Assessment of arch bridges often involves the determination of hanger forces. A common method to determine these forces is through vibration measurements, using the so-called taut-string method. The relation between natural frequency and hanger force is however strongly dependent on the vibrating length of the hanger, as on the connection of the hangers to the arch and the deck. In literature a method is described to determine vibrating lengths based on modal analysis. This paper describes finite element simulations and field tests to validate this extended taut-string analysis. Firstly a hanger is modeled with different boundary conditions, varying from a fully clamped to a fully hinged connection. By using the acceleration data from the simulation at different positions along the hanger, the hanger force is reconstructed with an accuracy of 97% to 100%. Field tests on a bridge with a symmetrical lay-out show that similar vibrating lengths are found for similar hangers, indicating a successful implementation of this extended taut-string analysis, leading to a higher accuracy in the hanger force determination.