King's Bridge, Stranmillis/Annadale Embankment, Belfast

King's Bridge is a four-span reinforced-concrete road bridge across the River Lagan, completed in 1912 and named after King George V. It was built for Belfast Corporation by contractors W.J. Campbell & Son to connect Ridgeway Street on the County Antrim side with Sunnyside Street on the County Down side. The bridge was designed by the Trussed Concrete Steel Company of Westminster.

The bridge is constructed entirely of reinforced concrete using the patented American Kahn system of reinforcement. The Kahn system, patented in America in 1903, employs steel bars of diamond cross-section with horizontal strips on diagonally opposite corners which are slit and bent upwards to bind the concrete more effectively under compression and tension. According to civil engineering historians Cox and Gould, King's Bridge is the earliest attested multi-span Kahn-type bridge in Britain and Ireland, and the first example in which the beams are continuous rather than a series of single-span bridges set end to end. There are no other identifiable Kahn bridges in Northern Ireland or elsewhere in Ireland.

The structure spans 195 feet overall with a width of 30 feet. Each pier comprises two uprights with angled cutwater ends, probably forming part of a submerged A-frame rather than separate piles. Above each pair of uprights sits a triangulated concrete frame carrying three continuous longitudinal beams. A longitudinal beam runs along each side, supporting the parapet and resting on vertical columns at the outside ends of the piers. These columns are embellished with semicircular-headed recesses on their outside faces. The three inner beams support smaller transverse beams running between the side beams, on which the deck slab is cast. The two middle spans are 50 feet long and rest on supporting longitudinal beams of 51 inches by 13 inches cross-section. The outer spans are 40 feet long and rest on three beams of 42 inches by 12 inches section. The two middle spans are slightly wider than the end ones, which are slightly inclined upwards from the bank towards the middle. A large cast-metal pipe, probably for water, is slung from the underside of the deck.

The parapets feature shallow rectangular panel recesses along their outer faces, punctuated by ten intermediate parapet piers rising from the main piers below. Each parapet pier carries a cast-iron lamp standard, with maker's details identifying D.W. Windsor of Ware, Hertfordshire, England. The lamps are electrified but no longer in use; modern lights have been added along the underneath edges of the deck for night illumination. The ends of the bridge parapets continue as quarter-circle concrete bank-retaining walls, which on the road side project just above footpath level and carry cast-iron posts that formerly supported two horizontal tubular steel railings, now replaced with vertical steel railings.

The carriageway carries two lanes of one-way traffic with a footpath on each side. Traffic lights are positioned at both ends, and a 7.5-tonne weight limit sign is present at the north-west end. The bridge originally carried two-way traffic but became one-way (north-west to south-east) following the opening of Governor's Bridge, a short distance upstream, in the 1970s.

The bridge was originally intended to align on a skew with the river to match the roads on either side, but the Belfast Harbour Commissioners, who held jurisdiction over the tidal stretch of the Lagan, insisted it be set at right angles to reduce impedance to barge traffic travelling to and from the Lagan Navigation to Lisburn and Lough Neagh.

The Stranmillis and Annadale Embankments on the Antrim and Down sides respectively were constructed afterwards in the 1920s. The bridge is captioned as King's Bridge on the 1919/20 Ordnance Survey maps and subsequent editions.

This is a rare surviving reinforced-concrete bridge from the early 20th century. Few concrete bridges were built before the First World War, making King's Bridge historically significant from a civil engineering perspective. The only earlier concrete road bridge in Northern Ireland is a small single-span example of 1909 at Drumlone, near Lisnaskea, County Fermanagh, reinforced according to the Hennebique patented system. Elsewhere in Ireland, only two earlier concrete bridges exist—a footbridge at Mizen Head, County Cork (1909), and another at Cruit Island, County Donegal (1911)—neither employing the Kahn system. The fact that King's Bridge has survived in such good condition for over a century is remarkable given the experimental nature of this innovative design.