BRIDGE REPAIR/REHABILITATION FEASIBILITY STUDY

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COMMERCIAL TIMBERS OF THE CARIBBEAN 15 conditions favorable for decay. Decay is an everpresent hazard in the tropics where the conditions of moisture and temperature are ordinarily ideal for the development of fungi. Unless preservative treatment is applied, only timbers with considerable decay resistance should be used for posts, poles, railway ties, foundations, and other uses. where the timber may become damp or wet. Decay resistance is not important where wood is used for furniture, cabinetwork, millwork, and other interior or protected uses. Then too, wood will not ordinarily decay in exterior uses where it is subject to frequent wetting, unless the construction is such that the wood is prevented from drying out after each wetting. Most decay occurs in wood with a moisture content above the fiber saturation point–about 30 percent moisture content. On the other hand, wood that is continuously water soaked or continuously dry will not decay. Thus, the underwater portion of piling and bridgework or air-dry timber at 20 percent or less moisture content is safe from damage. Wood kept at the air-dry moisture content of 15 to 20 percent in the Caribbean area is, consequently, in no danger of decay. However, decay is almost certain to occur if the construction allows any part of a board or timber to remain wet for long periods of time. The description in the text of the decay resistance of each timber is based on the durability of untreated heartwood, which is more durable than sapwood. It is doubtful if the sapwood of any species is durable without preservative treatment. Information on durability was available from published results of graveyard tests, pure culture laboratory tests, and from published observations on the durability of the different woods while in use. Information derived from graveyard tests, in which untreated heartwood posts of tropical species (either round or square) are set in the ground and inspected periodically for decay, is available from Surinam, British Guiana, Trinidad, St. Lucia, Panama, Puerto Rico, England, and the United States. The results sometimes vary between countries but are generally in good agreement. In pure culture tests small heartwood specimens are exposed to fungal attack under closely controlled laboratory conditions, and the relative durability of different woods is determined on the basis of the loss in weight through decay. The results of these tests at Yale University and the U.S. Forest Products Laboratory are in very good agreement. However, the results of graveyard tests and pure culture tests are not in agreement for some timbers. When this occurs, the laboratory tests generally show the higher decay resistance. It appears that the laboratory tests conducted under closely controlled conditions may be the most reliable. In the laboratory, it is not difficult to distinguish heartwood from sapwood; but in graveyard tests, it is sometimes very difficult in timbers without, well-defined heartwood to be certain whether the posts used contain heartwood or sapwood. This may be the reason for some of the discrepancies between different graveyard tests. Table 6 lists the timbers by durability classes, according to the published results of field and laboratory tests. Four classifications are used: Very resistant, resistant, moderately resistant, and nonresistant. When authors report differences in tests and results, the most consistent or reliable rating is used. Timbers reported to be quite variable in durability and those rated on the basis of general reputation alone are indicated by footnotes. RESISTANCE TO ATTACK BY TERMITES AND OTHER INSECTS The sections on durability in the timber descriptions contain a brief summary of the published information on damage by wood-attacking insects. Unfortunately, very little information is available concerning insect attack on the Caribbean timbers except for the comprehensive laboratory tests conducted by G. N. Wolcott (262, 263) on the resistance of woods to attack by the West Indian dry-wood termite (Cryptotermes brevis Walker) and a less comprehensive study of damage by subterranean termites of Trinidad timbers (39). Most information on other insect damage to logs and sawed products is based on casual observations and experience which, although generally reliable, is often influenced by local conditions peculiar to a small area. The most common wood-attacking insects in the Caribbean region are the ambrosia beetles (Scolytidae and Platypodidae), both dry-wood and subterranean termites (Order Isoptera), and powder-post beetles (Bostrychidae and Lyctidae). Ambrosia beetles, more often called pinhole borers, are a common menace in green logs and lumber and sometimes attack living trees. Both unseasoned sapwood or heartwood may be attacked. Attack by these insects is evidenced by numerous holes 1 / 50 to 1 / 8 inch in diameter, according to the species of pinhole borer responsible. Entry of pinhole borers is often associated with staining of the wood around the holes. Damage by this insect is liable to be severe if logs are not converted soon after felling or if they are not protected by insecticide sprays. Attack ceases when the timber is seasoned. Damage can be prevented in freshly sawed lumber or living beetles destroyed by dipping the product in a water solution containing 0.2 percent of gamma benzene hexachloride. It is also a common practice to include in the same solution an ingredient to prevent sap stain and keep the lumber bright.
16 U.S. DEPT. OF AGRICULTURE HANDBOOK NO. 207 TABLE 6.— Classification of Caribbean timbers as to their resistance to decay Trade name Scientific name Trade name Scientific name 1 Variable in decay resistance. 2 Based on reputation for durability; not substantiated by research.
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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),
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 289 and 290: 10 U.S. DEPT. OF AGRICULTURE HANDBO
Page 293: 14 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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