Strengthening of reinforced concrete buildings with soft story irregularity

Abstract

Turkey is one of the most earthquake-prone countries in the world. The studies on the damaged buildings with reinforced concrete structural systems, especially done after the 1999 Golcuk earthquake and other earthquakes in the past, showed that the negative effects of the structural irregularities in the buildings come to light through the impact of earthquake load. They also revealed that the regularity of structural systems is one of the main principles in the design of earthquake resistant reinforced concrete structural systems. In this study, two-story singlespan 1/3 scaled reinforced concrete test specimens having soft story irregularity (interstory stiffness irregularity) and insufficient earthquake resistance were tested by applying different strengthening methods. The purpose of strengthening applications is to eliminate the adverse effects of the soft story irregularity. Reversed-cyclic lateral load was applied on the test specimens to simulate the earthquake effect. While the upper stories in all the test specimens had infill walls, the lower stories had been strengthened using different types of steel bracings. The first frame was strengthened with K-type shaped (<>), the second one with straight. V-type (V) and the third with turned sideways V-type (>) steel diagonal elements. As a reference to these three strengthened frames, the following two frames, which were taken from another study, were used; a frame with both stories having infill walls and a frame with infill walls on the upper story, which is empty on the lower story. As a result of the study, load and displacement histories, hysteresis and envelope curves and energy dissipation graphs of these three strengthened reinforced concrete frames were obtained. Furthermore, all the experimental results, obtained graphs and the data from the reference frames were compared and interpreted. The results show that the frame strengthened with K-type steel bracings is the best solution to reduce the effect of soft story irregularity.