Most of the existing models on lateral-axial strain proposed for confined concrete are without the consideration of the onset of splitting cracks and did not separate the elastic and inelastic development of lateral strain (Marques et al. 2004, Mirmiran & Shahawy 1997, Teng 2007, Xiao 2010, Xiao 2000). Hence there are differences between the predicted and measured lateral strains, particularly when splitting cracks have formed. Since the confining stress provided by the confinement depends on the lateral strain developed and is normally after the splitting cracks have occurred, the neglect of the splitting crack formation can lead to significant errors in the predicted confining stress.