THE STRUCTURAL ASSESSMENT AND STRENGTHENING OF KALEMOUTH BRIDGE, SCOTLAND . DEVELOPMENTS IN STRUCTURAL ENGINEERING. PROCEEDINGS OF THE FORTH RAIL BRIDGE CENTENARY CONFERENCE, HERIOT-WATT UNIVERSITY, ENDINBURGH, SCOTLAND, AUGUST 21-23, 1990. VOLUMES 1 AND 2
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This paper describes the structural assessment and subsequent repair of the Kalemouth Suspension Bridge. The bridge spans approximately 57 m between suspension points, has a width between hangers of 4.6 m, and the suspension points are 4.9 m above road level. Each side of the bridge has a suspension chain consisting of pairs of links, connected together by three short coupling links and 2 nominally 54 mm diameter cross pins. The deck hangers are hung from each pinned connection and at the mid length of each bar link. The timber deck has an upward camber. Wooden handrails in the form 0.76 m high by 1.52 m diagonally braced panels provide stiffening trusses to both sides of the bridge. Examination indicated that the joints in the main suspension chains had corroded and that all the small links and pins should be replaced. A destressing rig was designed to support the load across each joint. The three small links and two pins were removed and replaced by new components, manufactured in speroidal graphite cast iron (nodular iron). The grade chosen for the replacement components has the same ultimate tensile strength similar to wrought iron but a slightly smaller elongation. All sets of three links and pins were proof loaded in the laboratory to check that their yield load was above 600 kN. The joints in the main chain where the chain passes over the supporting towers were strengthened rather than replaced, using stainless steel bars clamped to the ends of the adjacent long links and bearing on curved stainless steel plates at each side of the cast saddle. The old ground anchorages were made redundant by incorporating new reinforced concrete compression and tension piles connected to the joints near ground level. The whole of the deck and handrails were rebuilt. Canadian Douglas fir was used with galvanised mild steel fixings and below deck bracings. (TRRL)