Long-Term Bridge Performance High Priority Bridge Performance Issues

CHAPTER 1. INTRODUCTION AND OVERVIEW

The U.S. infrastructure is aging and deteriorating, while public State transportation departments are struggling to keep pace using limited resources. Bridges are critical components of the highway infrastructure; a bridge that is in poor condition or one that has inadequate functional capacities can cause a reduction in the operating capacity of the highway system. The problem is compounded when work is necessary to properly maintain, rehabilitate, or replace an existing structure or a series of structures. Bridge work sites usually involve one or more conditions that result in disruptions to safe, efficient, and economical traffic flow. These include lanes that are narrowed, shifted, or closed; live load restrictions; speed reductions; detours; and work zone related safety hazards. These conditions often result in moderate to severe impacts on local and regional economies and environments, such as loss of productive time because of traffic delays and detours, increased consumption of fuel, and increased engine emissions.

The Federal Highway Administration (FHWA) initiated the Long-Term Bridge Performance (LTBP) Program as authorized in the “Safe, Accountable, Flexible, and Efficient Transportation Equity Act: A Legacy for Users,” signed into law in August 2005. The LTBP Program is a 20‑year (minimum), multifaceted research effort that is strategic in nature. It is similar to the Long-Term Pavement Performance Program that has been under way for more than 20years. Critical aspects of bridge performance will be studied to better understand those issues and to improve performance related to those issues. This report describes how the high priority bridge performance issues to be studied under the program were identified and prioritized with the assistance of bridge owners and other key stakeholders in the bridge community.

Bridge performance is a multifaceted issue involving performance of materials and protective systems, performance of individual components of the bridge, and performance of the structural system as a whole. The performance of any single bridge or element of a bridge is dependent on multiple factors, many of which are closely linked. They include the original design parameters and specifications (bridge type, materials, geometries, load capacities); the initial quality of materials and quality of the as-built construction; varying conditions of climate, air quality, and soil properties; and corrosion and other deterioration processes. Other factors influencing performance include traffic volumes, counts and weights of truck loads, truck live load impacts, and damage sustained as a result of scour, seismic events, wind, etc. A final critical factor influencing performance is the type, timing, and effectiveness of preventive maintenance, of minor and major rehabilitation actions, and ultimately of replacement actions applied to the bridge. All of these factors combine to affect the condition and operational capacities of the bridge and its various structural elements at any given point in the life of the bridge. Currently, some important aspects of bridge performance are not well understood, and some of the main factors related to bridge performance are not well documented. Often, attempts at assessment of how bridges are performing are partly based on expert opinion and/or on analyses that are hampered by lack of crucial data and thus are dependent on one or more assumptions or generalizations.

Optimal performance of bridges is of paramount importance to support the fundamental mission of State transportation departments to provide the best service to the traveling public and commercial interests. It is also vital for minimizing the overall (lifecycle) costs of keeping bridges in service. Understanding bridge performance is a key factor in a State transportation department’s ability to address current bridge deficiencies (functional as well as structural) and to design and build better performing bridges for the future. Understanding performance is critical to the planning, design, and construction processes that lead to bridges that are easier, faster, and less costly to build and maintain, including the use of new and innovative bridge materials. More information on bridge performance can be found in the FHWA publication LTBP Bridge Performance Primer (FHWA-HRT-13-051).⁽¹⁾

To achieve a better understanding of bridge performance, it is necessary to examine bridge performance as a broad spectrum concept in which multiple issues sometimes compete and often are interrelated. A primary objective of the LTBP Program is to collect data, information, and knowledge on bridges. It is important to collect and prioritize the issues to be studied and the data items according to feasibility and economics, as well as relevance and value to gain a better understanding of bridge performance.

To assist with this challenge, the possible performance issues and the parameters influencing performance were first classified into four broad categories. This is the starting point for beginning to identify the performance issues that are most important to owners. As figure 1 shows, the primary issues in bridge performance are the following:

• Structural condition—durability and serviceability (including fatigue).
• Functionality—user safety and service.
• Costs (State transportation department and users).
• Structural integrity—safety and stability in failure modes.

Figure 1. Illustration. Categories of bridge performance issues.

Many of the important parameters that influence these four categories of bridge performance are listed in table 1.

Table 1. Categories of bridge performance and influencing factors.

LTBP PROGRAM OVERVIEW

The overall objective of the LTBP Program is to inspect, evaluate, and periodically monitor representative samples of bridges nationwide to collect, document, maintain, and manage high-quality quantitative performance data over an extended period of time. This will require taking advantage of sensing technologies and nondestructive evaluation and testing tools in addition to typical bridge inspection approaches. It will also require close collaboration among stakeholders, State transportation departments, academia, and industry to gather data that are available but not currently gathered into a single database by anyone in the bridge community. The LTBP Program is designed in part to collect critical performance data that is not available elsewhere and merge it with data gathered from available sources.

It is anticipated that the LTBP Program will provide a better understanding of bridge deterioration, focusing on its numerous causes, including loads, environment, and de-icing chemicals. The program will also collect information regarding the effectiveness of current maintenance and improvement strategies. It is envisioned that data on bridges will be stored in the Bridge Portal, a new tool developed for the LTBP Program, and will be used to solve a variety of bridge condition assessment and management problems, to develop new tools, and to advance the state-of-the-knowledge of bridge management, design, maintenance, and preservation.

GENERAL DATA REQUIREMENTS FOR THE LTBP PROGRAM

An early requirement during the development of the program was to establish what specific aspects of bridge performance are most critical to FHWA, State transportation departments, and other public bridge-owning State entities. Following this, these aspects of bridge performance were evaluated to determine whether they could be adequately studied with the available LTBP Program resources. Finally, the issues were ranked in priority order to determine which issues would be addressed first.

The selection of performance issues to study under LTBP is intrinsically linked to the feasibility of collecting the data necessary to study the issues. In addition to owner input on the priority for performance issues, input from the owners on data to collect, and that could feasibly be collected, was critically important. The owners know what types of data are already being collected by their State transportation departments, as well as how it is stored and how accessible it is for transfer to the LTBP Program database. With regard to field inspection data to be collected, the owners must approve and allow all aspects of field testing on their bridges. Another reason for owner input on data needs is that the owners know what types of decision support tools would be most useful in their decisionmaking processes. This also helps define the LTBP data needs.

The issue of data to be collected was an important part of the discussions with owners about the performance issues to be studied and was included in the objectives of the focus group meetings described in chapter 2. It is the subject of the upcoming FHWA report Identifying Long-Term Bridge Performance Data Needs.