e-mosty March 2019 Long Span and Multiple Span Bridges - Page 29

CABLE ANCHORAGES Subterranean gravity type anchorages are located adjacent to both bridge abutments. For a long span bridge, limiting the accumulated travels at the superstructure/substructure interfaces is essential in maintaining acceptable service life of all the mechanical units. The massive reinforced concrete structures have lengths of 48 meters and heights of approximately 38 meters. The longitudinal dampers are velocity dependent devices effectively restraining deck movements caused by transient load conditions while allowing slow thermal movements. Connections of the main cables to each of the 18- meter long x 10-meter wide anchorage blocks utilizes grouted post-tensioning tendons anchored in the bottom of the blocks. The dampers have a fuse or load limiter protecting the interfacing structures against overloading from rare events such as exceptionally high turbulent wind conditions or major seismic events. The anchorages bear directly on the underlying soil and do not require pile foundations. Bottom elevations of the anchorages are +14.1 for the North Anchorage and +2.3 for the South Abutment. The end stoppers limit the maximum longitudinal travels of the bridge deck, thus reducing the displacement capacity requirements for all the mechanical units. Large swivel modular expansion joints are specified to accommodate significant movements (up to ±1.3 m longitudinal relative displacements) and meet the seismic performance requirements. CONCLUSION In summary, the design of this unique structure has overcome the difficult local conditions and tight technical requirements to produce a state-of- the-art structure which, once constructed, will hugely improve the communications between the Isla Grande de Chiloe and the continent. CABLES AND SUSPENSION SYSTEM The main cables consist of 60 prefabricated strands each, with 127 wires per strand. 5.4 mm galvanized strand with a breaking strength of 1860 MPa is specified. Each of the two cables has a total steel area of approximately 0.17 square meters. Wrapped cable diameters are approximately 0.52 meters. Each cable is supported by saddles at the top of the three pylons and two saddles within the anchorage splay chambers. Suspenders connect to the main cable with bolted cable clamps at a typical longitudinal spacing of 20 meters. Zinc coated wire rope suspenders with a tensile strength of 1610 MPa are specified. As it is the case with the deck, the cable will be provided with a state-of-the-art de-humidification system to prevent corrosion of the wires and extend its design life. The system will inject dry air at regular intervals into the cable. A neoprene cover along its length will minimize air loss. 1/2019