Composite steel-concrete beams are used widely in bridge and building construction as the main structural elements in flexure. Bridges have a design life and this may be reduced if traffic flows are increased or environmental degradation occurs. Similarly, building beams may become compromised for serviceability or strength when loads on floor systems are increased. These changes may reduce the design life and strength of such members and thus replacement or retrofitting may need to be considered. One method of retrofitting (stiffening and strengthening) a composite steel-concrete beam is to externally post-tension the beam. The study was conducted using the finite element program "ANSYS". Nonlinear material models for the components of the composite beam were used in the finite element model. The outcomes got from finite element analysis were confirmed against available experimental results. A broad parametric study was conducted to explore the effect of converting simple composite beam into partially continuous beam externally post-tensioned . This covers: load deflection behaviour, strain in concrete, strain in the steel beam, converting the simple beam into a continuous beam, verifying an external post-tensioned simple beam