BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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Fig. 11. Application of fiber-reinforced polymer composite shells to predamaged wood pile Fig. 9. Tube vacuum bag placed over system inhibitor as an additive to the polymer matrix (Haeberle et al. 2002). Laboratory Prototypes—Fabrication The feasibility of the repair method was demonstrated in the laboratory by fabricating FRP composite shells and restoring “damaged” wood pile prototypes (Fig. 11). Marine borer damage was simulated by reducing the cross-sectional area of the pile. The space between the wood core and the FRP composite shells was filled with a grouting system. Two different grouting materials were used: (1) portland cement-based (inorganic) structural grout (Fig. 12), and (2) polyurethane-based (organic) nonstructural grout with shear connectors that transfer loads from the wood pile to the FRP composite shells (Fig. 13). Laboratory prototypes were fabricated for two types of experiments: (1) pushout tests by compression loading to characterize the interface response (wood/ grout/shear connector/FRP composite) (Lopez-Anido et al. 2004a); and (2) full-size bending tests to characterize the overall structural response (Lopez-Anido et al. 2003). Installation Procedure To implement the repair method in waterfront applications, a possible step-by-step installation procedure was developed and is presented. Step 1: Clean Existing Wood Pile Wood piles usually have marine fouling organisms growing on them. Even though achieving good bonding between the grout and the wood core is not expected, cleaning will be helpful. The marine organisms are primarily organic matter, and their presence creates voids in the grout, making it weaker and reducing the interlocking that is required for the repair system to work efficiently. Cleaning can be performed using a water jet without excessive pressure (USACE 2001). Excessive pressure can cause more damage to the already vulnerable wood pile. Cleaning can also be achieved by scraping off the marine organisms with a modified scraper that conforms to the shape of the wood pile (Hardcore 1999). Fig. 10. Demolding of cured fiber-reinforced polymer composite shell Fig. 12. Fiber-reinforced polymer composite repair system with cement-based grout 84 / JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES © ASCE / FEBRUARY 2005
Table 1. Cost Items for FRP Composite Shells Fabricated in Laboratory Cost per fiber-reinforced polymer composite shell Item ($) Fiber reinforcement 101 Resin 70 Catalyst 8 Fabrication supplies 114 Labor preparation 70 Labor application 15 Total 378 Note: Prices are for shells having a diameter of 394 mm and a length of 4.88 m. Fig. 13. Fiber-reinforced polymer composite repair system with shear connectors and polyurethane grout Step 2: Place Shear Connectors at Wood-Grout Interface If shear connectors, such as lag screws, are required at the woodgrout interface, they must be driven deep enough into the wood pile to be effective. The connectors need to extend as much as the thickness of the grout to serve as spacers. Step 3: Position First Fiber-Reinforced Polymer Composite Shell Around Wood Pile The longitudinal slit along the length of the FRP composite shell is opened and the shell is placed around the damaged wood pile. Step 4: Apply Adhesive on First Shell A coat of underwater epoxy adhesive is applied on the interior surface of the second shell and on the exterior surface of the first shell, if possible. The use of trowels is recommended to help spread the adhesive. Step 5: Position Second Shell The second shell is slid around the first one with the longitudinal slits or gaps staggered (preferably 180°) to avoid lines of weakness. This step is repeated for additional shells staggering the longitudinal slits. Step 6: Strap Shells Together It is necessary to use straps or other means to apply pressure on the FRP composite shells to hold them in place until the adhesive cures and also to force out any trapped water between them. Straps should be spaced at approximately 0.6 m intervals for satisfactory pressure to be applied to the adhesive contact area. Step 7: Drive Fiber-Reinforced Polymer Composite Shield to Required Depth into Mud Line After curing of the adhesive, the FRP composite shield can be driven into the mud line, which needs to be loosened. This can be achieved either by using a water jet that stirs and loosens the mud or by digging around the wood pile to the required depth and then backfilling the hole. Step 8: Drill Holes and Place Shear Connectors If shear connectors are required for the transfer of loads from the wood pile to the FRP composite shield, then holes need to be drilled and the shear connectors placed before grouting. This will ensure that any possible voids are filled by the grout and no possible access points remain for marine borers to enter and damage the wood pile. If the holes are to be drilled underwater, then an air drill will be necessary. In the laboratory, regular steel threaded rods were used, but galvanized steel rods should be used in field applications to reduce corrosion. Step 9: Prepare Grout and Pump it into Place After the FRP composite shield is driven into the mud, then the grout material can be pumped. Grout should be pumped from the bottom to avoid segregation. Cost Analysis To assess the commercial feasibility of the wood pile repair method, a preliminary cost analysis was conducted. For this purpose, the cost of repairing full-size wood piles in the laboratory was calculated. The cost was divided among the following items: (1) materials, (2) fabrication supplies, and (3) labor for preparation and application. Material costs included the cost of the fiber reinforcement, resin, and catalyst. The fiber reinforcement cost for a typical composite shell, which has a diameter of 394 mm and a length of 4.88 m, was $101. The fiber reinforcement cost included the CSM mat cost, $17 per shell, and the woven unidirectional fabric cost, $84 per shell. The resin cost for a typical composite shell was $70 and the catalyst cost was $8. The cost of fabrication supplies per shell included peel ply, $40; release film, $25; distribution media, $16; plastic tubing, $8.50; bagging film, $12; sealant tape, $7; and vacuum line, $5.50. The labor cost to prepare materials, supplies, and the mold for VARTM/SCRIMP fabrication of one shell was based on the time required, 3 1 2 h, for two student workers to complete the task at a wage rate of $10 per hour; therefore the total cost for labor application was $70 per shell. The labor application cost was based on the time required for one student worker to mix the resin and infuse the part. In the laboratory, 1 1 2 h were spent to complete the infusion process; therefore the total labor application cost was $15. The total cost for one shell was $378, where the cost items are summarized in Table 1. The total cost for repairing a typical wood pile with a diameter of 335 mm using 4.88-m-long FRP composite shells can be determined by adding the cost of the underwater epoxy adhesive, $200, to that of the cement-based grout with a thickness of 50 JOURNAL OF PERFORMANCE OF CONSTRUCTED FACILITIES © ASCE / FEBRUARY 2005 / 85
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BRIDGE REPAIR/REHABILITATION FEASIB
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1.0 EXECUTIVE SUMMARY The existing
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such there is a risk that the proje
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3.0 BRIDGE DESCRIPTION Bridge Numbe
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Photo 2 - Present Mitchell River Br
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4.0 ELEMENT CONDITION & REHABILITAT
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Based on the 1997 load rating analy
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promotes growth in the number and s
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4.2.2 Deck NBIS Condition Rating: 5
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Rehabilitation Scope: In order to m
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4.2.5 Railings NBIS Condition Ratin
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Functionality and Safety: Eliminati
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Although in-place preservative trea
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The bascule span timber stringers c
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Repair Scope: Although the timber m
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Use of an all steel counterweight w
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additional force effects, the speci
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typically loose. The steel guardrai
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Functionality and Safety: The cap b
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The surface decay and deterioration
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the interior of the piles where the
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Load Capacity: The current loss in
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Visual Impacts: Replacement of the
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Condition Description: There are cu
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5.0 OTHER CONSIDERATIONS 5.1 Naviga
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SUMMARY OF TIMBER ELEMENT SERVICE L
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5.3 Funding The project is currentl
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navigation opening. The estimated c
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• 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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Page 271 and 272: Table 1- Residual MITC content in D
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Page 305 and 306: APPENDIX F FRP Pile Jackets
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Page 309 and 310: Fig. 5. Cross section of wood pile
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Page 315 and 316: Hardcore Composites. (2000). Hardsh
Page 317 and 318: CALCULATION COVER SHEET Project Nam
Page 319 and 320: URS Corp. 260 Franklin Street Bosto
Page 336: APPENDIX I Correspondence
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