BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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4.6.2 Approach Guardrail/Transitions NBIS Condition Rating: 5 (Fair) Condition Description: The steel guardrail attached to the back face of the wing walls is typically loose. There is minor impact damage to the north approach guardrail at the west approach to the bridge. The steel guardrail does not meet current design standards and thus does not adequately protect motorists from the bridge end hazards. The steel guardrail does no include proper end treatments and transitions to the bridge. The steel guardrail is also acting as a pedestrian railing along the sidewalk. The steel guardrail does not meet current design standards for a pedestrian railing protecting a drop-off hazard including railing height and opening width. Repair Scope: Reattach the loose guardrail attached to the back of the abutment wing walls. Rehabilitation Scope: See 4.4.1 above for additional discussion. Provide crash-tested timber guardrail in line with the new traffic railing on the bridge and along the approach roadway for a length of approximately 120 feet to provide the required advancement length required to protect motorists from the bridge end hazard. Provide the required proper end terminations and transitions to the bridge traffic railing. Replace the guardrail at the back of the sidewalk with new timber pedestrian railings that meet current safety standards for drop-off hazards. This will work will need to be worked with the modifications to the abutment wing walls and new concrete sidewalks. 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 guardrails do not affect the load capacity of the bridge. Maintenance: The continued use of the existing guardrails is not a significant maintenance concern. New timber guardrails and pedestrian railings are not anticipated to introduce significant additional maintenance requirements in the short-term but may introduce minor additional maintenance in the long-term with additional timber members to be maintained. Visual Impacts: Modifications to the abutments to accommodate the wider sidewalks, pedestrian railings and traffic railing are a visual departure from the existing configuration. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 47 Final Report
5.0 OTHER CONSIDERATIONS 5.1 Navigation Opening As identified above, the bascule span currently provides 19’-4” of horizontal clearance between fenders. The bascule leaf is approximately 23’-8” from pivot to tip and rotates to a maximum angle of approximately 75 degrees from the horizontal position in the fully raised position. With the bascule leaf in the fully raised position, the bascule leaf overhangs the west fender and provides unlimited vertical clearance for a width of approximately 15’-2” between leaf tip and east fender. Reportedly the bridge does not currently open to its originally intended opening angle due to concerns with the bridge operation. Replacement of the operating equipment with new equipment that allows the bridge to pivot to its full intended opening angle will at best only provide the original 15’-2” wide clear opening identified above. Reportedly there are numerous impacts to the east fender system as boaters navigate to clear the raised bascule leaf. Due to the significant challenges of navigating this narrow opening, boating interests have requested for improvements to the navigation opening and have confirmed that a minimum horizontal clear opening with unlimited vertical clearance for a width of 25 feet would meet their needs. Evaluation of the bascule span geometry confirmed that limited improvements to the navigation width can be gained within the existing constraints. A slight shift of the pivot point to the west will permit the bascule span to be raised to a steeper opening angle. The shift combined with a bascule span opening angle of 82.5 degrees yields a clear width with unlimited vertical clearance of 19’-4”, which equals the clear distance between fenders. However, this is still significantly less than the 25’-0” clear opening width requested by the boating interests. Physical restrictions limit the amount this opening can be improved as follows: 1. A greater shift results in a longer bascule span from pivot to tip, which requires greater amount of counterweight to balance the span. There are two limitations that limit the size of the counterweight. The first is the limitation on the length of the counterweight, which is restricted by the limited underdeck clearance and the requirement that the counterweight not become submerged when the bascule span fully opens at high tide. The second is the limitation on the counterweight thickness, which is restricted by the limited clearance between the underside of the stringers that support the counterweight and the Bent 7A piles with the bascule span fully raised. The limitations on the size of the counterweight govern the amount of shift that can be made. 2. With the bascule span fully raised, the extension of the operating rope past the defector sheave must be of a minimum length in order to meet maximum horizontal deflection angles. The current length of extension of operating rope at the current maximum opening angle is already close to the minimum recommended. In order to improve this, the offset of the sheave pole relative to the pivot needs to increase. This shift is possible with the relocation of the sheave poles from their current location on Bent 7A to Bent 6. As the recommended repairs and rehabilitation include replacement of significant portion of the bridge, there is a risk that the US Coast Guard may consider and classify the project as a bridge replacement instead of a repair or rehabilitation and as such require improvements to the Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 48 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 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: Condition Description: There are cu
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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