A large number of structures are currently approaching service life of 50 years, and they are designed according to previous codes with significant lower actions, hence there is a need for the assessment of their conditions. In Croatia there are still no particular standard or manual that would help the engineers in assessing the condition of the existing structures, hence they either use standards for new structures or rely on their own assessment. This thesis provides a description of two partial factor methods for existing structures presented by the International Federation for Structural Concrete (fib) in its 2016 bulletin titled "Partial Factor Methods for Existing Concrete Structures." They are the Design Value Method (DVM) and the Adjusted Partial Factor Method (APFM), which use a certain reliability index and reference period to determine a reduced value of the partial safety factor, which is then used to determine the design value of action and resistance. These methods are applied to determine the load bearing capacity of the Posedarje bridge through an assessment of its bending moment resistance and shear force resistance. Even though the assessment shows that the bridge does not fulfill the necessary load-bearing capacity criteria, it has been proven that these methods result in reduced effects of actions and greater resistance of a structure in comparison to the eurocodes. A comparison of the obtained results also show that the Adjusted Partial Factor Method results in greater safety in comparison to the Design Value Method.