An old steel bridge located in Melbourne, Australia, was strengthened with carbon fibrereinforced polymer (CFRP) laminates. A prestressed unbonded CFRP system was used in strengthening the bridge. A long-term wireless monitoring system was installed on the strengthened girders to monitor the strain evolution of the CFRP laminates, the temperature readings on the adhesive layer and air temperature. Short-term monitoring devices were also mounted on the girders for the purpose of on-site measurement. The on-site measurements were recorded when the bridge was subjected to a 42.5-ton loaded truck before and after strengthening. The results showed significant decreases in the bending stresses at the bottom of the girders when prestressed un-bonded CFRP laminates were used. This paper presents a linear finite element modelling of the bridge with the CFRP strengthening system. The results were validated using field measurements and a parametric study was carried out to understand the effect of change in temperature on the stress development on the steel girders. The paper also presents details of the bridge modelled with the prestressed unbonded strengthening sys-tem. The results showed good validation of the model, and the insignificant effect of the change of temperature on the prestressed strengthened girders.