Failure and post-failure aspects of mechanical response of concrete structures to compression and tension

The mechanical response of concrete to tension and compression including pre- and post-peak portions are examined in this thesis. Pre-peak normally consists of three parts; plastic, elastic, and brittle that can be obtained by any load-control testing machine. Failure is occurred when a network of major cracks is formed at peak stress while failure criterion describes failure behaviour of concrete under triaxial loading. Post-peak is a mixture of material and structural responses of concrete after failure and unlike the pre-peak is significantly influenced by geometry of specimen and stiffness of loading frame. Stress–deformation curve is used in displacement-control mode. Strain softening is a post-peak highly localized phenomenon caused by coalescence of micro-cracks that forms a damage zone after peak stress while load-carrying capacity is diminished.
In total 102 uniaxial/triaxial compression/tension tests are conducted on 102 concrete cylindrical 150 × 300 mm specimens in accord with ASTM standards. Major fracture pattern of cone/shear and cone for concrete specimens under uniaxial and triaxial compression tests are recognized respectively. An empirical classification; Concrete Quality Designation (CQD), is introduced in this research that classifies concrete to six classes, based on the UCS. It can be applicable in practical purposes.
A new strength criterion is developed for concrete based on the mathematical function of Bineshian criterion (2000) having three parameters; however, new constant values are determined for different CQDs. It can provide linear and nonlinear envelopes capable of describing triaxial actual data for both compressive and tensile quadrants and provides credible estimations of these values similar to those determined in laboratory with correlation and accordance coefficients adjacent to 1 and 0 respectively.
Concrete Damage Plasticity (CDP) constitutive model is used for a CQD-G class plain concrete in Abaqus. Suitable constitutive parameters for the behavioural model are determined using experimental data, analytical methods, and other sources while proper results obtained from numerical simulations using FEA. Findings in this sector of the research are applicable in numerical modelling and simulations of failure and post-failure responses of concrete and especially in design of high strength concrete (CQD-G class) structures and concrete-like brittle materials like rocks.