Model updating for a thin steel sheet welded structure

Abstract

Modern large, complex engineering structures normally encompass a number of substructures which are assemble together by different types of joints. Although the highly sophisticated finite element method is used to predict dynamic behaviour of assembled complete structures, the predicted results of assembled structures are often considerably different from the experimental results. The inaccuracy of predicted results is believed to be largely due to the invalid assumptions about the initial finite element models and/or initial parameter values, particularly those about joints, boundary conditions and also loads. Therefore, model updating methods are usually used to improve the initial finite element models by using the measured results. This paper is concerned with the application of model updating methods to a welded structure that consists of several substructures made from thin steel sheets and are assembled together by a number of spot welds. A welded structure with a large surface is susceptible to initial curvature due to its low flexible stiffness or manufacturing or assembling errors, and to initial stress due to fabrication, assembly and welding process of substructures. Nevertheless, such initial stress is very difficult to estimate by theoretical analysis or to measure. This paper puts forward the idea of including initial curvature and/or initial stress (which may have a large effect on some natural frequencies) as an updating parameter for improving the performance of the finite element model of a structure made from thin steel sheets. In addition, this paper also discusses the effects of spring suspension towards the experimental modal results. The accuracy and efficiency of the ideas are discussed and then are validated with the experimental results.