequences for scenarios in which the chance to assess and repair a bridge is not possible following a recent mainshock. This research analytically explored a parameterized set of 20 reinforced concrete bridge piers which share several geometrical and material properties with typical bridge bents that support many Canadian bridges. Of those piers, half are designed using current PBD guidelines provided in the 2019 edition of the CHBDC, whereas the remaining half are designed with insufficient transverse reinforcement commonly found in the bridges designed pre-2000. To support this study, a nonlinear fiber-based modelling approach with a proposed material strength degradation scheme is developed using the OpenSEES finite element analysis software. A multiple conditional mean spectra (CMS) approach is used to select a suite of 50 mainshock-aftershock ground motion records for the selected site in Vancouver, British Columbia, which consist of crustal, inslab, and interface earthquakes that commonly occur in areas near the Cascadia Subduction zone. Nonlinear time history analysis is performed for mainshock-only and mainshock-aftershock excitations, and static pushover analysis is also performed in lateral and axial directions for the intact columns, as well as in their respective post-MS and post-AS damaged states. Using the resulting data, a framework for post-earthquake seismic capacity estimation of the bridge piers is developed using machine learning regression methods, where several candidate models are tuned using an exhaustive grid search algorithm approach and k-fold crossvalidation. The tuned models are fitted and evaluated against a test set of data to determine a single best performing model using a multiple scorer performance index as the metric. The resulting performance index suggests that the decision tree model is the most suitable regressor for capacity estimation due to this model exhibiting the highest accuracy as well as lowest residual error. Moreover, this study also assessed the fragility of the bridge piers subjected to mainshock-only and mainshock-aftershock earthquakes. Probabilistic seismic demand models (PSDMs) are derived for the columns designed using current PBD guidelines (PBD-compliant) to evaluate whether the current PBD criteria is sufficient for resisting aftershock effects. Additional PSDMs are generated for the columns with inadequate transverse reinforcement (PBD-deficient) to assess aftershock vulnerability of older bridges. The developed fragility curves indicate an increased fragility of all bridge piers for all damage levels. The findings indicate that adequate aftershock performance is achieved for bridge piers designed to current (2019) CHBDC extensive damage level criteria. Furthermore, it is suggested that minimal damage performance criteria need to be developed for aftershock effects, and the repairable damage level be reintroduced for major route bridges.
Author: M. Lee Marsh
Publisher: Transportation Research Board
ISBN: 0309223806
Category : Technology & Engineering
Languages : en
Pages : 138
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Book Description
"TRB's National Cooperative Highway Research Program (NCHRP) Synthesis 440, Performance-Based Seismic Bridge Design (PBSD) summarizes the current state of knowledge and practice for PBSD. PBSD is the process that links decision making for facility design with seismic input, facility response, and potential facility damage. The goal of PBSD is to provide decision makers and stakeholders with data that will enable them to allocate resources for construction based on levels of desired seismic performance"--Publisher's description.
Author: National Cooperative Highway Research Program
Publisher: Transportation Research Board
ISBN: 0309067537
Category : Bridges
Languages : en
Pages : 55
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Book Description
Author: Michel Ghosn
Publisher: Transportation Research Board
ISBN: 0309087503
Category : Bridges
Languages : en
Pages : 183
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Book Description
Chapter 1. Introduction -- Chapter 2. Reliability models for combinations of extreme events -- Chapter 3. Calibration of load factors for combinations of extreme events -- Chapter 4. Conclusions and future research -- References -- Glossary of notations -- Appendixes.
Author: Nathan W. Harrison
Publisher:
ISBN: 9781124682358
Category : Columns
Languages : en
Pages : 542
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Book Description
As part of a Federal Highway Administration (FHWA) sponsored research project to study highway system resilience, a 40 percent scale curved steel plate girder bridge is to be constructed and subjected to earthquake simulation at the Large Scale Structures Laboratory on the University of Nevada, Reno (UNR) campus. The 145 foot long bridge model is to have three-spans, supported on two single-column bents with hammer-head pier caps, and have a subtended angle of 104°. The purpose of the shake table testing is to study the seismic system behavior of the bridge as well as additional bridge components including; conventional columns, isolation, ductile-cross frames, abutment behavior, and the seismic behavior of bridges including the effects of live load. Ultimately design recommendations will be developed from this research. The research presented in this document is the results of preliminary analysis and design of conventional reinforced concrete bridge columns and substructure elements as part of the larger project to examine global seismic behavior of the scaled bridge model. In order to prepare for seismic testing of the scaled bridge model, extensive pre-experimental numerical analysis was performed. Finite element models were developed using SAP2000 and non-linear time-history analysis was performed to investigate the seismic response of the bridge model. Analytical bridge models were analyzed using both 16-inch and 20-inch column diameters and various abutment support conditions. The models were subjected to two levels of horizontal bidirectional earthquake excitation representing a design level earthquake and a large amplitude earthquake intended to cause column failure. Using the results from the analysis, preliminary construction plans were prepared for one set of columns and the adjacent substructure components using the provisions from the AASHTO Guide Specifications for LRFD Seismic Bridge Design. In addition to the investigation into column performance, a parametric study was performed to determine axial response of the bearings at both the abutments and piers when subjected to seismic loading. The numerical analysis showed that system effects due to superstructure-substructure interaction can cause column flexural response that is typically not observed with stand-alone column tests. The effects of bridge horizontal curvature was shown to have a significant impact on the axial performance of the bearings in which the response was not uniform for all bearing at one support location. As a component of the analysis and design, two strut-and-tie models were developed to provide adequate joint detailing in order to ensure capacity protection of the column-to-bentcap connection under multiple cycles of seismic loading.
Author: Andres Oscar Espinoza
Publisher:
ISBN:
Category :
Languages : en
Pages : 666
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Book Description
Abstract Seismic Performance of Reinforced Concrete Bridges Allowed to Uplift During Multi-Directional Excitation by Andres Oscar Espinoza Doctor of Philosophy in Engineering - Civil and Environmental Engineering University of California, Berkeley Professor Stephen A. Mahin, Chair The behavior of bridges subjected to recent moderate and large earthquakes has led to bridge design detailed for better seismic performance, particularly through wider bridge foundations to handle larger expected design forces. Foundation uplift, which is not employed in conventional bridge design, has been identified as an important mechanism, in conjunction with structural yielding and soil-structure interaction that may dissipate energy during earthquakes. Preventing uplift through wider foundations looks past the technical and economical feasibility of allowing foundation uplift during seismic events. The research presented in this thesis is part of a larger experimental and analytical investigation to develop and validate design methods for bridge piers on shallow foundations allowed to uplift during seismic events. Several analytical and some experimental studies have been performed to assess rocking and or uplift of shallow foundation systems, however they have evaluated systems with a limited range of footing dimensions and seismic excitations. As such, there is an uncertainty in the information needed to base a performance evaluation and develop design methods. The purpose of this study is to investigate, through experimental and analytical studies, the seismic performance of uplifting bridge piers on shallow foundations when considering different ground motions and footing dimensions. As well as to identify key differences in performance evaluation criteria for conventional and uplifting bridge pier systems. The experimental study dynamically tested a single reinforced concrete bridge column specimen with three adjustable footing configurations grouped by footing dimension, and tested for various combinations of one, two, and three components of seismic excitation. Groups one and two evaluated uplifting systems where the column was limited to elastic loading levels while group three considered inelastic column loading levels. All test groups remained stable and exhibited some rocking and or uplift during testing. Analytical models were developed and validated using the experimental testing results to predict local and global footing and column response. Reliable estimates of forces and displacements during elastic and inelastic response were achieved. To assess the seismic performance of a range of bridge pier systems allowed to uplift a parametric investigation using the validated analytical models was performed in which the column was modeled per conventional design criteria to ensure adequate strength and flexural ductility. The parameters varied include footing width, ground motion excitation, and elastic or inelastic column response. Response of the uplifting bridge pier systems was found to be sensitive to the structural periods, magnitude of excitation, and footing width.
Author: Joseph Wieser
Publisher:
ISBN:
Category : Electronic books
Languages : en
Pages : 1040
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Book Description
Seat-type bridge abutments are most commonly used to support the end spans of curved highway bridges. This type of abutment is often selected to eliminate unbalanced stresses in the superstructure under service loads, in particular thermal expansion and contraction. However, depending on the width of the expansion gap, large earthquakes may cause the expansion gap to close which results in bridge-abutment interaction. This phenomenon was studied in a federally-funded research project examining the seismic performance of curved highway bridges at the University of Nevada, Reno. As a part of this research a 2/5 th scale model of a 3-span curved steel girder bridge was constructed on four multi-degree-of-freedom shake tables. Two configurations of the bridge one without bridge-abutment interaction and one with nonlinear bridge-abutment interaction were tested. The purpose of these tests was to: (i) identify the influence of bridge-abutment interaction on the global seismic response of the bridge, (ii) characterize the force-deformation characteristics of dynamic bridge-abutment interaction, and (iii) provide experimental data used to calibrate numerical models of bridges including bridge abutment interaction. Based on the experimental investigation it was concluded that bridge-abutment interaction shortens the effective period of vibration of the bridge, which results in decreased deck displacement and increased total base shear demands. However, the increase in base shear demand is resisted by the abutments which results in a net reduction in column shear demand. Though the deck displacement is reduced at the mid-span of the bridge, the active displacement of the deck at the abutments is increased due to the increased in-plane deck rotation generated as a result of the sudden changes in eccentricity between the center of mass and center of stiffness. The amount of in-plane rotation is shown to depend on the phasing and intensity of the ground motion. Interaction between the bridge and abutment backwall can generate significant radial shear forces through contact friction. These radial forces limit the radial displacement of the bridge while in contact with the backwall particularly after the radial shear keys have failed. However, depending on the details of the abutment backwall local damage may occur. In general, engaging the passive resistance of the backfill soil was able to improve the seismic response of the bridge by reducing damage to the columns and adding an additional form of energy dissipation. Both rigorous 3D finite element and simplified grillage models of the experimental model were validated using available software. Good agreement between the numerical models and the experimental data were obtained using both models however the computational effort was greatly reduced using the simplified grillage model. A grossly simplified 3DOF model of the bridge analyzed using the linear multi-modal response spectrum method was shown to give a prediction of the peak displacement response with minimal complexity. Finally, a parameter study determined that the degree of curvature, size of expansion gap, column diameter, and abutment backfill soil type all influence the response of the bridge. Based on the small scale parameter study conducted herein, bridge designers are encouraged to optimize the combination of expansion gap width with the selection of column diameter to minimize the column and/or abutment soil ductility demands.
Author: S. Ivorra
Publisher: WIT Press
ISBN: 1784663158
Category : Technology & Engineering
Languages : en
Pages : 289
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Book Description
Research studies on the preparation for and mitigation of future earthquakes, an area of increasing importance to many countries around the world, comprise this volume. The selected papers included in this book have been prepared by experts from around the world in the fields of earthquake engineering relevant to the design of structures. As the world’s population has concentrated in urban areas resulting in buildings in regions of high seismic vulnerability, we have seen the consequences of natural disasters take an ever higher toll on human existence. Protecting the built environment in earthquake-prone regions involves not only the optimal design and construction of new facilities, but also the upgrading and rehabilitation of existing structures including heritage buildings, which is an important area of research. Major earthquakes and associated effects, such as tsunamis, continue to stress the need to carry out more research and a better understanding of these phenomena is required to design earthquake resistant buildings and to carry out risk assessment and vulnerability studies.
Author: Abdullah S E S E Almutairi
Publisher:
ISBN:
Category :
Languages : en
Pages : 436
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Book Description
The conducted study is directed towards enhancements in performance assessment of highway bridges under a wide range of earthquake input shaking scenarios. Seismic response of the superstructure is highly influenced by the global bridge-ground characteristics as an integral system. Therefore, nonlinear representation of the bridge deck, columns, abutments, and foundation response are to be integrated within a unified framework. On this basis, a performance-based earthquake engineering (PBEE) framework was extended and utilized to estimate the post-earthquake loss. To facilitate systematic execution of this analysis framework, a graphical user-interface was further developed and employed. For calibration purposes, a Finite Element (FE) model of an existing large heavily instrumented bridge system at Eureka, California (Samoa Channel Bridge) was developed. Calibration was undertaken based on the recorded earthquake response. Numerical simulations of the bridge model under seismic loading conditions were conducted. Simulation results show that the recorded data provide valuable insights to understand the seismic bridge response and to reliably estimate the damage. Using a practice-oriented pushover procedure, the response of a bridge subjected to liquefaction-induced lateral spreading was investigated. The analysis framework and representative results are presented, where the abutment lateral slope displacement is resisted by the entire bridge configuration. Permanent ground deformation induces longitudinal displacement on the abutment and consequently the entire bridge system. As such, the response of the bridge and its pile foundations were investigated and correlated with the imposed lateral spreading displacement. Overall, the novel contributions and findings are summarized as follows: (1) A bridge-ground seismic response computational analysis tool was further developed for routine practical applications; (2) In this tool, a PBEE framework was extended to handle multi-span bridge-ground systems within an integrated simulation environment; (3) Calibrated by recorded earthquake response, a framework was implemented for a representative large instrumented bridge-ground system in California to illustrate the involved response mechanisms and PBEE outcomes; (4) For response under lateral spreading considerations, a global bridge-ground systematic analysis framework was proposed and developed; (5) Patterned after an existing bridge in California, the framework was implemented with parametric studies addressing the procedure assumptions and potential retrofit bridge configurations.
