Non Model Approach Based Damage Detection in RC Frame with Masonry Infill

The major portion of existing infrastructure worldwide continues to be at a potential risk of failure on account of aging, corrosion and overloading principally during earthquakes. Their prolonged use beyond design service life proliferate damage that manifests itself in the form of cracks. The conventional safety evaluation techniques such as visual inspection and non-destructive test (NDT) entail time and effort and require that the vicinity of damage is known at priori and the portion of structure being inspected is readily accessible. This calls for an urgent need to facilitate real time structural assessment for early detection and diagnosis of cracks. Structural Health Monitoring (SHM) identifies damage by virtue of changes in the overall vibration response of the buildings. The paper focuses on real-time damage detection based on vibration studies accomplished by Structural Health Monitoring team of Central Building Research Institute (CBRI). The experiment was performed on the 1:3 scaled model of 6-story RC frame with masonry infill in the Building dynamics laboratory of CBRI. The forward problem is attended by inducing step-by-step damage in infill to investigate the changes in dynamic response as a result of change in physical properties of the structure. Recorded time histories are processed for Frequency Response Spectra (FRS) with Fast Fourier Transform (FFT) and mode shapes are obtained. Changes in natural frequency and modal curvature for each of the five damage cases are analyzed for damage detection and location in the structure. An Algorithm for damage identification viz. Curvature Damage Factor (CDF) approach is presented.