DEVELOPMENT OF CDF, CFM AND CFCM METHODS FOR DAMAGE DETECTION IN THE MIDDLE OF BRIDGE DECKS

Structural damage detection has gained increased attention from the scientic community since unpredicted major hazards, most with human losses, have been reported. Aircraft crashes and catastrophic bridge failure are some examples. Security and economic aspects are important motivations for increasing research into structural health monitoring. Since damage alters the dynamic characteristics of a structure, namely, its Eigen properties (natural frequencies and modes of vibration), several techniques based on experimental modal analysis have been developed in recent years. In this article, a new method, based on developing the curvature damage factor method (CDF), change in exibility method (CFM) and change in exibility curvature method (CFCM) is presented. For this purpose, the three span Bozorgmehr Bridge, located in Esfahan, Iran, and a ve-span bridge previously designed by an expert are used. The numerical model of the Bozorgmehr Bridge is veried by comparing the ve primary natural frequencies with those obtained from experimental testing. In applying these methods, the mode shapes and natural frequencies of the damaged and undamaged bridges, are used. Damage is created on an element located in the middle of the deck. The four levels of damage considered are 15%, 30%, 70% and 90% reduction in the module of elasticity. It is shown that if mode shapes, as previously are simply extracted from one longitudinal section, the methods cannot always detect the damaged cross sections or the damaged longitudinal sections. But, if as shown in this article, the mode shapes are obtained from several longitudinal sections, these methods will be able to assess the damaged cross sections as well as the damaged longitudinal sections. It is also concluded that, when using the CDF method, the maximum content of CDF calculated for cross sections on itself cannot always show the damage locations. and it is necessary to consider the changes in value of CDF for several longitudinal sections too and, then, decide about damage locations.