Lrfd Metal Loss And Service Life Strength Reduction Factors For Metal Reinforced Systems

This digest summarizes key findings of NCHRP Project 24-28A, "Validate the Results of NCHRP Project 24-28," conducted by McMahon & Mann Consulting Engineers, P.C., under the direction of the principal investigator, Kenneth L. Fishman. The digest is based on the project final report authored by Dr. Fishman.

TRB's National Cooperative Highway Research Program (NCHRP) Report 675: LRFD Metal Loss and Service-Life Strength Reduction Factors for Metal-Reinforced Systems explores the development of metal loss models for metal-reinforced systems that are compatible with the American Association of State Highway and Transportation Officials' Load and Resistance Factor Design Bridge Design Specifications.

"Mechanically stabilized earth (MSE) walls are an important class of infrastructure assets whose long-term performance depends on various factors. As with most all other classes of assets, MSE walls need periodic inspection and assessment of performance. To date, some agencies have established MSE wall monitoring programs, whereas others are looking for guidance, tools, and funding to establish their own monitoring programs. The objective of this synthesis project is to determine how transportation agencies monitor, assess, and predict the long-term performance of MSE walls. The information used to develop this synthesis came from a literature review together with a survey and interviews. Of the 52 U.S. and 12 Canadian targeted survey recipients, 39 and five, respectively, responded. This synthesis reveals that unlike bridges and pavements, MSE walls and retaining walls in general are often overlooked as assets. Fewer than one-quarter of state-level transportation agencies in the United States have developed some type of MSE wall inventory beyond that which may be captured as part of their bridge inventories. Fewer still have the methods and means to populate their inventories with data from ongoing inspections from which assessments of wall performance can be made. In the United States, there is no widely used, consistently applied system for managing MSE walls. Wall inventory and monitoring practices vary between agencies. This synthesis examines existing practices concerning the nature, scope, and extent of existing MSE wall inventories. It also examines the collection of MSE wall data, including the types of performance data collected, how they are maintained in wall inventories and databases, the frequency of inventory activities, and assessment practices relevant to reinforcement corrosion and degradation. Later parts of this synthesis discuss how MSE wall performance data are assessed, interpreted, and used in asset management decisions. This synthesis finds that the most well-implemented wall inventory and assessment system in the United States is the Wall Inventory Program developed by FHWA for the National Park Service. However, this system, like some others, uses 'condition narratives' in a process that can be somewhat cumbersome and subjective. Other systems use more direct numeric scales to describe wall conditions, and an advantage of such systems is that they are often compatible with those used in assessments of bridges. As experience with MSE walls accumulates, agencies will likely continue to develop, refine, and better calibrate procedures affecting design, construction, condition assessment, and asset management decisions. One portion of this synthesis is dedicated to summarizing the actions taken thus far by survey respondents to improve the long-term performance of their MSE walls. Many agencies prescribe the use of a pre-approved wall design and/or wall supplier. Other actions or policies frequently focus on drainage-related issues."--Summary.

An efficient and accurate inventory of a state highway agency's assets, along with the means to assess the condition of those assets and model their performance, is critical to enabling an agency to make informed investment decisions in a Transportation Asset Management (TAM) environment. Today, new technologies provide fast and improved ways to gather, process, and analyze data. The key is to identify and gather the most useful, reliable, cost-effect information and use it to make informed decisions for asset management. Four key infrastructure areas have been identified as primary asset components; pavements, bridges, geotechnical features, and roadside appurtenances. Each area contains multiple categories and data elements important for sound decision making. Although some similarities exist in these four primary categories, the nature of data collection may differ, depending on the asset type. The, sheer number of data elements and the length of asset networks for pavements and roadside appurtenances render the automated highway speed data collection method a necessity rather than a luxury. However, the discrete nature of bridges and geotechnical features make the automated mobile data collection method on a network level unfeasible with today's technology. Important issues in the collection process include precision, subjectivity and variability of the process itself, as well as speed, safety of the survey crew, proximity of the public, cost, etc. Although previous research has attempted to address these issues and determine the most appropriate method(s), the question remains as to which roadway data collection system is best for state highway agencies given real world constraints. This research set up a "sealed envelope" experiment wherein the identification, location, description, and quality of the asset data elements are known only to NCSU researchers. Vendors are informed of only the data necessary to perform their evaluation. To support this effort at 95-mile test course near Raleigh, North Carolina was identified, which contained a sampling of pavement, roadside, geotechnical and bridge elements. This document reports on the findings from the study