No 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 Gölcük 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 single-span 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.

In the design of earthquake-resistant reinforced-concrete structural systems, the necessity to construct a regular structure is one of the main principles. Building irregularities generally become obvious with the effect of a seismic load. It is crucial that the irregularities of structural systems should be considered properly with respect to the conditions determined by the building codes. In this study, the soft-storey irregularity that causes most of the losses and damage in earthquakes was investigated with respect to the criterions of various national building codes. Eleven sub-models were produced on the basis of a general building model, and they were analyzed with respect to the conditions of the codes relating to the soft-storey phenomenon using the SAP 2000 structural-analysis program. The first-storey heights of the models were different from each other while all the other parameters and the geometries were the same. In this way, the codes were compared in terms of the effect of the storey height on the formation of a soft storey. Eventually, it was observed that, especially in the Japanese Seismic Code, the soft-storey irregularity is handled very sensibly and safely.

Reinforced concrete buildings that are not properly designed, constructed, or supervised, might not have the resistance to bear even their own weight. When the effects of deformation in the concrete over time are added to the loads, great damages and even collapses can be seen. In this study, the performance of reinforced concrete buildings under axial loads was investigated. The effect of creep in concrete over time was also evaluated. Creep deformation has been integrated into the analysis with a simple method. A total number of 20 8-storey reinforced concrete frame buildings were modeled via ETABS. In each model, only column dimensions and concrete compressive strengths have been changed. The models were analyzed under the combined effect of axial loads and creep. As a result, the effect of concrete compressive strength and column dimensions on collapse in reinforced concrete buildings under the mentioned effects was examined. The results showed that column dimensions should be much high to prevent collapse when low strength concrete is used in buildings. In addition, a formula that can be used to determine the parameters of concrete quality and column cross-sectional areas required against collapse is proposed for the preliminary design of similar types of buildings.