Historic Structures

John Bright Iron Bridge No. 1, Carroll Ohio

Date added: November 13, 2015 Categories: Ohio Bridges

A contract for the "building of this bridge has not been found, "but it has been suggested that a number of references in the Commissioners' Journals for dates in 1884 and 1885, all referring to the Smith Mill Bridge in Liberty Township, are for this iron bridge. There was a Smith Mill by Poplar Creek, hence the name Smith Mill Bridge. Augustus Borneman was paid $1000 for the Smith Mill Bridge in June 1884, and in July he was paid a further $400. In January 1885 he received $520 making a total of $1920 - a high price for 1885.

As with the John Bright No. 2 Covered Bridge, which pre-dates No. 1 by about three years, there was, according to the Commissioners Journals a covered combination truss bridge on this site, prior to the building of the metal bridge. That bridge stood from 1876 to 1884. As with the predecessor to the covered bridge no reason is given for the need to replace it, but perhaps it is relevant that 1884 was a year in which flooding was a problem in that area.

Structurally the bridge is almost exactly the same as the John Bright No. 2 Covered Bridge, but it is constructed entirely in iron. However, the iron bridge has no secondary strengthening as in the wooden arch of the covered bridge, and is virtually unchanged. The vertical end posts bear ornamental urns, and there is a plaque on the nothern portal stating that the bridge was built by the Hocking Valley Bridge Works, which was owned by Augustus Borneman.

Some of the structural differences between this and the covered bridge are due to the fact that a different material was used. In this structure the vertical posts are six inch channels joined together by diagonal lacing. The end posts also are made of channels, linked this time by a plate. The upper chord is constructed in the same way, and the suspension chain hangs down between the vertical posts, although it is made of flat eye-bars instead of the square rods used at the covered bridge. The plates are riveted to the channels in the end posts and upper chord, but otherwise pins were used for all structural connections in this bridge, as they were on the covered bridge. There is horizontal diagonal bracing between panels in the plane of the upper chord, and of the deck, but tension rings are not used here as they are on John Bright No. 2. Instead, two diagonals simply cross each other but each one is itself made up of two rods. These have threads on their inner ends and are linked by a sleeve nut. This bridge has an overall length of 90 feet and the deck is 15 feet wide.

It has been suggested that the design of the John Bright Bridges, considered unusual, was derived from an 1875 bridge patent by William Black (US patent No. 166,960 dated 24 August 1875). Black was incidently a former partner of HBVW's owner, Augustus Borneman (see below). His patent is similar in appearance to the John Bright Bridges, although other patents, more closely resembling the John Bright Bridges exist. It has inclined (not vertical) end posts, and a suspension chain of eye bars, called a catenarian tension-arc by Black. The posts and upper chord are again built-up of iron channels and plates. Posts are set between the upper chord and the arc to, according to the patent, "communicate the strain at right angles,or nearly so, to the tension-arc ... at the point of contact therewith." Black claims various elements of the design as being his invention. These connection details, and the method of suspending the deck, are different to those used by Borneman. He emphasizes the use of a specially designed cap to join the ends of the upper chords to the posts, and also to protect that joint. This is not used on the Bright bridges. In the John Bright Iron Bridge the upper chord sits over the end post (it also projects beyond it, but the projection is merely decorative, not structural). The bottom chord is connected to the end post by a pin connection and is composed of eye-bars. That connection is covered by two separate cast iron plates: one is attached to the under side of the upper chord projection, while the other is a plaque bearing the name of the Hocking Valley Bridge Works, and blocks off the end of the upper chord. The ornamental urn is set on a third cast iron plate.

However, two similar truss patents have been noted which more closely resemble the John Bright Bridges. One is W. 0. Douglas' "Improvement in Truss-Bridges" (US patent No. 202,526 dated 16 April 1878). It is a lenticular truss, with the design making use of two chords, one in compression and one in tension joined together at the extremities. The chords can be hipped or parabolic, but in all cases the two are bound together by vertical posts and diagonals. Deck Beams, which support the roadway, run laterally from panel point to panel point, and is supported by vertical hangers suspended from the bottom chord. The design is visually not dissimilar to that of the Bright bridges, although the upper chord is a curved member. The other patent is Archibald McGuffie's "Improvement in Construction of Bridges" (US patent No. 55,954 dated December 186l). McGuffie's design is almost identical to the John Bright bridges. A suspension chain consisting of lengths of double eye-bars with the ends welded together by joint blocks. The joint blocks (the points where braces, suspension rods supporting the deck, and vertical posts all meet on the line of the suspension chain) consist of large pins inserted through the links. This chain is suspended from the upper chord. The ends of the chain are stirrups with screw threads at the ends, which pass through the upper chord and are held there by nuts. The upper chord is of "a sectional tubular cast-iron". Diagonal braces run from the upper chord to the joint blocks, the connection with the chord being at the next panel point along from the one where the brace starts.

It is explained in McGuffie's patent that: "By combining the chord posts and braces with the catenary series of links in the manner above described to truss the links in the true catenary line, the tendency of any one part of the girder to sink more than another is prevented, for if a load (it is stated) rests at one point, the weight of the whole truss is tending to operate against it and counteract the tendency to depression at that point."