Document Type: Research Paper


1 Unit of Applied Mechanics, University of Innsbruck, Technikerstr. 13, 6020 Innsbruck, Austria

2 Unit of Engineering Mathematics, University of Innsbruck, Innsbruck, Austria


Recently, two of the authors have introduced the collapse capacity spectrum
methodology, which allows the assessment of the collapse capacity of highly inelastic P-delta
sensitive regular frame structures without performing non-linear time-history analyses. The main
ingredient of this method is the collapse capacity spectrum, which represents the seismic collapse
capacity of an inelastic non-deteriorating single-degree-of-freedom system vulnerable to the Pdelta
effect as a function of its initial period, negative post-yield stiffness ratio, viscous damping
coefficient, and the shape of the hysteretic loop. In the present study, multiple linear regression
analyses are applied to provide enhanced analytical expressions of these spectra. The record-torecord
uncertainty of the collapse capacity is captured through median, 16th and 84th percentile
spectra. For several test systems analytical collapse fragility functions based on these spectra are
set in contrast with the corresponding sorted individual collapse capacities. These examples prove
the superiority of the proposed analytical expressions compared to its original formulation.