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Project Information
Project ID:   FHWA-PROJ-11-0048
Project Name:   Monitoring of the Milton-Madison Bridge
Project Status:   Completed
Start Date:  June 13, 2011
End Date:  October 31, 2013
Contact Information
Last Name:  Ocel
First Name:  Justin
Telephone:  202-493-3080
E-mail:  justin.ocel@dot.gov
Office:   Office of Infrastructure Research and Development
Team:   Bridge and Foundation Engineering Team [HRDI-40]
Program:   High-Performing Steel Bridge
Project detail
Roadmap/Focus area(s):   Infrastructure Research and Technology Strategic Plan and Roadmap
Project Description:   The Federal Highway Administration discovered that the Milton-Madison Bridge is currently under replacement. This is a combined through and deck truss spanning the Ohio River between the towns of Milton, KY, and Madison, IN. The three approach spans on the Indiana side are simply supported deck truss spans built relatively low off the ground. Brief conversations indicate that the approach spans will be control demolished by either thermally cutting or shearing individual members one at a time. This affords two unique opportunities to monitor this bridge’s approach spans. First, live load data can be captured under ambient traffic to gain an understanding of real stress ranges in a 1929-era riveted truss with built-up members. This data will be critical to the future laboratory testing that will be conducted as part of an internal redundancy pooled fund study (if initiated). Second, and more important, monitoring during controlled demolition will provide key data, such as shock factors during instantaneous member removal and dead load redistribution, both of which would be important for the calibration of structural redundancy models in the National Cooperative Highway Research Program (NCHRP) Project 12-87. Demolition of the three approach span deck trusses is currently scheduled for spring 2012.
Goals:   To determine the degree of structural redundancy of a simply supported twin deck truss through experimentation.
Background Information:   The term “fracture critical” is perhaps one of the most widely debated in the steel bridge arena. The term carries certain negative connotations that are frequently referenced in various media and it haunts maintenance budgets for nearly every State in the United States. The National Bridge Inventory Standard defines a fracture-critical member as “a steel member in tension, or with a tension element, whose failure would probably cause a portion of or the entire bridge to collapse.” The most contentious part of the definition is how to assess whether the entire bridge would fail and what degree defines failure. Often redundancy is used to define the likelihood of collapse, and there are three recognized types of redundancy: load path, structural, and internal. The National Highway Institute class, “Fracture-Critical Inspection Techniques for Steel Bridges,” teaches students that fracture-critical members are those that do not possess load path redundancy, which refers to the number of parallel elements in the system. Having three or more parallel elements is considered sufficient for load path redundancy (i.e., main girders of a two-girder system are considered fracture critical, while they are not considered fracture critical for a three-girder system). Structural redundancy accounts for the ability of the system to redistribute loads before a collapse mechanism forms, and internal redundancy accounts for a member actually being built up from many parallel elements itself. The last two forms of redundancy are rarely used to attain exemption from fracture-critical inspection criteria.  The ongoing National Cooperative Highway Research Program (NCHRP) Project 12-87 will be defining the analysis criteria needed to reliably utilize structural redundancy to attain fracture-critical exemption. It will do this by defining systems-based analysis techniques, but will require sturdy calibration to known failures of systems with low redundancy. Trusses are an example of a system that typically does not have a load path redundancy, but that may possess structural redundancy from three-dimensional system behavior. A second project currently under solicitation is Transportation Pooled Fund Solicitation 1290, which will focus specifically on internal redundancy of built-up members. This project will grow fatigue cracks in built-up members and then subject them to rapid loading at an extreme temperature to replicate a fracture event. The outcomes of both projects will play critical roles in Federal Highway Administration’s future policy decisions regarding fracture critical member design and inspection.
Product Type:   Techbrief
Technical report
Test Methodology:   Full-scale experimental on an in situ bridge.
Expected Benefits:   Greatly reduced inspection cost, provided the definition of "fracture critical" can be expanded to include more situations based on internal and structural redundancy, not just load path redundancy.
Deliverables: 1. Name: "TECHBRIEF: Evaluation of Member and Load-Path Redundancy on the US-421 Bridge Over the Ohio River"
Product Type(s): Techbrief
Description: The deliverable is a final report written by the contracted agency outlining its methodology of instrumenting the bridge and monitoring through typical live loads as well as through demolition. The contractor will also summarize those results and how they pertain to current Federal Highway Administration policy on fracture-critical inspections.
Publication URL(s):
2. Name: "Evaluation of Member and Load-Path Redundancy on the US-421 Bridge Over the Ohio River"
Product Type(s): Technical report
Description: full contractors report outlining all aspects of the testing
FHWA Topics:   Roads and Bridges--Structures
TRT Terms:   Redundancy
Field Tests
Steel Bridges
FHWA Disciplines:   Structures
Subject Areas:   Bridges and other structures
Maintenance and Preservation


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