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REPORT
This report is an archived publication and may contain dated technical, contact, and link information
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Publication Number:  FHWA-HRT-17-039    Date:  January 2016
Publication Number: FHWA-HRT-17-039
Date: January 2016

 

FHWA Research And Technology Evaluation: Gusset Plates Final Report

2. Evaluation Design

Evaluation Design logoThis evaluation sought to understand how FHWA’s investment in gusset plate research improved the design and rating of gusset plate bridges. The evaluation team’s primary hypothesis was that FHWA’s R&T activities led to the development, adoption, and application of improved design standards and guidelines for rating gusset plate bridges. A secondary related hypothesis was that FHWA’s R&T activities led to new knowledge of the design and load rating of gusset plates diffused throughout the industry. These hypotheses are discussed in greater length in the Evaluation Findings chapter.

Figure 2 on the next page shows the logic model for the Gusset Plate Project and illustrates the links between key inputs, activities, outputs, outcomes, and impacts.[g] The main outcome was the adoption of revised AASHTO design specifications as part of the LRFD BDS and MBE. A secondary outcome was that new knowledge on the design and load rating of gusset plates was diffused to pertinent stakeholders. These outcomes were directly informed by three key FHWA outputs: NCHRP WOD 197, TA 5140, and Load Rating Guidance and Examples for Bolted and Riveted Gusset Plates in Truss Bridges (FHWA-IF-09-014). NCHRP Project 12-84 was the main effort that led to NCHRP WOD 197. Other key activities included developing technical advisories and guidelines, giving presentations at important conferences and AASHTO meetings to encourage buy-in, and FHWA’s ongoing coordination and collaboration with NTSB.[h]

This figure presents the logic model for the Gusset Plate project. The logic model is comprised of five columns of data, organized from left to right: Inputs, Activities, Outputs, Outcomes, and Impacts. Each column has a list underneath. Under Inputs, the list reads from top to bottom: NTSB investigation and final report, FHWA R&T funding, FHWA staff and technical expertise, and NCHRP funding. Under Activities, the list reads from top to bottom: NCHRP Project 12-84, developing technical advisories and guidelines, presentations at meetings, FHWA coordination with NTSB. Under Outputs, the list reads from top to bottom: NCHRP Document 197, Technical Advisory 6140, and Load Rating Guidance and Examples for Bolted and Riveted Gusset Plates in Truss Bridges (FHWA-IF-09-014). Under Outcomes, the list reads from top to bottom: Adoption and of revised AASHTO design specifications (LRFD BDS and MBE) and Diffusion of new knowledge of the design and load rating of gusset plates. Under Impacts, the list reads as improved bridge safety.

Figure 3. High-level logic model.

 

2.1 Evaluation Scope and Feasibility

The evaluation focused on FHWA R&T gusset plate investigations, including testing and research done in response to NTSB Recommendation H-08-001, which culminated in 2013 in the adoption of AASHTO standards on gusset plate design and load rating.

NTSB’s Recommendation H-08-001 for FHWA, issued in January 2008, reads:

For all non-load-path-redundant steel truss bridges within the National Bridge Inventory, require that bridge owners conduct load capacity calculations to verify that the stress levels in all structural elements, including gusset plates, remain within applicable requirements whenever planned modifications or operational changes may significantly increase stresses.(5)

NTSB’s November 2008 recommendations for FHWA—H-08-017, H-08-018, and H-08-019—address separate issues, including the development of a bridge design quality assurance and quality control program, requiring that bridge owners assess truss bridges using nondestructive evaluation technologies where appropriate, and updating bridge inspector training courses and materials. (7,8,9);[i]

Initiated in 2009, FHWA conducted research on proper methods to measure corrosion and section loss in inspections of single- and multi-plate gusset plate designs. That research is currently in publication. However, that work is not part of the scope of this evaluation, as preliminary interviews with State department of transportation (DOT) bridge personnel and AASHTO Subcommittee on Bridges and Structures (SCOBS) members indicated it is too early to measure the meaningful effects of this research.[j] State DOTs have varying schedules for bridge inspections and data was unavailable for the evaluation team to gather on recent State bridge inspections and changes resulting from updates to the MBE.

The scope of this evaluation is limited to the efforts that led to the eventual adoption of AASHTO’s revised standards for the design and rating of gusset plate bridges. This scope includes a description of how FHWA research helped NTSB identify the cause of the bridge collapse and allowed swift responses from FHWA, NCHRP, and AASHTO to the NTSB recommendations, as shown in figure 4 on the next page.

The left of the image begins with the collapse of the I-35W Bridge in 2007. Arrows indicate where an action or output influenced additional outputs. The lower right of the image has a legend indicating which agencies produced each output. FHWA is a yellow box, NCHRP a purple dotted box, AASHTO a red dotted box, and NTS a blue dotted box. The upper bubble represents the project outputs that fall within the scope of the evaluation. Within this bubble, the flow of outputs are, starting on the left: the collapse of I-35 W Highway Bridge (August 1, 2007) influenced NTSB Recommendation H-08-001 (January 15, 2008), which influenced NCHRP 12-84 (October 1, 2008 to January 31, 2013) which influenced NCHRP Web-Only Document 197 (May 2013), which influenced AASHTO Load and Resistance Factor Design Bridge Design Specifications 7th Edition (2014). The NTSB Recommendation H-08-001 (January 15, 2008) also influenced FHWA Technical Advisory 5140.29 (January 15, 2008), which influenced FHWA Load Rating Guidance and Examples for Bolted and Riveted Gusset Plates in Truss Bridges FHWA-IF-09-014 (February 2009). Both NCHRP Web-Only Document 197 (May 2013) and FHWA Load Rating Guidance and Examples for Bolted and Riveted Gusset Plates in Truss Bridges FHWA-IF-09-014 (February 2009) influenced AASHTO Manual for Bridge Evaluation - 2nd Edition with 2014 Interim Revisions (2013). The collapse of I-35 W Highway Bridge (August 1, 2007) also influenced FHWA Technical Advisory 5140.27 (August 2, 2007).The lower section displays project outputs outside the scope of evaluation. Starting on the left, the flow outputs begin with NTSB Accident Report NTSB/HAR-08/03 (November 14, 2008), and the three NTSB recommendations included in it. NTSB Recommendation H-08-017 influenced FHWA Guidance on QC/QA in Bridge Design (September 2011). NTSB Recommendation H-08-018 influenced FHWA Technical Advisory S140.31 (January 29, 2010), which influenced FHWA Evaluation of Section Loss Due to Corrosion in Single and Multi-Plate Gusset Connections Using Non-Destructive Technologies (2013). NTSB Recommendation H-08-019 influenced both FHWA Updated Bridge Inspector’s Reference Manual (February 2012) as well as Revised FHWA inspection training courses (2011-2012).

Figure 4. Flow diagram of project outputs by organization. [k]

 

2.2 Evaluation Methodology

To collect evaluation data, the Volpe team conducted in-depth interviews with key stakeholders and reviewed and analyzed documents from FHWA, NTSB, and a selection of States.

Evaluation Participants and Key Questions

Volpe interviewed NTSB investigators on the I–35W Bridge investigation, FHWA engineers, and members and leaders of various Technical Committees of the AASHTO Subcommittee on Bridges and Structures (SCOBS). A list of major stakeholders is included in table 1 below.

Table 1. Stakeholders

Stakeholder Role
FHWA Office of Corporate Research, Technology, and Innovation Management Evaluation Program Leader
FHWA Office of Infrastructure Research & Development (R&D) Technical Program Leader
National Transportation Safety Board NCHRP Project 12-84 Principal Investigators
AASHTO Subcommittee on Bridges and Structures I–35W Bridge collapse investigators and staff
Transportation Research Board National Cooperative Highway Research Program Decision makers who worked on updates to AASHTO’s LRFD Bridge Design Specifications and the Manual for Bridge Evaluation; chairs and former chairs of Technical Committee T-14 (Structural Steel Design); representatives responsible for disseminating information to AASHTO member agencies
Volpe Research Cosponsor

The Volpe team interviewed:

See appendix B for a complete list of stakeholder interviews and their relevance.[l]

These interviews sought to document:

Table 2 provides general questions Volpe asked during interviews with FHWA and NTSB stakeholders.

Table 2. General Questions for Stakeholder Interviews

Agency Question
FHWA What was your interaction with NTSB leading up to its first set of recommendations, H-08-001, during and following the onsite investigation?
FHWA What was the timeline, from idea generation through implementation, for conducting research and eventually publishing the NCHRP report?
FHWA What expertise and activities did FHWA contribute to NCHRP Project 12-84 and the final NCHRP WOD 197 report?
NTSB After FHWA fulfilled its particular role with the onsite investigation, how did your agencies continue to work together? What were the next steps in the process that eventually led to the NCHRP Project 12-84?
NTSB What is the process for bridge and highway investigations? Why, when, and how did you involve FHWA in the process?
NTSB How did you involve FHWA in the process for developing your recommendations following the I–35W Bridge investigation?
NTSB Describe the technical expertise and resources FHWA provided during and after the I–35W Bridge investigation.

 

Table 3. Most Important Documents from Review

Document Affiliated Agency Relevant Information
Accident Report NTSB/HAR-08-03 Collapse of I–35W Highway Bridge Minneapolis, Minnesota August 1, 2007 NTSB Final report presenting the conclusion of the NTSB’s investigation of the I–35W Bridge in Minneapolis.
Safety Recommendation H-08-001 NTSB First recommendation from NTSB to FHWA following I–35W Bridge collapse, before the investigation was closed.
Safety Recommendation H-08-001 Correspondence between NTSB and FHWA NTSB, FHWA Correspondence between the two agencies regarding the recommendation that FHWA encouraged bridge owners to rate gusset plate load capacity.
FHWA Technical Advisory (TA) 5140.29 FHWA Strongly encouraged owners to include gusset plates as part of a load rating, and ensure gusset plate capacity is adequately considered for prior ratings.
FHWA-IF-09-014 Load Rating Guidance and Examples For Bolted and Riveted Gusset Plates In Truss Bridges FHWA First publication from FHWA providing specific guidelines to bridge owners in meeting the requirements of FHWA TA 5140.29.
NCHRP Web-Only Document 197 Guidelines for the Load and Resistance Factor Design and Rating of Riveted and Bolted Gusset-Plate Connections for Steel Bridges NCHRP Final document with gusset plate load rating specifications that FHWA developed for AASHTO; served to close out NCHRP Project 12-84.
Accident Report NTSB/HAR-08-03 Collapse of I–35W Highway Bridge Minneapolis, Minnesota August 1, 2007 NTSB Final report presenting the conclusion of the NTSB’s investigation of the I–35W Bridge in Minneapolis.

 

Document Review

Table 3 highlights documents that informed the Volpe’s evaluation. The Volpe team obtained these documents through web searches and correspondence with stakeholders. See appendix C for a complete list of documents the team reviewed.


g A logic model is a visual depiction of program components-including inputs, activities, outputs, outcomes, and impacts–that are linked in a chain of causality. It describes the relationship between program resources, planned activities, and expected results. It is not meant to be a comprehensive or linear description of all program processes and activities, but rather it explains the theories of change that drive the design of a program and provides relevant hypotheses that can be tested in an evaluation.

h These activities were led by different offices within FHWA.

i See appendix D for a full description of NTSB's written recommendations for FHWA.

j A list of stakeholder interviews, including these preliminary discussions with State DOT bridge personnel and AASHTO SCOBS members, is in appendix E.

k Figure generated by research team.

l Stakeholders at four State DOTs were also interviewed prior to a change in the scope of the evaluation. These stakeholders are listed in appendix B.

 

 

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