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
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Weak Tensile Strength

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Many, almost all of us would have come across the statement " Concrete is weak in Tension",
why is it so.........

Concrete is not a homogeneous material like steel which is strong in both tension as well as compression. It is a composite material and is obtained by mixing cementing materials, water and aggregate (and sometimes admixtures).

Interfacial Transition zone (ITZ) in  concrete

The "interface zone" is the weakest link in the structure. When compressing, that interface only serves to transfer compressive stresses from one aggregate to the next. That does not require exceptional strength.
Under tension, the aggregates are trying to pull away from each other so this interfacial transition zone has to bear tensile stresses to holds the whole system together.  Since its strength significantly weaker than the aggregates, so the failure starts at much lower stresses.


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