BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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Functionality and Safety: The timber masts have no significant affect on functionality and safety. Shifting the masts in conjunction with the replacement of the operating equipment will improve accessibility. Load Capacity: The timber masts may be undersized for operating forces meeting current design standards (see 4.3.6 below). Replacing the masts with a larger members or strengthening the masts with carbon fiber can be used to address this potential concern. Maintenance: Installation of FRP sheets to the sides of the masts may increase maintenance as it may be necessary to provide minor maintenance including reapplication of protective coatings, repair of adhesives and/or periodic replacement of the carbon fiber. Replacing the masts now would reduce maintenance in the short-term by reducing the need to make periodic repairs to the deteriorating masts or to reapply in-place preservative treatments. Visual Impacts: Replacing the timber masts in-kind would not introduce a visual impact. The addition of FRP sheets to the exterior surfaces of the timber masts may introduce a visual impact. 4.3.5 Paint/Coating (Steel Counterweight Box) NBIS Condition Rating: 5 (Fair) Condition Description: The rear third of the steel counterweight box that contains the concrete and steel ballast exhibits moderate to heavy surface corrosion with minor overall corrosive deterioration and localized areas with moderate section loss. The bolts used to secure the counterweight to the underside of the timber stringers also exhibit moderate to heavy corrosion with minor overall section loss. The galvanized coating on the steel box and mounting bolts no longer adequately protects the steel from corrosion as much of the zinc that cathodically protects the steel has been consumed. The corrosion of the steel is largely attributed to the dipping of the rear end of the counterweight box into the saltwater each time the bridge is raised at high tide and low clearance above the saltwater. Repair Scope: As a minimum, the steel counterweight box should be sand-blasted and recoated. It is recommended that the new coating also contain zinc (similar to that of the previous galvanizing.) Zinc can be field applied as either a paint coating or by way of hot spray application (metalizing). Metalizing has a higher initial cost but is known to have a longer service life than zinc paint coatings. In addition, it is recommended that the portion of the counterweight that dips into the water also be sealed with a coal tar epoxy or polyurea coating that limits exposure of the counterweight to the saltwater. The corroded mounting bolts for the counterweight should be replaced. Alternatively, the counterweight can be replaced with a new counterweight fabricated using stacks of stainless steel plate (in lieu of a combination of concrete and steel) and stainless steel mounting bolts. This will reduce maintenance and extend the service life of the counterweight. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 29 Final Report
Use of an all steel counterweight will permit reduction in the length of the counterweight with the potential to prevent the counterweight from dipping in the saltwater. Rehabilitation Scope: The counterweight may need to be replaced with a new heavier counterweight in conjunction with new heavier timber stringers (see 4.3.1 above.) Similar to the Repair Scope, it is recommended that the counterweight be completely replaced using stacks of stainless steel plate, stainless steel mounting bolts and a shorter counterweight. Functionality and Safety: The counterweight does not affect the functionality and safety of the bridge. Load Capacity: The timber stringers will need to be evaluated for the additional weight from a heavier counterweight. The counterweight will be heavier if the counterweight is made shorter and if heavier stringers are provided. Currently, the design of the stringers is not governed by the weight of the counterweight and thus it is not anticipated that larger stringers would be needed due to a heavier counterweight. Maintenance: Cleaning and painting the existing steel counterweight box will require recurring ongoing maintenance to recoat the steel and to replace mounting bolts. Replacement of the counterweight using stainless steel and using a shorter, heavier counterweight that keeps the counterweight from dipping in the saltwater will further extend the service life and reduce maintenance. Visual Impacts: Repair or replacement of the counterweight is not anticipated to introduce a visual impact as the proposed modifications do not significantly change the overall configuration of the bascule span or other parts of the bridge. 4.3.6 Operating Equipment NBIS Condition Rating: N/A Condition Description: The condition of the bridge operating equipment is not described in the Structures Inspection Field Reports. However, there are numerous reported concerns with the frequent required maintenance and unreliable operation of the bridge. Photo 7 - Operating Equipment Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 30 Final Report
Page 1 and 2: BRIDGE REPAIR/REHABILITATION FEASIB
Page 3 and 4: 1.0 EXECUTIVE SUMMARY The existing
Page 5 and 6: such there is a risk that the proje
Page 7 and 8: 3.0 BRIDGE DESCRIPTION Bridge Numbe
Page 9 and 10: Photo 2 - Present Mitchell River Br
Page 11 and 12: 4.0 ELEMENT CONDITION & REHABILITAT
Page 13 and 14: Based on the 1997 load rating analy
Page 15 and 16: promotes growth in the number and s
Page 17 and 18: 4.2.2 Deck NBIS Condition Rating: 5
Page 19 and 20: Rehabilitation Scope: In order to m
Page 21 and 22: 4.2.5 Railings NBIS Condition Ratin
Page 23 and 24: Functionality and Safety: Eliminati
Page 25 and 26: Although in-place preservative trea
Page 27 and 28: The bascule span timber stringers c
Page 29: Repair Scope: Although the timber m
Page 33 and 34: additional force effects, the speci
Page 35 and 36: typically loose. The steel guardrai
Page 37 and 38: Functionality and Safety: The cap b
Page 39 and 40: The surface decay and deterioration
Page 41 and 42: the interior of the piles where the
Page 43 and 44: Load Capacity: The current loss in
Page 45 and 46: Visual Impacts: Replacement of the
Page 47 and 48: Condition Description: There are cu
Page 49 and 50: 5.0 OTHER CONSIDERATIONS 5.1 Naviga
Page 51 and 52: SUMMARY OF TIMBER ELEMENT SERVICE L
Page 53 and 54: 5.3 Funding The project is currentl
Page 55 and 56: navigation opening. The estimated c
Page 57 and 58: • Continued replacement, repair a
Page 59 and 60: APPENDICES A. Existing Bridge Plans
Page 74: APPENDIX B Structures Field Inspect
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PAGE 3 OF 22 CITY/TOWN B.I.N. BR. D
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CITY/TOWN B.I.N. BR. DEPT. NO. 8.-S
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PAGE 2 OF 7 CITY/TOWN B.I.N. BR. DE
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APPENDIX C Load Rating Summary (199
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MAINTENANCE AND REHABILITATION OF T
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Figure 14-1. - Many covered bridges
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(discussed later in this chapter),
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Figure 14-5. - Liquid wood preserva
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wood, and other openings to the atm
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Table 14-1. - Number and size of ho
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member noting treatment information
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Figure 14-11. - Splicing and scabbi
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STRESS LAMINATING Stress laminating
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ond between separated sections, inc
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onding the old and new pile section
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GENERAL PROCEDURES FOR EPOXY REPAIR
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openings will allow epoxy to escape
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Another quality control problem is
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6. Avent, R.R. 1985. Factors affect
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Integrated Remedial Protection of W
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Figure l-Effect of fumigant applica
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Table 1- Residual MITC content in D
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of reinvasion (Forsyth and Morrell,
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might represent the best option, wh
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In: Ritter, M.A.; Duwadi, S.R.; Lee
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Present and Potential Commercial Ti
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2 U.S. DEPT. OF AGRICULTURE HANDBOO
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10 U.S. DEPT. OF AGRICULTURE HANDBO
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APPENDIX F FRP Pile Jackets
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about its hazard to human health. T
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Fig. 5. Cross section of wood pile
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(Lopez-Anido et al. 2004c). For exa
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Table 1. Cost Items for FRP Composi
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Hardcore Composites. (2000). Hardsh
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CALCULATION COVER SHEET Project Nam
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URS Corp. 260 Franklin Street Bosto
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APPENDIX I Correspondence
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BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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