Performance Evaluation of Deteriorating Highway Bridges Located in High Seismic Areas

This paper studies the life-cycle performance and cost of reinforced concrete highway bridges subjected to earthquake ground motions while they are continuously exposed to the attack of chloride ions. The penetration of chloride ions into the concrete is simulated through a finite difference approach that takes into account all the parameters that can affect the corrosion process. From simulation results, the corrosion initiation time is predicted, and the extent of structural degradation is calculated over the entire life of the bridge. A group of detailed bridge models with various structural attributes are developed to evaluate the changes in the structural capacity and seismic response of corroded bridges. For the purpose of the probabilistic seismic risk assessment of bridges, the seismic fragility curves are generated and updated at regular time intervals. The time-dependent fragility parameters are employed to investigate the life-cycle cost of bridges by introducing a performance index that combines the effects of probable seismic events and chloride-induced corrosion. The proposed approach provides a multihazard framework that leads to more realistic performance and cost estimates.     

Probabilistic Seismic Demand Models and Fragility Estimates for Reinforced Concrete Highway Bridges with One Single-Column Bent

In performance-based seismic design, general and practical seismic demand models of structures are essential. This paper proposes a general methodology to construct probabilistic demand models for reinforced concrete (RC) highway bridges with one single-column bent. The developed probabilistic models consider the dependence of the seismic demands on the ground motion characteristics and the prevailing uncertainties, including uncertainties in the structural properties, statistical uncertainties, and model errors. Probabilistic models for seismic deformation, shear, and bivariate deformation-shear demands are developed by adding correction terms to deterministic demand models currently used in practice. The correction terms remove the bias and improve the accuracy of the deterministic models, complement the deterministic models with ground motion intensity measures that are critical for determining the seismic demands, and preserve the simplicity of the deterministic models to facilitate the practical application of the proposed probabilistic models. The demand data used for developing the models are obtained from 60 representative configurations of finite-element models of RC bridges with one single-column bent subjected to a large number of representative seismic ground motions. The ground motions include near-field and ordinary records, and the soil amplification due to different soil characteristics is considered. A Bayesian updating approach and an all possible subset model selection are used to assess the unknown model parameters and select the correction terms. Combined with previously developed capacity models, the proposed seismic demand models can be used to estimate the seismic fragility of RC bridges with one single-column bent. Seismic fragility is defined as the conditional probability that the demand quantity of interest attains or exceeds a specified capacity level for given values of the earthquake intensity measures. As an application, the univariate deformation and shear fragilities and the bivariate deformation-shear fragility are assessed for an example bridge.     

Probabilistic Strength Estimates and Reliability of Damaged Parallel Wire Cables

Cable reliability analysis involves the combined evaluation of cable capacity and cable load in a probabilistic manner. Assessment of cable capacity is only possible through visual inspections of the wires, field sampling, laboratory analysis of the degraded wire populations, and analytical techniques. In addition to a brief presentation of cable mechanics and deterministic models that approximate cable strength, this paper discusses inspection methodologies and statistical methods of estimation of the sizes of the degraded wire populations, and wire properties, leading to cable capacities. These capacities are described by probability distributions. The paper also discusses fundamentals of reliability analysis as they apply to bridge cables. Load criteria of present standard specifications (such as AASHTO or other international codes) are not applicable to long-span suspension bridges. The paper discusses criteria of bridge loading and reliability indices for bridge cables. More work is needed in the evaluation of loading for long-span bridges.     

Cracking and Reinforcement Corrosion in Short-Span Precast Concrete Bridges

A nationwide survey revealed 14 states having bridges comprised of precast, nonprestressed, concrete channel beams. Currently, the Arkansas State Highway and Transportation Department (AHTD) bridge inventory includes approximately 389 in-service bridges using 5.79?m precast channel beams that were constructed using 1952 AHTD bridge details. Results from a statewide inspection of these bridges conducted by the writers revealed bridges with extensive concrete longitudinal cracking at the flexural reinforcing steel level and exposed reinforcing steel. Approximately 2,000 beams in 95 precast concrete channel beam bridges were inspected during a statewide investigation; longitudinal cracking at the reinforcing steel level was observed in 60.4% of the beams and exposed flexural reinforcement in 21.2%. A combination of flexure cracking from the live-load overloads and the presence of moisture has led to this high level of beam deterioration. The source of this moisture is humidity and water seepage at joints between adjacent beams. This paper examines the causes of longitudinal cracking deterioration by examining the influences of water permeation and humidity on the corrosion of flexural reinforcement in precast concrete channel beams.     

Load Rating and Reliability Analysis of an Aerial Guideway Structure for Condition Assessment

Aerial guideways are elegant transportation structures that are seen at airports, theme parks, and crowded urban areas. The guideways generally consist of continuous, prestressed concrete beam spans, precast concrete columns, and steel beam-column connections. Although there are guidelines prepared as a supplement to conventional highway and railway bridge design codes, aerial guideways form a different class, relatively less studied compared to common highway bridges. The primary objective of this paper is to present a study to better understand the structural behavior and capacity used in an existing guideway structural system which has been in service for about 35?years. The load demand on the guideway system has increased by about 50% over the years. The structural system is composed of six-span continuous prestressed concrete bridge segments. In order to develop models that bound the possible existing condition of the structure, several models are developed by changing the most critical parameters. The critical parameters are categorized as material properties, prestress losses, boundary conditions, and continuity conditions. Sensitivity studies are conducted using eight parametric models for simulations with moving loads for the two different train types. The load rating and reliability indexes are computed for all the cases under different loading conditions. The parameters that have the most influence on the load rating and reliability are also presented. The information generated from these analyses can be utilized for better-focused visual inspection and can also be used for developing a long-term structural monitoring plan.     

Probabilistic Models for Spatially Varying Mechanical Properties of In-Service GFRP Cladding Panels

The physical uncertainty associated with fiber-reinforced polymer composites has to be quantified and dealt with for their widespread use to be reliable. Developing probabilistic models based on experimental studies form an important part of this task. In the present paper, such models are developed for glass fiber-reinforced polymer (GFRP) composites based on an experimental study on panels obtained from Mondial House, a 32?year old building demolished in 2006 in London. Having an average size of 1.5?m×1.7?m and made of chopped strand mat composites, these panels have been exposed to varying ambient conditions, protected only by a fire retardant gel coat for self-cleaning. Tensile and compressive tests are performed to quantify the variability in stiffness and strength properties of these panels. Intra- and interpanel effects and correlations between random variables are studied using statistical methods. A range of probability distributions is tested and suggestions are made with regard to their suitability for modeling different mechanical and geometric properties.     

Proposal of an Integrated Index for Prioritization of Bridge Maintenance

The bridge rating used in bridge management systems commonly uses only a structural condition. Factors such as seismic risk, hydraulic vulnerability, and strategic importance are commonly used in an isolated fashion. However, these factors are relevant when there is no possibility to calibrate deterioration models. This research uses the needs-based framework for developing an integrated bridge index (IBI) as an aid for prioritization and decisions made on maintenance and rehabilitation of bridges. The index weighs the structure distresses, hydraulic vulnerability, seismic risk, and strategic importance of the bridge. The index was calibrated using visual inspection, survey to experts, and regression analysis. After, the index was applied on six bridges placed on a primary road of Chile. To organize visual inspection, bridge inventory, and compute IBI and rank bridges, a software was developed. The calibration of the IBI index shows a correlation of 98% and all the parameters obtained were significant. Further research is needed to integrate cost with the proposed index and allocate maintenance activities.     

Probabilistic Capacity Models and Fragility Estimates for Reinforced Concrete Columns based on Experimental Observations

A methodology to construct probabilistic capacity models of structural components is developed. Bayesian updating is used to assess the unknown model parameters based on observational data. The approach properly accounts for both aleatory and epistemic uncertainties. The methodology is used to construct univariate and bivariate probabilistic models for deformation and shear capacities of circular reinforced concrete columns subjected to cyclic loads based on a large body of existing experimental observations. The probabilistic capacity models are used to estimate the fragility of structural components. Point and interval estimates of the fragility are formulated that implicitly or explicitly reflect the influence of epistemic uncertainties. As an example, the fragilities of a typical bridge column in terms of maximum deformation and shear demands are estimated.     

Survey and Evaluation of Damaged Concrete Bridges

It is well known that the U.S. bridge inventory stands in need of repair. For a rational allocation of U.S. investment resources to bridge maintenance, life cycle cost and probabilistic methods must be used. This requires a quantitative estimate of the remaining strength over the intended lifespan for a given bridge. Although nondestructive evaluation methods are becoming established for bridge inspection purposes, specific recommendations for the application of these methods for individual bridges do not exist. This study focuses on reported damage and damage modeling for concrete bridges, with particular attention to Colorado bridges. A survey on degradation mechanisms is briefly presented. Bridge damage is reviewed for a variety of concrete bridges based on information in the literature and from field studies performed by the Colorado Department of Transportation. A catalog of damages and examples that illustrate the variety and severity of damage in these bridges are presented. For the bridges considered in the survey, the most common source of damage is water leaking through deck joints. A method for predicting strength loss is applied to a typical bridge in Colorado. It is shown that corrosion initiation occurs more quickly and normalized strength loss is much greater for shear than for flexure. It is also shown that many reinforced concrete bridges under corrosion attack may be more vulnerable to shear than to bending failure. The results can be used to identify critical elements for inspection and repair, and to assist in the development of rational maintenance planning strategies for concrete bridges.     

Multiple Limit States and Expected Failure Costs for Deteriorating Reinforced Concrete Bridges

Accurate predictive analyses such as those associated with structural reliability and life-cycle costing are needed for the development of Bridge Management Systems. The present paper presents models for reliability and life-cycle cost analyses of reinforced concrete bridges damaged by corrosion. A stochastic deterioration process for corrosion initiation and propagation and then crack initiation and propagation are used to examine the effect of cracking, spalling, and loss of reinforcement area on structural strength and reliability. This will enable expected costs of failure for serviceability and ultimate strength limit states to be calculated and compared for different repair strategies and inspection intervals. It was found that, for a typical reinforced concrete slab bridge, the reduction of structural capacity at the time of severe cracking or spalling is relatively modest and causes probabilities of collapse conditional on spalling to increase by about an order of magnitude. Hence, expected costs of failure for serviceability were significantly higher than the expected costs of failure for ultimate strength limit states.     

Determining Appropriate Fatigue Inspection Intervals for Steel Bridge Members

As part of the National Bridge Inspection Standards, owners of public bridge structures are required to perform a Fracture Critical Inspection on steel superstructures that contain primary structural elements having no load path redundancy, e.g., two girder systems. Such inspections are looking to identify damage or deterioration such as corrosion and fatigue cracking that may lead to failure of the critical member. The Oregon Department of Transportation is responsible for the inspection of 196 fracture critical structures that are subjected to widely varying service and environmental conditions. These conditions range from coastal bridges in a fairly corrosive environment with moderate traffic volumes, to large and complex structures in urban areas that experience large volumes of traffic, to very benign conditions in the sparsely populated eastern regions with very low traffic volumes. In response to these widely varying service conditions, Oregon has developed a method to better categorize steel superstructures for fatigue inspection priority and frequency. This method is not only proving to save unnecessary inspection costs but increasing the inspection quality by concentrating resources where they are most needed. This paper presents a simple and practical method of evaluating fatigue inspection periods.     

退化钢筋混凝土桥梁概率耐久性评估方法

提出了考虑时间、空间变异特性的退化钢筋混凝土桥梁耐久性概率评估的随机有限元方法.首先,通过考虑钢筋与混凝土之间时变的粘结滑移关系及腐蚀钢筋的应力应变关系,采用弥散裂纹方法对退化钢筋混凝土桥梁进行有限元分析.然后,提出了退化钢筋混凝土桥梁耐久性概率评估的随机有限元分析方法,基于文献及现场调查的数据,采用蒙特卡罗仿真方法对钢筋均匀及点锈蚀、混凝土保护层厚度、表面氯离子含量、氯离子扩散系数及腐蚀率等进行随机抽样,考虑这些时变及空间变异的因素对钢筋混凝土桥梁可靠度的影响.最后,以天津滨海新区的一座钢筋混凝土梁桥为例分析了所提方法的应用.     

Reliability-Based Assessment of Suspension Bridges: Application to the Innoshima Bridge

Many suspension and cable-stayed bridges were designed and constructed between Honshu Island and Shikoku Island in Japan. All these bridges were designed according to the allowable stress design method. In the allowable stress design method, it is not possible to quantify the reliabilities of both bridge components and the entire bridge system. Therefore, in light of current reliability-based design philosophy, there is an urgent need to assess the safety of suspension bridges from a probabilistic viewpoint. To develop cost-effective design and maintenance strategies, it is necessary to assess the condition of suspension bridges using a reliability-based approach. This is accomplished by a probabilistic finite-element geometrically nonlinear analysis. This study describes an investigation into the reliability assessment of suspension bridges. The combination of reliability analysis and geometrically nonlinear elastic analysis allows the determination of reliabilities of suspension bridges. A probabilistic finite-element geometrically nonlinear elastic code, created by interfacing a system reliability analysis program with a finite-element program, is used for reliability assessment of suspension bridges. An existing suspension bridge in Japan, the Innoshima Bridge, is assessed using the proposed code. The assessment is based on static load effects. Reliabilities of the bridge are obtained by using 2D and 3D geometrically nonlinear models. Furthermore, damage scenarios are considered to assess the effects of failure of various elements on the reliability of undamaged components and on the reliability of the bridge. Finally, sensitivity information is obtained to evaluate the dominant effects on bridge reliability.     

Structural Condition Assessment of Sewer Pipelines

The need of immediate supportive measures for sustainability of municipal infrastructures calls for better understanding of the behavior of various infrastructure network systems and their components. This paper presents a study which uses artificial neural networks to investigate the importance and influence of certain characteristics of sewer pipes upon their structural performance, expressed in terms of condition rating. In this study, back propagation and probabilistic neural network (NN) models were developed and validated. The data used in the development of these models were provided by the municipality of Pierrefonds, Quebec. It comprised of parameters related to sewer pipelines, pipe diameter, buried depth/cover, bedding material, pipe material, pipeline length, age, and closed circuit television (CCTV) based structural condition rating. The first six parameters are the independent variables of the models whereas CCTV based condition rating for these pipes is the dependent variable (i.e., the output of the models). The developed NN models were used to rank the parameters, in order of their importance/influence on pipe condition. It was found that, among the studied parameters, material attributes have highest influence on pipe structural condition, respectively, followed by the geometric and physical attribute group. Sensitivity analysis was then performed to simulate the structural condition of a pipe at a range of values of each input parameters. Results of sensitivity analysis describe the nature and degree of the influence of each parameter on pipe structural condition. The developed models are expected to benefit academics and practitioners (municipal engineers, consultants, and contractors) to prioritize inspection and rehabilitation plans for existing sewer mains.     

Probabilistic Seismic Demand Model for California Highway Bridges

A performance-based seismic design method enables designers to evaluate a graduated suite of performance levels for a structure in a given hazard environment. The Pacific Earthquake Engineering Research Center is developing a framework for performance-based seismic design. One component of this framework is a probabilistic seismic demand model for a class of structures in an urban region with a well-defined seismic hazard exposure. A probabilistic seismic demand model relates ground motion intensity measures to structural demand measures. It is formulated by statistically analyzing the results of a suite of nonlinear time-history analyses of typical structures under expected earthquakes in the urban region. An example of a probabilistic seismic demand model for typical highway bridges in California is presented. It was formulated using a portfolio of 80 recorded ground motions and a portfolio of 108 bridges generated by varying bridge design parameters. The sensitivity of the demand models to variation of bridge design parameters is also discussed. Trends derived from this sensitivity study provide designers with a unique tool to assess the effect of seismicity and design parameters on bridge performance.     

Renovation of a Safety-Inspection Methodology for River Bridges

River bridges and related infrastructural elements need to be monitored and inspected periodically for deterioration and loss of function due to aging, adverse hydraulic conditions, and chemical attacks. Necessary protective works and related actions should then be implemented to increase safety. Types of items to be inspected would be categorized as structural, geotechnical, hydraulic, and structural material conditions. Requirements for periodic inspections and the ways of handling these activities were discussed within the framework of the aforementioned aspects. Since each bridge authority has its own inspection grading system according to variations in local conditions and the socioeconomic status of the country, a common core methodology should be implemented such that comparisons with different case studies are meaningful. The aim of this study is the renovation of the current inspection system in Turkey, in order to implement it primarily for saving human life, as well as promoting Turkey’s economy, labor, and manpower. An algorithm, based on evaluating components of the main body, earth-retaining facilities, and serviceability, as well as hydraulic aspects, is proposed. This renovation enables the identification of rank-based prioritization of events. The evaluation and interpretation steps were displayed with the help of a case study.     

Closed-Form Fragility Estimates, Parameter Sensitivity, and Bayesian Updating for RC Columns

Reinforced concrete (RC) columns are the most critical components in bridges under seismic excitation. In this paper, a simple closed-form formulation to estimate the fragility of RC columns is developed. The formulation is used to estimate the conditional probability of failure of an example column for given shear and deformation demands. The estimated fragilities are as accurate as more sophisticated estimates (i.e., predictive fragilities) and do not require any reliability software. A sensitivity analysis is carried out to identify to which parameter(s) the reliability of the example column is most sensitive. The closed-form formulation uses probabilistic capacity models. A Bayesian procedure is presented to update existing probabilistic models with new data. The model updating process can incorporate different types of information, including laboratory test data, field observations, and subjective engineering judgment, as they become available.     

Time-Dependent Reliability of PSC Box-Girder Bridge Considering Creep, Shrinkage, and Corrosion

Bridge performance undergoes time-varying changes when exposed to aggressive environments. While much work has been done on bridge reliability under corrosion, little is known about the effects of creep and shrinkage on the reliability of concrete bridges. In this paper, the CEB-FIP model for creep and shrinkage is applied by using finite-element (FE) analysis in conjunction with probabilistic considerations. Verification is made by comparing the analytical findings with existing test data. More specifically, a time-dependent reliability assessment is made for a composite prestressed concrete (PSC) box-girder bridge exposed to a chloride environment. This realized via an advanced probabilistic FE method. The postcracking behavior of the thin-walled box girder is described using composite degenerated shell elements, and importance sampling is used to improve the efficiency of the reliability analyses. It is shown that concrete creep and shrinkage dominate during the early stages of bridge structure deterioration. This is accompanied by a decrease in reliability owing to the combined action of creep, shrinkage, and corrosion. The reliability indexes for the serviceability and the tendon yielding limit state fall below the target levels prior to the expected service life. Therefore, early maintenance and/or repair measures are required.     

Probabilistic Capacity Models and Fragility Estimates for Reinforced Concrete Columns Incorporating NDT Data

Knowing the ability of reinforced concrete (RC) bridges to withstand future seismic demands during their life-cycle can help bridge owners make rational decisions regarding optimal allocation of resources for maintenance, repair, and/or rehabilitation of bridge systems. The accuracy of a reliability assessment can be improved by incorporating information about the current aging and deterioration conditions of a bridge. Nondestructive testing (NDT) can be used to evaluate the actual conditions of a bridge, avoiding the use of deterioration models that bring additional uncertainties in the reliability assessment. This paper develops probabilistic deformation and shear capacity models for RC bridge columns that incorporate information obtained from NDT. The proposed models can be used when the flexural stiffness decays nonuniformly over a column height. The flexural stiffness of a column is estimated based on measured acceleration responses using a system identification method and the damage index method. As an application of the proposed models, a case study assesses the fragility (the conditional probability of attaining or exceeding a specified capacity level) of the column in the Lavic Road Overcrossing for a given deformation or shear demand. This two-span concrete box-girder bridge located in Southern California was subject to the Hector Mine Earthquake in 1999. Pre- and postearthquake estimates of the univariate shear and deformation fragilities and of the bivariate shear-deformation fragility are computed and compared. Both displacement and shear capacities are found to decrease after the earthquake event. Additionally, the results show that the damage due to the Hector Mine Earthquake has a larger impact on the shear capacity than the deformation capacity, leading to a more significant increment in the shear fragility than in the deformation fragility.     

Design Method of a Hanger System for Long-Span Suspension Bridge

A parallel wire strand (PWS) rope instead of a strand rope of the center fit rope core type was used as the hanger rope in the world's longest suspension bridge, the Akashi Kaikyo Bridge, one of the Honshu-Shikoku Bridges in Japan. The strand ropes of the center fit rope core type are inconvenient and uneconomical to maintain as 100–200 m-long hanger ropes. This paper presents the design method for the PWS hanger system in long-span suspension bridges. The structural characteristics, structural analysis, stress calculation, and the examination of fatigue against random wind load of the PWS hanger system were also investigated.