Gateway Bridge
The bridge carries two independent carriageways, each with four lanes 3.65 meters width, two shoulders of 3.0 meters width and a 1.5 meter wide sidewalk for emergency use adjacent to the outer shoulder. The bridge comprises pairs of steel box girder arch ribs supporting twin decks, each carrying one carriageway. Support to the deck is provided by conventional reinforced concrete piers, inclined prestressed concrete arms, and steel hangers attached to the arch ribs. The decks are connected transversely at selected locations by full depth crossbeams. Each deck comprises a constant depth, post-tensioned in-situ concrete multi-cell box girder with transverse cantilever frames. The box girder decks are required to resist torsional forces induced by the eccentric hanger positions and their own self-weight. Transversely there are crossbeams and diaphragms arranged to suit the requirements within each section of the bridge. At the outer edges, there are cantilever ribs, at centres varying from 10 to 20m, which support the outer lane, vehicle parapets, an emergency footway and an architectural outer parapet, and lighting columns. The overall length of the bridge is 912 metres between abutments and the width between parapets is 23.6 metres for each deck. The concrete substructure and steel arches form in profile a continuous flowing line, the steel arch components of which comprise the Marina arch of about 50m span, Main Channel Arch of about 144m span and the Secondary Channel Arch of about 74m span. The steel arch ribs have a fully encastre connection to the supporting concrete piers. Temperature movements in the arches are therefore restrained.