The Powerscourt covered bridge spans the upper reach of the Chateauguay River near the hamlet of Powerscourt, Huntingdon County, Quebec. It is on the First Concession north of the American border in the Township of Elgin, and carries the county road over the river into the Township of Hinchinbrooke. The bridge was constructed by a Mr. David Will on a contract let by the Township of Elgin on November 2, 1857. Work proceeded over a number of years until the structure, originally known as Percy's Bridge, was completed in 1861. 1 Today, the Powerscourt covered bridge is the only example of a McCallum inflexible arched truss bridge extant in the world, and is one of the oldest covered bridges in Canada.
The Powerscourt covered bridge is a two span structure resting on three masonry piers, a central pier in mid-stream and an end pier at each river bank. All three piers are of regular coursed stone masonry construction, and are free standing. In effect, the end piers are not the conventional abutment built into the river bank, but stand in the river a short distance out from the banks. This is a structural feature, isolating the end piers and hence the arched truss from the lateral pressure to which abutments are subjected. The superstructure of the bridge is 186 feet long overall. It consists of two McCallum truss spans, each 85 feet long and an 8 foot extension, or shelter panel, at each end extending out over the approaches. Each truss span is functionally independent, connected one with the other only by the roof sheathing over the centre pier. The roof line is irregular, being horizontal along the ridge and eaves of the shelter panels at each end, but curved over the trusses in keeping with the curved upper chord of the McCallum inflexible arched trusses. The sides of the bridge are covered with vertical board and batten weatherboarding with an opening, three feet or more wide, along the top under the roof eaves to admit air and light.
The bridge is 20 feet wide overall, and there is an ll foot roadway height clearance over the wooden plank deck. The portals of the bridge are totally unadorned, framed by the end posts of the shelter panels and a horizontal strut connecting the top of the end panel posts. There is no weatherboard siding in the gable ends. Inside the bridge, the trusses are lined with horizontal planking, up to a height of about three feet above the deck, from one end to the other.
Each of the four trusses, two to each span, of the Powerscourt bridge is made up of eight panels. The panels are formed by dual timber posts notched into the curved upper chord and the horizontal lower chord. Within each panel, there are dual diagonal braces with a single counter-brace crossing between the diagonal braces. An arch brace crosses each of the two end panels of the trusses from the top chord down to the top of the masonry end pier. In effect, the bracing pattern is a slight modification of the McCallum inflexible arched truss which generally had three arch braces on the same pattern, crossing over the three end panels respectively. The curved upper chord of the truss is made up of three timbers bolted together, and the bottom chord of four timbers of similar construction. The floor beams rest on the bottom chord, and support longitudinal stringers on which the wooden planks forming the deck of the bridge are nailed. On the bridge approaches, heavy stringers sheeted with wooden planks carry the deck extension from the end piers to the river bank.
The trusses are connected by horizontal struts joining the upper chords at the panel posts. To further strengthen the trusses against overturning with the thrust of the rafters and wind loads, the struts are framed with diagonal braces, in both the horizontal and vertical plane, at the junction of the strut with the upper chord of the truss. Some of the braces are bolted to the strut, but most are notched with mortise and tenon joints. A single vertical post at the mid-point of the strut supports the ridge board of the gable roof. All of the bridge frame timbers are adze-hewn in keeping with the age of the structure. 2
With the exception of the roof, and the gable ends, the Powerscourt covered bridge appears to have changed very little over the years. The original roof of cedar shingles was renewed in kind down to 1950, but thereafter a tin roof was substituted and the roof rafters replaced. The deck planking of the bridge has been renewed, perhaps several times over, but the truss timbers and the stone masonry piers no doubt date from the erection of the bridge in 1861. The bridge was repaired extensively in 1881, 1894 and 1950. At one time, the timbers of the bridge were painted white and the weatherboard siding, both inside and outside, was painted grey. Today, the paint is faded, but both colour schemes are still in evidence with the exception of the rafters of the new roof which were left un- painted. 3
The McCallum lnflexible Arched Truss
The McCallum inflexible arched truss was invented, and patented in 1851, by Daniel Craig McCallum a carpenter-bridge builder of Rochester, New York. The novelty of his truss was in the curved upper chord which added an arch action to the truss and in the long diagonal braces, passing through the three end panels of each truss, which carried the thrust of the arch down to the piers/abutments. 4 As of 1851, covered bridges in North America were being constructed with parallel chord trusses of various different patterns: for short spans, the simple kingpost truss, Queenpost truss, or multiple kingpost truss which had been known for centuries in Europe; and for long spans, either the Town lattice truss, the Long truss, the Howe truss, or occasionally the Pratt truss, all of which were of American invention dating from 1820, 1830, 1840 and 1844 respectively. Prior to 1820, American bridge builders had also used a composite arch-truss, the Burr arch-truss, for long span covered bridges. It consisted of a multiple kingpost truss combined with a massive timber arch springing from the abutments, in what was a heavy, indeterminate structure that had long since fallen out of favour. 5 The McCallum arched truss revived the idea of using an arch to strengthen a parallel chord truss, but the arch was now made an integral part of the truss through arching its top chord. In effect, the McCallum arched truss was essentially a Long truss, with vertical posts and diagonals forming an 'X' in each panel, but with the addition of an arched upper chord and diagonal arch braces at the end of the truss. 6
The inflexibility, or exceptional stiffness, of the McCallum arched truss made it especially attractive for railway bridge construction. 7 North American railways had been erecting covered bridges of various truss types since the l83O's; 8 and during the period from 1851 to ca. 1868, the McCallum patented bridge truss was widely introduced on North American railways. 9 McCallum, who had moved to New York, prospered as a bridge engineer. At various times over the next decade, he was employed as General Superintendent and/or as a consultant to the bridge construction departments of the New York and Erie Railway, and the Atlantic and Great Western Railway, and was the President of the McCallum Bridge Company. During the American Civil War, with the rank of Brigadier-General, McCallu managed all of the military railroads in the United States. In that capacity, he erected over 26 miles of bridges (presumably utilizing his own truss design), while transporting Union troops and keeping them supplied in the field. Elsewhere, the McCallum inflexible arched truss bridge was erected on many of the new railroads under construction in the American west. 10
In Canada, covered bridges utilizing the McCallum inflexible arched truss are known to have been constructed on the St. Lawrence and Atlantic Railway (later the Grand Trunk Railway- Canadian National Railways). 11 On its completion in August 1853, the St. Lawrence and Atlantic connected Longeuil on the St. Lawrence River opposite Montreal, with Portland, Maine, via St. Hyacinthe, Richmond and Sherbrooke, in the Eastern Townships of Quebec. 12
Despite its structural merits, the McCallum inflexible arched truss proved complicated to construct, requiring skilled crews and experienced bridge contractors to frame and erect it. Although McCallum tried to promote his arched truss as a "common roadway bridge", covered bridges constructed on North American roads continued to utilize the older parallel chord trusses that local carpenters were capable of framing and erecting. Indeed, the Powerscourt, Quebec, covered bridge is the only McCallum inflexible arched truss structure known to have been erected on a roadway in North America. This does not preclude others having been constructed on roadways, and long since demolished and forgotten, but it does indicate the extent to which the McCallum arched truss was regarded as being peculiarly suited to the needs, and building resources, of railways. 13 Even on railways, however, only an estimated 15O McCallum inflexible arched truss covered bridges were ever built. 14 From the l840's through to the l870's, when the widespread introduction of prefabricated iron truss bridges rapidly rendered wooden truss covered bridges obsolete, most railway covered bridges continued to be constructed with the Howe truss which was far easier to construct and maintain than the McCallum arched truss. 15 In both the United States and Canada, covered bridges continued to be constructed as late as the l960's on secondary roads in areas where timber was abundant. These bridges invariably utilized the simpler trusses developed prior to the introduction of the McCallum inflexible arched truss, 16 as reflected in the surviving covered bridges in Canada.
Canadian Covered Bridges
Covered bridge construction in Canada has been confined principally to the provinces of New Brunswick and Quebec as witnessed by the relative number of surviving structures. Covered bridges were unknown in Newfoundland and, with the exception of four covered bridges reputed to have been constructed recently in British Columbia, were not constructed in western Canada. Only seven are known to have been built in Ontario, and three in Nova Scotia. 17 In contrast hundreds of covered bridges were built in New Brunswick, 18 and over a thousand in Quebec. 19 Today, there are no covered bridges extant in Nova Scotia, one remains in Ontario, and 80 are known to have survived in New Brunswick and about 118 in Quebec. 20 Among surviving covered bridges, by far the oldest are found in Quebec. Ontario's sole remaining covered bridge, at West Montrose, was erected in 1881, 21 and with the exception of two structures dating from 1899, all of the New Brunswick covered bridges, for which dates of construction are known, were constructed in the twentieth century. 22 In contrast, at least eight Quebec bridges date from the nineteenth century, including two which have attained an exceptional age: the Cook Bridge, near Cookshire on the Eaton River, Brome County; and the Powers- court Bridge over the Chateauguay River, Huntingdon County. Some controversy surrounds the Cook Bridge. The covered bridge erected on that site in 1835 is generally recognized as being the first covered bridge built in Quebec; but there is disagreement as to whether the present Cook covered bridge is the original 1835 structure or a replacement reputed to have been erected in 1868. 23 Depending on the resolution of this question, the Powerscourt bridge erected in 1861 may well be the oldest covered bridge extant in Canada.
In North America, some 21 different truss types, exclusive of minor variations, have been found employed in covered bridge construction; 24 but in Canada road bridge builders have tended to stick with a few standard truss patterns which were also highly popular in the United States. The McCallum inflexible arched truss was employed in constructing covered bridges on at least one Canadian railway; but otherwise the same standard truss types were also used in constructing Canadian railway bridges. Today, no railway covered bridges survive; but the standard trusses constructed are well-represented in surviving roadway covered bridges. In New Brunswick, most of the extant covered bridges are of a Howe truss design, with a dozen or so examples of the Burr arch-truss and a single Town lattice truss. 25 In Quebec, the types of truss found on surviving covered bridges reflect a geographical pattern related to the period at which covered bridge construction was introduced into an area.
In Quebec, covered bridges were first erected in areas of loyalist settlement, notably the Eastern Townships in the early 19th century, and were erected by individuals as toll bridges or by local builders on contract for municipalities. In these areas, the standard trusses in use in the neighbouring American states were introduced. Elsewhere in the province, covered bridges were built for the most part in the twentieth century as part of an effort by the provincial Department of Colonization to open up the interior of Quebec to settlement. The Department of Colonization adopted the Town lattice truss for construction, and today almost all of the surviving Quebec covered bridges are of a Town lattice truss design with but minor variations. 26 The exceptions, found in areas of loyalist settlement, include a single Queenpost truss span in Pontiac County and several multiple-kingpost truss and Howe truss covered bridges in the Eastern Townships. 27 The McCallum inflexible arched truss on a roadway bridge at Powerscourt, Huntingdon County, is an anomaly. It can only be accounted for by the presence of railway bridges of the same type constructed in the area less than a decade previous to its construction. The Powerscourt bridge builder, David Will, must have gained knowledge and experience in constructing such a complicated truss through working with a bridge building crew on the St. Lawrence and Atlantic Railway. At 20 feet in width, the Powerscourt bridge is remarkably wide for a covered bridge; but otherwise its dimensions are unexceptional. Canada has several remarkably long covered bridges extant in New Brunswick. Indeed, the longest covered bridge in the world is the Hartland, New Brunswick, bridge over the St. John River. That seven span, Howe truss, structure erected in 1920 has an overall length of 1,282 feet, 28 and was plaqued by the Historic Sites and Monuments Board of Canada in 1980. In Quebec, the longest covered bridge is the four span Notre-Dame-de-la-Providence bridge in Beauce County. Erected in 1928, it has a total length of 495 feet with individual town lattice truss spans of about 123 feet in length. The vast majority of Quebec covered bridges are single span structures, but double span bridges, such as at Powerscourt, are fairly common constituting about one-sixth of the total. 29
The Powerscourt covered bridge is not only the sole remaining example of a type of bridge but rarely constructed on roadways, but is the only McCallum inflexible arched truss bridge extant in the world. Its curved roof line over the arched trusses distinguishes it from all other covered bridges, and it has a number of other notable features that mark it as being a bridge of unusual and superior construction. In the first place, the vertical board and batten weatherboard siding is extremely rare on covered bridges. Quebec bridges were generally sided with clapboard or tongue-and-groove boards nailed on horizontally; whereas in New Brunswick, where vertical weatherboarding was the norm, the boards were merely butt-jointed along their edges. The opening left along the eaves, however, is a standard feature on covered bridges.
The stone masonry substructure of the Powerscourt bridge is an uncommon feature both in respect to the material of construction and positioning of the piers. Most covered bridges extant today either have rock-filled timber crib piers/abutments or rest on a concrete substructure replacing the original timber cribs. Moreover, generally the trusses at the ends of covered bridges rest on abutments built into the river bank, rather than on free-standing end piers as on the Powerscourt bridge.
With the exception of the tin roof and rafters, the Powerscourt bridge is the original structure erected on the First Concession road over the Chateauguay River, Elgin Township, County of Huntingdon, in l86l. It is now 123 years old, and is definitely the second oldest, if not the oldest, covered bridge extant in Canada. By any standards, it is a venerable bridge, and is unquestionably unique in preserving an example of a type of bridge truss --- the McCallum inflexible arched truss --- that has long since vanished elsewhere.
1 "Powerscourt Bridge Boasts McCallum Truss", Huntingdon Gleaner, March 22, 1950; and "Powerscourt Covered Bridge", ibid.
2 Description based on "Powerscourt Bridge Boasts McCallum Truss", Huntingdon Gleaner, March 22, 1950, xerox forwarded by Gérald Arbour, Directeur, "Société Québécoise des Ponts Couverts inc", from research material provided courtesy of Richard Sanders Allen, and an analysis of photographs taken of the Powerscourt bridge in 1981, furnished courtesy of Gaston St-Arnaud, Chef du Service de l'entretien des structures, Ministere des Transports, Québec, December 16, 1983.
3 "Powerscourt Bridge Boasts McCallum Truss", Huntingdon Gleaner, March 22, 1950; "Powerscourt Covered Bridge", ibid; and Telephone Communication, March 20, 1984, from Helene Boudreau, Secretary-Treasurer, Elgin Council, Athlestan, Québec, conveying information extracted from the Elgin Council Minutes, Township Records 1855 - 1895, photostats to follow.
4 "General Daniel Craig McCallum", Scientific American, Vol. XL, 18 January 1879, p. 37.
5 On the evolution of covered bridge trusses in North America, see Robert W. Passfield, "The Upper Dorchester Covered Bridge, Westmoreland County, New Brunswick", Historic Sites and Monuments Board, Agenda Paper #12, June 1977.
6 R.E. Wilson, "Twenty Different Ways to Build a Covered Bridge", p. 141, in American Society of Civil Engineers, American Wooden Bridges, New York: A.S.C.E. Historical Publications No. 4, 1976.
7 Wilson, "Twenty Different Ways to Build a Covered Bridge", p. 141.
S Hegen Petersen, Kissing Bridges, Brattleboro, Vermont: The Stephen Greene Press, 1965, p. 34; and Richard Sanders Allen, Covered Bridges of the Northeast, Brattleboro, Vermont: The Stephen Greene Press, 1957, p. 17.
9 "The McCallum Truss Incorporated in Powerscourt Bridge", Huntingdon Gleaner, 22 March 1950, xerox forwarded by Gerald Arbour, Directeur, Société Québécoise de Ponts Couverts inc., from material provided courtesy of Richard Sanders Allen.
10 "McCallum,Daniel Craig", Dictionary of American Biography, Vol. ll, p. 565; and "Personal - General Daniel Craig McCallum", Railroad Gazette, Vol. ll, 3 January 1879, p. 9.
11 "The McCallum Truss Incorporated in Powerscourt Bridge", Huntingdon Gleaner, March 22, 1950.
12 The "Société Québécoise des Ponts Couverts inc", has an old photograph of one of the McCallum inflexible arched truss covered bridges erected, and long since demolished, on the St. Lawrence and Atlantic Railway near Sherbrooke (Gerald Arbour, Directeur, to R.W. Passfield, January 20, 1984).
13 "The McCallum Truss Incorporated in Powerscourt Bridge", Huntingdon Gleaner, March 22, 1950; and "Powerscourt Bridge Boasts McCallum Truss", ibid.
14 Wilson, "Twenty Different Ways to Build a Covered Bridge", p. 141.
15 David Plowden, Bridges: The Spans of North America, New York: Viking Press, 1974, pp. 38-39; and Allen, Covered Bridges of the Northeast, p. 103.
16 Petersen, Kissing Bridges, pp. 22-25; and Plowden, Bridges, pp. 39-40.
17 Lyn and Richard Harrington, Covered Bridges of Central and Eastern Canada, Toronto: McGraw-Hill Ryerson, 1976, pp. vi, viii, & 74; and Earle Lockerby, "Covered Bridges, A Canadian Geographic Pictorial", Canadian Geographic, June/July 1983, p. 39.
18 New Brunswick, Department of Tourism, Covered Bridges of New Brunswick, (Pamphlet, n.d.), p. 6.
19 Quebec, Department of Tourism, Ponts couverts, Quebec covered bridges, (Pamphlet, n.d.), p. 4.
20 Lockerby, "Covered Bridges, A Canadian Geographical Pictorial", p. 39.
21 Provincial Archives of Ontario, Record Group 14, Historical Collection, Department of Highways of Ontario, information Section, "West Montrose Covered Bridge".
22 Harrington, Covered Bridges of Central and Eastern Canada, pp. 85-87.
23 Henri-Paul Thibault, Rapport préliminaire sur Les Ponts Couverts Du Québec, Ministere des Affaires culturellesz Québec, Juin 1981, pp. 14 & 31.
24 Wilson, "Twenty Different Ways to Build a Covered Bridge", p. 129.
25 National Society for the Preservation of Covered Bridges, World Guide to Covered Bridges, 1972 ed.; and Harrington, Covered Bridges of Central and Eastern Canada, p. 18.
26 Quebec, Department of Tourism, Ponts couverts, Quebec covered bridges, (Pamphlet, n.d.), p. 4.
27 Ibid., pp. 15, 32-35.
28 Harrington, Covered Bridges of Central and Eastern Canada, p. 10.
29 Thibault, Les Ponts Couverts Du Quebec, pp. 25-26; and Québec, Ministere des Affaires culturelles, Les Ponts Couverts Du Quebec: Beauce et Estrie, (Pamphlet, n.d.).