Keywords: computer modeling, non-linear analysis, high strength concrete beams, plastic rotation, moment redistribution, reinforced concrete.

The reinforced concrete beams follow a non linear behaviour for high levels of loading and continuous beams may differ from the elastic distribution of bending moments. A redistribution of the moments obtained from the linear elastic theory is the easiest and the least accurate procedure to predict the non linear behaviour. This non linearity is due, firstly, to the cracking of concrete and, later, for higher loads, to the yielding of steel. At the sections where the yielding of steel takes place, the stiffness is so lowered that a plastic hinge can be assumed to have taken place.

When a plastic analysis, a non linear analysis or a linear analysis followed by redistribution of bending moments is used to predict the structural behaviour of the beams, the critical sections should have the necessary plastic rotation capacity to allow the predicted behaviour at failure. When some doubts may arise, then an explicit calculation of this capacity must be carried out. Two different procedures might be followed to evaluate the rotation capacity: either to plot the relationship for the critical section, or to use the graphs proposed by codes of practice (for instance, Eurocode 2). As far as calculation complexity and exactness are concerned, these two procedures are very different. In order to achieve a compromise between the amount of calculation work and the exactness of the results, the authors have developed a new computational procedure that model the behaviour of the critical sections. This new procedure takes into account the influence of the main factors on the relationship.

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