SCI precast prestressed I-Girders are frequently used in medium to long-span precast bridges from 13 to 30m span. The sections have been well accepted by designers primarily because of the very economical designs achievable.
They are used in conjunction with a deck slab which works compositely with the girders. Intermediate and end diaphragms are generally used to optimise lateral load transfer among the girders forming the deck.
Because they are not as aesthetically pleasing as box sections like the Super-T, I-Girder bridge decks are more frequently used in bridges with lower visibility.
Three girder depths are readily available and are designated Types 2, 3 & 4. These sections are designed generally as fully prestressed using a mix of straight and deflected strands. Approximately 30% of the strands are deflected at about 1.5 to 2mm each side of girder centreline. Alternatively straight strands only with suitable debonding is an available design approach. Strands are placed on a 50mm x 50mm grid, 25mm each side of girder centreline at each end and bundled at maximum eccentricity at mid-span between the deflecting locations. Concrete of grade S50 at 28 days and strength at transfer of prestress of 35 Mpa is commonly specified.
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