BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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Repair Scope: With the significant deterioration, including one reported structural failure, and due to the significant potential for more severe conditions than that known based on visual observation, the structural deck likely has limited remaining service life without corrective action. As such, it is recommended that the timber structural deck be completely replaced. Even if it were shown that the condition of the structural deck was not critical, it is not a good candidate for in-place preservative treatments (see 4.3.1 below) to extend the service life. The 4x8 timber planks are too small for internal treatments. The surface treatments have limited service life (approximately 5 years) requiring frequent reapplication, which is a concern due to the limited access to the top of the deck that is covered by the timber wearing surface. Removal of the timber wearing surface every 5 years to reapply the preservative treatment is not a practical solution. Many of the more effective preservatives include toxic chemicals that may be a concern for human contact and that may be an environmental concern due to the potential contamination from spills or excess preservative chemicals that leech out of the deck. 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: The proposed work has no significant impact on functionality and safety. Load Capacity: The current load rating does not identify a substandard load carrying capacity for the structural deck. However, the single structural failure indicates that the deteriorated condition of the deck has introduced localized areas with reduced load carrying capacity. Replacement of the structural deck planks will restore any loss in load carrying capacity. Maintenance: Replacing the timber structural deck would reduce maintenance in the short-term by reducing the need to perform repairs to the existing deck or to reapply in-place preservative treatments. Details that facilitate future replacement of the timber wearing surface may extend the service life of the timber structural deck including use 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. Visual Impacts: It is not anticipated that replacing the timber structural deck would introduce visual impacts as the structural deck can be replaced in-kind. 4.2.3 Sidewalks NBIS Condition Rating: 6 (Satisfactory) Condition Description: The timber sidewalks are part of the timber structural deck (see 4.2.2 above.) Repair Scope: See 4.2.2 above for details. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 17 Final Report
Rehabilitation Scope: In order to meet accessibility standards, the sidewalk in Spans 1, 8 and 12 would need to be widened 1’-7” to provide a minimum clear sidewalk width of 3’-0” in those spans and the other sidewalks would need to be widened 7” to provide a clear sidewalk width of 5’-0” behind the new crash tested timber traffic railings (see 4.1.5 above and 4.2.4 below.) Functionality and Safety: Wider sidewalks that meet accessibility standards proposed under the Rehabilitation Scope would improve accessibility, while the current sidewalk width does not provide this access. Maintenance: See 4.2.2 above for details. Visual Impacts: See 4.2.2 above for details. Minor widening of the sidewalk to meet accessibility standards is not anticipated to introduce a visual impact. 4.2.4 Curbs NBIS Condition Rating: 5 (Fair) Condition Description: The timber curbs are generally sound, but contain widespread minor to moderate splits and checks of varying severity throughout. In addition there is severe decay of a 3 foot length of the south curb near the bascule span. Similar to other timber members, 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 interior 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. Increased water absorption promotes decay by providing the required source of moisture required by fungi that feed on the wood. Larger splits and checks will retain a greater amount of moisture. Most of the preservative treatment in the curbs has leeched out of the members and thus no longer protects the timber from decay. The cut ends of the curbs are not sealed, and although the cut ends are not located where water typically ponds, some of the water on top of the curb drains over the cut ends, which permits water to absorb into the ends of the curbs. Water absorption in the cut ends of the curbs promotes decay near the ends of the curbs. As discussed above, neither the bridge railing nor the timber curbs meet current standards for safety. Low level brush curbs, such as the 1’-1” high curbs on this bridge, have a history of causing errant vehicles that strike the curb to lose control and rollover. The timber curbs are constructed of a series of individual 8x8 timber members in 12 to 18 feet lengths. The curb segments are misaligned as much as 1½” in some locations creating potential snag hazards for passing vehicles. Repair Scope: The presence of significant splits and checks, the lack of remaining preservative treatment, untreated end cuts, opportunities for retained moisture and exposure introduce conditions conducive to continuing decay. Although the existing bridge curb members currently Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 18 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: 4.2.2 Deck NBIS Condition Rating: 5
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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