BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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Several piles in Bent 10 include addition of a 12x12 timber build-ups at the top of the pile that was spliced in line with the pile. Based on the appearance of these pile build-ups, which is similar to the piles, they are likely the same age as the piles and were likely added when those piles were originally installed to add length to the pile or to replace a damaged section of the tops of the piles. Photo 8 - Piles and Bracing Twelve (12) of the piles including six (6) in Bent 1, three (3) in Bent 2, one (1) in Bent 3 and two (2) in Bent 4, all from among the original piles from 1925, were wrapped in plastic from just above the mudline to just above the tidal zone. The plastic was added in 2005 to slow or stop further marine borer attack and further section loss to these piles. The plastic wrap obscures the piles from visual inspection. Tactile inspection (i.e. sounding and probing) is also not recommended on these piles due to the potential of damaging the plastic wrap. As such, there is no practical means to perform routine inspection of these piles and to periodically determine whether the condition is deteriorating beneath the plastic. The timber piles typically exhibit heavy marine growth extending from the mudline through the tidal zone obscuring some of the surface of the piles from visual inspection and preventing full tactile inspection. All of the existing piles contain creosote preservatives. However, most of the piles are typically bleached indicating that the creosote has leeched from the older piles and thus no longer protects the piles from surface decay and marine borer attack. The creosote preservative in the newer piles is in greater quantity; however, there is evidence that the quantity has reduced somewhat due to ongoing leeching of the material. The piles typically exhibit evidence of surface decay and marine borer attack at and above the tidal zone of varying severity throughout the bridge. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 37 Final Report
The surface decay and deterioration is considered minor in 75% of the piles, moderate in 15% of piles and significant in 10% of the piles. The piles throughout the bridge also contain checks and splits of adequate width and depth to penetrate the outer portion of the piles that contains the preservative treatment. This permits moisture and fungal spores to gain access to the interior of the pile where there is no preservative treatment, which creates conditions conducive for development of internal fungal decay. The checks and splits are considered minor in 75% of the piles, moderate in 15% of piles and severe in 10% of the piles. Two of the piles (one in Bent 4A and one in Bent 6) exhibit extensive splits at the top of the piles where the piles connect to the cap beams. In general, the tops of the piles are sound. However, there is no evidence that the cut ends of the top of the piles were field treated with preservative or sealed either during the original construction, widening or reconstruction. As such, the cut ends provide opportunities for moisture absorption and decay at the tops of the piles. There is evidence of active marine borer attack in approximately one-third of the piles throughout the bridge. In addition to the twelve (12) piles wrapped in plastic with previously identified marine borer attack, there are six (6) piles with marine borer attack extending from the mudline through the tidal zone, nineteen (19) piles within the tidal zone and four (4) piles near the mudline only. The most severe deterioration has occurred to a pile in Bent 8, which reportedly includes approximately 80% loss in cross section to the pile. The marine borer attack is primarily from teredo worms that consume the interior of the pile where there are no chemical preservatives. However, there is evidence that limnoria (gribble) has also attacked the exterior surface of the timber. The teredo worms have typically bypassed the chemical preservatives in the surface of the piles and have accessed the interior of the piles through bolt holes in the piles. A number of the holes that were previously used for bolting timber bracing members to the piles, but are no longer used due to changes in the bracing configuration, were left open for a period of time. After the discovery of marine borer attack, bolts were inserted into the open holes to prevent access. However, the bolts have typically failed as a result of corrosive deterioration. Other holes typically became open when the bolts attaching the timber bracing members failed due to corrosive deterioration. The galvanized steel bolts used to secure battered piles to plumb piles and timber bracing members to the piles typically exhibit severe corrosive deterioration throughout the bridge. Repair Scope: The creosote preservative in the existing timber piles have contributed to a relatively long service life for piles in this environment. However, significant splits and checks in the piles, significant loss of preservative chemicals in a large number of piles, continued loss of chemical preservatives in the other piles, evidence of surface decay and significant potential for internal decay, and evidence of significant marine borer attack all substantially limit the remaining service life of the piles unless corrective action is taken. Similar to the other timber elements of the bridge, there are options for in-place preservative treatment of the piles including both internal and surface treatments. However, many of the same risks and concerns for in-place preservative treatments of other elements apply to the piles with Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 38 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: Functionality and Safety: The cap b
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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