Rehabilitation of reinforced concrete frames with non-seismic details using eccentric steel braces

This paper presents quasi-static cyclic loading tests of reduced scale reinforced concrete Eccentrically Steel Brace (ESB) retrofitted and bare portal frames. A hollow square steel brace was attached to the beam diagonally at a distance of L-Beam/8 from the beam ends for enhancing the seismic performance of deficient frames. Results indicated promising behavior of ESB retrofitted frame opposed to the bare frames and shifted the damage mechanism from severe shear cracking and column flexural hinging to beam flexural cracking. ESB retrofitted frame also increased lateral force-displacement capacity, stiffness and hysteretic damping compared to the bare frames. The test results were also used to calibrate a nonlinear modeling technique proposed using a finite element based program. Additionally, a nonlinear dynamic acceleration time history analysis were carried out for two-story ESB retrofitted and bare frames and inter-story drift limits were identified for each structure. The study also confirms the importance of joint detailing's and its beneficial role in improving the seismic performance of frames under earthquake ground motions.