M. A. Kafi - Civil Engineering Faculty, Semnan University, Semnan, Iran
A. Kheyroddin - Civil Engineering Faculty, Semnan University, Semnan, Iran
R. Omrani - Civil Engineering Faculty, Semnan University, Semnan, Iran

The seismic strengthening methods are very important in earthquake-prone countries. Steel divergent bracing with replaceable link beam tied in steel frame and embedded in a concrete frame is a new method for a concrete frame strengthening. That is low cost and easy repairable after an earthquake.In this article six concrete frame strengthening methods have been investigated, including X-bracing, reverse chevron bracing, divergent bracing with concrete link beam, divergent bracing with steel link beam connected to steel columns in the steel frame, divergent bracing with steel link beam connected to the steel frame and with steel columns between those two, divergent bracing with steel link beam connected to the steel frame. All strengthening models are attached to concrete frames by a steel frame surrounding them . These models are investigated by ETABS and PERFORM-۳D softwares. In concrete frame strengthed by steel divergent bracing with steel link beam, the base shear is decreased about ۲۰%, steel consumption decreased to ۴۰% in ۶-story, and ۱۵% in ۱۴- and ۲۰-story compared to X-bracing, and the existing to allowable stress ratio decreased to ۵۰% in ۶-story, to ۴۰% in۱۴-story and ۳۵% in ۲۰-story. As the structure's height is increased, the interaction between the frame and the brace, and the lateral force in the frames increased. Nonlinear static and dynamic analysis have shown more elastic hardness, ductility, behavior coefficient, and base shear in strengthed concrete frame with divergent bracing with steel link beam connected to the steel frame model than others.

Eccentric Braced Frame Bracing, Steel braced frame, strengthening, Concrete Moment Frame, Ductility