Crack Detection in a Simply Supported Rc Beam Using Simplified Laplacian

This paper describes the detection and identification of cracking severity in a reinforced concrete beam using modal data. Experimental modal test was performed on the beam before and after application of load of increasing intensity to induce a single crack at a fixed location. Modal parameters extracted were categorised into hvo groups, namely local response parameter (mode shape data) and global response parameters. Local&d changes such as cracking reduce the stiffness of the structnre, and therefore caused a localised change in the discrete function of the mode shape. From a previous research [‘I, Laplacian Operator was initially proposed. However, when applied to a non-homogenous and composite material such as reinforced concrete, the operator was too sensitive and did not yield meaninghI results. Hence, a simplified Laplacian operator was suggested. In this investigation, it was found that global response such as natural frequency is a good indicator to detect the occurrence of the deterioration in the strwtnre. However, the local response data such as mode shape was required to detect the defect location accurately and a simplified Laplacian operator worked quite successfnlly. Furthermore, it was observed that the higher frequency modes tend to detect the occurrence of cracking in the earlier stages.