The growing popularity of timber bridges is not only due to their economy, strength, durability and nostalgic ties to America's early history. It also is their warm, aesthetic presence and harmony with the environment that causes design firms and local government agencies to value this historical material much as their ancestors did.
Many of the bridges which received awards in the recent National Timber Bridge Award competition were specifically designed to enhance and protect the delicate environments where they span creeks, rivers, waterways and wetlands.
National Timber Bridge Awards were presented to 15 outstanding bridges located across the nation. The major sponsors of the program are APA-The Engineered Wood Association, the American Institute of Timber Construction, the U.S. Forest Service-Wood in Transportation Program and the Federal Highway Administration. Supporting sponsors are the American Wood Preservers Institute and Roads & Bridges magazine.
Judges for the competition were Thomas Williamson, P.E., APA-The Engineered Wood Association; Michael Caldwell, P.E., American Institute of Timber Construction; Ed Cesa, U.S. Forest Service; and Sheila Duwadi, P.E., Federal Highway Administration.
The following is a brief description of some of the first-place award winners.
Vehicular Bridge (main span greater than 40 ft)
Military Road Bridge
When two counties in upper New York decided to replace a deteriorating concrete bridge over West Canada Creek, they turned to an engineering firm that recommended a glued laminated spandrel arch design with glulam bents, deck and railings.
The underdeck design was chosen for the Military Road Bridge based on the advantages of geometric constraints, protection from weather, vehicular impact, ease of construction and competitive costs.
"Additionally, glued laminated timber was selected for its architecturally appealing features," the engineers reported.
The bridge deck has longitudinal glulam timber panels on transverse glulam floor beams.
Special galvanized saddle connections tied the bents to the glulam arch segments. The arches span 132 ft. The total length of the bridge is 180 ft and the width is 27.5 ft. Total construction cost was $1,001,000.
Owner: Herkimer and Oneida Counties, N.Y.
Design/Consulting firm: Barton & Loguidice, P.C., Syracuse, N.Y.
Contractor/Erector: Tioga Construction Co., Herkimer, N.Y.
Engineer: Barton & Loguidice, P.C., Syracuse, N.Y.
Another vehicular bridge over 40 ft which won an Award of Merit in the competition was the Gardiner Road Bridge in Port Townsend, Wash.
Vehicular Bridge (main span less than 40 ft)
Vehicular Bridge
The designers of this 75-ft-long timber bridge had to operate within stringent restrictions which required that any crossing of the delicate wetlands in Washington, Conn., must make only a minimum impact on the environment. It is 11 ft wide.
Three pairs of graceful 103?4-in.-deep curved glulam timber sections create the bridge structure. Each glulam section spans 25 ft between concrete piers and abutments.
Glulam sections were formed as arches and then laid on their sides. Each panel acted as a monolithic slab, transferring and spreading the wheel loads of vehicles laterally. Glulam rails form wheel curbs that trace the deck's curved edge.
Owner: II Poggio, Washington, Conn.
Design/Consulting Firm: Gray Organschi Architecture, New Haven, Conn.
Engineer: Gibble Norden Champion Brown, Old Saybrook, Conn.
Pedestrian Bridges
Bemis Bridge
This graceful asymmetrical cable-stayed bridge across the Saco River connects homes in Harts Location, N.H., to the outside world and carries skiers and hikers to Mount Washington. Designers were challenged by the special requirements set down for the new bridge which directed that the span be unobtrusive with environmental appeal, require low maintenance, not impede the spring runoff and be built within a limited budget.
Basic materials include glued laminated timber girders and deck, galvanized steel pipe rail, a 53-ft steel tower and galvanized cable. The unique structure is the only asymmetrical cable-stayed bridge in New England. Because of the creative design, there are no piers in the Saco River to impede spring runoff or impact this classic New Hampshire trout stream.
The bridge is 165 ft long. It is handicap accessible with a 5-ft width which provides enough space for a wheelchair to turn around.
Owner: Town of Hart's Location, N.H.
Design/Consulting Firm: H.E. Bergeron Engineers, Conway, N.H.
Contractor/Erector: Bayview Construction, Portsmouth, N.H.
Engineer: H.E. Bergeron Engineers, Conway, N.H.
Rehabilitation of Existing Bridges
Tohickon Aqueduct
The waters of history flow swiftly over and under the Tohickon Aqueduct "water bridge" in Bucks County, Pa. The glued laminated timber bridge carries the Delaware Canal on three spans totaling 210 ft over Tohickon Creek.
The first aqueduct bridge in this location was built during the 1830s, when Andrew Jackson was president. The current timber aqueduct is the fifth bridge, following the deterioration of previous metal truss and concrete designed spans built in the past century.
The current bridge is a timber burr truss design. It is engineered to bear the water loads over the three 66-ft spans of the Tohickon Aqueduct, supporting 350 tons of water within its trunkway. In the rehabilitation, the superstructure system allowed the timber trusses to bear directly on new caps on the existing stone substructures. The trusses were engineered to be redundant so either the trusses or the arches alone could bear the fully loaded structure. The new timber tow path was cantilevered over the creek and the entire structure was sheathed as a "covered bridge."
The cost was $2.1 million. An estimated $1 million was saved based on revised specifications for modern glulam timber fabrication and construction.
Owner: Pa. Dept. of Conservation and Natural Resources, Harrisburg, Pa.
Design/Consulting Firm: Simone Jaffe Collins Inc. Landscape Architecture, Berwyn, Pa.
Contractor/Erector: J.D. Eckman Inc., Atglen, Pa.
Structural Engineer: DCF Engineering Inc., Cary, N.C.
Project Engineer: Pa. Dept. of Conservation and Natural Resources, Harrisburg, Pa.
Substructure Engineer: Pa. Dept. of Environmental Protection, Harrisburg, Pa.
Covered Bridges
Embarras River Bridge
Covered bridges may be the only American structures which are still built with the same designs and craftsmanship employed during the Colonial era.
The first-place award winner for covered bridges in this year's award program is the Embarras River bridge in Cumberland County, Ill. It is reported to be the longest single span covered timber bridge in the U.S. without a posted load restriction. The new bridge is reminiscent of the original span over the Embarras River, built in the early 1800s as part of the historic Cumberland Trail.
The $2.8 million bridge is a 200-ft single-span structure which utilizes a combination of parallel chord trusses and three-hinged parabolic arches to satisfy stringent loading and deflection criteria. It was designed to be a cultural and tourist attraction as well as a functioning highway bridge on U.S. Highway 40.
Owner: Cumberland County Highway Dept., Toledo, Ill.
Design/Consulting Firm: Rhutasel and Associates, Centralia, Ill.
Contractor/Erector: O'Neil Bros. Construction, Danville, Ill.
Engineers: Elmer G. Pyle, P.E., S.E., Rhutasel and Associates Inc. and Enterprise Engineering Consultants, Peshtigo, Wis.
For more information about the timber bridge award program, contact Tom Williamson, APA-The Engineered Wood Association, 7011 S. 19th St., Tacoma, WA 98466, at 253/620-7407, e-mail: [email protected].
