U.S. Department of Transportation
Federal Highway Administration
1200 New Jersey Avenue, SE
Washington, DC 20590
202-366-4000
Federal Highway Administration Research and Technology
Coordinating, Developing, and Delivering Highway Transportation Innovations
 |
| This report is an archived publication and may contain dated technical, contact, and link information |
| breadcrumb |
Publication Number: FHWA-HRT-04-098 |
Covered Bridge ManualPDF Version (8.35 MB)
PDF files can be viewed with the Acrobat® Reader® |
The Transportation Equity Act for the 21st Century (TEA-21) as amended by the TEA-21 Restoration Act established the National Historic Covered Bridge Preservation Program (NHCBPP). This program includes preservation of covered bridges that are listed, or are eligible for listing, on the National Register of Historic Places. It includes research for better means of restoring and protecting covered bridges. It also includes technology transfer to disseminate information on covered bridges as a means of preserving our cultural heritage. The development of the Covered Bridge Manual is one of the research projects funded through NHCBPP.
The broad objectives of the NHCBPP research program are to find means and methods to restore and rehabilitate historic covered bridges to preserve our heritage using advanced technologies, and to assist in rehabilitating and restoring these bridges. The specific objectives of this research project are to provide comprehensive support to those readers involved with maintaining, assessing, strengthening, or rehabilitating any covered bridge.
The manual is intended primarily for engineers and historic bridge preservationists to provide technical and historical information on preservation of covered bridges. It will also be of interest to others involved with these bridges—including lay people, owners, and contractors.
The manual is separated into several sections with a number of chapters devoted to the specifics of each. The sections include background, description of bridge components, technical engineering issues, existing bridges, and references. The appendices include multiple case studies of existing bridge rehabilitation and construction of new authentic covered bridges.
This manual does not supersede any other. This publication is the final version of the manual.
This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.
The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers' names appear in this report only because they are considered essential to the objective of the document.
QUALITY ASSURANCE STATEMENT
The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.
| 1. Report No
FHWA-HRT-04-098 |
2. Government Accession No.
N/A |
3. Recipient's Catalog No.
N/A |
|
|
4. Title and Subtitle Covered Bridge Manual |
5. Report Date
April 2005 |
||
|
6. Performing Organization Code
N/A |
|||
|
7. Authors(s)
Phillip C. Pierce, P.E., Robert L. Brungraber, P.E., Ph.D., Abba Lichtenstein, P.E., and Scott Sabol, P.E. Chapter 19 was authored by J.J. Morrell, Department of Wood Science and Engineering, Oregon State University and S.T. Lebow, U.S. Forest Products Laboratory, Madison, WI. |
8. Performing Organization Report No.
FAU-OE-CMM-04 |
||
|
9. Performing Organization Name and Address
Phillip C. Pierce, P.E. 6738 County Highway 14 Treadwell, NY 13846 |
10. Work Unit No. (TRAIS)
N/A |
||
|
11. Contract or Grant No.
DTFH61-00-C-00116 |
|||
|
12. Sponsoring Agency Name and Address
Office of Infrastructure R&D |
13. Type of Report and Period Covered
Final Report October 2000– November 2004 |
||
| 14. Sponsoring Agency Code | |||
|
15. Supplementary Notes
Contracting Officer’s Technical Representative (COTR), Sheila Rimal Duwadi, P.E., Office of Infrastructure Research and Development (R&D); John O’Fallon, P.E., Office of Infrastructure R&D |
|||
|
16. Abstract
This manual provides guidance to those involved with all aspects of the work, from initial inspection and evaluation, through the engineering of rehabilitation, to construction issues. Broadly speaking, this manual covers general terminology and historic development of covered bridges. The manual also addresses loads, structural analysis, connections, and design issues. The last sixchapters contain discussions of evaluation, maintenance, strengthening, and preservation of existing covered bridges; historic considerations of existing structures; and provide a state-of-the-art guide on wood preservatives for covered bridges. Historic preservation requirements as they relate to the U.S. Department of Interior standards for these important and unusual structures also are provided. The appendices include an extensive series of case studies. The manual focuses on the nuances of the engineering aspects of covered bridges, including some issues not addressed currently by national bridge specifications. The chapter on timber connections provides a comprehensive discussion of covered bridge joinery and represents an important contribution to covered bridge engineering. |
|||
|
17. Key Words
Covered, Bridge, Manual, Design, Construction, Rehabilitation, Historic, Preservation |
18. Distribution Statement
No restrictions. This document is available to the Public through the National Technical Information Service; Springfield, VA 22161 |
||
|
19. Security Classif. (of this report)
Unclassified |
20. Security Classif. (of this page)
Unclassified |
21. No. of Pages
341 |
22. Price
N/A |
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized (art. 5/94)
PREFACE
This manual attempts to fill in gaps in the literature about the nuances of covered bridges. It deals with quirks about them known to the team of four experienced engineers who have prepared this manual. Yet, the relatively small number of covered bridges in the United States and their geographic dispersion makes it impractical for any team to have first-hand knowledge of all aspects of all covered bridges. There are, no doubt, some issues that have not been included herein.
For readers who have attempted to document the strength of covered bridges, this manual may not contain the answers to all questions. There are several things about covered bridges that continue to defy explanation: How have they survived as long as they have, subject to the abuse of vehicles weighing substantially more than the vehicles familiar to the builders of these bridges? How does an engineer explain the discrepancy between theoretical weakness and observed performance?
Some research projects have focused specifically on various aspects of covered bridges, and research continues. Yet the relatively small number of covered bridges makes the potential return on investment in that research relatively limited, and other research awaits funding.
Having offered the above caveat, we hope this manual is interesting and useful.
Chapter 2. Covered Bridges: Form, Use, and Terminology
Chapter 3. Historical Development of Covered Bridges
The Development of Truss Concepts in Europe
Early Truss Construction in the United States
The First Covered Bridge in the United States
Prevalence, Prominence, Demise, and Resurgence
Chapter 8. The Engineering Challenge
Chapter 9. Design and Analysis Specifications
American Association of State Highway and Transportation Officials
The National Design Specifications for Wood Construction
Specifications for Minimum Loads
Glued-Laminated Timber Specifications
Chapter 10. Issues Related to Wood
Chapter 15. Evaluating Existing Bridges
Field Examination and Inspection
Individual Member Assessment Through Strength Ratio Concepts
Analytical Evaluations for Vehicle Capacities (Load Rating)
Analytical Evaluation for Pedestrian Density Capacities
Destructive Testing of Components Removed From Bridges
Less Authentic Repair and Strengthening of Trusses
New Methods of Strengthening Trusses
Floor System Repair and Strengthening
Summary of Recommended Actions
Chapter 17. Preserving Existing Covered Bridges
Chapter 18. Historic Considerations With Existing Structures
National Register of Historic Places
Historic American Engineering Record
State Historic Preservation Offices
The Advisory Council on Historic Preservation
U.S. Secretary of Interior’s Standards for Historic Preservation
Chapter 19. Initial Preservative Treatment of Wood in Covered Bridges
Preventing Fungal and Insect Attack
Methods of Preservative Treatment
Environmental Considerations for Treatment
Appendix C. Rehabilitation of Fitch’s Covered Bridge
History of the Bridge and Condition Prior to Current Project
Modifications/Rehabilitation as Part of Current Project
Appendix D. Rehabilitation and Resiting of the Brown’s River Covered Bridge, Westford, VT
Appendix E. A Tale of Two Bridges
Speed River Covered Bridge, Guelph, Ontario, Canada
Twin Bridges, North Hartland, VT
Appendix F. Smith Covered Bridge Over the Baker River
Main Truss and Arch Configuration
Superstructure Fabrication and Erection
Appendix G. Caine Road Covered Bridge, Ashtabula County, OH
Appendix H. Replacement of the Mill Covered Bridge, Tunbridge, VT
Appendix I. Rehabilitation of the Paper Mill Covered Bridge, Bennington, VT
Appendix J. Replacement of the Power House Covered Bridge, Johnson, VT
Nontechnical Covered Bridge Information
Technical Information—Books / Articles Relevant to Covered Bridges
Articles Related to Covered Bridges
Figure 1. Chiselville Bridge, Sunderland, VT
Figure 2. Eagleville Bridge, Washingtion County, NY
Figure 3. A classic historic covered bridge, the Taftville Bridge, Woodstock, VT
Figure 4. Typical covered bridge, Upper Falls Bridge, Weathersfield, VT
Figure 5. Pony truss covered bridge, Comstock Bridge, East Hampton, CT
Figure 6. Bridge diagram—general terminology
Figure 7. Diagram of queenpost truss—general terminology
Figure 8. Floor system with stringers and floor beams—Warren Bridge, VT
Figure 9. Floor system with floor beams, but without stringers—Hutchins Bridge, VT
Figure 10. Running planks—Hutchins Bridge, VT
Figure 11. An unusual upper lateral system—Seguin Bridge, VT
Figure 12. Lower lateral system—Williamsville, VT
Figure 13. Unusual ship knee braces—Village or Great Eddy Bridge, in Waitsfield, VT
Figure 14. Shelter panel covering of truss ends—Fitch’s Bridge, Delaware County, NY
Figure 15. A shelter panel separate from the trusses—Hamden Bridge, Delaware County, NY
Figure 16. Framing of the independent shelter panel—Hamden Bridge, Delaware County, NY
Figure 18. Bolster beams—Worrall’s Bridge, Rockingham, VT
Figure 19. Blenheim Bridge—longest clear span in the United States
Figure 20. Rare, old double-barrel covered bridge—Pulp Mill Bridge, Middlebury, VT
Figure 21. Classic use of a natural formation as an abutment—Red Bridge, Morristown, VT
Figure 23. Salisbury Center Bridge—Herkimer County, NY
Figure 24. Brown Bridge—Shrewsbury, VT
Figure 25. Diagram of kingpost truss
Figure 26. Diagram of kingpost truss with subdiagonals
Figure 27. Diagram of queenpost truss
Figure 28. Diagram of multiple kingpost trusses
Figure 29. Shear failure of a vertical at a notch—Mill Bridge, Tunbridge, VT
Figure 30. Example of a broken tail from ice impact—South Randolph Bridge, VT
Figure 31. Bowing of bottom chord due to impact from ice floes—South Randolph Bridge, VT
Figure 32. Diagram of conventional and modified Burr arch
Figure 33. Connection of arch to post—Wehr Bridge, Lehigh County, PA
Figure 34. Diagram of Town lattice truss
Figure 35. Diagram of Long truss
Figure 36. Long truss bottom chord wedge—Downsville Bridge, Delaware County, NY
Figure 37. Wedges between counter and floor beam in a Long truss—Hamden Bridge, Delaware County, NY
Figure 38. Diagram of Howe truss
Figure 39. Diagram of Paddleford truss
Figure 40. Transverse floor beams and longitudinal decking—Fitch's Bridge, Delawary County, NY
Figure 42. Mortise-and-tenon connection in floor beam—Downsville Bridge, Delaware County, NY
Figure 43. End notches of floor beams used in a Town lattice truss—West Dummerston Bridge, VT
Figure 44. Timber dowel reinforcement of post—Mill Bridge, Tunbridge, VT
Figure 45. Installation of distribution beams—Union Village Bridge, VT
Figure 47. Nail-laminated decking being removed—Fitch's Bridge, Delaware County, NY
Figure 49. Running plank installation—Taftsville Bridge, VT
Figure 51. Classic gable roof—Forksville Bridge in Sullivan County, PA
Figure 52. A flat roof bridge—Hogback Bridge, Madison County, IA
Figure 53. Example of rafter ties—Northfield Falls Bridge, VT
Figure 54. Unusual detailing of a portal—Upper Falls Bridge, Weathersfield, VT
Figure 55. Example of portal extension—Wehr Bridge, Lehigh County, PA
Figure 56. Lateral brace connection at tie beam—Fitch's Bridge, Delaware County, NY
Figure 57. Traditional knee brace—Salisbury Center Bridge, Herkimer County, NY
Figure 58. Alternative and stronger style of knee brace—Hamden Bridge, Delaware County, NY
Figure 59. Another alternative knee brace—Hopkins Bridge, Enosburgh, VT
Figure 60. Check brace at bottom chord—Brown's River Bridge, Westford , VT
Figure 61. Check brace at top chord—Quinlan Bridge, Charlotte, VT.
Figure 62. Chin brace—Elder's Mill Bridge, Watkinsville, GA
Figure 63. Interior curbing—West Dummerston Bridge, VT
Figure 64. Squeeze timber approach railing—Hamden Bridge, Delaware County, NY
Figure 65. Approach railing and bridge curb—Paper Mill Bridge, Bennington, VT
Figure 66. Transition from approach railing to inside curb—Mill Bridge, Tunbridge, VT
Figure 67. Original stone high abutment in good condition—Upper Falls Bridge, Weathersfield, VT
Figure 68. Supplemental pile bents—Hamden Bridge, Delaware County, NY
Figure 69. Abutment stem and wing wall identification
Figure 71. Parged stone abutment stem
Figure 72. Damage to stone wall caused by tree roots
Figure 73. Modified original stone abutment—Fitch’s Bridge, East Delhi, Delaware County, NY
Figure 74. Bearing block installation—Brown’s River Bridge, Westford, Vermont
Figure 75. Bolster beam—Fuller Bridge, Montgomery, VT
Figure 76. Hold-down anchor—Paper Mill Bridge, Bennington, VT
Figure 77. Thetford Center Bridge, exterior view, Thetford, VT
Figure 78. Thetford Center Bridge, interior view, Thetford, VT
Figure 79. Surface evidence of powder post beetles
Figure 80. A covered bridge with painted siding—Wehr Bridge, Lehigh County, PA
Figure 82. H20 design truck vehicle (after AASHTO standard specifications)
Figure 83. HS20 design truck vehicle (after AASHTO standard specifications)
Figure 84. Lane load configuration (after AASHTO standard specifications)
Figure 85. Snow load on covered bridges can cause failure—Power House Bridge, Johnson, VT
Figure 87. Another example of collapse by wind—Smith Bridge at Brownsville, VT
Figure 88. The Smith Bridge before collapse.
Figure 91. Three-dimensional image of computer simulation—distorted from load
Figure 92. A heavy timber Burr arch—Wehr Bridge, Lehigh County, PA. 124
Figure 94. Large bolster beam supported on bearing blocks—Hall Bridge, Rockingham, VT
Figure 95. A bolster formed of concrete—Village or Great Eddy Bridge, Waitsfield, VT
Figure 96. Distribution beam system—Worral’s Bridge, Rockingham, VT
Figure 97. No X lateral system and no knee braces—Comstock Bridge, East Hampton, CT
Figure 100. Example of tensile failure of a bottom chord element in a World War II timber building
Figure 101. Example of a tensile failure of a bottom chord in a covered bridge
Figure 103. Simple lap joint, with through-plane connectors
Figure 104. Simple lap joint, with in-plane connectors
Figure 105. Grain orientation of rectangular in-plane connector
Figure 106. Lap joint with bypassing leaves and end grain bearing surfaces
Figure 107. Lap joint with tapered halves and connectors
Figure 108. Bolt-of-lightning joint
Figure 109. Eccentricity in member layout and prying at connectors
Figure 110. Eye-and-wedge clamping bolt, hand-forged
Figure 111. A double-leaf lap joint, with through connectors
Figure 112. Butt joint with steel fish plates
Figure 113. Butt joint with fish plates—wooden plates
Figure 114. Butt joint with bars and rods splice
Figure 115. Simple lap joint for compression members
Figure 116. Simple bearing joint at angled notch
Figure 117. Top and bottom chord connections to vertical
Figure 118. Truss vertical at bearing seat with critical shear face
Figure 119. A sistered diagonal
Figure 120. Example of pegs added to increase the shear capacity
Figure 121. Long truss with counter timbers
Figure 122. Town lattice trusses with identical versus mirrored web members
Figure 123. Town lattice truss connections need to be inspected carefully
Figure 124. Sistered lattice web at chord connection
Figure 126. A solid-sawn end post—Fuller Bridge, Montgomery, VT
Figure 127. An inclined end treatment—Bartonsville Bridge, Rockingham, VT
Figure 128. The corresponding interior end post—Bartonsville Bridge, Rockingham, VT
Figure 129. Intermediate posts—Worrall’s Bridge, Rockingham, VT
Figure 131. Load sharing between arch and superimposed truss
Figure 132. Tie beam to top chord connection
Figure 133. A set of upper braces
Figure 134. Added verticals at tie beams in Town lattice truss
Figure 135. Tie beam to top chord connection details, first diagram
Figure 136. Tie beam to top chord connection details, second diagram
Figure 137. Tie beam to top chord connection details of failed joint
Figure 138. Siding nailers spaced away from truss elements
Figure 139. Fitch’s Bridge, Delaware County, NY
Figure 140. Brown’s River Bridge, Westford, VT
Figure 141. Racked two-span continuous bridge—West Dummerston, VT, before its recent rehabilitation
Figure 142. Example of sag—Station Bridge, Cambridge, VT, before rehabilitation
Figure 143. A chord butt joint in trouble—Station Bridge in Northfield, VT
Figure 145. Dial gauges used to measure the load response
Figure 146. Three-element test specimen
Figure 147. Tensile tests on lattice elements
Figure 149. Sister elements in Town lattice—Silk Road Bridge, Bennington, VT
Figure 151. Partial post replacement in multiple kingpost truss—Union Village Bridge, VT
Figure 153. Metal elements added to an existing bottom chord—Lincoln Bridge, Woodstock, VT
Figure 154. An arch element added to a Town lattice structure—Scott Bridge, Townshend, VT
Figure 157. Spliced lattice tail replacements—River Road Bridge, Troy, VT
Figure 158. Use of steel bolts in chord replacement—Kingsley Bridge, Shrewsbury, VT
Figure 159. Installation of metalwork beneath a timber floor beam—Wehr Bridge, Lehigh County, PA
Figure 161. Good siding details—Fitch’s Bridge, Delaware County, NY
Figure 162. Good siding details around a window—Fitch’s Bridge
Figure 164. Consequences of the poor entrance drainage in figure 163
Figure 165. A trench drain at a bridge entrance—Fitch’s Bridge, Delaware County, NY
Figure 166. Sacrificial timbers beneath truss elements
Figure 167. Accumulation of debris and asphalt encasing timber elements
Figure 168. Bridge at the Green, Arlington, VT
Figure 169. Comstock Bridge, East Hampton, CT
Figure 170. Museum at Shushan Bridge—Washington County, NY
Figure 171. Brown Bridge,Shrewsbury, VT
Figure 172. Lower Cox Bridge, Northfield, VT
Figure 178. How NOT to relocate a covered bridge for repair work.
Figure 183. Diagonal to post connections at the top chord indicating significant overstress
Figure 187. Final inside view. Note the lighter-colored replacement members
Figure 189. Deterioration at end
Figure 190. Older “hung” floor
Figure 191. Partially removed 1976 floor
Figure 192. South Abutment prior to work
Figure 193. North Abutment prior to work
Figure 194. Longer trusses and new recess in existing abutment
Figure 195. Reworked internal bracing system
Figure 196. Partially installed deck
Figure 197. Installing cedar shakes
Figure 198. Siding details during installation
Figure 199. Approach railing configuration at north entrance
Figure 200. Elevation view of completed bridge
Figure 201. View of south entrance and railing configuration
Figure 202. Internal view of completed bridge
Figure 203. As the bridge sat for 13 years
Figure 204. Replacement top chords
Figure 205. Hidden rot inside top of old post
Figure 206. Bridge moved, but not down off temporary cribs
Figure 207. View of shear dowel reinforcement
Figure 208. Reconstructed east abutment
Figure 209. Underway on dollies
Figure 210. On top of the bypass bridge—ready to be slid sideways
Figure 212. Bridge perspective view
Figure 213. Typical bridge section
Figure 214. Raising the trusses
Figure 215. Hartland Bridge on the move
Figure 216. Observers watching a bridge move past
Figure 217. Bridge in place awaiting final lowering
Figure 219. Main truss and arch during construction showing shouldered and wedged timber connections
Figure 222. Existing site with poor alignment
Figure 223. New abutment construction on new alignment
Figure 224. New stub abutment stem
Figure 226. Three chord elements
Figure 227. Adding siding before truss lifting and installation
Figure 228. North truss in position and secured
Figure 229. Both trusses erected
Figure 230. Installation of roof trusses and purlins
Figure 231. Installation of wood shingles
Figure 234. Destroyed March 4, 1999
Figure 235. View in December, 2002
Figure 236. A view of the original bridge
Figure 237. Wooden peg reinforcement of post corbel
Figure 239. Closeup of the failed corbel after the repair
Figure 240. Bar-and-rod connector tensile splice
Figure 241. Transition from approach rail to inside curb
Figure 242. Bridge being moved into position
Figure 243. Oxen power and capstan
Figure 245. New pad at East Abutment—truss erection underway
Figure 246. Entrance of completed bridge
Figure 247. The bridge before work
Figure 248. Modified knee braces
Figure 249. Cranes and truck positioning the trusses
Figure 250. Bridge following reopening
Figure 251. Opening day parade
Figure 252. Completed replacement truss
Figure 253. Bridge before collapse
Figure 254. Bridge after collapse from snow
Figure 255. Double bottom chord arrangement with scarf joint
Figure 256. Connection between deck and bottom chord
Figure 257. Heel connection details
Figure 258. Connection of tie beam, truss vertical, and rafter plate
Figure 260. Power house replica, Johnson, VT
Figure 261. Old Stone Fort Bridge, Schoharie County, NY
