Most research to date on estimation of building fragility has focused on statistical extrapolation of results for selected individual structures. In this study the characteristics of structures in a target inventory are used to estimate fragilities. Consideration is restricted to the class of building structures consisting of mid-rise (5 story) L-shaped steel moment frame (LSMF) buildings. Statistically significant predictors for rapid response assessment are identified using Design of Experiments (DOE) and statistical tools, and appropriate seismic response metamodels are developed. Vulnerability functions for 3D LSMF structures are estimated using the metamodels with efficient Monte Carlo simulation. The use of metamodels reduces required computations and makes it practical to carry out probabilistic response calculations in this manner. The methodology is used to construct estimates for the fragilities of a class of LSMF structures as well as to specific individual LSMF structures.