Seismic Fragility Analysis For Highway Bridges With Consideration Of Soil Structure Interaction And Deterioration PDF Download

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Seismic Fragility Assessment of Highway Bridges

Seismic Fragility Assessment of Highway Bridges
Author: Seyyed Nima Mahmoudi
Publisher:
Total Pages:
Release: 2015
Genre:
ISBN:

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"Fragility curves are useful tools for reliability evaluation of structures as well as for identifying the most vulnerable components. This study focuses on the seismic fragility analysis of highway bridges. Two main approaches are used for this purpose: component-based and system-based fragility analyses. The seismic vulnerability of two existing bridges located in Montreal are assessed as case studies.The main goal of this study is to develop reliable seismic fragility curves for highway bridge structures considering all significant uncertainties involved. Uncertainties include those associated with modelling structural behavior, seismic inputs and definition of component capacities. The procedures are implemented for the fragility assessment of two existing bridges as case studies. For this purpose, deterioration due to corrosion of reinforcing steel and its effects on structural behavior are included, as well as validation of the Finite Element Model using dynamic properties obtained from ambient noise measurements. Proposed methods for the selection of appropriate set of ground motion records, the type of model analysis and probabilistic modeling of component capacities are presented and illustrated for the two case studies.Two stochastic methods are proposed for validating the Finite Element Model of a bridge. The first method is based on classical hypothesis testing procedures while the second uses a Bayesian updating approach. The stochastic methods are also used to update the input parameters, detect probable major damage in the bridges and determine the confidence interval on model responses as a function of laboratory test data and field observations.In order to limit the uncertainties involved in seismic inputs, a state-of-the-art ground motion record selection procedure based on Conditional Mean Spectrum (CMS) is used. Incremental Dynamic Analysis (IDA) is performed to evaluate the record to record variability in seismic responses and to capture the nonlinearity in structural component behaviors.The first part of the thesis describes the application of component-based fragility analysis for the seismic vulnerability assessment of highway bridge structures. IDA is performed on the validated Finite Element model of the structure using an appropriate set of ground motion records. The results are used for estimating the relationships between ground motion intensity measures and component demands. A Joint Probabilistic Seismic Demand Model (JPSDM) is fitted to the results in order to develop component and system fragility curves of the structure.Since the component based fragility analysis of complex structures comprising a large number of components requires enormous computational efforts, in the second part of this study, a system-based approach for developing seismic system fragility curves is proposed which uses Support Vector Machines (SVM). SVM is a state-of-the-art machine learning technique which is used to discover patterns in highly dimensional and complex data sets. In this application, SVM is used to determine the relationship between ground motion intensity measures and peak structural responses. Seismic fragility curves are developed using Probabilistic SVM (PSVM). Finally, the efficiency of the proposed PSVM method for its application to vector-valued ground motion Intensity Measures (IM) as well as traditional single-valued IM are investigated." --


Seismic Design and Retrofit of Bridges

Seismic Design and Retrofit of Bridges
Author: M. J. N. Priestley
Publisher: John Wiley & Sons
Total Pages: 704
Release: 1996-04-12
Genre: Technology & Engineering
ISBN: 9780471579984

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Because of their structural simplicity, bridges tend to beparticularly vulnerable to damage and even collapse when subjectedto earthquakes or other forms of seismic activity. Recentearthquakes, such as the ones in Kobe, Japan, and Oakland,California, have led to a heightened awareness of seismic risk andhave revolutionized bridge design and retrofit philosophies. In Seismic Design and Retrofit of Bridges, three of the world's topauthorities on the subject have collaborated to produce the mostexhaustive reference on seismic bridge design currently available.Following a detailed examination of the seismic effects of actualearthquakes on local area bridges, the authors demonstrate designstrategies that will make these and similar structures optimallyresistant to the damaging effects of future seismicdisturbances. Relying heavily on worldwide research associated with recentquakes, Seismic Design and Retrofit of Bridges begins with anin-depth treatment of seismic design philosophy as it applies tobridges. The authors then describe the various geotechnicalconsiderations specific to bridge design, such as soil-structureinteraction and traveling wave effects. Subsequent chapters coverconceptual and actual design of various bridge superstructures, andmodeling and analysis of these structures. As the basis for their design strategies, the authors' focus is onthe widely accepted capacity design approach, in which particularlyvulnerable locations of potentially inelastic flexural deformationare identified and strengthened to accommodate a greater degree ofstress. The text illustrates how accurate application of thecapacity design philosophy to the design of new bridges results instructures that can be expected to survive most earthquakes withonly minor, repairable damage. Because the majority of today's bridges were built before thecapacity design approach was understood, the authors also devoteseveral chapters to the seismic assessment of existing bridges,with the aim of designing and implementing retrofit measures toprotect them against the damaging effects of future earthquakes.These retrofitting techniques, though not considered appropriate inthe design of new bridges, are given considerable emphasis, sincethey currently offer the best solution for the preservation ofthese vital and often historically valued thoroughfares. Practical and applications-oriented, Seismic Design and Retrofit ofBridges is enhanced with over 300 photos and line drawings toillustrate key concepts and detailed design procedures. As the onlytext currently available on the vital topic of seismic bridgedesign, it provides an indispensable reference for civil,structural, and geotechnical engineers, as well as students inrelated engineering courses. A state-of-the-art text on earthquake-proof design and retrofit ofbridges Seismic Design and Retrofit of Bridges fills the urgent need for acomprehensive and up-to-date text on seismic-ally resistant bridgedesign. The authors, all recognized leaders in the field,systematically cover all aspects of bridge design related toseismic resistance for both new and existing bridges. * A complete overview of current design philosophy for bridges,with related seismic and geotechnical considerations * Coverage of conceptual design constraints and their relationshipto current design alternatives * Modeling and analysis of bridge structures * An exhaustive look at common building materials and theirresponse to seismic activity * A hands-on approach to the capacity design process * Use of isolation and dissipation devices in bridge design * Important coverage of seismic assessment and retrofit design ofexisting bridges


Seismic Modeling, Quantifying and Protection of Highway Bridges Considering Shaking and Lateral Spreading

Seismic Modeling, Quantifying and Protection of Highway Bridges Considering Shaking and Lateral Spreading
Author: Yazhou Xie
Publisher:
Total Pages: 232
Release: 2017
Genre:
ISBN:

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This dissertation systematically addresses the modeling, quantifying, and protection of highway bridges against earthquake hazards. Firstly, the research substantially improves the p-y spring based simulation method to predict the seismic responses of highway bridges that accounts for various soil-structure interaction effects. Closed-form formulae are provided for the p-y spring input parameters to capture the bridge-embankment interaction effects, based on which an integrated step-by-step modeling procedure is developed. The procedure is applied to simulate the seismic responses of a well instrumented highway overcrossing and validated against the recorded responses during the 1992 Petrolia earthquake. Secondly, the study derives a response modification factor to quantify the relative impact of liquefaction induced lateral spreading with respect to seismic shaking on column drifts for highway bridges. The column drift response under lateral spreading is correlated to the crust layer energy imposed on the pile foundation at bridge piers. Under seismic shaking, the column drift ratio is directly related to the peak ground acceleration. By normalizing the column drift under the lateral spreading to that of under the seismic shaking, the proposed modification factor captures key features of how columns respond under both lateral spreading and seismic shaking, and offers reliable column drift demand predictions. Thirdly, this study investigates the effectiveness and optimal design of seismic protective devices for highway bridges. Component-level fragility functions are developed by using the probabilistic seismic demand analysis. To transparently quantify the bridge performance at the system level, seismic repair cost ratios are derived to combine damage probabilities, damage ratios and replacement costs of critical bridge components. Thereafter, a multi-objective genetic optimization method with the Pareto optimal concept is employed to identify the optimal design parameters of protective devices. Subsequently, the research derives a consistent performance index to facilitate the performance-based design and optimization of seismic protective devices. By converting the system-level repair cost ratio to be a function of median-level engineering demand parameters, a uniform design surface is generated for various protection designs. The derived surface can be easily implemented in the performance-based seismic protection design and optimization without iteratively updating the design goal when a new group of design parameters are considered. The robustness of the proposed method is examined in a case study to identify the optimal protection designs by using a genetic optimization scheme. Lastly, the study derives the seismic demand models for bridge rocking columns with foundation on rigid supports when subject to horizontal near-fault strong motions. The system equations of motion are derived and solved to incorporate the column flexibility and the rocking impact mechanism. By representing the near-fault ground motions with corresponding pulses, dimensional analyses are carried out to regress the closed-form expressions of system's drift and uplift demands. A rigorous validation process is implemented to demonstrate that the proposed models can be used with confidence to predict the seismic demands of the rocking system directly from structural and ground motion characteristics.