Model type effects on the estimated seismic response of a 20-story steel moment resisting frame

Finite element models of varying sophistication may be employed to determine a
building’s seismic response, with increasing complexity potentially offering higher fidelity at
the cost of computational load. To account for this effect on the reliability of performance
assessment, model-type uncertainty needs to be incorporated, as distinct to the uncertainty
related to a given model’s parameters. At present, only placeholder values are available in
seismic guidelines. Instead, we attempt to accurately quantify them for a modern 20-story steel
moment-resisting frame. Different types of 3D, 2D multi-bay, and 2D single-bay multi-degreeof-freedom models are investigated, together with their equivalent single-degree-of-freedom
ones, to evaluate the model dependency of the response both within each broad model category,
as well as among different categories. In conclusion, ensemble values are recommended for the
uncertainty in each model category showing that for the perfectly-symmetric perimeter-frame
P-Δ sensitive building under investigation, the uncertainty stemming from 3D versus 2D, or
distributed versus lumped plasticity models is lower than the governing record-to-record
variability.