Shake table experiments and numerical simulation on the effects of damage and strengthening on dynamic behavior of RC frames

This study presents an investigation on the effects of damage and strengthening on the dynamic behavior of buildings. Forced vibration tests were carried out on the shake table of two 1/3 scale, 3D, 2-story, single-span reinforced concrete frame specimens produced in laboratory. The damage was created by weakening the joint areas. Then the damaged zones were repaired and strengthening methods using in-plane reinforced concrete shear walls and X-shaped steel diagonal bracings were applied. The aim here is to perform a dynamic-based performance evaluation of these two commonly used global systemic strengthening techniques in practice. A total of more than 105 forced vibration experiments were carried out under 4 different intensities of dynamic load in different conditions of the specimens. Dynamic parameters were determined with the experimental modal analysis method. Moreover, story displacements time history, base shears time history, base shear-top displacement hysteresis curves, and lateral translational stiffnesses were obtained. In addition, numerical analyses using ETABS finite element software were also conducted. As a result, it was observed that the damage reduced the lateral translational stiffnesses by about 50%, steel bracings increased the stiffness in the damaged condition by 147% and RC shear walls increased it by 381%. On average, the 1st natural frequency decreased by 36.5% in the damaged conditions, increased by 83% in the strengthened conditions compared to the damaged conditions. Strengthening of the members tends to limit the soft story behavior. In general, although its application is difficult, the best performance in all studied parameters was obtained from the specimen strengthened with in-plane reinforced concrete shear walls.