Historic Structures

McConnells Mill Covered Bridge, Ellwood City Pennsylvania

Date added: March 18, 2016 Categories: Pennsylvania Bridges

The covered bridge located in McConnelPs Mill State Park in Lawrence County, Pennsylvania, is a bridge that has considerable aesthetic appeal, in part because of its surroundings. Nestled in a magnificent gorge surrounded by foliage and next to an old grist mill that gives the area - and the bridge - its name, the McConnell's Mill Bridge, completed in 1875, seems the epitome of the traditional American covered bridge. Rising from stone abutments over Slippery Rock Creek, its red-painted board-and-batten exterior gives the bridge the semblance of a barn over a river, allowing it to shed its associations with engineering and technology and enter the realm of architecture.

The bridge coverings were built to prevent the wooden trusses from inclement weather and rot, extending their useful life indefinitely, depending upon maintenance. Their widespread construction marked the beginning of the end for the ferry as a principal means oftransport across rivers, and it is believed that nearly 1,500 of them were built in Pennsylvania during the nineteenth century—far more than any other state.2 It is also believed that wooden covered bridges were first built on a widespread scale in America, and it is known that the truss designs patented by American engineers like Theodore Burr, Ithiel Town, Stephen H. Long, Robert J. Smith, and William Howe influenced the course of bridge-building worldwide.

A variety of different truss systems were used for covered bridges during the late eighteenth century and throughout the nineteenth, as bridge technology improved to allow for longer spans that could withstand heavier loads. One such system was patented by William Howe in 1840, combining a variation of a regular king-post truss with diagonal wooden members acting in compression and vertical iron rods acting in tension.

The McConnell's Mill Bridge was one of many covered bridges built in Pennsylvania with a Howe truss; today, only four remain. Its 91'-0" length makes it the longest of the four remaining Howe truss bridges in Pennsylvania, and it is also the oldest of the four with most of its original members intact. Much of the 120-year-old structure is still in remarkably good condition for its age - its only substantial alterations are a steel truss supporting the wooden deck and asphalt roofing paper that was attached to the roof beams in the late 1950s. These additions, however, have allowed the bridge to provide continuous vehicular service.

While the McConnell's Mill Bridge no longer serves its early economic function as a passageway over the creek for the distribution of flour produced by the mill, it is a principal attraction in the state park. Since the mill was transformed into a museum in the 1960s, many of those who come to visit the mill combine their trip with a walk through the bridge. Many also take photographs either of the bridge alone or of friends and family using the bridge as a backdrop. Its significance in the history of American engineering notwithstanding, the small bridge continues to attract attention for its aesthetic appeal.

With iron becoming acceptable as a bridge-building material by the 1850s, Massachusetts-bom William Howe patented a double-intersection truss in 1840 that employed wrought-iron rods as vertical tension members between wooden diagonals. Howe's brother-inlaw, real-estate speculator Amasa Stone, promoted use ofthe Howe truss in his native Ohio and patented a form of it that became a standard in 1846. This form traditionally included heavy wooden members with the exception of transverse beams, vertical end posts, the top and bottom chords, and the bolted connections. Howe and Stone's truss patent improved upon the design patented by Stephen Harriman Long in 1839, which included diagonals pre-tensioned by driving wedges on the vertical members. Howe's truss made Long's obsolete by devising a method to pre-stress diagonals by tightening nuts rather than driving wedges. There were variations on the truss, one of which adds a second wooden diagonal to each panel. The McConnell's Mill Bridge employs this crossed-diagonal system.

In 1841 and 1842, Stone formed a company with Azariah Boody to promote and fabricate Howe trusses. Because the iron rods and the wooden compression members could be standardized, by the mid-nineteenth century the Howe truss had become the nation's most popular truss for railroad bridge construction. The Howe truss's successful use of iron tension rods, at an early stage, gave bridge builders confidence in the strength and applicability of that material.

For a time, bridge engineers building Howe trusses combined wooden beams with castand wrought-iron members. As the railroads continued to demand sturdier bridges, however, it was not long before all-iron bridges, followed by statically determinate all-steel prefabricated truss bridges, were spanning America's waterways. The introduction of iron members into bridge construction was later seen as a crucial moment in bridge engineering history, the gradual end of wooden bridges and the introduction of all-metal bridges that came to dominate American bridge building in the late nineteenth century.

Wooden members had become nearly extinct around the country by the early twentieth century, but in the 1870s, Howe truss bridges were still very popular for both railroad and vehicular bridge construction. While the Burr arch-truss remained the most popular mode of construction for the small wooden covered bridges over streams, creeks, and rivers in America's rural areas, in the mid- and late-nineteenth century a sizable number of covered bridges were built with Howe trusses. Most of the Howe truss covered bridges, however, were built in Ohio, Indiana, and Oregon; only a comparative handful were built in the eastern United States. Although Pennsylvania has always had far more covered bridges than any other state, only four Howe truss covered roadway bridges are known to have existed in the state at any one time.

In Lawrence County, despite its important role in the once-vibrant lumber industry of northwestern Pennsylvania, bridge building moved quickly from simple log "stringer" bridges to spans of iron and steel. The "age" of covered bridge building, from 1820 to 1900 (when Pennsylvania is estimated to have had approximately 1,500 covered bridges), went by relatively unnoticed in the watershed of the Ohio River, which includes nearly all of western Pennsylvania. Of the covered bridges that were built, however, many of them were erected in Lawrence County, and there is evidence that at least seventeen of them existed in the county at one time or another. Today, only McConnell's Mill Bridge and Banks Bridge, the latter an 1889 Burr arch-truss over Neshannock Creek in Wilmington Township, still exist.

The manner in which the trussing system of the McConnell's Mill Bridge developed and how it fits in with the history of American bridge building provides only part of the story, however. A bridge at this location would probably never have been built at all had not McConnell's Mill been there in the first place. Indeed, the story ofthe bridge was - and continues to be - linked to the mill that later gave its name not only to the bridge, but also to the state park around it.

The mill, however, was neither the first mill at the site, nor was it originally owned by a McConnell. In fact, there were mills, dams, and bridges along Slippery Rock Creek in the vicinity of the current McConnell's Mill as early as 1825. The first mill on the site, a four-and-a half- story structure, was built by Daniel Kennedy in 1852, whose descendants had settled in the region in 1808. The mill made use of a dam built earlier by Johnson Knight to power one of his many mills.

In 1867 or 1868, Kennedy's Mill was struck by lightning and burned to the ground. Only some of the foundation stones remained, but Kennedy paid for the reconstruction of the mill (with one less story) on that foundation, and it was operating again by 1869 or 1870. In 1874, the dam at the site was washed away, and a 12'-6" dam was erected in its place.

What was later called the McConnell's Mill Bridge was not the first bridge at the site, either. In December 1861, viewers inspected and approved a county-built bridge over Slippery Rock Creek "where the public road to Butler crosses said creek," noting that Andrew Buchanan and James McKee had fulfilled the contract to build the bridge and that it had been completed in a "substantial and workmanlike manner."

Kennedy passed away on 14 June 1872, shortly after building his second mill, and it was purchased by three men named Mehard, Oliver, and Graham. In May 1875, James F. McConnell, Thomas McConnell, and Samuel Wilson bought the mill property. As ownership of the mill was being transferred to McConnell, Wilson, and Company, workers were putting finishing touches on the nearby covered bridge. The new owners were soon to benefit tremendously from the bridge, but its construction had been requested earlier by area inhabitants.

Transportation to and from the area was important enough that Slippery Rock Township residents filed a petition in the Lawrence County Courthouse on 7 September 1874 indicating that a bridge was "much needed" over Slippery Rock Creek at Daniel Kennedy's Mill and that the cost of erecting said bridge would be "too heavy and burdensome" for the township's inhabitants to afford. They requested that the judges of the county appoint viewers to inspect the site and see if the request should be granted. On the same day, the judges appointed Archibald McMillan, David Frew, and Jacob Shaffer to act as viewers. Each of the viewers lived within three to five miles west of the bridge site along the New Castle and Butler Road.

three to five miles west of the bridge site along the New Castle and Butler Road.16 On 15 September 1874, the viewers went to the site and returned with a unanimous decision that a bridge was "much needed" and reiterated the inhabitants' earlier concerns about cost. They determined that a new bridge, 90'-0" between abutments, should be erected with county funds on the site of the old bridge. They also determined that the new abutments should be 17'-0" high and be placed "immediately" in front of the old abutments. The court approved the viewers' recommendation on 15 December 1874, and construction began shortly thereafter.

The petitioners then selected the firm of Bell and Breckenridge to provide the work for the abutments and entered into a contract with J. B. White and Sons for the superstructure. Bell and Breckenridge were paid $4.60 per peck of twenty-five cubic feet, and J. B. White and Sons were paid $19.75 per linear foot.

On 27 May 1875, the petitioners asked the court to appoint "proper persons" to inspect the finished bridge and make a report to the court, noting that the "said bridge is now completed." The court selected Robert Francis, Samuel Kildoo, and Joseph Mehard as viewers. It was around this time, in May 1875, that Mehard, Oliver, and Graham sold their interest in the mill to McConnell, Wilson, and Company.

By 25 October 1875, it was noted in the court records that the viewers had not yet inspected the bridge. On 13 November 1875, however, the viewers reported to the court that the masonry and superstructure were completed according to specifications. The bridge was probably completed, however, in the First half of 1875.