Risk-Based Management Guidelines for Scour at Bridges with Unknown Foundations (2007) / Chapter Skim
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Pages 56-68
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From page 56... ...
NCHRP 24-25 Page 56 Phase II Final Report 5. SCOUR RISK MANAGEMENT GUIDELINES If we consider the fact that there are approximately 400,000 bridges over water, that over 60,000 of these have unknown foundations, and that research shows that – on average –approximately 80 fail due to scour every year, these facts strongly indicate that the strategies employed by bridge owners to prevent scour failure are working, even for bridges with unknown foundations.
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NCHRP 24-25 Page 57 Phase II Final Report No No No No Yes No Are scour countermeasures warranted? Are foundation reconnaissance and scour analysis warranted?
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NCHRP 24-25 Page 58 Phase II Final Report 5.1. Can the Foundation Be Inferred?
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NCHRP 24-25 Page 59 Phase II Final Report 2. Evaluate scour using FHWA HEC-18 (2)
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NCHRP 24-25 Page 60 Phase II Final Report and death – not from the bridge failure, but from the natural disaster - may be too great to bear if such a route is not available due to failure. For high priority structures, the following steps should be taken.
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NCHRP 24-25 Page 61 Phase II Final Report 5.3.1. Does the Bridge Meet Minimum Performance Level?
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NCHRP 24-25 Page 62 Phase II Final Report the footing bottom. If the foundation is piles, use foundation reconnaissance to determine depth of piles.
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NCHRP 24-25 Page 63 Phase II Final Report installing countermeasures, then ASM is probably not warranted. If ASM is warranted, then the lifetime risk of failure (PL)
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NCHRP 24-25 Page 64 Phase II Final Report criticality of bridge structures and the potential for loss of life, analysis to illuminate proper countermeasure design is probably worth more than 20% of total cost. If the cost of foundation reconnaissance and scour analysis is less than 50% of the estimated cost of countermeasures, the following steps should be taken.
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From page 65... ...
NCHRP 24-25 Page 65 Phase II Final Report If the cost of foundation reconnaissance and scour analysis is greater than the estimated cost of countermeasures, then proceed to Section 5.4, entitled "Install Countermeasures without Field Reconnaissance and Scour Analysis".
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From page 66... ...
NCHRP 24-25 Page 66 Phase II Final Report reconnaissance and scour analysis warranted and follow the recommendations in the "Is Foundation Reconnaissance and Scour Analysis Warranted? " subsection.
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From page 67... ...
NCHRP 24-25 Page 67 Phase II Final Report frequent scour measurements should be initiated. These markers or triggers should be reviewed and/or updated after each scour inspection.
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From page 68... ...
NCHRP 24-25 Page 68 Phase II Final Report Closure instructions might include load restrictions, lane closures and total closure criteria. The method of closure should also be described (e.g.
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