Effective slab width in prestressed twin-girder composite decks

The paper shows the shear-lag effect in slabs of twin-girder steel-concrete composite decks due to the main prestressing techniques such as support settlements, bonded cables inside the concrete slab, and external slipping tendons. The analysis is performed by means of a beam model taking into account the loss of planarity for the slab cross section, the flexibility of the shear connection, and the time-dependent behavior of the concrete. A linear elastic behavior is considered for the steel beams and shear connection while viscoelastic behavior is assumed for the concrete slab. A parametrical analysis is carried out on realistic bridge decks for each kind of prestressing technique, by varying the span length and the girder spacing. The distribution of longitudinal normal stresses in the slab is shown for each prestressing technique and the effective slab widths are then evaluated and compared with those suggested by ENV 1994-2 for different span lengths and for different spacing of the beams.