The structural behaviour of prestressed concrete beams is considerably affected by different nonlinear phenomena occurring in the post-cracking and crushing regimes, such as snap- back or snap-through instabilities. Design procedures included in current technical Standards are not able to take…
The structural behaviour of prestressed concrete beams is considerably affected by different nonlinear phenomena occurring in the post-cracking and crushing regimes, such as snap- back or snap-through instabilities. Design procedures included in current technical Standards are not able to take into account the actual flexural crushing regime, since the adopted constitutive laws overlook the strain-softening and strain-localization behaviour of the concrete matrix. Moreover, design provisions are usually based on Plasticity Theory, leading to completely disregard size-scale effects and ductile-to-brittle transitions as functions of the beam depth. The present work intends to outline a comprehensive theoretical framework for prestressed concrete structural behavior by means of a Fracture Mechanics approach. The Cohesive/Overlapping Crack Model (COCM) is able to simulate the strain-softening and strain-loaclization behaviour of concrete both in tension and compression, predicting the nonlinear crushing behaviour of prestressed concrete beams. As a matter of fact, the correct estimation of scale effects on maximum reinforcement percentage requires a thorough knowledge of the complex phenomena characterizing the compression crushing failure, leading to define the field in which prestressed concrete structures can develop a safe ductile behaviour. New standard requirements for an effective structural design are formulated.