DEFECTIVE AREA RATIO CALCULATING DEVICE AND DEFECTIVE AREA RATIO CALCULATING METHOD FOR COMPOSITE STRUCTURE

PROBLEM TO BE SOLVED: To provide a defective area ratio calculating device and a defective area ratio calculating method for composite structures that can calculate with high accuracy, without relying on the worker's feel, the ratio of defective areas to the whole boundary surface between a bottom steel sheet and concrete of a composite floor slab in a composite floor slab checkup process.SOLUTION: After drawing a master curve MC of echo heights each corresponding to each of multiple simulated defects by transmitting and receiving a low-frequency ultrasonic wave to and from a simulated body on which the multiple simulated defects differing from one another in size are arranged and, at the same time, calculating a beam size B of the low-frequency ultrasonic wave from a point where the echo heights on the master curve MC becomes constant, the defect size at multiple measuring points are calculated by applying each of the echo heights obtained by sessions of transmission and reception of the low-frequency ultrasonic wave from the multiple measuring points on a composite floor slab W to the master curve MC, the ratio of the defect size at each measuring point to the beam size B of the low-frequency ultrasonic wave is taken as the defective area ratio at the measuring point, and the average of the defective area ratios of all the measuring points is taken as the defective area ratio of the whole measuring range.