Initial crack detection in concrete plate and shell structures using concept of earthquake ground motions

Abstract

Many methods and sensors have been developed for crack detection in concrete structures and for earthquake ground motion detection, respectively. In a previous study, a seismo-accelerometer based on spring-mass strong motion seismo-accelerograph has been developed for the purpose of detecting earthquake waves travelling through the earth crust from the epicenter at faultline. This study aims to apply the method developed in previous study to detect wave from crack initiation point on the surface of plate and shell concrete as a new alternative for initial crack detection method. This study focused on the development of a downscaled seismo-accelerometer of previous study for better ease of use. Concrete plate and shell specimens were selected in this study as the travel of wave from crack initiation point in the specimen mimic to that of earthquake waves travelling through the earth crust from the epicenter at the faultline. Magnetometer technology and spring-mass system formed the fundamental design aspect of the seismo-accelerometer. In Objective 1, the seismo-accelerometer was designed using Finite Element Modelling to attain natural period of 1 second, required for spring-mass based strong motion accelerograph. The modelling yield natural period of 0.99475 second and verified experimentally with Harmonic Shake Table test yielding 1.2 seconds, which is in the acceptable range. Ground motion test was carried out at Ranau Meteorological Station and the results were compared with international earthquake database. Earthquakes detected are in Sabah and nearby regions. Crack induction tests on factory-ready concrete plate and shell specimens were carried out in Objective 2, where the results shown that the concept of ground motion detection can be used for crack detection purposes. The crack detection equations for factory-ready concrete plate and shell are Mcrack,plate = log10A + 0.6919 and Mcrack,shell = log10A + 0.7115, respectively. Objective 3 provides the proof that the ground motion detection can be applied for crack detection based on crack wave attenuation on structures such as concrete plate and shell which have the same configuration as earth crust, where the earthquakes occur. Thus, the seismo-accelerometer developed in the study can be used for earthquake ground motion detection if placed on the bedrock or ground, and can be used for crack detection if placed on structures with similar configuration to earth crust such as concrete plate and shell structures. This contributes towards both Structural Health Monitoring and Seismic Monitoring apart from providing an alternative method to existing methods in both fields.