Strut and tie models for analysis-design of external beam-column joints

Strut and tie models have been developed for external beam–column joints with and without joint stirrups. The modelling is fraught with difficulties that include determining forces at joint boundaries and strut dimensions. In view of these difficulties, it was found necessary to define strut widths empirically. Test data were used to show that stirrups can increase joint shear strength by less than their yield capacity. The model accounts for this by using a stiffness analysis to determine the proportion of joint shear force resisted by the stirrups at failure. The resulting model predicts joint shear strength more realistically than existing non–finite–element methods and some finite–element techniques. It is necessarily complex but capable of incorporation in spreadsheet–based design techniques. The authors believe that the behaviour of beam—column joints is too complex to be modelled realistically with simple strut and tie models. If a simple design method is required, the authors recommend their simplified empirical method.