BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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• The bridge was completely replaced in 1925 with a shorter twelve-span timber bridge with a single-leaf timber bascule span. The overall width of the 1925 bridge was 15’-4”. The bridge included an all timber superstructure with steel pipe railings on both sides and all timber substructure and foundations except for concrete abutments. • The bridge was widened in 1949 to the north to provide 24’-0” clear roadway width and 3’-0” raised sidewalks on both sides with an overall width of 30’-0”. During the widening, Bent 5 was removed and steel beams were installed in Spans 5 and 6 to support the timber superstructure including an intermediate steel hanger beam where Bent 5 was previously located. The steel beams were supported on two new pile bents, Bent 4A and Bent 6A. The steel pipe railings were relocated to the back of the new raised sidewalks. Additional piles were added to supplement the existing piles for the widened configuration. The widened bridge included an all timber superstructure except for the steel framing in Spans 5 and 6 and all timber substructure and foundations except for concrete abutments. • In 1980, the bridge superstructure was completely replaced to its current configuration retaining only the existing timber piles and concrete abutments. In the new configuration, wider sidewalks were provided in all but the first, last and bascule spans and the sidewalks were placed at deck level behind timber curbs. The pivot for the bascule span was relocated to the opposite side of the channel and a new Bent 7A constructed, while the existing Bent 7 was removed. Additional piles were added to supplement the existing piles and timber pile caps and bracing replaced. The steel framing in Spans 5 and 6 was removed and Bent 5 was reconstructed. • Periodic minor repairs to the bridge have been performed since the bridge was reconstructed in 1980 including replacement of portions of the timber wearing surface, replacement of the lifting beam, installation of plastic wrap on some of the timber piles, and other miscellaneous minor repairs. Photo 1 - Present Mitchell River Bridge - South Elevation Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 7 Final Report
Photo 2 - Present Mitchell River Bridge - Roadway Section Looking East The bridge currently has a clear roadway width of 24’-0” and carries one lane of traffic in each direction with sidewalks located each side of the roadway behind timber curbs and with timber bridge railings at the back of sidewalk. In Spans 2 thru 7 and Spans 9 thru 11 the sidewalks are 5’-9” wide with an overall bridge width of 37’-6”. In Spans 1, 8 and 12, the sidewalks are 2’-9” wide with an overall bridge width of 31’-6”. There is a tapered transition in sidewalk width in Spans 2 and 11 (see Appendix A.) The superstructure includes a 3x8 sawn lumber plank timber wearing surface with the planks oriented at 60 degrees to the roadway centerline and which extends the width of the roadway. The timber wearing surface is supported on and nailed to 4x8 sawn lumber plank timber structural deck with the planks oriented perpendicular to the roadway centerline and that extends the full width of the bridge. The timber deck is supported on 6x16 sawn lumber stringers at 15½” on center. The timber curbs consist of 8x8 sawn lumber members elevated on top of 6x8 spacers at 6 feet on center. The timber bridge railing consists of 8x8 posts, 6x6 top rails, 10x5 intermediate rails and 6x4 bottom rails/curbs. The timber for the bridge structural members was specified as pressure treated Dense Select Douglas Fir-larch with waterborne preservatives. The deck planks were specified as No. 2 Grade Douglas Fir-larch without pressure treating. The timber piles contain creosote preservative. The substructure at the ends of the bridge consists of concrete abutments supported on timber piles. The abutments include integral concrete wing walls (retaining walls) that extend along the approach roadway at the back of sidewalk that retain the roadway embankment. The retaining walls extend beyond the bridge ends approximately 16 feet at the NW quadrant, 84 feet at the SW quadrant, 16 feet at the NE quadrant and 60 feet at the SE quadrant. The embankments adjacent to the abutments and retaining walls along the waterway contain rubble rip rap slope Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 8 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: 3.0 BRIDGE DESCRIPTION Bridge Numbe
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 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
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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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