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Coordinating, Developing, and Delivering Highway Transportation Innovations

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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

3. Evaluation Findings

Evaluation Findings logoThis section discusses key findings, framed by the hypotheses mentioned in the previous chapter and detailed below. The findings illustrate the two key roles FHWA played leading to the adoption of revised AASHTO standards:

  1. Working with NTSB from the initial collapse and providing vital technical expertise.

  2. Working with NCHRP to advance Project 12-84 and collaborating with AASHTO to ensure the results included in NCHRP WOD 197 (the document that served to close out NCHRP Project 12-84) informed the changes to AASHTO standards (LRFD BDS and MBE).

3.1 Improved Specifications for the Design and Load Rating of Gusset Plates

Hypothesis: FHWA’s R&T activities led to the development, adoption, and application of improved specifications for the design and load rating of gusset plates.

There are many administrative details and approvals associated with starting a federally-funded research program. It can take years for an idea to grow into a refined topic and approach.

However, for the Gusset Plate Project FHWA was well-positioned to lead the initial research effort on gusset plate design and load ratings and ensure the research was conducted swiftly.

Finding: FHWA’s technical expertise in bridge infrastructure and its prior history of working with NTSB was critical during the bridge investigation.

Immediately following the collapse, NTSB investigators called FHWA engineers to assist on scene. Before the I–35W Bridge collapse, NTSB and FHWA worked together on numerous investigations going back to 1967, with two investigations in the recent past. One investigated an overpass collapse in Golden, CO, in 2004, and the other investigated a tunnel ceiling panel collapse on I–90 in Boston, MA, in 2006. During these investigations, NTSB and FHWA worked hand-in-hand and developed a good working relationship.

For the Golden, CO, overpass collapse, NTSB sought FHWA’s assistance performing structural testing and to provide specialized knowledge of bridge behavior. Following the I–90 tunnel collapse, FHWA was quickly on scene and conducted research on parameters that affect the behavior and performance of ceiling anchors. This ongoing relationship was instrumental in assembling the appropriate staff to efficiently respond to the I–35W Bridge collapse. Immediately after the collapse, NTSB got in touch with technical experts at FHWA and had structural engineers on site within a day.

FHWA staff expertise on gusset plate design and load ratings informed NTSB’s specific load rating calculations, as well as further research in its materials lab. FHWA provided the knowledge and expertise on gusset plate performance that led NTSB to conclude a gusset plate design error caused the collapse. The following quotes from NTSB staff who worked with FHWA during the investigation show that NTSB depended on FHWA for infrastructure-related domain expertise. [m]

We wanted them to assist in bringing their technical expertise in bridges into the investigation. We worked very closely with FHWA in the early on-scene phase, even while the structure was still in the river. – NTSB staff

Those are the guys who do research there who could provide us with expertise, which is what we want, we want the experts. – NTSB staff

Early on they were on scene. They did bring in their knowledge of bridge inspection practices and bridge design. Somebody from FHWA sat down and did the initial calculations based on the information to apply that to gusset plates and to the nodes on the superstructure, so they were doing a lot of work either for us or in conjunction with our folks in the materials lab to make the early-on assessment of what was going on. – NTSB staff

NTSB uses a party system to conduct investigations. A party system investigation relies on multiple stakeholders who contribute expertise across all phases of the investigation, from onscene to the feasibility and adoptability of final recommendations. The following quotes highlight FHWA’s knowledge of gusset plate design and performance that made its experts indispensable to NTSB, particularly in formulating the second set of recommendations for FHWA and AASHTO.

We want to have enough dialogue with them to accurately portray what the problem is and where we think we can go with a potential solution. I know FHWA was very much involved in that. We had numerous meetings throughout the course of the investigation to sit down and discuss our findings and concerns…It was through the course of those meetings we collectively had in our minds, here’s where we need to move forward and the best way to approach how to make those changes, and FHWA was involved quite a bit in that process. – NTSB staff

It was probably the summer…when we came down to saying there’s an issue with the inspection process, and that gusset plates aren’t being looked at to the degree we think they should be. That’s when we first started having the dialogue with Federal Highway saying, “Here’s some additional work to be done.” Prior to that, the focus of the case was what can we do to prevent having design errors make their way through the initial phase of a planned construction project, to the fact that they can remain in there to the point where they’re being built. – NTSB staff

As indicated in the final quote above, NTSB stakeholders initially said they considered what should be done to prevent gusset plate design errors from becoming part of planned construction projects. During the investigation, FHWA and NTSB determined that fewer truss bridges are being constructed, as they are a less popular option, but many such bridges will exist in States’ inventories for a long time to come. The focus of the recommendations turned to how States should maintain existing structures to prevent another collapse like the one that happened in Minnesota. While NTSB continued to develop its recommendations, FHWA conducted full-scale gusset plate load testing and continued to evaluate the state of practice for gusset plate design. This action from FHWA, to begin testing and to take a leadership role in gusset plate research, was unique and vitally important, as illustrated by the following quote:

When I found out how much work they were doing I was actually kind of surprised they really went after it. That was a substantial investment on their part. I give them a lot of credit for going after it.
– NTSB staff

Finding: FHWA’s coordination with key stakeholders contributed to an accelerated timeline leading to the close of NTSB recommendations.

AASHTO, FHWA, and NTSB stakeholders all reported that NTSB and FHWA frequently communicated while NTSB developed the final safety recommendations. NTSB wanted to accurately portray the problem identified in the bridge collapse investigation and to provide actionable recommendations, especially since AASHTO and FHWA would be responsible for fulfilling them.

Minnesota DOT and the engineering firm that designed and constructed the bridge were involved in discussions with NTSB, but FHWA was a main participant in NTSB meetings about the gusset plate problem and potential solutions. It became clear during the investigation that the gusset plate design problem had national implications, and FHWA was in a position to provide support on a far-reaching solution because of their unique expertise and Federal role. As one NTSB stakeholder explained in the quote below, FHWA’s close collaboration and coordination with NTSB was a major contributing factor to closing out NTSB’s recommendations.

Our dealings with FHWA have for several years been very good and strong with open dialogue, compared with our relationship with [another Federal agency]—you can see the number of our recommendations still open for that agency, compared to FHWA. – NTSB staff

Additionally, several NTSB staff members noted FHWA’s willingness to engage with NTSB. FHWA’s time and resource investments toward the NTSB investigation and recommendations process meant FHWA-specific recommendations were closed relatively quickly.

All recommendations for the Minneapolis bridge were closed within 5 years, which is perfect—we expect (the timeline) to be about 5–7 years. That is our average rate, 5–7 years, and we try to stick to that. And we’re trying to stick to that even more than we have in the past. Some agencies take much longer, some recipients take much longer. – NTSB staff

Our relationship with FHWA has allowed us to have good collaboration and led to recommendations that can be strong and meaningful and enacted in a short amount of time. – NTSB staff

Finding: FHWA’s commitment to bridge research and the decision to jointly fund the NCHRP effort accelerated the research timeline from initiation to conclusion.

Initial scoping efforts began in May 2008 for what would eventually become NCHRP Project 12‑84. Within 2 months FHWA and NCHRP reached an agreement to jointly fund the research, and the first meeting of NCHRP Panel 12-84 was convened. The project kicked off in October 2008, less than 1 year from initial scoping. The quick initiation of the research project was integral in helping FHWA accelerate the research timeline and move closer to the desired outcome of updating AASHTO’s specifications (LRFD BDS and MBE).

It was about manpower and funding, the idea that you could pool the resources and deliver the product so much faster, competently, which was in this case serving the needs of the industry because this was a safety issue that needed to be addressed in the near term…It was the fact that we had the ability to reprioritize and be more nimble in our processes and the work we had ongoing that allowed us to react that way. – FHWA staff

AASHTO SCOBS commissioned an NCHRP report in response to the NTSB investigation. Because FHWA released interim recommendations on gusset plate design shortly after the I–35W Bridge collapse, AASHTO stakeholders selected FHWA to be the Principal Investigator on the NCHRP report on gusset plate performance and design. In addition to providing expertise, FHWA offered matching funds to conduct the research and develop the NCHRP report. FHWA was able to redirect funds regarding steel bridge research to the Gusset Plate Project.[n] The typical life of an NCHRP project concludes about 6–7 years after funding is approved. In the case of 12-84, answers were needed much faster for gusset plates than this typical time range. FHWA was able to hit the ground running without going through the development of a request for proposal (RFP) and contractor selection that usually takes approximately two years.

[FHWA] was already working on the subject, on the analysis of the bridge that failed. So, they were, if you will, already miles down the road looking for the answer as opposed to the normal process to put out the RFP, wait for anybody interested in doing that work to submit a proposal, evaluate the proposals and on and on. By using FHWA, they were already working on the subject, so whatever they were doing was chargeable to FHWA until such time as the NCHRP project contract was signed. But from then on AASHTO, through NCHRP, was sharing in the cost. In many ways it was a no-brainer in this instance to go to FHWA as the contractor. Because of the exigency of the situation it was decided, ok let’s pool the money and let FHWA be the Primary Investigator. – Former AASHTO representative

FHWA invested funds to initiate research and provided vital technical expertise, led and carried out various research approaches, and managed contractors. Combined, those elements sped up the research timeline and more rapidly led to the development of revised specifications for load rating and gusset plate design.

3.2 Diffusion of Knowledge about Design and Load Rating of Gusset Plates

Hypothesis: New knowledge about the design and load rating of gusset plates was diffused among stakeholders because of FHWA’s R&T activities.

In addition to carrying out the initial research that developed into the work of NCHRP Project 12‑84, and coordinating the contracts falling under that project, FHWA actively spearheaded efforts to inform and engage pertinent stakeholders. FHWA staff provided ongoing updates to AASHTO SCOBS and its technical committees, and led extensive efforts to reach stakeholders by presenting at conferences, universities, workshops, and industry group meetings.

Finding: FHWA’s active and ongoing engagement of transportation stakeholders expedited delivery of new information regarding the design and load rating of gusset plates.

Correspondence between NTSB and FHWA regarding NTSB Safety Recommendation H-08-001 demonstrates the depth, breadth, and speed of communication on gusset plate performance and rating in the transportation community in the months and years following the I–35W Bridge collapse (see appendices D and E). A review of correspondence between NTSB and FHWA (see appendix E) concerning Recommendation H-08-001 shows that FHWA embarked on internal and external outreach efforts related to gusset plate research.

After FHWA released its first technical advisory—TA 5140.29—in January 2008 (following NTSB’s first safety recommendation), FHWA and AASHTO provided ongoing technical assistance and guidance to FHWA field offices and bridge owners about load rating and evaluation of gusset plates on steel truss bridges.(6) Additionally, FHWA offered several teleconferences with FHWA field offices and State DOTs to resolve issues and answer questions. In 2009, FHWA published “Load Rating Guidance and Examples for Bolted and Riveted Gusset Plates in Truss Bridges”—FHWA-IF-09-014—using the load and resistance factor rating and the load factor rating methods, with illustrated examples.(10)

The agency also sponsored several national teleconferences to familiarize FHWA and State bridge engineers with using the FHWA guidance. FHWA also organized a seminar in June 2009 titled, “Load Rating of Gusset Plates of Connections of Steel Truss Bridges” at the International Bridge Conference held in Pittsburgh, PA.(11) FHWA held a subsequent webinar series on the inspection and load rating of gusset plates using the FHWA guidance. All of these activities were vital in ensuring that appropriate stakeholders were continually updated and educated on the evolution of research and findings related to gusset plate design and load rating.

Moreover, FHWA delivered introductory and update presentations to various audiences during the course of NCHRP Project 12-84, and after the 12-84 panel had concluded its activities. The dates and types of outreach activities are included in appendix F.

m Please refer to appendix E for further information.

n Stakeholders provided this information in interviews with the evaluation team. Please refer to appendix B for a list of persons interviewed.



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