This investigation is aimed to unveil the detailed design, manufacturing, and implementation process of high capacity MR-dampers for applications in seismic response control, typically in conjunction with tuned mass dampers. The goal is to design and predict the response of large-scale MR dampers by using multi-physics analysis tools capable of modeling the interaction between fields, such as magnetic and fluid dynamics. With this objective in mind, a finite element (FE) model for 3D analysis of MR-dampers was built by using ANSYS. In this model the magnetic field is represented through Maxwell equations while the fluid dynamics model by the Navier-Stokes representation. The magnetic and fluid problems are coupled through the viscosity of the magneto-rheological fluid, which in turn depends on the magnetic field intensity. As an example, the FE model was applied to a 15 [ton] damper already installed in a building in Santiago, which was subjected to a number of experimental tests. The construction of the damper was done locally and included several technical challenges in the protection of coils and automatic control. For this article, sinusoidal simulation tests are performed in order to validate the experimental force-velocity and force-deformation constitutive relationships presented. Analytical and experimental results of the 15 [ton] MR-damper showed very good agreement with the predicted behavior by using the FE model. The observed differences are due the compressibility of the fluid, which was not considered in the numerical model.