ABSTRACT

Modal strain energy based methods for damage detection have been received much attention in recent years. The purpose of this paper is to investigate and compare the effectiveness of a traditional modal strain energy method (Stubbs index) and a recently developed modal strain energy decomposition (MSED) method for damage detection for a three-dimensional frame structure. Damage localization for diagonal braces, horizontal beams under partial degree of freedoms (DoFs) is considered. Several damage scenarios including single damage and multiple damages are simulated. The two damage detection methods are applied to detect the damage(s) for each damage case. Useful results are obtained for both single damage scenarios and multiple damage scenarios, which can be used as a guide for damage detection.

INTRODUCTION

Offshore platforms, which work in hostile environment, are continuously exposed to wave loads and may result in critical damage from fatigue or ship collision. Clearly the development of robust techniques for early damage detection and localization is crucial to avoiding the possible occurrence of a catastrophic structural failure. Structural damage detection based on vibration measurements holds promise for the global nondestructive damage detection of structures. The essential idea behind this type of methods is that damage would alter the stiffness, damping or mass of the structure, and so as to change the modal parameters such as modal frequencies and mode shapes. That is to say, changes of modal parameters can be used as a damage indicator. Doebling et al. (1998) present a thorough review of the vibration-based damage identification methods. But most of them have some limitations in practice. For example, some methods need mass normalized mode shapes; some methods need complete mode parameters (including structural rotational degree of freedoms, high modal parameters), or some methods need the input force to have been measured.

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