BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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COMMERCIAL TIMBERS OF THE CARIBBEAN 9 TABLE 3.— Caribbean timbers grouped as to their ease of air-seasoning Trade name Scientific name Trade name Scientific name Stains resulting from sap-staining fungi penetrate into the sapwood (not heartwood) and cannot be removed by surfacing. The discoloration of the wood is visible as specks, spots, streaks, or patches. At times it can be seen throughout the entire sapwood layer. Shortly after the lumber is cut from the logs, it may become infected by airborne fungi. Stains develop rapidly and noticeable discoloration may be evident within 24 hours after conversion. Stain may be controlled by piling products immediately after conversion., so that the wood’s surface dries rapidly. This is often impractical, or results in excessive seasoning degrade from the too rapid loss of moisture during the early stages of drying. Stain may also be controlled by dipping, spraying, or brushing the wood with antiseptic solutions, such as chlorinated phenols, organic mercury compounds, and borax. Numerous commercial products are also on the market for this use. Early treatment is imperative : once sap stain is established it cannot be controlled by treating the wood surface with chemicals. Rapid air-seasoning or kiln-drying below 20 percent moisture content is the most effective control measure once sap stain is present.
10 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 207 Most information on kiln-seasoning of Caribbean timbers has been developed by the Forest Products Research Laboratory in England. Frequeut reference is made in this text to the kiln schedules recommended for different, timbers in their “Kiln Operator’s Handbook” (222). One of their more recent publications, No. 42, provides new schedules for faster drying and more severe kiln conditions. Any reader interested in kilnseasoning of tropical American timbers should acquire these publications for details on kiln schedules and recommended operating techniques. The U.S. Forest Products Laboratory, Madison, Wis., also lists kiln schedules in its report D-1791 that may be used for tropical hardwoods by experienced kiln operators. SHRINKAGE AND MOVEMENT Freshly sawed lumber contains from 30 to more than 300 percent water, based on the ovendry weight of the wood. The percentage of moisture varies according to species. In the green condition, dense, close-grained wood contains less moisture than open-grained, less dense wood. As an example, very heavy woods often contain 30 to 40 percent moisture in the green condition, compared to as much as 300 percent or more in some very light woods such as balsa. Water is present in wood in two forms; as free water in the cell cavities and intercellular spaces of the wood and as absorbed water held in the walls of the wood elements. When the free water is removed but all the absorbed water remains in the cell walls, the wood is said to hare reached the fiber saturation point. This condition occurs at about 30 percent moisture content but may vary considerably between species. Shrinkage does not occur in wood until this point has been reached. However, as a piece of wood dries, the outer part is reduced to a moisture content below the fiber saturation point sooner than the interior. Consequently, the whole piece may show some shrinkage near the surface before the average moisture content reaches the fiber saturation point. Wood shrinks as it loses moisture below the fiber saturation point. Wood that, has reached the airdry condition at. 15 percent moisture content has undergone about half the shrinkage possible. For each 1 percent loss of moisture-below the fiber saturation point (30 percent moisture content), wood shrinks about, one-thirtieth of the total possible shrinkage. Shrinkage values are normally calculated and reported as the total shrinkage from green to ovendry wood, and expressed as a percent, of the original green volume. For Caribbean timbers, shrinkage values are presented on this basis in table 4, and in the sections discussing shrinkage of the timbers in the text. Shrinkage from green to 15 percent moisture content (the air-dry moisture content often used for timbers in this area) amounts to half the total shrinkage. Shrinkage to 10 percent and 20 percent moisture contents amounts to 2 / 3 and 1 / 3 of the total shrinkage respectively. Wood generally shrinks about twice as much in the direction of growth rings (tangential) as across the growth rings (radial) and very little along the grain (longitudinal). Consequently, wood that contains cross grain (interlocked) or irregular grain will shrink more longitudinally than straight-grained wood because of the tangential and radial surfaces. The total shrinkage in all directions quoted as one sum is termed volumetric shrinkage. The relationship of radial shrinkage to tangential shrinkage is often an indication of the inherent tendency of a wood to cup and otherwise distort during seasoning. Generally, woods that have a low ratio of tangential to radial shrinkage season with less cupping and other defects than woods with a higher ratio. Likewise, because of the greater shrinkage in the direction of the growth rings, “flat-sawed” or “plainsawed” boards are more a t to cup and surface check than “quartersawed” or “edge-grained” boards. Flat-sawed boards are also subject to greater shrinkage across the surface and less in thickness than quartersawed boards. I n genera!, heavier pieces of wood shrink more than lighter pieces of the same species. There are, however, many exceptions where heavy species shrink less than those that weigh less and where lightweight woods have large shrinkage values. Recent studies at. Yale University (250) show that tropical woods, with few exceptions, undergo lower shrinkage than United States woods of similar density. They found no correlation between volumetric shrinkage and specific gravity, indicating something other than weight was the dominant factor controlling shrinkage. Shrinkage during drying is to some extent a criterion of subsequent shrinkage and swelling that will occur in the wood as a result of changes in atmospheric conditions. Wood is exposed to continuous daily and seasonal changes in relative humidity. Its tendency to absorb or give off moisture to come into balance with the surrounding air is accompanied by swelling or shrinking of the wood. This movement may be in the same proportions as the initial shrinkage in seasoning. In the absence of specific movement values, it IS reasonable to assume a dimensional change of onethirtieth of the shrinkage from green to ovendry for each l-percent change in moisture content. However, recent studies at the Forest Products Research Laboratory in England show that all woods do not undergo dimensional changes in response to changed atmospheric conditions in proportion to their initial shrinkage values (108). They found that some woods shrink appreciably in drying, yet may undergo comparatively small dimensional changes in use.
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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
Page 237 and 238: MAINTENANCE AND REHABILITATION OF T
Page 239 and 240: Figure 14-1. - Many covered bridges
Page 241 and 242: (discussed later in this chapter),
Page 243 and 244: Figure 14-5. - Liquid wood preserva
Page 245 and 246: wood, and other openings to the atm
Page 247 and 248: Table 14-1. - Number and size of ho
Page 249 and 250: member noting treatment information
Page 251 and 252: Figure 14-11. - Splicing and scabbi
Page 253 and 254: STRESS LAMINATING Stress laminating
Page 255 and 256: ond between separated sections, inc
Page 257 and 258: onding the old and new pile section
Page 259 and 260: GENERAL PROCEDURES FOR EPOXY REPAIR
Page 261 and 262: openings will allow epoxy to escape
Page 263 and 264: Another quality control problem is
Page 265 and 266: 6. Avent, R.R. 1985. Factors affect
Page 267 and 268: Integrated Remedial Protection of W
Page 269 and 270: Figure l-Effect of fumigant applica
Page 271 and 272: Table 1- Residual MITC content in D
Page 273 and 274: of reinvasion (Forsyth and Morrell,
Page 275 and 276: might represent the best option, wh
Page 277 and 278: In: Ritter, M.A.; Duwadi, S.R.; Lee
Page 279 and 280: Present and Potential Commercial Ti
Page 281 and 282: 2 U.S. DEPT. OF AGRICULTURE HANDBOO
Page 287: 8 U.S. DEPT. OF AGRICULTURE HANDBOO
Page 291 and 292: 12 U.S. DEPT. OF AGRICULTURE HANDBO
Page 305 and 306: APPENDIX F FRP Pile Jackets
Page 307 and 308: about its hazard to human health. T
Page 309 and 310: Fig. 5. Cross section of wood pile
Page 311 and 312: (Lopez-Anido et al. 2004c). For exa
Page 313 and 314: Table 1. Cost Items for FRP Composi
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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BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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