This study proposes an ''optimal'' spectral acceleration based intensity measure (IM) to assess the collapse capacity of generic moment frames vulnerable to the P-delta effect. The IM is derived from the geometric mean of the spectral pseudo-acceleration over a certain period interval. The optimized IM includes for first time a flexible lower limit for the period interval, corresponding to the structural period associated with the exceedance of 95% of the total effective mass. This flexible lower limit bound provides an efficient IM, independently of the contribution of higher modes to the total response. The upper bound period is 1.6 times the fundamental period to account for period elongation due to inelastic deformations and gravity loads. In a parametric study on generic frames, structural parameters are varied to quantify the performance of this IM compared to classical benchmark IMs. The ''optimal'' IM provides minimum, or close to the minimum, dispersion for the entire set of frames with different fundamental periods of vibration, number of stories, and P-delta vulnerability.

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Abstract. In this paper the influence of material deterioration on the seismic collapse capacity of PDelta vulnerable frame structures is quantified. The main objective is to reveal and to validate the range of applicability of the proposed equivalent single-degree-of-freedom (ESDOF) system for assessment of the global collapse capacity. This is achieved through comparison of the median collapse capacity of PDelta vulnerable generic frame structures that exhibit material deterioration in strength and stiffness with outcomes of the corresponding ESDOF system based on the derived transformation rules. Sets of planar generic frame structures are compiled varying the governing structural parameters for seismic collapse independently. In all cases, the collapse capacity is calculated using incremental dynamic analysis. Record-to-record variability of the collapse capacity is studied using a set of ordinary earthquake records compiled in FEMA-P695.

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