BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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4.1.2 General Condition Ratings: The Massachusetts Department of Transportation - Structures Inspection Field Reports document the National Bridge Inspection Standards (NBIS) Condition Ratings. (See Appendix B.) The NBIS Condition Ratings, which consist of a numerical code (based on a scale of 0 to 9, where 0 describes a “Failed Condition” and 9 describes an “Excellent Condition”) provide a uniform standard for bridge inspectors and describe the overall general characterization of the physical condition of the entire deck, superstructure and substructure components of the bridge. The NBIS Condition Ratings reported in the 2004, 2006, 2008 and 2010 Structures Inspection Field Reports were as follows: SUMMARY OF NBIS CONDITION RATINGS ITEM 2004 2006 2008 2010 Deck 6 (Satisfactory) 6 (Satisfactory) 6 (Satisfactory) 5 (Fair) Superstructure 6 (Satisfactory) 5 (Fair) 6 (Satisfactory) 6 (Satisfactory) Substructure 4 (Poor) 4 (Poor) 4 (Poor) 4 (Poor) • Satisfactory denotes that structural elements show some minor deterioration. • Fair denotes that all primary structural elements are sound but may have minor section loss, cracking, spalling or scour. • Poor denotes advance section loss, deterioration, spalling or scour. The Structures Inspection Field Reports indicate a continuing gradual reduction in the overall physical condition of the bridge. The increase in the NBIS Condition Rating of the Superstructure between 2006 and 2008 reflects slight improvements following the repairs to the superstructure performed in 2007. Due to an NBIS Condition Rating of 4 (Poor) for the Substructure, the bridge is classified as “Structurally Deficient”. This does not signify that a bridge is unsafe; rather it signifies that significant structural members are in need of repair. 4.1.3 Load Capacity/Restrictions: According to the 1980 bridge reconstruction plans, the design live loading for the existing bridge was the AASHTO H20-44 truck loading which has a 20 ton gross vehicle weight and two axles (8,000 pounds and 32,000 pounds separated by a distance of 14 feet). This design loading is lighter than both the AASHTO HS20-44 design live load and the current AASHTO LRFD HL- 93 design live load. Live load capacity calculations for the bridge were last performed in 1997 for both the Inventory and Operating Levels. The Inventory Level is considered the load level at which the structure can be subjected to indefinitely and is consistent with design level loading for new bridges. The Operating Level is considered the maximum load level that the structure can safely withstand and is consistent with current overload provisions and is the level at which Massachusetts Department of Transportation (MassDOT) establishes load restrictions and weight posting. Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 11 Final Report
Based on the 1997 load rating analysis, all members of the bridge have capacities in excess of Operating Level capacities (see Appendix C.) As such, load restrictions and weight posting were previously waived. Although the bridge does not currently require load restrictions, the load rating analyses revealed that two elements of the bridge have load carrying capacities less than the Inventory Level capacities. These elements are the shear capacity of the bascule span timber stringers and the shear capacity of the Bent 7A timber bent cap that supports the bascule span. Load capacities less than the Inventory Level capacities indicate that the structural member may not have adequate capacity to carry current loading indefinitely and that degradation of the elements under loading is eventually expected. Furthermore, in accordance with FHWA guidelines, if the existing bridge was to remain and was rehabilitated, a design exception would need to be granted to allow the members with substandard Inventory Level capacity to remain. Otherwise the substandard members would need to be strengthened or replaced with stronger members. According to the 2010 Structures Inspection Field Report, the condition of the bridge has not changed sufficiently to warrant a new load rating evaluation. 4.1.4 Functional Evaluation and Roadway Safety The existing bridge contains geometry that is considered substandard (i.e. the geometry does not meet current design standards.) Specifically, the narrow 24’-0” clear roadway width between curbs for two travel lanes is considered substandard. Because of the geometry, the bridge has a Deck Geometry Rating of 2 (Intolerable with a High Priority of Replacement) and as such, the bridge qualifies as “Functionally Obsolete”. In accordance with FHWA guidelines, as the bridge is also currently classified as “Structurally Deficient” it cannot also be classified as “Functionally Obsolete”. Bridges that qualify as both “Structurally Deficient” and “Functionally Obsolete” are classified as “Structurally Deficient”. If sufficient improvements were made to the deficient structural members without corresponding improvements to the geometric features, the existing bridge would then be classified as “Functionally Obsolete”. Photo 3 - Approach Sidewalk and Guardrails The existing bridge does not contain traffic railings that are crash tested in accordance with NCHRP 350 as required by current design standards. Low-level curbs, such as the existing 1’-1” high timber curbs, have a history of causing errant vehicles that strike the curb to lose control and rollover. The traffic railings are required to meet Test Level 2 (TL-2) crash testing criteria as a minimum, which are appropriate for use on local collector roads, with favorable site Repair/Rehab. Feasibility Study March 10, 2011 Bridge No. C-07-001 (437) 12 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: 4.0 ELEMENT CONDITION & REHABILITAT
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
Page 59 and 60: 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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