DAMAGE DETECTION IN BUILDING USING MODE SHAPE SLOPE AND CURVATURE

Abstract

Structural Health Monitoring is a field focusing to enhance structural serviceability by periodic safety evaluation of the structural strength and stability. If the damages in the structure can be detected early, the structure can be saved from collapsing by using the proper retrofitting techniques. In this thesis, mode shape slope and curvature method has been used to detect damage and understand which mode’s derivative are capable of detect damage in the building at different story. Three different height of building has been considered to understand the efficiency of the damage detection technique for the first five mode shape derivative of the building. First, damage is introduced in the building by reducing the stiffness of that story where damage is need to be detect by using the mode shape slope and curvature method. Modal analysis is done, to obtain the natural frequency and mode shape of the undamaged and damaged building. With the help of the central difference method, the derivatives of the mode shape have been calculated for the both buildings. Forward difference method is used at the fixed end of the building while backward difference method is used at the free end of the building. After obtaining the derivatives (i.e. 1st derivative and 2nd derivative), difference between undamaged and damaged mode shape slope/curvature is calculated and then normalized them to unity. Normalized mode shape slope and curvature is plotted to detect the damaged location in the building, A MATLAB programme has been written for the analysis of the undamaged and damaged building. It has been observed from the result show mode shape based methods are capable of detecting the damages. The difference between undamaged and damaged mode shape slope shows a higher value between damaged story and story before it. A sudden rise in function values such function known as Dirac-delta function in mathematical terms. The difference between iv undamaged and damaged mode shape curvature changes it sign at the damaged location and reaches very large positive value at damaged location. Results shows mode shape curvature is capable of detect damage easily as compared to mode shape slop. It has been observed from the results that few higher mode of the building start contributing in damage detection as the height of the building increases. Low level damage can be also detected from the mode shape slope and curvature method.