National Bridge Inspection Standards Research Articles

Bridge Inspection – Progression of Bridge Inspection Toward Preservation and Corrosion Mitigation for Improving Asset Management

The primary intent of bridge inspection is safety. Thus, the focus during the initial development of bridge inspection guidelines, including National Bridge Inspection Standards (NBIS), was on making sure structures are safe for the traveling public. NBIS are mandated by federal statute at 23 U.S.C. 144 and implemented under 23 CFR 650 subpart C. Most changes since the inception of NBIS have been due to failures, but recently the focus has shifted to include bridge/ asset management. As such, there has been an increased emphasis on using inspection data for bridge management purposes and on preservation to make sure these structures are not only safe but also can be maintained cost-effectively to minimize life cycle costs. This requires shifting the focus from predominantly visual inspection to supplementing visual inspections with advanced technologies. In this paper, the authors discuss the changes that have occurred since their 2009 Materials Evaluation article.

Reclassifying Fracture Critical Members (Non-Redundant Steel Tension Members) to System Redundant Members in a Steel Arch Bridge

The American Association of State Highway and Transportation Officials (AASHTO) Load and Resistance Factor Design Bridge Design Specifications define fracture critical members (FCMs) as steel primary members, which are subject to tension and whose failure would probably cause the collapse of a portion of or the entire bridge. FCMs not only lead to additional material procurement and fabrication quality requirements, but bridges with FCMs need to meet the requirements of special mandatory bi-annual hands-on inspections in additions to the routine planned bridge inspections per the National Bridge Inspection Standards. The special mandatory inspections for FCMs are a considerable budgetary constraint for asset owners while still not providing definite safety proofs within the period in between the inspections. Designation of FCMs should be carefully scrutinized in a new bridge constructed with high-quality materials and well-designed details. In 2012, the Federal Highway Administration published a memorandum introducing system redundant members (SRMs), which are identified through refined analysis and exempted from the inspection requirements for FCMs. A new AASHTO Guide Specification released in 2018 outlines a detailed procedure for the reclassification of FCMs as SRMs. This paper summarizes the analyses and results of a detailed FEA performed for a newly designed steel arch bridge. The analyses considered potential failure scenarios at the edge girder of the steel arch bridge and demonstrated the available redundancy in the system to distribute the loads by satisfying the performance criteria set forth in the AASHTO Guide Specification. Reclassification of the FCMs as SRMs could help the asset owner to reallocate their strained resources more efficiently.

A State-of-the-Art Review of Bridge Inspection Planning: Current Situation and Future Needs

Inspections are important to ensuring adequate safety and performance of a bridge throughout its service life. Bridge inspections are highly connected with maintenance decisions and can help in managing maintenance activities while maintaining a reliable bridge network. Routine inspections are the most common type of highway bridge inspections in the United States. The National Bridge Inspection Standards (NBIS) requires that, for almost all bridges, a routine inspection should be conducted at least every 24 months. However, limitations of current bridge inspection practices impact the quality of information provided about bridge conditions and the subsequent decisions made based on that information. Much research in the field of bridge inspection planning has been conducted to assist bridge inspectors in the inspection planning process and improving routine inspections. Accordingly, the goal of this study is to provide an overview on current bridge inspection practices in the United States and conduct a systematic literature review on innovations in the field bridge inspections planning while investigating research gaps and future needs. This paper provides a background on the history of bridge inspection in the United States, including current bridge inspection practices and their limitations and analyzes the connections between nondestructive evaluation techniques, deterioration models, and bridge inspection management. The primary emphasis of the paper is a thorough analysis of research proposing and investigating different methodologies for inspection planning and scheduling. Studies were analyzed and categorized into three main types of inspection planning approaches, based on: reliability, risk-analysis, and optimization approaches. The study revealed gaps and limitations in the current proposed techniques for inspection planning. The findings of this review will help in characterizing the current state of bridge inspection programs and future research needs to enhance inspection programs and reduce the gap between inspection practice and research.

Statistical Forecasting of Bridge Deterioration Conditions

AbstractThe United States has more than 615,000 bridges. US national bridge inspection standards developed by the Federal Highway Administration (FHWA) require routine inspections of these bridges ...

An Integrated Uncertainty-Based Bridge Inspection Decision Framework with Application to Concrete Bridge Decks

The limitations of the standard two-year interval for the visual inspection of bridges required by the U.S. National Bridge Inspection Standards have been well documented, and alternative approaches to bridge inspection planning have been presented in recent literature. This paper explores a different strategy for determining the interval between inspections and the type of inspection technique to use for bridges. The foundational premise of the proposed approach is that bridge inspections are conducted to increase knowledge about the bridge’s current condition, and therefore, are only required when uncertainty about the knowledge of the bridge condition is too high. An example case of a reinforced concrete bridge deck was used to demonstrate how this approach would work. The method utilized deterioration models for predicting corrosion and crack initiation time, considering the uncertainty in the models’ parameters. Bridge inspections were used to update the current condition information and model parameters through Bayesian updating. As this paper presents a new idea for inspection planning, not all of the data or models necessary to fully develop and validate the approach currently exist. Nonetheless, the method was applied to a simulated example which demonstrates how the timing and means of bridge inspection can be tailored to provide the required data about individual bridges needed for effective bridge management decision making.

Load rating of tied-arch bridge systems

The National Bridge Inspection Standards require highway departments to inspect, evaluate, and determine load ratings for structures defined as bridges located on all public roads. Load rating of bridges is performed to determine the live load that structures can safely carry at a given structural condition. Bridges are rated for three types of loads, design loads, legal loads, and permit loads, which is a laborious and time-consuming task as it requires the analysis of the structure under different load cases. Several tools are currently available to assist bridge engineers to perform bridge rating in a consistent and timely manner. However, these tools support the rating of conventional bridge systems, such as slab, I-girder, box girder and truss bridges. Recently, several innovative bridge systems have been developed, such as tied-arch bridge systems used in the construction of Ravenna and Columbus bridges in the state of Nebraska, USA. The objective of this paper is to present the procedures and models developed for the load rating of tied-arch bridges. This includes developing analytical models and performing rating factor calculations in accordance to AASHTO Load and Resistance Factored Rating specifications. Three-dimensional finite element models were developed and rating calculations were performed for the primary structural components assuming various percentages of section loss and using the most common legal and permit loads in addition to AASHTO live loads. Analysis and rating were also conducted for an extreme event where one of the hangers is fully damaged.

Implementing a Successful Risk-Based, Data-Driven Scour Program

The adoption of risk-based and data-driven (risk–data) approaches is leading to a successful FHWA Scour Program for highway bridges. FHWA, which has oversight for 463,000 bridges spanning waterways, estimates that 60% of bridge failures have hydraulic-related components. Prominent scour failures led to the FHWA Scour Program’s use of legal authority under the National Bridge Inspection Standards. The fundamentals of the FHWA Scour Program include scour evaluations and development of action plans. Quandaries for bridge owners include prioritization and the appropriate level of effort for these fundamentals. In 2011, FHWA implemented a risk–data approach for oversight of the National Bridge Inspection Program. Specific to scour, bridge owners compare the consequence of failure (risk) against facility operational characteristics (data). The risk–data approach prioritizes and applies resources toward bridges posing the greatest threat to public safety or disruption of vital services. The keys to the program’s success are outreach to facilitate progress; comprehensive enhancements to publications and training; and promotion of risk–data within policy, programmatic, stewardship, deployment, and research initiatives.

Load Rating Highway Bridges in the United States: The State of Practice

In the United States, a bridge must meet federal requirements in inspection and load rating set forth in the National Bridge Inspection Standards (NBIS). This article (a) introduces the federal requirements about load rating highway bridges in the United States; (b) discusses the current state of practice in load rating; and (c) provides an overview of the load and resistance factor rating (LRFR) method that Federal Highway Administration (FHWA) is promoting.

Special Issue on Bridge Inspection and Evaluation

Bridge inspection and evaluation are essential parts of a bridge management program to ensure public safety by making sure that bridges have sufficient capacity to safely carry loads allowed on them. National Bridge Inspection Standards (NBIS) set minimum standards for the inspection and evaluation of highway bridges in the United States to ensure bridge safety. These standards set requirements for type and frequency of bridge inspections, reporting requirements, personnel qualifications, organizational responsibilities, need for quality control and assurance, and follow-up procedures to address critical findings, resulting from inspections. In most cases, the NBIS suggests a 24-month general inspection interval for bridges, and current inspections are mostly visual based.

Overview and Comparison of Nationwide Underwater Bridge Inspection Practices

The National Bridge Inspection Standards (NBIS) were originally created in 1971 and subsequently updated in 1988 and 2004 (effective 2005). The U.S. Code (23USC151) and the Code of Federal Regulations (23CFR650 Subpart C) outline the national bridge inspection program. FHWA requires that all highway bridges with a submerged substructure be inspected underwater to assess the structural integrity with certainty. Since each state program manager has the responsibility and authority to manage his or her own program under the federal regulations, a variety of local policies, procedures, and techniques are currently employed across the United States, which all comply with the NBIS. An overview is provided of nationwide activities, and underwater inspection techniques and methods used by various states are compared. All underwater inspection techniques and methods are described in detail, with the associated advantages and limitations of each discussed. Also discussed are various state-specific policies on underwater inspector qualifications, underwater inspection intervals, data-gathering techniques, inspection report content, and state policies for non–NBIS-covered structures less than 20 ft long. Historical data on trends for managing underwater inspection programs are reviewed, and future anticipated trends are discussed. Although railway bridges, ferry terminals, and port facilities are not discussed, many underwater inspection techniques and methods are also frequently used on those transportation structures by their maintaining agencies. Data would be informative to all program managers dealing with underwater inspection work.

Bridge Inspections Using Electronic Handheld Data Collectors

For assessment of the condition of an owner's assets, accurate, efficient data collection is required to monitor reliability, ensure security, and maintain sustainability. Replacing cumbersome clipboards, pencils, and paper with an electronic data collection system is a way to streamline the data collection process, improve the accuracy of data collection, and enhance management of all asset data. At the request of the Pennsylvania Turnpike Commission (PTC), a consultant developed and used a handheld data collection system for the National Bridge Inspection Standards (NBIS) inspections for more than 800 bridges on the Pennsylvania Turnpike. In addition to developing the data collection system, the same consultant was chosen to perform a second 2-year cycle of routine inspections, this time using the electronic data collection system, instead of handwritten reports. Many of the same personnel worked on both inspection cycles; this situation provided a unique opportunity to compare the two ways of collectin...

Routine Highway Bridge Inspection Condition Documentation Accuracy and Reliability

Routine inspection is the most common form of highway bridge inspection to satisfy the requirements of the National Bridge Inspection Standards. The accuracy and reliability of documentation generated during these inspections are critical to the allocation of Department of Transportation construction, maintenance, and rehabilitation resources. Routine inspections are typically completed using only the visual inspection technique and rely heavily on subjective assessments made by bridge inspectors. In light of this, and given the fact that visual inspection may have other limitations that influence its reliability, the Federal Highway Administration initiated an investigation to examine the reliability of visual inspection as it is currently applied to bridges in the United States. This paper will summarize results from this study related to the accuracy and reliability of routine inspection documentation. A number of important conclusions were developed from the experimental study. Generally, it was found...

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.

Reliability and Accuracy of Routine Inspection of Highway Bridges

Routine inspection is the most common type of highway bridge inspection completed to satisfy the requirements of the National Bridge Inspection Standards. Routine inspections of highway bridges are typically completed using only visual inspection (VI) and rely heavily on subjective assessments made by bridge inspectors. Given this practice and the fact that VI may have limitations that affect its reliability, the Federal Highway Administration completed a comprehensive study to examine the reliability of VI as it is currently practiced in the United States. The accuracy and reliability of condition ratings generated through routine inspections of six in-service and decommissioned highway bridges were studied. These timed inspections were completed in normal summer weather conditions under direct observation. To ensure that results from this study would be applicable to normal bridge inspections, state department of transportation bridge inspectors made up the study sample, which included 49 inspectors from 25 states, representing a diverse cross section of the bridge inspector population. Results of the study indicate that routine inspections are completed with significant variability. Specifically, 95 percent of primary bridge element condition ratings will vary within two rating points of the average, and only 68 percent of these ratings will vary within one rating point. Additionally, the National Bridge Inspection Standards definitions of condition rating may not be sufficiently refined to allow for reliable routine inspection results.

The Silver Bridge Collapse Recounted

The bridge spanning the Ohio River between Point Pleasant, W. Va., and Gallipolis, Ohio, known as the Silver Bridge, was designed and built during 1927–28. It was the first eyebar suspension bridge in the United States, and it received much attention for making engineering history. After some 40 years of service, the bridge collapsed without warning on December 15, 1967 during the evening rush hour, when the bridge was crowded with heavy traffic. The collapse resulted in the loss of 46 lives and nine injuries. A thorough investigation revealed that the collapse of the bridge was caused by the failure of the north eyebar of the north chain at the first panel point west of the Ohio tower. The eyebar had developed a cleavage failure at the lower position of its head. The tragedy of this bridge failure led to the approval of the 1968 National Bridge Inspection Standards by the U.S. Congress.

Inventory of Highway Infrastructure Problems Through Bridge Inspection

Today, bridge inspection is a very systematic procedure. In order to assist in this effort, national bridge inspection standards have been developed for the use of various state and county agencies. This paper presents an overview of the inspection procedures used and investigates problems associated with the implementation of inspection standards. It recommends that additional funds are required to train inspectors and to purchase equipment necessary to perform thorough inspections. The study was conducted in a typical region on the Gulf Coast. On‐system inspections revealed deteriorations that were, for the most part, cosmetic in nature. The deficiencies encountered were found not to greatly affect the structural integrity of the facilities under investigation. However, the off‐system inspections revealed that 41.2% of the structures in this category have a load‐carrying capacity below H10. In addition, 8.3% of off‐system bridges were recommended for closure. Various recommendations that can be followed...

Bridge Analysis and Rating System

In compliance with the requirements of the Highway Safety Act of 1968 and the National Bridge Inspection Standards promulgated by the Federal Highway Administration the Pennsylvania Department of Transportation has developed a computer-based system for computation of inventory, operating, and safe load capacity ratings for most types of bridges in Pennsylvania. The main objective of this presentation is to examine how the bridge analysis and rating system can be utilized by engineers to convert field inspection data and plan information into these ratings for bridges. The system gives inventory, operating and safe load capacity ratings for four AASHTO loadings and the Pennsylvania Maximum Legal Load. Ratings for any special live loads having up to 24 axles may be obtained in place of the standard loads. Ratings are automatically computed for all loadings for all members of a bridge.