| Because of the inadequacies and the local nature of the present techniques for structural integrity diagnosis, there is a growing need for developing new global techniques for monitoring the health of structures, like bridges, buildings, etc. The problem of structural integrity diagnosis can be divided into three sub-problems, namely, damage detection, damage location, and damage quantification. The emphasis of this work is on the last two sub-problems, i.e., developing global techniques to determine the location and amount of damage. The developed techniques should require measurement of only a few of the low frequency modes and should not require development of an analytical model of the structure being tested.; Based on estimation of the flexibility matrix of structures, two new integrity diagnosis methods are developed. The first method, called the flexibility difference method, is applicable only to beam type structures and can only determine the location of damage. The second method, called flexibility based method for integrity diagnosis, can determine both location and amount of damage and is applicable to both beam and truss type structures.; The two proposed methods are applied to several numerical examples ofbeams and trusses. Damage in these numerical examples is simulated as a reduction in stiffness of an entire element of the structure. Finite element analysis is performed to obtain natural frequencies and mode shapes of the structures. Results of the numerical examples demonstrate the effectiveness of the proposed integrity diagnosis methods.; In any experimental survey, measurements can only be taken at limited degrees of freedom. Two mode shape expansion techniques, namely, Dynamic Expansion Technique and System Equivalent Reduction and Expansion Process (SEREP), are studied to expand the mode shapes. These expansion techniques were successful in expanding mode shapes for only some of the damage locations.; Finally, experiments are performed on wide flanged beams to demonstrate the effectiveness of the flexibility difference method. Damage is simulated by cutting through the beam using a jig saw. Natural frequencies and mode shapes are obtained by performing vibration testing and modal analysis. Using only the lowest three modes, a saw cut 0.5 inch long in a 4 inch wide flange could be successfully located. |
