Chapter 4 Triple Friction Pendulum: Does It Improve the Isolation Performance? Felix Weber, Peter Huber, Hans Distl, and Christian Braun Abstract The working philosophy of the triple friction pendulum (FP) is to generate low friction in the region of 1.5–2% combined with high stiffness due to the small effective radii of the articulated slider assembly at low peak ground accelerations (PGAs), to produce medium friction around 3–5% and medium stiffness by simultaneous sliding on surfaces 1 and 4 at PGAs corresponding to the design basis earthquake (DBE), to generate increasing friction with further increasing PGAs up to the maximum credible earthquake (MCE) by the high friction of surface 4 in the region of 10% and, eventually, to produce considerably increased stiffness at PGAs beyond of MCE in order to reduce the maximum required displacement capacity of the triple FP. This study first investigates if this design philosophy results in enhanced isolation of the primary structure compared to the conventional FP. For this, the triple FP according to the above mentioned design concept is numerically tested for several earthquakes that are scaled to various PGAs in order to operate the triple FP within all its sliding regimes with associated isolation efficiencies. These results are compared to those of the conventional non-adaptive double FP with equal friction coefficients on its sliding surfaces and same effective radii as those of concave plates 1 and 4 of the triple FP to ensure equal isolation time periods. The first study demonstrates that the conventional FP outperforms the triple FP for most of the PGAs except for very small PGAs below 1–2 m/s2 depending on the earthquake. This finding is explained by the facts that the small effective radii of the articulated slider assembly reduce the isolation time period and therefore the isolation of the structure and splitting the friction into medium and high values on surfaces 1 and 4 cannot improve the isolation performance since the relative motion amplitudes on surfaces 1 and 4 are reverse whereby the energy dissipation is not enhanced compared to the conventional double FP with equal friction coefficients. The second study shows a way how the triple FP with four friction coefficients, four effective radii and four displacement capacities can be optimized for maximum isolation of the primary structure. This study points out that the optimized triple FP converges to the optimized double FP which explains the similar isolation performances. Thus, the triple FP does not improve the isolation of the structure compared to the conventional friction pendulum. Keywords Curved surface slider • Earthquake • Friction • Isolation • Pendulum • Seismic 4.1 Introduction Conventional spherical friction pendulums (FP) such as single and double FPs are often used isolator. The triple FP with the articulated slider assembly in between of the two main concave sliding surfaces has become famous because it generates displacement amplitude dependent stiffness and friction behaviors [1, 2]. According to [1, 2] the triple FP is intended to produce low friction and high stiffness at small bearing motion amplitudes and peak ground accelerations (PGA), respectively, to exert increasing friction at significantly reduced stiffness at medium bearing displacement amplitudes and PGAs, respectively, due to the design basis earthquake (DBE), to generate further increasing friction at further lowered stiffness at large bearing displacement amplitudes and PGAs, respectively, due to earthquakes between DBE and the F.Weber ( ) Maurer Switzerland GmbH, Neptunstrasse 25, 8032 Zurich, Switzerland e-mail: F.Weber@maurer.eu P. Huber • C. Braun MAURER SE, Frankfurter Ring 193, 80807 Munich, Germany e-mail: P.Huber@maurer.eu; Braun@maurer.eu H. Distl Maurer Söhne Engineering GmbH & Co. KG, Frankfurter Ring 193, 80807 Munich, Germany e-mail: Distl@maurer.eu © The Society for Experimental Mechanics, Inc. 2017 J. Caicedo, S. Pakzad (eds.), Dynamics of Civil Structures, Volume 2, Conference Proceedings of the Society for Experimental Mechanics Series, DOI 10.1007/978-3-319-54777-0_4 27
RkJQdWJsaXNoZXIy MTMzNzEzMQ==