Date of Award

Spring 1986

Document Type

Thesis

Degree Name

Master of Science in Civil Engineering - (M.S.)

Department

Civil and Environmental Engineering

First Advisor

Methi Wecharatana

Second Advisor

Dorairaja Raghu

Third Advisor

Paul C. Chan

Abstract

Fracture behavior of concrete has been a subject of investigation for the past two decades. The need of understanding the complete tensile response of concrete is absolutely essential for theoretical modelling as well as design application of plain concrete structures.

In this study, attempts were made to investigate the validity of two important fracture parameters, namely, the fracture energy and the critical crack tip opening displacement. Three types of test specimen, dog- bone shaped tension specimen, notched beam and compact tension specimen, were investigated. These tests were conducted using the closed-loop MTS 810 strain-controlled testing system. For the uniaxial tension specimen (dog- bone), monotonic and cyclic loadings were employed to observe the complete post-peak response of concrete. Inaddition, fracture energy, critical crack opening displacement and the variation of post-peak elastic Young's Modulus, were studied. Four different mix-proportions of mortar and one mix of concrete were used to study the effect of matrix composition on the uniaxial tensile response of concrete. Three controlled grain sizes of sand were used to study the effects on maximum post-peak displacement, i.e., the critical crack opening displacement.

In addition to the direct tension test, the ASTM standard fracture specimens were also investigated. To study the size effect on fracture energy, three different sizes of compact tension specimen and one notched beam were used. Test results from the ASTM standard specimens were compared with those observed from the direct tension test.

The results of the above investigation reveal that fracture energy is a specimen size-dependent fracture parameter. It can be inferred from these results that the critical crack opening displacement is a material property influencing the fracture characteristics. From this study, a unique normalized post-peak stress-displacement relationship was found to exist. Such relationship is essential to most proposed theoretical models.

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