Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information (2022)

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3   Background The National Bridge Inspection Standards (NBIS) is the federal government regulation that mandates the inspection and evaluation of all bridges1 measuring 20  feet and longer in the United States (23 CFR 650 Subpart C). In cooperation with AASHTO, FHWA developed the NBIS as part of the Federal-Aid Highway Act of 1968, following the collapse of the Silver River bridge in West Virginia, as described by FHWA [1]. Historically, the NBIS required an inspec- tion of all bridges at least every 2 years and an evaluation of each bridge to determine the safe load-carrying capacity of the bridge and to assess whether load restriction via posting is required. Recent updates to the NBIS established a risk-based inspection interval for bridges that can be as frequent as every 12 months or as long as 72 months between inspections. These requirements focus on ensuring the safety of the traveling public and the continual flow of commerce. A load rating is defined as the evaluation to calculate the safe load-carrying capacity of a bridge for a specific type of load. In its simplest form, a load rating is specified by the equation: RF C DL LL (1.1)= − where C is the capacity of an element or member, DL denotes the force or stress in the element or member because of dead load, LL indicates the force or stress in the element or member as a result of live loads, and RF represents the load rating factor. If the load rating factor is greater than 1, the element has sufficient capacity to carry the dead load and the live load forces. How- ever, if RF is less than one, the element does not have sufficient capacity to carry the demanded loads. The load rating factors for every element or member of a bridge would be calculated for all required dead and live loads, and the lowest RF determines the load rating for the bridge for a given load. The AASHTO MBE [2] outlines in detail the load rating process. Three different approaches are used for load rating, and all of them follow the basic form in Equation 1.1: allowable stress rating (ASR), load factor rating (LFR), and load and resistant factor rating (LRFR). These three procedures have evolved over the years; for example, federal requirements specify that all bridges designed using the Load and Resistance Factor Design (LRFD) and the HL-93 load after October 1, 2010, must be rated by using LRFR, as noted by FHWA [3]. C H A P T E R 1 Introduction 1 Per 23 CFR 650: “A structure including supports erected over a depression or an obstruction, such as water, highway, or rail- way, and having a track or passageway for carrying traffic or other moving loads, and having an opening measuring along the center of the roadway of more than 20 feet between undercopings of abutments or spring lines of arches, or extreme ends of openings for multiple boxes, where the clear distance between openings is less than half of the smaller contiguous opening.”

4 Load Rating of Bridges and Culverts with Missing or Incomplete As-Built Information To conduct a load rating, an engineer requires certain information about the bridge, includ- ing the overall geometry of the bridge; geometry of individual elements and members; type of bearings, supports, and connections; material properties; reinforcing details and strand pat- terns; expected live loads; and data about traffic on the bridge. Such information is usually incor- porated in design drawings, as-built drawings, shop drawings, and specifications. With all of the necessary information in hand, an engineer can conduct a theoretical analysis of the bridge to determine each of the terms in Equation 1.1 and arrive at the controlling load rating factor. When some or all of the information is missing, the engineer must make other assumptions to compute the load rating, so the load rating process becomes more difficult and less certain. Load ratings are used in part to allocate federal funding to agencies and to plan for repairing, replacing, and rehabilitating bridges. Therefore, load ratings can affect the movement of goods throughout a region when bridges have load restrictions, as described by Gao [4]. Load ratings thus are vitally important to the continued safe and efficient operation of the highway system. The reasons for missing information are numerous, but a substantial ramification is clear: the process of determining a load rating for bridges with missing as-built information can pose a sig- nificant challenge. Furthermore, no uniform procedure indicates how to handle the load rating of bridges with missing information, and some research suggests that the approaches in use vary significantly from state to state, as noted by Cuaron, Jauregui, and Weldon [5] and by Lequesne and Collins [6]. Thus, this synthesis report responds to the need to clarify the current state of practice regarding load rating of bridges with missing or incomplete as-built information. Objectives The objectives of this project are to gather and synthesize information on the methods that state agencies currently use to load rate bridges and culverts in their inventory when as-built plans are missing or information on the bridge is incomplete. In this way, the project aims to establish and document the current state of practice for load rating of bridges of this type, identify gaps in the knowledge base, and recommend possible areas for future research. Scope The scope of the synthesis includes a review of relevant documents, reports, guidelines, and papers that address load rating of bridges if plans or other information is missing. The state of practice was established through a survey of state agencies and follow-up interviews. The survey addressed, among other topics, identifying the most common types of bridges that lack plans or information, application of NDT and destructive testing technologies, use of diagnostic and proof load testing, and details of the methods employed at the state level to load rate bridges with missing information. The scope surveyed neither local agencies nor consultants. Approach The synthesis included four tasks: (1) literature review, (2) survey of state agencies, (3) follow-up interviews, and (4) review and selection of case examples. A literature review identified papers, reports, guidelines, and other documents relevant to the project. The literature search relied on the Web of Science, Compendex, and Transport Research International Documentation (TRID) databases, three widely used and comprehensive online databases. The execution of different keyword searches cast a broad net for literature. These results were progressively narrowed and refined until the search clearly captured relevant work.

Introduction 5   After a review of source titles and abstracts, any materials deemed relevant were downloaded or obtained through other means. Based on a more detailed review of these materials, Chapter 2 describes the documentation with particular relevance to the project. Chapter 3 outlines the state of practice based on (1) a search of manuals, guidelines, and other documents developed by state departments of transportation (DOTs) and FHWA, primarily through a manual search of agency websites; and (2) information of this type provided by the DOT representatives who completed the survey. The survey of state DOT agencies basically established the current state of practice. The online Qualtrics survey included 36 questions and requested a broad range of information. The discus- sion of the state of practice in Chapter 3 summarizes the survey results (detailed more fully in Appendix B). Following the literature review and synthesis of the survey results, the synthesis report team conducted 14 follow-up interviews with selected agency representatives who returned the survey. The multiple factors considered when selecting the agencies for follow-up included the pro- cedure used to load rate bridges with missing information, size of the state’s bridge inventory, approximate percentage of bridges with partial information, specific feedback supplied in the survey, and cited examples. The results of the follow-up interviews are described in the state of practice in Chapter 3. The states generated 24 potential case examples, which underwent a detailed review. Given the diverse state approaches to load rating bridges with missing information—and the numerous types of bridges—this report cannot address all possible combinations. The selected case examples in Chapter 4 showcase methodologies of varying complexity. To be concise in this report, the following conventions are used: • Bridges and culverts with missing or incomplete as-built information are denoted simply by the acronym BCMI. • In addition, general references to a bridge (or bridges) are understood to mean bridge and culvert (or bridges and culverts). • References to “state DOTs” include the transportation agencies of the District of Columbia and all territories of the United States. Report Organization The report is divided into five chapters. Chapter 1 (this chapter) introduces the background, objectives, scope, approach, and organi- zation of the report. Chapter 2 summarizes the relevant literature on load rating bridges with missing or incom- plete as-built information. Chapter 3 highlights the current state of practice, based principally on the results of the survey of state agencies, the review of state documents, and the follow-up interviews. Chapter 4 details seven case examples obtained from the states. These examples illustrate the varying approaches that the states use to load rate bridges with partial information. Chapter 5 presents a summary, conclusions, and potential future research options. Appendix A reproduces the survey. Appendix B details the survey results.