SIZE EFFECT ON DIAGONAL SHEAR FAILURE OF BEAMS WITHOUT STIRRUPS

Presents the results of recent tests on diagonal shear failure of reinforced concrete beams without stirrups. The beams are geometrically similar, and the size range is 1:16. The test results indicate a significant size effect and show a good agreement with Bazant's law for size effect. Scatter of the test results is much lower than that previously found by studying extensive test data from the literature, which have not been obtained on geometrically similar beams. The tests also show that preventing bond slip of the longitudinal bars (by providing end anchorage with hooks) causes an increase of the brittleness number of the beam. It is concluded that the current design approach, which is intended to provide safety against the diagonal crack initiation load, should be replaced or supplemented by a design approach based on the ultimate load, in which a size effect of the fracture mechanics type, due to release of stored energy, must be taken into account. A relatively simple adjustment of the existing formula might be sufficient for design, although determination of the brittleness number of the beam deserves more study.