Smart structures are civil or mechanical structures that can automatically and intelligently react to external dynamic loadings such as vibration shocks, strong winds, destructive waves, and earthquakes. The use of magnetorheological (MR) dampers has been of increasing interest in smart structures as they have reliable, stable and fail-safe operations, small energy requirements, and fast responses. The challenges of MR damper structural control rest with the complex dynamics involved, high nonlinearity due to the force--velocity hysteresis, nonaffinity, and constraints of the control system with the magnetization current as its input. To address these problems, this paper presents the modeling and control design as well as the implementation results of a second-order sliding mode controller for the MR dampers embedded in the building structures subject to quake-induced vibrations. Based on the static hysteresis model of the MR damper using computationally tractable algebraic expressions, algorithms are proposed to control directly the magnetization current to the dampers, configured in a differential mode to counteract the offset force. The effectiveness of the proposed technique is verified in simulation by using a building model under quake-like excitations. The experimental results are provided on a laboratorial setup tested on a shake table.