Research in New Zealand over the last two and a half decades has shown that elongation in plastic hinge regions can have a very significant effect on the seismic performance of reinforced concrete buildings. It was found that elongation arises due to (i) plastic strain in reinforcing bars caused by inelastic rotation, and (ii) unrecoverable tensile strains in compression reinforcement. A number of empirical formulas have been proposed to predict elongation. However, there are currently no analytical models that can accurately predict elongation in the plastic hinges. Consequently, the influence of elongation on the seismic performance of reinforced concrete structures cannot be predicted analytically. This paper describes a plastic hinge model for the computer analysis package, ‘RUAUMOKO’, which can predict both the flexural and elongation response of plastic hinges in reinforced concrete beams. Experimental and analytical results are compared in the study. With the completion of this newly formed element, seismic analyses may be made of structures containing potential plastic hinges to assess the significance of elongation on seismic performance.