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Federal Highway Administration > Publications > Research > Structures > Covered Bridge Manual

Publication Number: FHWA-HRT-04-098
Date: APRIL 2005

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Appendix G. Caine Road Covered Bridge, Ashtabula County, OH

The picture shows a Pratt truss bridge with an extended portal spanning misaligned steep, rocky banks over a bend in the river.

Figure 221. Final bridge.

As a part of its 175th birthday celebration, Ashtabula County, OH, appropriated $100,000 to purchase materials for the construction of the county's 14th covered bridge. The new covered bridge replaced an old steel truss bridge. The Ashtabula County Highway Department performed the construction. A Pratt truss design was selected for its efficiency and cost-effectiveness. The Pratt truss construction consists of vertical timber posts, timber chords, and diagonal steel rods. This was the first covered bridge of Pratt truss construction in Ashtabula County.

Caine Road is a township highway with a traffic volume of fewer than 400 vehicles per day. It was determined that a 5.5-m- (18-ft) wide, 4.4-m- (14.5-ft) high, HS20-44 loading bridge would be built.

The picture shows a winding road leading to and away from the bridge with the former steel pony-truss bridge poorly aligned.

Figure 222. Existing site with poor alignment.

The first phase of construction was to build new abutments. They are standard stub abutments that bear directly on bedrock. The total height of abutments was 5.2 m (17 ft). Rock channel material would later be placed to provide erosion and scour protection. To correct both stream and highway alignment problems, the decision was made to relocate the new bridge. After the new bridge was built, the stream was relocated to flow under the new bridge.

To solve the alignment problems, the bridge was relocated and the stream subsequently rerouted. The picture shows the first construction phase of building new standard stub abutments that bear directly on bedrock.

Figure 223. New abutment construction on new alignment.

The picture shows the detail of the concrete abutment stem that is double-faced with extra reinforcement and two concrete stems protruding from the top of the abutment.

Figure 224. New stub abutment stem.

The main trusses were built with Southern Pine glue-laminated lower chords and floor beams. To minimize the number of tension splices in the lower chords, 19.5-m- (64-ft) long timbers were used. Splices consisted of steel plates with bolts and 100-mm- (4-inch) diameter shear plates. The upper chords and verticals were built with solid-sawn Southern Pine. The upper chords were triple metric needed 150x400x7.3m (6"x16"x24') long. Also in the plane of the trusses are metric needed 75x250x2.4m (3"x10"x 8') oak timber diagonals that act as spacers between the elements.

The picture shows four workers assembling the bridge. Two are using a pry bar for the truss assembly.

Figure 225. Truss assembly.

The picture shows the triple-chord assembly with horizontal and diagonal oak members as spacers between the pine chords.

Figure 226. Three chord elements.

The picture shows workers laying vertical siding, but working horizontally before the truss was lifted for installation.

Figure 227. Adding siding before truss lifting and installation.

All chords and verticals are triple element members with approximately 75 mm (3 inches) between the elements. Twin steel diagonal tension bars pass through the gaps. The diagonal bars range in size from 50-63 mm (2-2.5 inches) diameter. Bearing plates are provided to transmit the load to the chords. Grooves are provided in the chords to resist lateral movement of the plates. The ends of the tension bars are threaded for the tightening nuts.

The floor beams (two per panel) are 220x420x6.7m (8¾"x 16½"x 22') spaced 1.2 m (4 ft) apart. They are hung from the lower chords using two 22mm (7/8'") diameter bolts at each end. 150 mm by 230 mm (6"x 8") white oak timbers are attached on the floor beams and run longitudinally at a 405-mm (16-inch) spacing. The next layer consists of 75-mm- (3-inch) thick transverse white oak planking. 2" thick oak runners were used to smooth out the ride in the bridge.

The roof system consists of 7/12 pitch trusses with a 100 mm x 200 mm (4"x 8") upper chords and twin 100 mm x 150 mm (4"x 6") lower chords. The roof truss spacing is 1.2 m (4 ft). Purlins are 75 mm x 100 mm (3"x 4") members spaced at 200 mm (8 inches). Wood shingles were nailed to the purlins.

Sway bracing consists of 100 mm x 250 mm x 3.0 m (4"x10"x10') oak knee braces at 2.4-m (8-ft) spacing. Upper lateral bracing consists of 200 mm x 200 mm (8"x 8") transverse with diagonal cross bars.

For longevity, the main trusses and floor beams were treated to prevent deterioration. All steel hardware was hot-dip galvanized.

The side view shows the bridge abutment with the north truss being lifted and set in position by a crane. Details reveal the inside superstructure posts and diagonals of the bridge.

Figure 228. North truss in position and secured.

This longitudinal view shows the whole crane installing the opposite (south) truss so that both walls are set on the abutments.

Figure 229. Both trusses erected.

This longitudinal view shows the bridge set on the abutments with the walls tied together with the roof trusses and horizontal purlins or tie beams.

Figure 230. Installation of roof trusses and purlins.

The longitudinal view shows four workers (two on scaffolding and two on the trusses) installing wood shingles on the roof.

Figure 231. Installation of wood shingles.

The last view is an aerial shot that shows a straight road with the new realigned bridge and riprap along the rerouted river. The river's path is more defined than the before picture with a straighter road crossing over the river.

Figure 232. Completed bridge.

All photos courtesy of John Smolen

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