Strength reduction factor-ductility-period relationships for single degree of freedom systems

The relationship between the strength reduction factor, the ductility demand and the structural period is important for the seismic demand estimation for both new and existing structures. This relationship is closely related to the ground motion characteristics, the hysteresis type of structures, the structural period, strength and ductility. The aim of this study is to determine the relationship between the strength reduction factor, the ductility demand and the structural period. Nonlinear time-history analyses of elastoplastic single degree of freedom systems are carried out under the effect of 60 ground motion records using a MATLAB code. Ground motion records which are recorded on different site classes are considered so that the soil effect can be taken into consideration. The variation of the ductility demand with respect to the structural period, site class and strength is determined. A simple equation is proposed as a result of the aforementioned variation of the ductility. Furthermore, it is observed that the ductility demand is almost constant beyond a certain period. This period mainly changes with the soil type and the strength reduction factor. In the short period range, the ductility demand increases as the structural period decreases. Also, the higher strength reduction factor causes the higher ductility demand. Keywords: Strength reduction factor, ductility, period, single degree of freedom system, elastoplastic system