Date of Award

2013

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Civil and Environmental Engineering

First Advisor

Ghrib, Faouzi,

Second Advisor

Cheng, Shaohong

Keywords

Applied sciences, Concrete fracture parameters, Digital image correlation, Fracture processzone, Inverse analysis, Strain softening, Wedge splitting test

Rights

CC BY-NC-ND 4.0

Abstract

Concrete is one of the oldest materials used for construction, yet it still poses fundamental problems for engineers and researchers. The most critical problem is the propagation of cracks in concrete structures, but the mere presence of cracks does not necessarily mean that the concrete structure has reached the limit of its service life; however, instability caused by the propagation of these defects could result in the failure of a concrete structure. Thus, the focus of fracture mechanics is on assessing the stability of a structure, rather than detecting the presence of cracks. An accurate analysis of the progress of a fracture is required for assessing the integrity of a concrete structure and to predict its future performance. Accordingly, finite element analysis was used to model the performance of cracked concrete structures using available damage models, which require accurate evaluation of the mechanical and fracture properties. While concrete's mechanical properties are well known, the identification of concrete's fracture parameters poses an ongoing challenge. Concrete is a heterogeneous material with complicated fracture patterns. Therefore, sensors attached directly to the specimen to measure the crack opening do not provide accurate measures. The objective of this research is to develop a new methodology to study a cracked concrete structure's performance using a non-contact technique to monitor the development of the fracture process zone without causing interference during fracture. Consequently, Digital Image Correlation was chosen and applied successfully to the Wedge Splitting Test to study a cracked structure's response, represented by the mean of the load-crack tip opening displacement. Since the WST is an indirect fracture test, the experimental data was used to identify concrete fracture parameters by means of inverse analysis based on the cohesive crack model. The associated forward problem is based on the cracked hinge model, which is capable of accounting for the softening phenomenon. The use of Digital Image Correlation made it possible to study the dynamics of crack propagation. Experimental observations are thoroughly discussed, with special attention being placed on the monitoring of the crack's evolution, and the variation of dissipated energy and tensile damage along the crack path.

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