Intensity measures that reduce collapse capacity dispersion of P-delta vulnerable simple systems

Abstract

The study evaluates two alternative seismic intensity measures (IMs) that reduce the collapse capacity dispersion of inelastic non-degrading single-degree-of-freedom (SDOF) systems vulnerable to the P-delta effect. This dispersion of collapse capacity is caused by record-to-record variability, which refers to frequency content variation of the ground motions used in the dynamic analyses. This reduction (of dispersion) is achieved utilizing efficient elastic pseudo-spectral acceleration based IMs. The first set of evaluated IMs is based on the spectral pseudo-acceleration averaged in a certain period interval between the structural period and an elongated period. The ''optimal'' lower bound of the period interval corresponds to the structural period of vibration, since naturally in an SDOF system no higher modes effects do exist. The ''optimal'' upper bound of the period interval for averaging, referred to as elongated period, is found to be 1.6 times the system period. The second IM considered in the study is the 5 % damped spectral pseudo-acceleration at the system period in the presence of gravity loads, which is a single target IM. The most widely accepted IM, the 5 % damped pseudo-spectral acceleration at the system period without P-delta, serves as the benchmark IM. The results show that both proposed IMs lead to a reduction of the collapse capacity dispersion compared to the benchmark IM outcomes. The IM based on the averaged spectral acceleration of the ''optimal'' period interval is more efficient up to a negative post-yield stiffness ratio of 0.45, while the single target IM based on the system period in the presence of gravity loads is superior for extreme negative post-yield stiffness ratios larger than 0.45. Additionally, the sufficiency and the scaling robustness property of the considered IMs with respect to the natural logarithm of the record-dependent individual collapse capacities is discussed for a wide range of structural configurations.

Optimal intensity measure based on spectral acceleration for P-delta vulnerable deteriorating frame structures in the collapse limit state

“…The resulting period intervals DT are S a;gm ðT 1 ; 1:6T 1 Þ, S a;gm ðT 1 ; 2:0T 1 Þ, and S a;gm ðT 1 ; 1:3T 1 Þ. Tsantaki et al (2017) found that the period interval from T ð1Þ ¼ T 1 to T ðnÞ ¼ 1:6T 1 leads on average to the smallest collapse capacity dispersion of P-delta vulnerable SDOF systems.…”

“…They found that the optimal parameters depend strongly on the actual deformation of the structure, i.e., elastic, moderately inelastic, or at onset of collapse. Bianchini et al (2009) Bianchini et al (2009), where S a is discretized at 10 log-spaced periods within DT, Tsantaki et al (2017) discretized S a at equally spaced periods T ðiÞ within DT (Fig. 1d),…”

“…Based on parametric IDAs on P-delta vulnerable highly inelastic SDOF systems, Tsantaki et al (2017) found that the upper elongated period T ðnÞ leading to the minimum RTR dispersion of the collapse capacity is around 1:6T SDOF , fluctuating between 1:4T SDOF and 2:0T SDOF . According to this study, for these SDOF systems the ''optimal'' lower bound period T ð1Þ corresponds to the elastic period, i.e., T ð1Þ ¼ T SDOF .…”

“…The studies of and Tsantaki et al (2017) have shown that for P-delta vulnerable singledegree-of-freedom (SDOF) systems this IM based on the geometric mean concept of spectral accelerations satisfies better the properties of efficiency and sufficiency, compared with outcomes of benchmark studies (Adam and Jäger 2012a;Jäger and Adam 2013;Tsantaki et al 2015), where the 5% damped spectral pseudo-acceleration at the structural period has been used as IM. In Eads et al (2015) the efficiency and sufficiency of a similar IM for collapse prediction of about 700 moment-resisting frame and shear wall structures has been evaluated.…”

Evaluation the P-Delta Effect on Collapse Capacity of Adjacent Structures Subjected to Far-field Ground Motions

“…Considering appropriate seismic intensity measure (IM) is important for nonlinear dynamic analyses. Tsantaki et al [9] proposed two IMs to reduce the collapse capacity dispersion of SDOF systems that are vulnerable to the P-Delta effect. The collapse capacity dispersion is caused by the ground motion variability and the variations of frequency content of ground motions.…”