Cracking and crushing in reinforced and prestressed concrete T-beams: An application of the Cohesive/Overlapping Crack Model

Recent studies suggested that classic models based on stress-strain constitutive laws are not able to thoroughly predict the behaviour of reinforced concrete (RC) and prestressed concrete (PC) structures and the ductile-to-brittle transitions that might arise for large size-scale beams as well as high-performance concrete matrices. On the other hand, Fracture Mechanics has been demonstrated to be capable of describing in a unified approach the mechanical instability phenomena occurring for RC beams in bending, such as concrete cracking in tension, steel slippage and/or yielding as well as concrete crushing in compression. In this framework, numerical analyses recently carried out by means of the Cohesive/Overlapping Crack Model (COCM) have defined scale-dependent upper and lower reinforcement limits, in which RC and PC beams exhibit a stable and ductile behaviour. In the present Thesis, the Cohesive/Overlapping Crack Model is extended to RC and PC beams having a T-shaped cross-section. In the first chapter, current design procedures as well as some important results obtained by means of Fracture Mechanics are addressed. In the second part, strain-localization phenomena in tension as well as in compression are introduced together with two Nonlinear Fracture Mechanics Models: COCM and Bridged Crack Model. In the third part, several numerical vs. experimental comparisons for RC T-beams are provided and some numerical investigations are carried out in order to highlight the effects of beam depth, steel yield strength, and concrete grade on the beam rotation capacity. Finally, in the fourth part, PC T-shaped beams are analysed and, analogously to the previous chapter, numerical vs. experimental investigations are presented.