Kirkton of Glenisla Footbridge
Location: Grid ref: NO 2127 6030. North of Blairgowrie.
This is a remarkable blacksmith-made footbridge over the River Isla in Angus, designed and erected in 1824 by John Justice Jr of Justice and Co of Dundee. It is of extremely lightweight construction, made of wrought iron with a wooden deck 3 ft 5 in. wide. Span 62 ft.
It is part suspension bridge, part rod-stayed bridge.
There are four wrought iron pylons, embedded in the stone abutments and braced by 3/4" diameter inclined stays. From each of these pylons four slender rods slope down to the deck members, the uppermost rods reaching to the deck's mid span. Further down each pylon there are two further rods which are incorporated into the handrailing to provide a degree of suspension for the deck. See photo 2.
The main deck members are remarkably slender, being flat bars approximately 1/4" thick and 3" deep, with lateral stiffening provided by wrought iron bars and by the wooden decking (photo 4). The new hardwood deck incorporates its own longitudinal wooden beams. The ends of the lateral bars pass through holes in the side members and the bottom of the handrail uprights, and are secured by tapered cotters. The ends of some of these bars also serve as attachment points for the diagonal stay rods. Some sources describe the pylons as being of H-section. In fact each pylon comprises three pieces: a central bar of square section; a flat plate of rectangular section; a forged plate with raised bosses whose faces are inclined to suit the angle of the individual stay rods (photo 6). The stay rods and the suspension rods are tensioned using threaded eye bolts.
The inclined stays are attached to the the pylons by stirrups (shackles) (photo 6). There is no provision for adjusting the tension. The stirrups are prevented from moving down the pylons by small pins inserted below the stirrups (photo 6).
Pairs of pylons are joined at the top by curved wrought iron bars of square section, and braced at the bottom by scrolled wrought iron brackets (photo 3). A self-closing gate is attached to the pylons at the southern end.
The Canmore entry is an excellent source of information on constructional details of the bridge.[1]
"It is one of the earliest surviving Scottish examples of a suspension bridge. The bridge is actually a cross between a suspension and a cantilever bridge, since the deck is suspended from the two low-slung stretcher wires braced by stays from pylons. At each end of the bridge, the piers are joined by a cast-iron arch, or overthrow, bolted to the mast-heads. At the top of each overthrow is a plaque inscribed: "Jn. JUSTICE DUNDEE 1824"."
The much larger Haugh of Drimmie Bridge, shares some similar design principles
See Also
Sources of Information
Source: RCAHMS contribution to SCRAN.
- [2] Canmore