BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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effectiveness of these chemicals is somewhat limited and has shown mixed results. In addition, the potential for spills and leeching of the toxic chemical preservatives into the marine environment raises environmental concerns with significant risk that the use of these treatments may not be permitted. A program of continuing to extend the service life of the bridge by way of piecemeal replacement of timber members, although technically feasible, is generally not cost-effective. Although it is technically feasible to replace a number of the more readily accessible timber elements on a piecemeal basis (e.g. bridge railing, curbs, timber wearing surface, sheave poles, lifting beams and bracing members) replacement of other timber elements that are not readily accessible requires removal of a significant portion of other elements of the bridge. For example, replacement of the structural deck planks requires removal of the timber wearing surface and curbs, replacement of the stringers requires removal of the structural deck, wearing surface and curbs, replacement of the timber cap beams requires replacement of the stringers, structural deck, wearing surface and curbs, and replacement of the piles requires complete removal of the superstructure and cap beams. It is sometimes possible to strengthen or replace a deteriorated portion of an existing member (e.g. a deteriorated section of a stringer, cap beam or pile.) However, this typically requires the addition of reinforcing plates to the members or temporary support of the structure while the deteriorated portion is removed and a new section inserted and spliced to the existing section to remain. This can introduce significant challenges in some locations due to limited space, interference with other members, limited access to fasteners, submerged connections, etc. Although technically feasible, these approaches to extending the life of the bridge significantly increase the cost to maintain the bridge. Although there are many examples of timber bridges where the service life has been extended in excess of a 100 years, most of these bridges are covered bridges located in non-coastal locations. Unlike covered bridges, where the roof structure and siding typically protect the main structural timber members, the Mitchell River Bridge is fully exposed to the weather, where the effects of continual exposure to moisture and sunlight accelerates deterioration and decay and reduces the service life of the timber. In addition, most covered bridges are not located in marine environments where timber foundations are subject to marine borer attack. In fact, many of the covered bridges are supported on stone foundations not susceptible to deterioration due to submersion in water. Although technically feasible, prolonging the service life of a timber bridge beyond 30 years in this environment requires a significant financial investment and maintenance commitment by the community and agreements by permitting agencies to support these efforts. Furthermore, now that it has been determined that the existing bridge is historic, the Town has a responsibility to maintain the bridge in a manner that will prevent the continued deterioration. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 51 Final Report
5.3 Funding The project is currently funded through the Massachusetts Department of Transportation Accelerated Bridge Program which includes funding participation from the federal government. Although funding for this project was originally intended for replacement of the bridge, the Accelerated Bridge Program covers both replacement and rehabilitation of structurally deficient bridges. The Federal Highway Administration (FHWA) currently has a policy that bridges replaced using federal funding be designed with a minimum service life of 75 years. Currently, it is not practical to design a timber bridge in this environment for a minimum 75 year service life. However, as a timber bridge will have a lower initial construction cost than a concrete and steel bridge, it is possible for a timber bridge with a 20 to 30 year minimum service life (following major repair, rehabilitation or replacement) to have an overall life cycle cost that is similar to a concrete and steel bridge with a 75 year service life. However, as a timber bridge will have a service life significantly less than that of a concrete and steel bridge, it is anticipated that the bridge will need to be replaced two or three times over a 75 year life cycle period. As funding under the Accelerated Bridge Program only covers the cost of initial project (not future construction projects) the Town would be responsible for the cost of future repair, maintenance, rehabilitation and/or replacement work. Even though a timber bridge can have similar overall life cycle costs as a concrete and steel bridge, it is likely that the Town would be responsible for a larger proportion of the life cycle cost. Funds for the Accelerated Bridge Program are only available through Fall 2016. As such, construction for the bridge must be complete before this date in order for the project to be eligible for these funds. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 52 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 and 48: Condition Description: There are cu
Page 49 and 50: 5.0 OTHER CONSIDERATIONS 5.1 Naviga
Page 51: SUMMARY OF TIMBER ELEMENT SERVICE L
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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