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<br />I <br />I " <br />I <br />I <br />I <br />I <br />i I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />II <br />I <br /> <br />FHWA TECHNICAL ADVISORY T 5140.20 <br />September 16, 1988 <br /> <br />(4) special attention should be focused on the routine <br />inspection of 'scour critical bridges, and on the <br />monitoring and closing as necessary of scour <br />critical and other bridges during and after floods. <br /> <br />4. EXISTING POLICY AND GUIDANCE. The following existing policy <br />and guidance serve as the basis for the recommendations set <br />forth in paragraph 3. <br /> <br />a. AASHTO Standard Specifications for Hiqhwav Bridoes. The <br />FHWA has accepted these specifications for the design of <br />highway bridges. They contain requirements for designing <br />bridges to resist scour. Particular attention is <br />directed to Article 1. 3.2, Hydraulic Studies, which <br />advises that, "Hydraulic studies . . . . should include <br />applicable parts of the following outline:" Included in <br />this outline is item 1.3.2.3 (b), Estimated scour depth <br />at piers and abutments of proposed structures. <br /> <br />b. AASHTO Manual for Bridge Maintenance. The FHWA endorses <br />the guidance contained in this manual for the maintenance <br />of bridges. Particular attention is directed to the <br />following two statements in support of the <br />recommendations contained in this Technical Advisory: <br /> <br />( 1) "The primary function of the bridge maintenance <br />program is to maintain the bridges in a con~tion <br />that will provide for safe and uninterrupted traffic <br />flows. The protection of the investment in the <br />structure facility through well programmed repairs <br />is second only to the safety of traffic and to the <br />structure itself." (p. 25.) <br /> <br />(2) "Determining an effective solution to a stream bed <br />or river problem is difficult. Settlement of <br />foundations, local scour, bank erosion, and channel <br />degradation are complex prOblems and cannot be <br />solved by one or two prescribed methods. A <br />geOlogist, hydraulic engineer, and structural <br />engineer are all needed for consultation prior to <br />undertaking the solution of a serious maintenance <br />problem. In some cases, certain remedial work could <br />actually be detrimental to the structure." I p .15 5. ) <br /> <br />5 <br />