AUGUST 12, 2014 – 10:10-10:50 HALL 1
Izmit Bay Suspension Bridge – Design and Construction
The Izmit Bay Suspension Bridge is located 60km south-east of downtown Istanbul and will carry the new Gebze-Orhangazi-Bursa-Izmir motorway across the Sea of Marmara at the Bay of Izmit. With a 1550m main span the suspension bridge will be the fourth longest bridge span in the world and the longest bridge span constructed worldwide in more than 10 years. The bridge is sited in one of the world’s most seismically active regions.
The tower foundation is designed as a caisson placed at a water depth of 40 m and the soil below the caissons is improved by a grid of 2 m diameter steel pile inclusions. A 3 m thick gravel bed separates the improved soil and the concrete caisson to provide a controlled sliding surface during seismic events. The purpose of the gravel layer is to act as a fuse under seismic loading by limiting the maximum interface shear friction and thereby reducing the seismic loads on the structure for high amplitude earthquakes. The North anchorage is located on land and the South anchorage on reclaimed land.
The deck is 30.1m wide, shaped as a closed steel box girder having a depth of 4.75m and carrying three lanes of highway traffic in each direction plus hard shoulders and cantilevering walkways for operational and maintenance use. Truss diaphragms at 5 m centers are used for minimum weight.
The main cables consist of 110-112 prefabricated parallel wire strands each having 127 galvanized wires with a nominal diameter of 5.91mm. The main cables are protected by S-formed wrapping wire, paint and a state-of-the-art dehumidification system.
The 236m tall H-shaped towers are fabricated in steel due to demands for high seismic loads and short construction time. Closed box sections are used for legs and cross beams.
A general description of the bridge design and construction works will be presented.