FLEXURAL DEFORMABILITY OF REINFORCED-CONCRETE BEAMS

In reinforced concrete beams, the sectional definition of the moment-c urvature relationship is not straightforward owing to the presence of cracks. In general, this problem has been solved by considering a repr esentative portion of the beam and by defining the curvature 1/r as th e ratio between the rotation of the portion considered and its length. Large portions of the beam with many cracks lead to ''average'' momen t-curvature relationship, while small portions delimited by two consec utive flexural cracks lead to ''local'' moment-curvature relationship. The difference between these two definitions is studied in this paper introducing a ''general model.'' With this model the entire beam is m odeled through a succession of blocks divided by flexural cracks takin g into account the bond between steel and concrete. Due to the practic al impossibility of univocal definition of the crack pattern evolution , it is proposed to use a ''range model.'' This ''range,'' delimited b y the curves of maximum and minimum deformability, includes the moment -curvature relationship (locals and average) obtained from all possibl e crack patterns.