A nonlinear/inelastic rooftop tuned mass damper frame

Reduction of a building's response to earthquake ground motion has been the focal point behind considerable research and structural engineering innovation in recent decades. For many years, engineers have understood that altering a structure's fundamental period offers the greatest opportunity for reducing its response to seismic ground motion. Innovations such as base isolation have been developed which enable a building's fundamental period to be out-of-phase with the soil dependent dynamic properties of the site, the result being a significant reduction of seismic accelerations, forces and overall damage. Other approaches utilize highly ductile structural frames which offer the benefit of sustaining service loads while being subjected to significant lateral distortion. Such systems enable lengthening of the fundamental period of the structure during nonlinear response which typically reduces the acceleration response. Furthermore, ductile systems utilize creative methods to dissipate earthquake energy in a stable manner to prevent the earthquake input energy from causing damage at sensitive regions of structural assemblies. Creative applications of mass and stiffness utilized as penthouse enclosures at the rooftop of structures offer the potential for changing a building's structural dynamic properties. This method has been termed a rooftop tuned mass damper frame (RTMDF). The incorporation of specific yielding mechanisms within these structures offers the potential of further modifying a structure's dynamic properties while also introducing methods for increased energy dissipation. The net result of this method is an inexpensive retrofit measure to improve the seismic performance of existing structures. The method also offers the potential for improving the expected performance of new structures or reducing construction costs of the seismic system. This research investigates the effectiveness of buckling restrained braces in rooftop tuned mass damper frames for reducing seismic response. This approach could be implemented for a relatively low cost at the roof of the suited structure. It will have the benefit of introducing designated yielding members (DYM's) for seismic energy dissipation in a controlled manner and will create an opportunity to lengthen the fundamental period of the original structure. These effects are complementary and offer the potential for reduction of seismic acceleration response and reduction of earthquake demand on the base structure.