BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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The effectiveness of the counterweight to balance the operating forces is lessened when it dips in the water at high tide and becomes somewhat buoyant, which increases the force in the operating ropes when the bascule span is raised. Maintenance: Replacement of the operating equipment with new operating equipment properly sized and designed to current design standards would reduce the wear and fatigue on the wire ropes, provide greater horsepower to overcome minor increases in load caused by ice, wind and friction. All of these will reduce maintenance requirements. Replacement of the electrical power and control equipment will also reduce the maintenance required to periodically repair the electrical equipment. Visual Impacts: The minimum recommended size for the new sheaves, pulleys and winch drums is approximately 36” in diameter. The significantly larger sheaves, pulleys and winch drums will be a significant visual departure from the existing equipment and thus may introduce a visual impact. Shifting the operating equipment outward by 1’-0” may also introduce a visual impact. 4.4 Substructure 4.4.1 Concrete Abutments NBIS Condition Rating: 5 (Fair) Condition Description: The abutment concrete is generally sound with minimal cracking and spalling that does not significantly reduce the integrity of the abutments. Previously installed 1/8” thick epoxy mortar applied to the exposed concrete surfaces of the abutments has cracked and spalled in isolated areas, primarily at the locations of construction joints where the abutments were previously modified. However, this condition is primarily cosmetic in nature. There is a single large spall, measuring 12”x9”x6”, at the top of the East Abutment back wall adjacent to the south sidewalk. The timber sills (caps) are typically sound with no apparent significant decay, although the sills contain splits and checks of a depth that permits fungal spores to access the center of the timber, where there are no preservatives, which increases the risk for decay. Much of the preservatives have leeched from the surfaces of the timber increasing the risk of surface decay as well. Moisture from the roadway deck joint, as evidenced by the moisture staining, is retained on top of the abutment breast walls adjacent to the sills, which promotes fungal decay. The backside and underside of the timber sills adjacent to the abutment concrete and the top of the sills directly below the timber stringers are not accessible for visual inspection, and thus the condition of these surfaces cannot be verified. The cut ends of the sills are not sealed, and although the cut ends are not located where water typically ponds, water running over the cut ends can absorb in to the ends of the sills, which promotes decay. The asphalt sidewalks along the wing walls (retaining walls) do not provide the required minimum clear width of 3’-0” and thus to not meet accessibility requirements. The top of the concrete wing walls is above the asphalt sidewalk surface with the height above the sidewalk varying along the length. The steel guardrail attached to the back face of the wing walls is Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 33 Final Report
typically loose. The steel guardrail does not meet standards of safety for protecting drop-off hazards. Repair Scope: The failed epoxy mortar spalls should be repaired. Although the timber sills are currently sound with no significant apparent decay, the size and depth of the current splits and checks, the limited remaining preservatives in the wood, and the current exposure introduces conditions conducive to fungal decay. As such, the remaining service life of the existing timber sills may be limited without corrective action. Similar to the timber stringers, there are options for in-place preservative treatment of the timber sills including both internal and surface treatments. However, many of the same risks and concerns for in-place preservative treatments exist for the sills with exception that the drilled holes for internal treatment are not likely to be significant and there are no access concerns. Due to the location of the timber sills adjacent to the waterway, there are significant concerns with the toxic chemicals and the potential for environmental contamination from spills or run-off of chemicals that leech from the sills. As such, in-place preservative treatments are not recommended for the timber sills. Rehabilitation Scope: In addition, to the Repair Scope, the abutments should be modified to accommodate wider sidewalks needed to satisfy accessibility requirements. This includes lowering the top of the wing walls and casting new concrete sidewalks that are approximately 2’- 0 wider, which can be accomplished by cantilevering the sidewalk past the exterior face of the wing walls. This work should be performed in conjunction with recommended improvements to the guardrails and pedestrian railings (see 4.6.1 below.) Functionality and Safety: The Repair Scope does not improve the functionality and safety. Without modifications and improvements to the abutment wing walls and the adjacent sidewalks, guardrails, curbs and railings, there will continue to be safety concerns for pedestrians and motorists and accessibility concerns. Proposed improvements to the abutment and approach roadway in the Rehabilitation Scope will improve safety by better protecting pedestrians from the drop-off hazard and motorists of the bridge end hazard. The modifications will also provide the required minimum sidewalk width for accessibility. Load Capacity: The current abutment deficiencies do not contribute directly to the load carrying capacity of the bridge. Maintenance: Replacing the timber sills 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. Visual Impacts: Modifications to the abutments to accommodate the wider sidewalks, pedestrian railings and traffic railing are a visual departure from the existing configuration and thus may introduce a visual impact. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 34 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: additional force effects, the speci
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
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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