CONCRETE LIBRARY OF JSCE NO. 11. JUNE 1988 EVALUATION OF THERMAL CRACK OCCURRENCE IN MASSIVE CONCRETE STRUCTURES (Reprint from Transaction of JSCE, Katsuhiko KIMURA Vol.6, No.378, 1987) Sadamu ONO SYNOPSIS Authors propose a probabilistic approach for the evaluation of thermal crack occurrences, which introduces thermal crack index, random variable defined in terms of the ratio of the concrete tensile strength to the thermally induced tensile stresses due to external restraints. Furthermore, this report discusses some factors affecting the thermal crack occurrence probability. It becomes clean that the degree of external restraint, tensile strength and calculation methods of thermal crack index are the most contributing factors. Keywords: mass concrete, thermal crack, external restraint, thermal crack index. K. Kimura is a chief engineer at Civil Engineering Division of Shimizu Corporation, Tokyo Japan. He received his Master of Engineering Degree from Nagoya Institute of Technology in 1975. He is a member of JSCE and JCI. S. Ono is a chief engineer at Civil Engineering Division of Shimizu Corporation, Tokyo Japan. He received his Doctor of Engineering Degree from Hokkaido University in 1985. He is a member of JSCE and JCI.