Click for next page ( 6


The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 5
5 CHAPTER ONE INTRODUCTION BACKGROUND girder, the definition of an FCM refers only to the critical ten- sion element of a member. In the case of an `I' or box girder, The inspection and maintenance of all types of bridges is the tension flange and the web plate(s) would be FCMs, as critical to the safety of the public and often critical to the well as the weld of the tension flange to the web. However, economy of a region. A bridge as defined in the AASHTO the compression flanges and the weld of the compression LRFD Bridge Design Specifications (LRFD Specifications) flanges to the webs would not be FCMs. According to the (1) is "a structure, including supports, erected over a depres- LRFD Specifications, longitudinal attachments welded to sion or an obstruction . . . having an opening measured along the FCM and greater than 4 in. (100 mm) in length in the lon- the center of the roadway of more than 20 feet" (6 m). Fail- gitudinal direction are also considered as FCMs. Bridges con- ure of a bridge as a result of inadequate inspection and main- taining FCMs are commonly referred to as fracture-critical tenance can lead to loss of life as well as incalculable user bridges (FCBs), although there are large parts of the bridge costs. To minimize the potential for such problems, signifi- that are not fracture-critical. cant public funds are spent inspecting and maintaining our nation's bridges. These funds should only be expended if FHWA has proposed that states create FCM inspection plans. There is therefore much interest in the current practices There is a payoff in lower future maintenance costs or of various states for inspecting and managing FCBs. How- The reliability (a measure of the relative safety) of the ever, before the development of such a plan, a more compre- bridge is inadequate and the inspection and maintenance hensive and unambiguous method of classifying bridges and will sufficiently improve the reliability. members as fracture-critical must be developed to ensure consistent application of such inspection standards. There is SCOPE AND OBJECTIVE also a need for other information related to FCMs that may be used to update the LRFR Manual and the current NBIS. The focus of this report is on the inspection and maintenance Finally, for obvious reasons, many owners are also concerned of bridges with fracture-critical members (FCMs). The LRFD about terrorist threats against FCBs. Specifications (1) define an FCM as a "component in tension whose failure is expected to result in the collapse of the bridge Therefore, NCHRP initiated this synthesis project to focus or the inability of the bridge to perform its function." Slight on inspection and management of bridges with FCMs. The variations of this definition can be found in the AASHTO/ objectives of this synthesis project were to AWS-D1.5 Bridge Welding Code (2), the AASHTO Manual for Condition Evaluation and Load and Resistance Factor Survey and identify gaps in the literature; Rating (LRFR) of Highway Bridges (LRFR Manual) (3), and Determine practices and problems with how bridge FHWA's National Bridge Inspection Standards (NBIS) (4). owners define, identify, document, inspect, and manage Note that by this definition substructures and superstructure bridges with fracture-critical details; and members made of concrete and other materials can also be Identify research needs. classified as FCMs, although in practice, typically, only steel superstructure members are so classified. The scope of the project included studying Although the definition indicates that failure of an FCM Inspection frequencies and procedures; may lead to collapse, it is not clear what loading would be Methods for calculating remaining fatigue life; necessary to cause the collapse. The definition leaves much Qualification and training of inspectors; to engineering judgment, and consequently there is disagree- Available and needed training; ment about what type of members should be classified as Experience with FCM fractures and problem details; FCMs, as is discussed in detail in chapter two. Examples of where inspection programs prevented failures; The LRFD Specifications note that designers are required Cost of inspection programs; to clearly indicate FCMs in the contract documents. Note that Retrofit techniques, including emerging technologies; although the term "member" is often used to refer to an entire Nondestructive evaluation (NDE);