Design standards of Reinforced Concrete (RC) bridges are generally based on a semiprobabilistic format using partial factors to take into account material, geometrical and load effect uncertainties. In the case of an existing bridge, the available information can be used to adjust partial factors given an acceptable target reliability level. However, gathering sufficient information on material properties may not be a straightforward task and the associated assumptions may have an impact on the assessment result. This paper focuses on the assessment of an existing RC bridge at the ultimate limit state using a semi-probabilistic format. First, the data are analysed by evaluating material properties. Then, uncertainty levels are evaluated, and partial factors are adjusted accordingly. Univariate and multivariate analyses are finally conducted to show the main effect of the partial factors’ adjustment on the assessment.