4 Triple Friction Pendulum: Does It Improve the Isolation Performance? 33 1.4 1.6 1 0.8 1.2 15 10 5 0 0 0 0 5 10 15 1.4 1.6 1 0.8 1.2 15 10 5 5 10 15 optimum optimum a b max( | üs+üg | ) (m/s 2) max( | üs+üg | ) (m/s 2) triple FP, Tiso=3.5s, El Centro NS, PGAopt=5.0m/s 2 double FP, T iso=3.5s, El Centro NS, PGAopt=5.0m/s 2 friction coefficient μ4 (%) friction coefficient μ 2 (%) friction coefficient μ1 (%) friction coefficient μ1 (%) Fig. 4.4 Optimization results for triple (a) and double (b) FPs for the El Centro NS accelerogram scaled to 5 m/s2 0 5 10 15 20 25 25 20 15 10 5 4 3 0 triple FP, Tiso=3.5s, Loma Prieta, PGAopt=7.5m/s2 optimum 0 5 10 15 20 25 25 20 15 10 5 4 3 0 double FP, Tiso=3.5s, Loma Prieta, PGAopt=7.5m/s2 optimum a b max( | üs+üg | ) (m/s 2) max( | üs+üg | ) (m/s 2) friction coefficient μ4 (%) friction coefficient μ1 (%) friction coefficient μ2 (%) friction coefficient μ1 (%) Fig. 4.5 Optimization results for triple (a) and double (b) FPs for the Loma Prieta accelerogram scaled to 7.5 m/s2 means that 1 and 4 must be designed similar to 1 and 2 of the optimal double FP and that the articulated slider assembly is not beneficial for maximum isolation due to its high stiffness which is equivalent to a low isolation time period. From Fig. 4.6 it is also evident that the conventional design of the triple FP [1, 2] is far from optimal and that the suboptimal solutions with equal friction coefficients perform almost as well as their optimal counterparts. 4.7 Summary First, the isolation performance in terms of absolute structural acceleration of the triple friction pendulum (FP) with parameters from literature is compared to that of the conventional double FP. Second, the triple and double FPs are optimized for minimum absolute structural acceleration and their isolation performances are compared subsequently. The first study demonstrates that the triple FP designed according to literature performs worse than the conventional double FP with suboptimal friction tuning. The second investigation demonstrates that both optimized FPs generate similar structural acceleration responses and total bearing displacements due to the fact that the triple FP mutates to the double FP due to the optimization.
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