BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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Photo 9 - Powder Point Bridge - Pile Condition • The above referenced article on Commercial Timbers of the Caribbean, referring to marine borers, states, “The most practical protection for piling and other timbers used in sea water is heavy treatment with coal-tar creosote or creosote-coal-tar solution.” Currently, the use of creosote preservative treatment of piles is restricted and there is widespread opposition to its use in marine environments in Massachusetts. However, proponents of creosote preservative treatments such as the Western Wood Preservative Institute, the Creosote Council, and others argue that the environmental concerns are unfounded and that there is no scientific evidence to support the concerns. Until these disagreements can be resolved, the restrictions on its use are likely to remain and there is a risk that creosote treated timber piles will not be permitted. As such, the preservatives currently supported for use on timber piles in this environment are less effective waterborne preservative chemicals, which yield a significantly shorter service life for the piles than creosote. It is recommended that the bolting hardware throughout bridge 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 piles do not affect the functionality and safety of the bridge. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 41 Final Report
Load Capacity: The current loss in section of the piles is not currently considered severe enough to reduce the load carrying capacity of the bridge to a capacity less than the other governing members of the bridge. However, if the piles are permitted to continue to deteriorate, it is likely that this condition will eventually be reached. The foundation capacity of many of the piles is unknown as there are no pile driving records indicating the depth to which the piles were installed or the driving resistance that was achieved. Although it is likely that the piles were driven to dense sandy glacial till material found 40 to 50 feet below the river bed, this cannot be confirmed. There is also no information regarding the design capacity of the 1925 piles. The predicted local scour (approximately 4 feet) will further reduce the load carrying capacity of the piles and the lateral stability. Although there is no reported significant settlement or loss in stability, the factors of safety for both axial capacity and lateral stability are unknown and thus there is a risk that the piles can settle under heavy loads or lose stability due to scour from a major storm event. Maintenance: Installation of FRP jackets to the piles may increase maintenance as it may be necessary to provide minor maintenance of the jackets. Based on the limited experience with these jackets, it is difficult to fully gauge the maintenance impacts. Replacing the timber piles 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. Visual Impacts: The installation of FRP jackets on the piles may introduce a visual impact, as the timber piles will be completely obscured by the jackets. Furthermore, the jackets will be significantly larger in diameter than the existing piles (approximately 18” to 20” in diameter instead of the current 12” diameter timber piles.) With the FRP jackets installed, the piles will effectively no longer be considered timber piles as they will be considered composite piles (i.e. FRP shell with a timber core.) 4.4.4 Timber Bracing NBIS Condition Rating: 4 (Poor) Condition Description: The timber lateral bracing members throughout the bridge were replaced, with the exception of the bracing members in Bents 4A and 6A, when the bridge was reconstructed in 1980. There are diagonal lateral bracing members secured to the piles in every pile bent with the exception of Bent 8 and diagonal longitudinal bracing members attached to the piles at the outside edge of the bridge between Bents 2 and 3, Bents 5 and 6 and Bents 8 and 9. The bracing sometimes include spacer boards to offset the bracing from the piles needed to accommodate misalignment of the piles. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 42 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: the interior of the piles where the
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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