Abstract ---The equipment of ambient vibration measurement and the technique of identifying fundamental periods and the corresponding mode shapes are fully developed in the past decades. If the easily measured dynamic parameters, such as fundamental vibration periods and mode shapes, can be used as the preliminary assessment of retrofitted buildings, it is certainly an easy and fast tool for seismic capacity evaluation.
The dynamic parameters identified from ambient vibration are in terms of stiffness, while the seismic capacities are associated with the strength of the buildings. In this research, 18 structural models are established and the two relationships between the stiffness and the strength are proposed according to the regression analysis of these models. One is the function of roof displacement ductility, while the other is the function of roof displacement ratio. Hence seismic capacity can be calculated using the dynamic properties from ambient vibration test and the proposed relationships. The contribution of brick walls, the corresponding PGA value and the determination of ductility are explained. The relationships proposed in this research not are only more flexible but also take more effects into consideration in comparison with other results in the literature. They can be further extended as an easy tool for preliminary assessment of seismic capacity of existing RC buildings.