FHWA Unknown Foundations Summit
Evolution of the Unknown Foundations Problem
Jorge E. Pagan-Ortiz, FHWA Office of Bridge Technology Principal bridge engineer--hydraulics, leader of FHWA hydraulics team, member of UF summit steering committee
FHWA took active approach in 1988 after bridge failure in NY. FHWA asked for data from dots on bridges. FHWA sent memo requiring States do scour evaluations for new and existing bridges.
Scour evaluation requirement established in Feb 1990.
Based on rating factors of item 113 of FHWA "Recording and Coding Guide"
Low risk, 4,5,7,8,9, susceptible, critical, UF, tidal bridges
National Bridge Scour Evaluation Program:
November 2003: evaluations completed over 344,000; scour critical bridges: over 26,000; UF: about 86,000 (161 interstate bridges, on minor rural roads); tidal bridges: over 900; scour susceptible: over 26,000.
Biannual progress of natl bridge scour evaluation prog:
See progress by dots, but low risk category increasing which is good, but UF also increasing not good. These are bridges not evaluated, FHWA not provided guidance on how to evaluate. Lack of guidance.
Fed-Aid Hiwy bridges with UF:
Urban: Interstate 60; principal arterial 1,000; minor art 1,800; collector 1,600; Rural
Non Fed Aid Bridges
Urban local 4,400
Other fed aid
National totals: FAH urban 4552 rural 9643
Non fah 4389 43978
Other fah 3490 8675
this is different than what reported, creates discrepancy
What is UF bridge?
Bridge lacking info on foundation type, elevation, material, dimensions, foundation condition (integrity)
Policy – all bridges over water shall be evaluated for scour vulnerability; but how do if don't have critical info?
Evaluation exemptions granted – not for intstate bridges coded U these should be a priority; dots need id foundation, materials, but tech is limited, cost is high
Plan of action to be developed for scour critical bridges—recommendation not requirement; required for scour critical bridges. Need be proactive.
Quality of Data base
Scour screening phase I of scour prog; give owners more tools
National Bridge Inventory (NBI) data base not consistent when compared with biannual Scour report database
Bridges under 10 yrs old coded 6 or U
Not good bridge tracking system prior to NBI, old bridges 40-60 yrs old, is not good.
Prior to NBI not good track system
Communication – design, construction and bridge inspection sections. Need share info
Lack of guidance from FHWA, priorities, resources
Technology – cost, reliability, need to apply to a priority to bridges
Disciplines involved—not just hydraulics issue, geophysics issue, need tools; identify length and integrity of materials; need info if a bridge can be widened and withstand extra loads
Involves: hydraulics engineer etc.
Much has been done so far…
Approach: NCHRP project 21-05 phases 1& 2; bridge owners; FHWA: geotechnical notebook issuance no. 16, non-interstate bridges exempted from evaluations, risk base
More is needed
Many years of internal discussion
FHWA technical team convened Nov. 16, 2004 to address issues. 2 outcomes: idea of working on synthesis, summit on UF.
Will cover "State of Practice"
Bring parties together who have in-depth knowledge, experience, and vested interest in Identify: applications and limits of technology
Determine capability, reliability and probable cost of nondestructive methods
Develop guidance and management strategies
Determine research needs
Q: During 100 years, we accumulated 1,000 UF cases. Are we well equipped to reduce number to zero? We're dealing with the past; important not to increase
JP: need good communication to not increasing UF bridges, better guidance, better technology. Not increase but reduce.
Q: Final item was unknown condition of foundation. Say that for almost any bridge. How to know what the condition is of 80-90 year-old bridges?
JP: Element can't be forgotten. Hard to determine integrity, could take years to develop technology. Important component of issue, don't have answer. Didn't want exclude, but don't have answer how to use technology to determine integrity or condition. Try to come up with best guidance possible.
Q: Subsurface conditions, don't have good definition of conditions we're in…
JP: True, we don't know the condition of the materials. Geotechs have raised issue. The question is, is the condition of the material good enough to allow us to use it to widen the bridge, need to be concerned about integrity of that material?
Q: I meant soil and rock conditions.
JP: That is another issue that needs to be addressed. I don't have answers, but we have experts here. If that another issue, need to include in UF problem to created guidance for it. That's reason not just a problem for the hydraulics people. It affects engineers across the board. Need managerial strategies to address issues and concerns.