SMEARED CRACK.. APPROACHES IN NUMERICAL SIMULATION OF FRACTURE

Abstract

In recent years, post-cracking modelling of concrete in Finite Element Analysis has been a subject of great interest amongst scholars. Despite a large number of efforts, the number of constitutive models that have been implemented successfully for simulating cracking in finite element analysis Is very small and that too for specific problems. It Is well understood from the past studies by various scholars that concrete and similar materials are capable of transferring shear forces across the rough concrete surfaces even after cracking starts due to interlocking. Moreover, the phenomena of tensile fracture of concrete is not sudden but is due to progressive microcracking and tortuous debonding which in turn means that the load displacement characteristics of a representative material volume shall exhibit a descending branch after peak load. Two methodologies have emerged to simulate cracking In finite element analysis•- the Smeared Crack Approach and the Discrete Crack Approach. In this thesis attention Is confined to the Smeared Crack Approach which in turn has been dealt using the elasticity based fixed as well as the rotating crack formats. Taking into consideration these concepts, two sets of subroutines, one for the fixed crack format and the other for the rotating crack format have been developed and included in a finite element program. Attention is focussed on the failure of material due to tension and tension-shear conditions without significant lateral compression. In these type of cases failure mode exhibits cracks in the form of separation. bands rather than friction along shear bands which Is due to cohesive properties dominating over the frictional properties. Although in this thesis, the material under consideration has been refered as 'concrete', the results obtained are valid for other brittle materials like rock and other civil engineering materials. It is concluded that finite element analysis using the smeared crack approach is capable of simulating cracking. The fixed crack format using this approach has a tendency of overestimating peak strength as compared to the rotating crack format.