A Finite Element based numerical model for a vibration based damage identification method for a 2.5D composite structure is discussed in this chapter. The linear dynamic response of an intact and a locally delaminated 16-layer unidirectional carbon fibre PEKK reinforced T-beam is analysed. A commercially available Finite Element package is employed for the numerical model. The aim of the model is to perform parametric studies. This virtual modelling replaces extensive experimental testing. The parametric study is preceded by an experimental verification of the numerical model. Subsequently, the capabilities of detection and localization of a delamination is analysed by varying the size and location of delamination, as well as the number of data points employed. The Modal Strain Energy Damage Index Algorithm is applied using the bending and torsion modes.