Deterioration Rates of Typical Bridge Elements in New York

The New York State Department of Transportation (NYSDOT) maintains an inventory of over 17,000 highway bridges across the state. These bridges are inspected biennially or more often as necessary. Bridge inspectors are required to assign a condition rating for up to 47 structural elements of each bridge, including 25 components of each span of a bridge, in addition to the general components common to all bridges. The bridge condition rating scale ranges from 7 to 1; 7 being new and 1 being in failed condition. These condition ratings may be used to calculate the deterioration rates for each bridge element, while considering the effects of key factors, such as the bridge material type, on the deterioration rates. This paper describes an approach based on the Weibull distribution to calculate the deterioration rates of typical bridge elements in New York State using historical bridge inspection data and compares the results with those using the traditionally used Markov chains approach. It is observed that the Weibull-based approach performs better in terms of the observed conditions than the traditionally used Markov chains approach for developing deterioration curves for different bridge elements. Both Markov chains and Weibull-based approaches have been incorporated into a computer program that generates the deterioration curves for specific bridge elements based on historical NYSDOT bridge inspection data dating back to 1981. Case studies on the deterioration rates of various bridge elements in New York State are presented to demonstrate the two approaches. The case studies show that the element deterioration rate information can be used to determine the expected service life of different bridge elements under a variety of external factors. This information is extremely valuable for making bridge management decisions. Based on the Weibull-based approach, the deterioration rates for typical bridge elements in New York State have been presented.     

Updating Bridge Reliability Based on Bridge Management Systems Visual Inspection Results

Bridge management systems have become increasingly sophisticated over the past decade and provide valuable information about the structural condition of all bridges in the national database. At the same time, reliability methods have gained increasing prominence and are used to forecast life-cycle performance over many decades of structural life. Such reliability analyses need to be updated based on the results of inspections. Specifically targeted nondestructive evaluations are the preferred solution, but are not always available for every bridge. This paper examines how the visual inspection data provided from bridge management systems already in place can be used to update the reliability of a bridge. The limitations and necessary modifications to current practice are discussed. The superstructure of a Colorado highway bridge deteriorating due to corrosion is used as an example.     

Condition Evolution in Bridge Management Systems and Corrosion-Induced Deterioration

Condition assessment in the Swiss bridge management system (KUBA-MS) is performed on the element level. Five condition states are defined based on visual appearance. In order to forecast the condition states of any given element at any given time a relationship must be established between the element age and its condition state. This relationship, which describes the condition evolution, can be obtained empirically from statistical analysis of pairs of consecutive condition assessments (inspections). Markov chains are used in KUBA-MS to represent condition evolution and the transition probabilities are determined using regression analysis of pairs of inspections. Unfortunately there are almost no inspection data for the worst and second worst condition states. The forecasts made using Markov chains are therefore not always reliable. In this paper an alternative approach is suggested, which takes into consideration the physical phenomena underlying element deterioration. This alternative approach is applied to chloride-induced corrosion of steel reinforcement, by far the most common deterioration mechanism in Switzerland. The chloride-induced corrosion is modeled mathematically and numerical simulations of the condition evolution for different values of model parameters are performed. The simulation results have been mapped to condition states as defined in KUBA-MS and Markov transition matrices have been calibrated to fit simulation results.     

Fuzzy Logic Based Condition Rating of Existing Reinforced Concrete Bridges

Fuzzy logic is a means for modeling the uncertainty involved in describing an event/result using natural language. The fuzzy logic approach would be particularly useful for remedying the uncertainties and imprecision in bridge inspectors’ observations. This study explores the possibilities of using fuzzy mathematics for condition assessment and rating of bridges, developing a systematic procedure and formulations for rating existing bridges using fuzzy mathematics. Computer programs developed from formulations presented in this paper are used for evaluating the rating of existing bridges, and the details are presented in the paper. In this approach, the entire bridge has been divided into three major components—deck, superstructure, and substructure—each of which is further subdivided into a number of elements. Using fuzzy mathematics in combination with an eigenvector-based priority setting approach, the resultant rating set for the bridge has been evaluated based on the specified ratings and importance factors for all the elements of the bridge. Then the defuzzified value of the resultant rating fuzzy set becomes the rating value for the bridge as a whole. It is argued that the methodology presented in this paper would help the decision makers/bridge inspectors immensely.     

Automated Data Acquisition for Bridge Inspection

Bridge management systems have a common need for a well-established inspection data acquisition system. Inspection data management requirements have expanded after establishment of new Federal Highway Administration regulations that require bridge inspection to be performed on an element-level basis. Currently, paper forms are the typical media used to record field-generated bridge inspection data. Better methods of data recording are needed to improve the accuracy and speed of the bridge inspection process. This paper discusses pen-based data acquisition technology and its potential in automating bridge inspection. The pen-based technology was utilized to develop an Automated Bridge Inspection System for the South Carolina DOT. As illustrated herein, the use of an automated inspection system simplifies the data processing effort, improves inspection data accuracy, and permits bridge inspectors to devote more time to the actual inspection process.     

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.     

Performance Prediction of Bridge Deck Systems Using Markov Chains

Bridge management systems have adopted Markov-chain models for predicting the future condition of bridge components, systems, and networks. These models are developed based on two assumptions. First, bridge inspections are performed at predetermined and fixed time intervals (i.e., constant inspection period). Second, the future bridge condition depends only on the present condition and not on the past condition (i.e., state independence). This paper evaluates the impact of these assumptions on the performance prediction of bridge deck systems using field data obtained from the Ministère des Transports du Québec. Transition probability matrices are developed for the different elements of the deck system and adjusted for the variation in the inspection period using Bayes’ rule. This investigation indicated that the variation in the inspection period may result in a 22% error in predicting the service life of a bridge deck system. Also, the statistical tests used to assess the validity of the state independence assumption of Markov chains showed that this assumption is acceptable with a 95% level of confidence, which is reasonable for network level analysis.     

Effect of equipment complexity on inspection performance.

62 experienced inspectors inspected 10 different items of electronic equipment covering a wide range of complexity, 8 or more inspectors inspected each item. Inspection performance was found to have an almost perfect inverse relationship with equipment complexity. The rank-order correlation between percentage of defects detected and pair comparison ratings of complexity was -.92; between percentage of defects detected and number of parts it was -.91. The results indicated that equipment complexity has a significant detrimental effect on inspection performance and that this effect cannot be overcome by extending the amount of inspection time allotted. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Optimal Inspection Scheduling of Steel Bridges Using Nondestructive Testing Techniques

A probabilistic approach is proposed to help select the most suitable nondestructive inspection (NDI) technique and associated optimal schedule for fracture-critical member/detail fatigue inspections on a specific steel bridge. The probability of detection (POD) function for the NDI technique, which is a measure of the detection accuracy, is employed. By combining probability calculations based on use of the POD function together with numerical Monte Carlo simulations of the crack propagation of the fracture-critical detail, a cost function is formulated that includes the expected cost of inspections and failure resulting from the chosen NDI technique and alternative inspection schedules. In summary, the selection of an NDI technique with an associated inspection schedule for fracture-critical inspections is formulated as an optimization problem that can guarantee minimum total cost. The inspection frequency is determined as part of the optimization that utilizes appropriate constraints on inspection intervals and a minimum acceptable (target) structural safety level. A case study for a box girder bridge is presented to demonstrate the application of the proposed probabilistic method.     

Condition Assessment of Corrosion-Distressed Reinforced Concrete Buildings Using Fuzzy Logic

A method is presented for obtaining condition index of corrosion distressed RC buildings. Method is developed using concepts of fuzzy logic and it integrates visual inspection with in situ investigations for carbonation and chloride content. Distress manifestations and repair priorities are classified. Condition is related to repair priorities through condition ratings. Repair priorities are fuzzy in nature as they are dependent on interpretation of the inspector. Questionnaire survey is prepared and responses are collected from the experts. Obtained data are used for development of fuzzy membership functions for defined repair priorities. A building can be subdivided into various elements. Observations for various distress manifestations are recorded for each element, using the format proposed. These observations are combined using fuzzy extension technique to obtain individual membership function for each element. Defuzzyfication using center of sum method provides with the combined building condition index (BCI) from elemental membership functions. Obtained BCI provides direct measure of condition and repair needs of the building. Developed methodology is explained through a case study on condition assessment of an academic building.     

Strength Evaluation of Deteriorated RC Bridge Columns

Condition-rating methods followed by load rating calculations are used for evaluating existing bridges in the United States. Ratings are assessed visually based on engineering expertise and experience, and in some cases supplemented by nondestructive tests. Good understanding of the effects of deterioration on the structural performance leads to better inspection procedures, planning, and cost-effective rehabilitation methods. This paper presents a bridge pier column strength evaluation method that can be adapted into a currently used bridge condition evaluation method. This method uses damaged material properties, and accounts for amount of corrosion and exposed bar length for each reinforcement, concrete loss, bond failure, and type of stresses in the corroding reinforcement. The proposed evaluation method provides a good estimate of the condition and load-carrying capacity of bridge piers that currently cannot be obtained by normal visual surveys. In addition, the proposed evaluation approach will help reduce repair costs, avoid overconservative condition ratings, and result in a more uniform level of safety of concrete bridge substructure in the United States.     

Analysis of Edge-Detection Techniques for Crack Identification in Bridges

Bridge monitoring and maintenance is an expensive yet essential task in maintaining a safe national transportation infrastructure. Traditional monitoring methods use visual inspection of bridges on a regular basis and often require inspectors to travel to the bridge of concern and determine the deterioration level of the bridge. Automation of this process may result in great monetary savings and can lead to more frequent inspection cycles. One aspect of this automation is the detection of cracks and deterioration of a bridge. This paper provides a comparison of the effectiveness of four crack-detection techniques: fast Haar transform (FHT), fast Fourier transform, Sobel, and Canny. These imaging edge-detection algorithms were implemented in MatLab and simulated using a sample of 50 concrete bridge images (25 with cracks and 25 without). The results show that the FHT was significantly more reliable than the other three edge-detection techniques in identifying cracks.     

Inspection, Condition Assessment, and Management Decisions for Commercial Roof Systems

Regular inspections are common for roof systems. In this paper, we consider the relationships among inspection condition assessment, leaks, and costs for roof systems. We analyze a visual inspection method and consider the use of inspection data, leaks, age, and costs as inputs to roof replacement decision making and argue that using all sources of information is beneficial.     

Formalism for Construction Inspection Planning: Requirements and Process Concept

Inspectors currently do not have adequate planning support to prevent inefficient or overlooked inspections and undetected defects. Underlying this problem is the lack of a planning formalism for specifying inspection goals and for developing and selecting inspection plans. This paper discusses the requirements for such a formalism. We describe sources of inspection knowledge and approaches for planning in general and for inspection planning specifically. We then describe a set of requirements for the representation and reasoning needed to support the use of available inspection knowledge to assist inspectors in the processes of creating sets of inspection plan alternatives and reducing that set to a smaller set of inspection plans for a given project.     

Using Soft Computing to Analyze Inspection Results for Bridge Evaluation and Management

The national bridge inventory (NBI) system, a database of visual inspection records that tallies the condition of bridge elements, is used by transportation agencies to manage the rehabilitation of the aging U.S. highway infrastructure. However, further use of the database to forecast degradation, and thus improve maintenance strategies, is limited due to its complexity, nonlinear relationship, unbalanced inspection records, subjectivity, and missing data. In this study, soft computing methods were applied to develop damage prediction models for bridge abutment walls using the NBI database. The methods were multilayer perceptron network, radial basis function network, support vector machine, supervised self-organizing map, fuzzy neural network, and ensembles of neural networks. An ensemble of neural networks with a novel data organization scheme and voting process was the most efficient model, identifying damage with an accuracy of 86%. Bridge deterioration curves were derived using the prediction models and compared with inspection data. The results show that well developed damage prediction models can be an asset for efficient rehabilitation management of existing bridges as well as for the design of new ones.     

Limit-State Surface Element Method: Application to Fatigue Reliability with NDE Inspections

A new method, named the limit-state surface element (LSSE) method, for problems in structural reliability is presented. The method is based on discretization of the limit-state surface into a finite number of elements. This allows for better representations of the failure surface in regions of high curvature than is possible with standard FORM techniques. The reliability is estimated as a sum of integrals over subdomains in the space of standard normal variables associated with the surface elements. Several benchmark problems are presented to demonstrate the accuracy and utility of the method, and a problem in fatigue reliability with NDE inspections is presented as a practical application of the method and a demonstration of the potential interrelations between QNDE and reliability assessment.     

Structural Testing of Prestressed Concrete Girders from the Lake View Drive Bridge

On the evening of December 27, 2005, the fascia beam supporting the east-side parapet wall of the third span of the Lake View Drive Bridge failed under the action of dead load. This paper describes the structural testing and posttest forensic examination of two girders recovered from the partially collapsed Lake View Drive Bridge. The objective of this paper is to describe the tests conducted and report the observations. An interior and an exterior prestressed concrete adjacent box girder were tested to failure in flexure. Prior to testing, an extensive visual inspection was conducted to assess the extant condition of the 42-year-old girders. Following testing, the girders were sawcut near their failure regions to permit an extensive forensic investigation. Conclusions based on the pre- and posttest inspections and test results are presented. Recommendations intended to reinforce issues that need to be considered in the bridge inspection and rating process of similar structures are presented.     

QUALICON: Computer-Based System for Construction Quality Management

This paper describes a computer-based system for construction quality management. The system tasks are derived from the elements of ISO 9001 standard and designed to integrate with other computer-aided project management functions. They can assist management in (1) the definition of requirements/criteria for design, construction, and quality management; (2) the development of inspection and test plans; (3) the tracking of actual inspection/test results; (4) the verification of their conformance to defined criteria; (5) the documentation of past experience in the form of standard templates for assisting the tasks involved; and (6) the generation of reports. A model was defined for representing the information used in the system tasks. The central role of the inspection and test plan representation was exploited to associate to construction components and processes, relevant inspections/tests, requirements/criteria, actual results, and nonconformance analyses. Templates were devised to enable the reuse of predefined packages of information, which recur from project to project. The developed system will render the assisted quality management tasks more effective. Its use was tested on data from different construction domains.     

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.