e-mosty March 2019 Long Span and Multiple Span Bridges - Page 28

DECK SYSTEM Cross beam depths for the South Pylon are 4.5 and 5.0 meters, while cross beam depths for the North Pylon are 4.8 and 6.0 meters. The horizontal dimension between the column centerlines at the saddle elevations is 22.2 meters. Column wall thicknesses vary between 500 mm and 1200 mm over their height. The Central Pylon arrangement is far more complex when compared to the other two pylons. Twin, longitudinally inclined columns have a separation of 37.6 meters at the top of the pile cap and join at approximately 100 meters above the cap elevation. These lower inclined columns have dimensions of 6.1 x 7 meters. A delta frame consisting of the pile cap with two inclined pylon column legs resists longitudinal loads applied to the pylon. Single columns with longitudinal dimensions varying between 14.9 and 6.1 meters extend from the top of the delta frames to the top of the 158.9- meter tall Central Pylon columns. Three cross beams transversely connect the pylon columns: two cross beams below the deck and one cross beam near the pylon top. As with the other two pylons, the Central Pylon columns have a slight transverse inclination, the horizontal dimensions between the column centerlines at the saddle elevations is 22.2 meters, and the column wall thicknesses vary between 500 mm and 1400 mm over their height. Seismic reinforcement detailing is provided in potential plastic hinge regions of pylon columns and cross beams. Additional safety margin is provided in design of potential brittle failure modes including shear in pylon columns and cross beams. Reinforcing steel in the column legs is detailed to accommodate seismic design demands in the column to crossbeams joints and column to pile cap joints. Owner requirements include designing to the AASHTO Seismic Design Specification and detailing lower portions potential plastic hinge regions of pylon columns and cross beams consistent with the Japanese seismic detailing practices. Cross beams of the central pylon are transversely post- tensioned to resist demands in the column joints. The suspended bridge deck section has a total width of 23.8 meters consisting of an 18.8-meter wide, four-lane motorway with and shoulders and a total width of 23.8 meters. There are no sidewalks. Suspenders located 22.2 meters apart transversely and 20 meters longitudinally connect the suspended deck to the main cables. The suspended bridge deck section is a trapezoidal, orthotropic steel box girder with longitudinal stiffeners on the top and bottom plates and a maximum depth of 3.72 meters. The deck is longitudinally continuous for 2,494 meters between the expansion joints North Abutment and South Pylon. Typical girded segment lengths are 20 meters, with other segment lengths occur near support locations and midspan areas. Truss diaphragms are located at typical 4-meter intervals and at the suspenders. Plate diaphragms are located at the North Abutment and Pylons. As it is normal with this type of decks, the details have been designed to minimize the effects of fatigue on the steel. The interior of the deck will have a de-humidification system to eliminate the possibility of corrosion and extend its design life. It will also be provided with both internal and external inspection gantries as well as access points at regular intervals. SUPERSTRUCTURE ARTICULATION Articulation of the suspension bridge consists of transverse bearings for the bridge deck at the three pylons and the north abutment; vertical pendulum bearings, end stoppers and expansion joints at two ends of the deck at the south pylon and the north abutment; and longitudinal dampers connecting the north end of the deck with the north abutment. The transverse bearings transfer significant lateral wind or seismic reaction forces to the interfacing substructures and at the same time accommodate large longitudinal relative displacements of the deck. The vertical pendulum bearings handle the combination of large longitudinal displacements and potential uplift forces at the two ends of the deck. 1/2019