Identification of Cracks in Box-Section Beams with a Cracked-Beam Element Model

Box-section steel members are widely used in different types of engineering structures. Identification of cracks in box-section members poses a particular challenge because of the section geometry. This paper presents a crack identification approach for box-section beam-column members based on a cracked-beam element model and using a finite-element (FE) model updating procedure. The cracked-beam element model is established by involving an additional local flexibility due to the crack, which is formulated using the fracture mechanics principles. To calculate the additional local flexibility, the stress intensity factors for cracks in box sections need to be established and this is achieved using an empirical approach combining FE simulation, parametric analysis, and regression. The cracked-beam element model is verified in terms of its predictions of the dynamic properties of cracked box-section beams against both FE simulated and experimentally measured modal data. Both thick-walled and thin-walled box-section beams have been considered in the FE simulated examples, while several box-section beams with different numbers of cracks have been tested in the experiment. Subsequently, the model is incorporated in the crack damage identification procedure. Results indicate that cracks can be identified correctly for beams with both single crack and multiple cracks and the identified crack parameters are of good accuracy.