4 Triple Friction Pendulum: Does It Improve the Isolation Performance? 31 0 1 2 3 4 5 6 0 0.5 1 1.5 2 2.5 3 3.5 Loma Prieta a 0.85 3.2 sliding regime V triggered (triple and double FPs) sliding regime V not triggered triple FP without isolator (max=6.936m/s2) double FP, μ1=μ2=6.5% double FP, μ1=μ2=4.5% 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 Northridge 1.12 6.45 0 1 2 3 4 6 7 5 sliding regime V triggered sliding regime V not triggered without isolator (max=6.107m/s2) double FP, μ1=μ2=6.5% double FP, μ1=μ2=4.5% b triple FP PGA (m/s2) PGA (m/s2) max( | üs+üg | ) (m/s 2) max( | üs+üg | ) (m/s 2) restrainers triggered restrainers triggered (triple and double FPs) Fig. 4.3 Isolation performances of triple FP according to literature and conventional double FP tuned by trial and error for Loma Prieta (a) and Northridge (b) accelerograms As Fig. 4.2a shows also two triple FPs with slightly different friction tunings of the main sliding surfaces 1 and 4 are computed. These simulations show that increased friction on the main sliding surfaces 1 and 4 avoids that the triple FP is operated in sliding regime V which improves the isolation performance compared to the triple FP according to literature [1, 2]. Nevertheless, these two triple FPs also perform worse compared to the double FP. 4.6 Isolation Performance of Optimized Triple Friction Pendulum 4.6.1 PGAs of Optimization Due to the nonlinearity of friction damping of both FPs their isolation performance depends on their relative motion amplitude [5] and consequently on PGA. Therefore, the optimizations of both FPs must be done for selected PGAs. The following PGAs for optimization are chosen here: • PGAopt D2.5m/s 2 representing a small DBE, • PGAopt D5m/s 2 representing a medium to large DBE, and • PGAopt D7.5m/s 2 representing a large DBE. 4.6.2 Isolation Time Period The optimizations of both FPs are made for the typical situation where the fundamental time period of the non-isolated structure is 0.83 s (1.2 Hz), the vertical load Wis 12MN, s D1% and the selected isolation time period is 3.5 s in order to shift the isolated structure into the time period range of good isolation. This leads to effective radii Reff 1 DReff 4 D1.522m for the triple FP and Reff 1 DReff 2 D1.522 m for the double FP. 4.6.3 Articulated Slider Assembly of Triple FP As the intention of the articulated slider assembly of triple FP is to trigger relative motion in the bearing at even very small PGAs the friction coefficients 2 D 3 are assumed to be 1.75% similar to the published data. According to the design
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