U.S. Department of Transportation
Federal Highway Administration
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Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
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| This report is an archived publication and may contain dated technical, contact, and link information |
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| Publication Number: FHWA-HRT-13-101 Date: November 2013 |
Publication Number: FHWA-HRT-13-101 Date: November 2013 |
The second breakout session focused on identifying changes in service load and foundation reuse. The goal of this session was to solicit high priority input for new research and to prioritize listed high priority items. The workshop participants were again divided into two groups and discussed the session topic on the morning of May 1. Following the discussion time, the participants reunited to summarize the group findings.
A list of preliminary topics for discussion at the breakout session was provided to attendees as a starting point for discussion topics. The topics included changes in service loads, foundation reuse, load testing, test plan, numerical modeling, research products and risk-based analysis.
An expanded list of topics is shown below.
Participants in Group 1 were as follows:
Participants in Group 2 were as follows:
Each group approached the discussion in a different way. Below are summaries of their discussions.
The following items were highlighted in the Changes in Bridge Loads and Foundation Reuse breakout session.
Changes in Bridge Loads—Changes in bridge loads is a key issue as the trucking industry is proposing higher truck loads, for example, raising weights from 80,000 lb to approximately 97,000 lb, and there are projections in a doubling of truck traffic in the near future.2 Key issues related to changes in bridge loads include how to use NDT/modeling to determine effects on bridges, including calibration of such efforts; rapid methods of load testing; guidance for unknown and known foundation characterization and evaluation; and the introduction of risk-based methodologies to reduce/optimize time and cost.
Foundation Reuse—For foundation reuse, the highest priority was development of methods and guidance for reusing known and unknown foundations. In particular, risk and reliability methods should be explored. Guidance on methods for increasing load capacity of foundations, determining resistance factors for LRFD design, evaluation of Allowable Strength Design designed foundations in an LRFD platform, and NDT field testing were discussed as needed items in this category.
The following items were highlighted during the Changes in Bridge Loads and Foundation Reuse breakout session.
End Products—States need end products that can help them characterize changes in bridge loads and foundation reuse. Tools should be developed that help determine what NDT methods are recommended for site and foundation characterization, and for capacity determination. Of particular need is the development of specific guidance for the reuse and assessment of remaining service life of foundations.
Research Needs—Specific research needs were identified to include new tools for integrity of buried structures, refined analysis of holistic structures, synthesis of bridge record keeping, identification of information needed to reuse foundations, and maintenance monitoring for load rating and numerical models.
Following the group discussions, the participants reconvened and each group presented their findings (summarized above), with discussion following. There was considerable discussion on the push from the trucking industry for higher loads on structures. Although the concerns have primarily been on the superstructure side, there are concerns and risks associated with the substructure also. For known foundations, it may be possible to estimate effects of increased loads, but for unknown foundations, there might be great difficulty. The increased loads issue relates directly to a data need, which is to understand how much additional load will be transmitted to the foundations. This could be determined through short-term monitoring efforts that would measure the extra load applied to the foundation from an extra load on the superstructure.
On the foundation reuse, the discussions focused on the need for a guidance document that outlines when a foundation can be reused and the information necessary to make such a determination. The guidance should provide direction on the exploration methods available for known and unknown foundations, particularly NDT methods. Strategies/methods for strengthening known and unknown foundations for reuse would be valuable. There was agreement that performance/reliability indicators are needed for the reuse of foundations. It was emphasized that a holistic measurement approach was desirable.
At the start of the workshop, there was reasonable agreement on the need for development of test sites. Several possibilities were discussed including decommissioned bridges, existing bridges, and test facilities (likely at TFHRC). The physical testing would be conducted in concert with specific and targeted numerical studies and geared towards understanding the load capacity of the substructure and foundation elements. The discussions throughout the workshop appeared to reduce the enthusiasm for development of test facilities; however, the continued and increased use of numerical studies was endorsed by the group.
Two key interactions were discussed that merit mention. Coordination with the FHWA LTBP Program was encouraged to prevent duplication of efforts. A possible venue for discussion of issues is the upcoming 2014 TRB annual meeting and the 2016 ASCE Structural Engineering Institute/Geo-Institute joint meetings. Of particular interest might be the idea of a prediction challenge of response of the superstructure and substructure to various imposed loads.
2 Legislation called the Safe and Efficient Transportation Act was proposed by the Coalition for Transportation Productivity (CTP), which would allow States to raise the interstate weight limits of transport trucks from current 80,000 lb to a maximum of 97,000 lb. CTP states that freight traffic in the United States is expected to at least double by 2035.(19)
