BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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exhibit only minor decay, the remaining service life of the curbs is likely limited without corrective action. In addition, as it is recommended that the timber wearing surface and timber structural deck be replaced, it is recommended that the timber curbs also be replaced. In-place preservative treatments (see 4.3.1 below) of the timber curbs are not recommended. Many of the more effective preservatives for both internal and surface treatment 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 curbs. Rehabilitation Scope: The Rehabilitation Scope would be the same as that above for the Repair Scope with the exception that the timber curbs would be replaced with traffic railings located in the same location as the curbs and that meet the crash testing criteria of NCHRP 350. Crash tested timber traffic railings would better protect pedestrians from vehicular traffic. There are available timber traffic railings that meet the crash testing criteria of NCHRP 350 that can be implemented. The timber posts for the traffic railing would need to be mounted to the sides of the timber stringers with adequate bracing diaphragms between the stringers. The timber stringers will need to be relocated and spaced to accommodate the new traffic railings. As the available crash tested timber traffic railings are wider than the existing curbs, the sidewalks and overall bridge width would need to be widened by approximately 1’-7” in Spans 1, 8 and 12 to provide a minimum sidewalk width of 3’-0” to meet accessibility standards and 7” throughout the remainder of the bridge to maintain a minimum sidewalk width of 5’-0”. Use of crash tested traffic railings permits use of the existing bridge railings as pedestrian railings (see 4.2.5 below for additional discussion.) Functionality and Safety: The Repair Scope would not address the safety concerns. Replacement of the low-level timber curbs with crash tested timber traffic railings proposed under the Rehabilitation Scope would improve the safety for both motorists and pedestrians. Load Capacity: The timber curb is not considered to contribute to the load carrying capacity of the bridge. As such, there is no reduction in load carrying capacity due to the deteriorated condition of this element. Similarly, a crash tested timber traffic railing would not be considered to contribute to the load carrying capacity of the bridge. Maintenance: Replacing the timber curbs now would reduce maintenance in the short-term by reducing the need to make periodic repairs to the deteriorating curb members or to reapply inplace preservative treatments. Visual Impacts: Replacing the timber curbs in-kind would not be considered a visual impact. Replacing the timber curbs with crash tested timber traffic railings, which are higher and have a more massive appearance than the existing timber curbs, may have a visual impact. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 19 Final Report
4.2.5 Railings NBIS Condition Rating: 6 (Satisfactory) Condition Description: The timber bridge railing members are generally sound, but contain splits and checks in the vertical posts, horizontal rails and curbs in isolated railing members throughout the bridge. These checks and splits retain moisture and provide an avenue for fungal spores to enter the wood, which promotes decay. Most of the preservative treatment in the timber railing members has leeched out of the members and thus no longer protects the timber from decay. The cut ends of the railings and curbs are not sealed, and although the cut ends for the railings are not located where water typically ponds, some of the water on top of the rails drains over the cut ends, which permits water to absorb into the ends of the rails. As the curbs rest on the sidewalk, they are located where water that ponds on the deck and will absorb into the ends of the curbs. Water absorption in the cut ends of the rails and curbs promotes decay near the ends. The cut ends of the top of the posts are capped with copper sheeting to prevent moisture from entering through the end grains. As noted above, water absorption results in volumetric expansion of the wood when it is wet and increased shrinkage of the wood as it dries. Significant volumetric change in the wood can act to work fasteners loose. Loose bolts securing the horizontal rails to the posts and curbs to the posts and sidewalk deck, would permit water retention in the small gaps between these elements, which promotes decay. As noted above, the bridge railings contain openings between horizontal rail elements of 8” where the NFPA Life Safety Code specifies that the openings in guards protecting drop-off hazards should not permit a 4 inch diameter sphere to pass. Repair Scope: The presence of 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 railing members currently exhibit minimal decay, the remaining service life of the railing will be limited without corrective action. In-place preservative treatments (see 4.3.1 below) of the timber railing are not recommended. The railing members are too small for internal treatments. Many of the more effective preservatives used in surface treatments 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 railings. As the existing railing elements have some remaining service life, it is possible to reuse portions of the railing, at least until deterioration has advanced to the point at which the railings are unsafe. Eventually the railing elements will need to be replaced in entirety. Rehabilitation Scope: The Rehabilitation Scope would be the same as that above for the Repair Scope with the exception that it is recommended that the pedestrian railing be modified such that the maximum opening between the horizontal rail elements not permit a 4” sphere to pass in Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 20 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: Rehabilitation Scope: In order to m
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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