The seismic fragility of steel frames subjected to narrow-band motions from the soft-soil of Mexico City is evaluated by means of different alternatives vector-valued ground motion intensity measures (IMs) comprised of two parameters. Because most of the seismic hazard maps around the world were developed for the spectral acceleration at first mode of vibration Sa(T1), all the vectors here considered are based in Sa(T1) as the first parameter. As the second parameter of the vector, the peak ground acceleration, peak ground velocity, duration, ID, RT1,T2 and Np are considered. The maximum inter-story drift and a recently proposed energy-based damage index for steel frames were employed for structural performance evaluation. It is observed, as expected, that spectral-shape-based vector valued IMs are the best proxies for seismic fragility analysis reducing the uncertainties in the structural response
