In the last years there has been an increasing interest to magnetorheological (MR) dampers and their applications to civil engineering. In particular they have been used as semi-active control devices for vibration mitigation due to external dynamic loads. These devices are highly nonlinear and thus accurate models of these devices are important for effective simulation and control system design. Two hysteretic models based on the normalized Bouc-Wen model are proposed in this paper to compare their effectiveness in a large scale MR fluid damper. A methodology for identification is proposed, and the obtained models are tested and validated experimentally.