Rio-Niteroi Bridge

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Rio-Niterói Bridge,the sixth longest  bridge in the world and the longest prestressed concrete bridge in the southern hemisphere also known as President Costa e Silva Bridge. It runs 13.290 kilometres (8.258 mi) long – 8.836 kilometres (5.490 mi) over water and the bridge's 300-metre (980 ft) central span is 72 metres (236 ft) high in order to allow the passage of hundreds of ships entering and leaving the bay every month.
OVER-WATER APPROACHES

The over-water approach spans consist of twin precast post tensioned concrete box girders constant span length of 80 m is used for the continuous spans. Expansion joints are provided 20 m from the piers in every fifth or sixth span. The structure depth is 4.7 m. The piers for the approach structure are of cellular reinforced concrete and rest on footing blocks near the water surface and on 2-m-diameter reinforced concrete piles reaching to competent founding strata below water. Precast concrete segments were cast in a yard, barged to the site, and lifted to the final position. Three basic types of precast elements were used: support sections over the piers, normal sections, and hinge sections at the expansion joints. Segments were erected in pairs by traveling gantries and post tensioned in place; the sequence was repeated until the span projected 40 m on each side of a pier axis.



The gantries then moved to the next span and the process was repeated. Concrete was added at the midspan joints; positive moment tendons were inserted, stressed, and grouted; and the span was made continuous. Four traveling gantries were used in the erection of the approach spans.


MAIN NAVIGATION SPANS
Site Constraints Sited in 22 m of water, the main spans were required to provide 60 m of vertical clearance for navigation without encroaching into the aviation space for aircraft approaching the international and domestic airports at Galleao and Santos Dumont. Because of the 72.4-m maximum height of the fixed structure above sea level and the necessary vertical clearance, only a girder type of bridge was considered. 
The selected structure is a three-span continuous steel box girder with spans of 200, 300, and 200 m. The 300-m main span is the longest unstayed girder span in the world surpassing the length of its nearest rival by 39 m. The 30-m end cantilevers and 44-m suspended spans complete the 848-m-long steel structure, which makes a smooth transition to the concrete approach spans. The depth of the structure varies from 4. 75 m at the juncture with the concrete structure to 13 m at the main piers to 7. 5 m over the navigation channel. For erection, the superstructure was divided into pieces of 44, 292, 176, 292, and 44 m.

Main Piers The main channel piers (Figure 7) are supported on forty 1.8-m-diameter reinforced concrete piles that are drilled into bedrock 50 to 60 m below sea level. Under each end pier, 32 piles are used. Design loads for the piles were 650 Mg per pile for dead plus live load and dead load plus 118 Mg of horizontal load at ultimate (4700 Mg per main pier for ship impact). Massive reinforced concrete footing blocks, extending from 2.5 m below to 2.5 m above sea level, rest on the large piles and support twin tapered hollow box pier shafts. The top of the end pier shafts is 59.96 m above sea level while the top of the main channel piers is at an elevation of 56.44 m.
MAIN SUPERSTRUCTURE
The two 12.2-m-wide roadways  support ed on a pair of steel boxes centered 13 .2 m apart. A central barrier, curbs, railings, and an epoxy asphalt wearing surface complete the traffic roadways.
The 44-m spans were assembled on a slipway, fitted with end bulkheads, and launched into the water as pontoons. Temporary jacking columns were erected alongside the pier shafts, and large temporary ring girders were assembled on top of the pier footings.The 44-m end spans weighing 225 Mg/box were floated to the site and lifted one box at a time by using jacking frames and wire rope tackle.
DESIGN METHODS
CONCRETE ELEMENTS
Ultimate design methods were used in the design of the reinforced and pre stressed concrete elements of the bridge.

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