Abstract: A steady beam is focused upon a target member located on a building structure. The target member moves with the deflection of the building structure and the movement of the target is communicated to a programmed controller which responds to the movement indicated by actuating tension adjusting members which are connected to an array of elastic steel rod-like tendons disposed adjacent the structure's main support members. The tension adjusting members are caused to apply tensile force to the tendons to counter the force causing the deflection of the structure and to inhibit the effect of the force on the structure's support members, thus diminishing the extent of deflection and dampening the oscillation of the structure which is incident to the restoration of the structure to a condition of equilibrium.