BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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The bracing members typically exhibit moderate to heavy deterioration and corresponding loss in section within the tidal zone due to marine borer attack. The south end of Bent 3, the north end of Bent 5, and the south end of Bent 8 represent the most severe conditions with the lower end of the bracing member exhibiting complete deterioration for a length of 4 to 5 feet. All of the existing bracing members contain creosote preservatives; however, much of the creosote has leeched from the bracing members in the tidal zone and thus no longer protects the bracing members from surface decay and marine borer attack. The creosote preservative in the upper portion of the bracing is in greater quantity; however, there is evidence that the quantity has reduced somewhat due to ongoing leeching of the material. The galvanized steel bolts that attach the bracing members to the piles exhibit heavy surface corrosion and moderate section loss in the tidal zones and light surface corrosion at other locations. Repair Scope: As the bracing members throughout the bridge include significant deterioration from marine borer attack, it is recommended that the timber bracing members including corresponding spacer boards be replaced. As the bracing members are partially submerged in saltwater and creosote preservative treatment of piles is restricted for use in marine environments, the bracing members will need to be replaced with dimensional lumber with water-borne preservative chemicals permitted for use in this environment. As the water-borne preservatives are less effective in protecting the timber, the bracing members are likely to have a limited service life. The use of tropical timber may increase the service life somewhat, but recent experience in similar applications indicates that the service life is still likely to be limited. It is recommended that the bolting hardware throughout bracing system be replaced with more corrosion resistant material such as Type 316 stainless steel that does not rely on sacrificial material with a limited service life (e.g. zinc coatings) to protect the bolts. Rehabilitation Scope: The Rehabilitation Scope is the same as that for the Repair Scope. Functionality and Safety: The bracing members do not affect the functionality and safety of the bridge. Load Capacity: The bracing members are required for the lateral stability of the structure and to reduce deflections that might make motorists and pedestrians feel uncomfortable. The lateral bracing does not otherwise directly affect the load carrying capacity of the structure. Maintenance: Replacing the timber bracing now would reduce maintenance in the short-term by reducing the need to make periodic repairs to the deteriorating timber or to reapply in-place preservative treatments. However, based on the limited anticipated service life of timber piles in this environment, maintenance would likely continue to be a significant long-term concern with the less effective water-borne preservatives. Use of tropical timber may increase the service life slightly and thus reduce maintenance somewhat, but because the durability of this timber is unreliable, the long-term maintenance is still anticipated to be a significant concern. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 43 Final Report
Visual Impacts: Replacement of the timber bracing is not anticipated to introduce a visual impact. 4.5 Channel & Channel Protection 4.5.1 Timber Fender System NBIS Condition Rating: 3 (Serious) Condition Description: The timber members that make up the fender system were replaced when the bridge was reconstructed in 1980. These members consist of a series of 6x12 vertical members and 6x12 horizontal members used to stiffen and mount the fender boards to the pile bents. There are also smaller horizontal members secured to the front of the vertical planks that serve as rub rails. The vertical planks for the rub rails typically exhibit moderate to heavy deterioration and corresponding complete loss in section within the tidal zone due to marine borer attack and decay. The existing vertical planks contain water-borne preservatives, much of which has leeched out of the members in the tidal zone. The horizontal members contain creosote preservatives, some of which has leeched out the members making it less effective in protecting the members. The east fender exhibits impact damage at both ends with several vertical planks that are leaning or that have rotated. The fenders do not include tapered features that help guide vessels approaching the opening. The galvanized steel bolts that attach the fender members to the pile bents exhibit heavy surface corrosion and moderate section loss. Repair Scope: As the boards that make up the fender system include significant deterioration from marine borer attack, it is recommended that these members be replaced. As the fender boards are partially submerged in saltwater and creosote preservative treatment of piles is restricted for use in marine environments, these boards will need to be replaced with dimensional lumber with water-borne preservative chemicals permitted for use in this environment. As the water-borne preservatives are less effective in protecting the timber, the fender boards are likely to have a limited service life. The use of tropical timber may increase the service life somewhat, but recent experience in similar applications indicates that the service life is still likely to be limited. It is recommended that the bolting hardware throughout fender system be replaced with more corrosion resistant material such as Type 316 stainless steel that does not rely on sacrificial material with a limited service life (e.g. zinc coatings) to protect the bolts. Rehabilitation Scope: The Rehabilitation Scope is the same as that for the Repair Scope. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 44 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 and 30: Repair Scope: Although the timber m
Page 31 and 32: Use of an all steel counterweight w
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: Load Capacity: The current loss in
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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