StatisticalPropertyofInternalCracksinConcrete

This paper presents a study on distributing feature of internal cracks, which is concerned about the statistical law of internal cracking. The fitness of Poisson distribution on the number of internal cracks and the fitness of log-normal distribution on the length of those cracks were discussed. Concrete specimens were observed for internal cracking by means of digital microscope after they were subjected to several types of cyclic loading. The agreement of shapes between expected distribution and observed histogram was verified. The expedience of applying probability distribution to the number as well as length of cracks was substanti- ated. This paper is limited to work on internal cracks observed on the surface cut perpendicular to the direc- tion of the compressive loading. I INTRODUCTION example, location or the exact size of internal cracks. The use of powerful microscopes has been In our study, the focus of interest is originally put on able to study the formation of internal cracks, and the field of damage assessment of concrete within some insight has been obtained on the change in sur- existing RC structures. This paper presents a study face feature of concrete. A direct observation conducted as a part of the series of investigation on method by means of microscope for studying micro- distributing feature of internal cracks. structure and crack growth within concrete was in- troduced by Hsu (I963) and Shah & Sanker (I987). I. I Relation between damages and internal cracks As demonstrated by them, a meso-level microscopic observation such as crack map could be useful tool Structures are subjected to a large number of loads for describing distributed internal cracking. applied during their design lives, and concrete is In addition, generally, for studying the internal known to deteriorate both in strength and in stiff- cracking properties of concrete, it is .required to get ness.