BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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Repair Scope: With the significant wear and deterioration, the existing timber wearing surface has reached the end of its useful service life and thus it is recommended that it be replaced in entirety. If the deck is replaced, it is recommended that the new timber planks be oriented parallel to the roadway centerline in lieu of the current 60 degree skew. This will reduce the number of joints in the deck surface that tires contact as vehicles cross the bridge, which will reduce abrasion and wear to the deck surface and improve the smoothness of the riding surface. In-place preservative treatments (see 4.3.1 below) are inconsequential as replacement of the timber wearing surface is recommended for other reasons. However, the timber wearing surface would not otherwise be a good candidate for in-place preservative treatments. Rehabilitation Scope: The Rehabilitation Scope would be the same as that above for the Repair Scope (i.e. no upgrades are required to meet current design standards.) Functionality and Safety: Replacing the timber wearing surface would improve certain aspects of the functionality and safety by providing a smoother riding surface. However, as a smoother riding surface will be conducive to faster travel speeds, the substandard roadway width and safety features become a more significant concern. Load Capacity: The timber wearing surface is not considered to contribute to the load carrying capacity of the deck. As such, there is no reduction in load carrying capacity due to the deteriorated condition of this element. Maintenance: Replacing the timber wearing surface would reduce maintenance in the short-term by reducing the need to periodically replace the existing deteriorating timber planks. However, the timber wearing surface is still expected to wear under abrasion from traffic loading, which will require that the timber wearing surface to be periodically replaced. Furthermore, it is not possible to completely eliminate small gaps between the wearing surface planks and thus there will still be small gaps between the planks that retain moisture, which promotes decay. Details that facilitate future replacement of the timber wearing surface may extend the service life of the supporting timber structural deck including reuse of predrilled holes in the timber structural deck that can be reused when the wearing surface planks are periodically replaced. Sealing or treating the cut ends of the planks may also reduce moisture absorption. A smoother riding surface will reduce vibrations that also act to work fasteners loose. Visual Impacts: It is not anticipated that replacing the timber wearing surface would introduce a visual impact as the timber wearing surface can be replaced in-kind. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 15 Final Report
4.2.2 Deck NBIS Condition Rating: 5 (Fair) Condition Description: The timber structural deck planks, which include the sidewalk areas, exhibit visual evidence of moisture retention and decay with staining and mildew on the underside between the timber stringers. Much of the preservative chemicals in the deck planks appear to have leeched from the timber and thus do not provide significant protection from decay. Although, the top surface of the structural deck beneath the timber wearing surface and the underside of the deck above the stringers is not accessible for visual inspection, the timber structural deck has experienced structural failure at one location in Span 4, which indicates that deterioration of the structural deck may be more significant than the visual evidence reveals. As described above for the timber wearing surface, moisture enters the small gaps between the timber wearing surface planks and is retained between the top of the structural deck and underside of the wearing surface, especially where the nails for the wearing surface planks have loosened. The underside of the deck exhibits signs of moisture retention and decay in varying severity throughout. Open nail holes in the top of the structural deck from attachment of timber wearing surface planks previously replaced, as well as splits and checks, provide opportunities for moisture and fungal spores to enter the structural deck planks to a depth beyond the preservatives, which promotes decay. As the top surface of the structural deck beneath the wearing surface and the underside of the structural deck above the stringers is not visible, it is not possible to visually confirm the condition of these areas. However, based on the observed condition of the accessible surfaces, it is likely that the condition of the non-visible surfaces is likely to be more severe due to the greater potential for retained moisture. The top surface of the structural deck in the sidewalks is visible and exhibits moderate deterioration with early signs of decay and significant splits and checks throughout. Similar to the timber wearing surface, the splits and checks in the top (horizontal surface) of the wood contribute to increased water absorption by providing easier access of the moisture to enter grains of the wood. The increased water absorption results in greater volumetric expansion of the wood when it is wet and increased shrinkage of the wood as it dries. The increased shrinkage promotes growth in the number and size of splits and checks in the wood, which further increases moisture absorption and provides an avenue for fungal spores to enter the wood. The significant volumetric change in the wood also acts to work nails loose. Increased water absorption also promotes decay by providing the source of moisture required by fungi that feed on the wood. Larger splits and checks will retain a greater amount of moisture. The ends of the timber structural deck planks exhibit early signs of decay. The cut ends of the structural deck are not sealed, and although the cut ends are not located where water typically ponds, water on the sidewalks drains over the cut ends as it drains through the openings in the pedestrian railing curbs, which permits water to absorb into the ends of the planks. Water absorption in the cut ends of the structural planks promotes decay near the ends of the planks. Based on the above conditions, it is expected that the deterioration and decay of the timber structural deck will continue and may accelerate. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 16 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: promotes growth in the number and s
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 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
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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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