The flexibility of welded joints is an important issue in design of car bodies. Two generic, 3-D, design-oriented models (simple and complex) are developed to represent the compliant behavior of multibranch flexible joints. The simple model consists of torsional springs restraining the relative rotation of the joint branches in the three planes, while all branches are assumed to be rigidly connected in translation. Coupling between motions in different planes is neglected. The complex model accounts for such coupling. A statistical system identification method is proposed for inferring the model parameters from the static response of the structure. The method is demonstrated by applying it to a simple cube frame structure and a car body. Finally, the two models are compared in terms of their ability to predict static response. / Ph. D.