Structural seismic vulnerability assessment is one of the key steps in a seismic risk management process. Structural vulnerability can be assessed using the concept of fragility. Structural fragility is the probability for a structure to sustain a given damage level for a given input ground motion intensity, which is represented by so-called fragility curves or surfaces. In this work, we consider a moment-resisting reinforced concrete frame struc- ture in the area of the Cascadia subduction zone, that is in the South-West of Canada and the North-West of the USA. According to shaking table tests, we first validate the capability of an inelastic fiber beam/column element, using a recently developed concrete constitutive law, for representing the seismic behavior of the tested frame coupled to either a commonly used Rayleigh damping model or a proposed new model. Then, for each of these two damping models, we proceed to a structural fragility analysis and in- vestigate the amount of uncertainty to be induced by damping models.