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The reliability of friction dependencies under real earthquakes has rarely been validated and the effect of the velocity and temperature increase caused by bidirectional excitation on the maximum displacement remains unclear. In this study, friction dependencies were validated using full-scale dynamic tests under earthquake response orbits, and their contribution to the maximum displacement was assessed under strong ground motions. In general, friction dependencies are still applicable to real earthquakes. Moreover, the effect of velocity increase can be ignored, but the effect of temperature increase on displacement is significant, particularly under ground motions with large magnitudes and small distances to faults. [ABSTRACT FROM AUTHOR]

Hysteretic dampers are used to dissipate earthquake-induced energy in base-isolated structures by acquiring inelastic deformations, rendering their hysteretic behavior of vital importance. The present paper focuses on investigating the behavior of U-shaped steel dampers under bidirectional loading; this is significantly different from their corresponding uniaxial behavior. Two main sets of loading tests on full-scale specimens are conducted in this regard: (i) quasi-static tests with simple histories and (ii) dynamic tests with realistic loading histories. Based on the results obtained in the quasi-static tests, an interaction curve that accounts for the reduction of the cyclic deformation capacity is proposed. However, the fidelity of this relation must be assessed under loading conditions similar to those of a seismically isolated structure subjected to an earthquake, which represents the goal of the second set of tests. The results of the dynamic tests validate the proposed interaction curve for estimating the deformation capacity of U-shaped steel dampers under bidirectional loading. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Energy dissipation devices are necessary for base-isolated buildings to control the deformation in the isolation system and to dissipate the earthquake-induced energy. U-shaped steel dampers (also known as U-dampers) dissipate energy through plastic deformation of specially designed U-shaped steel elements. This type of device can be installed at several locations in the isolation system. U-dampers have been widely used in Japan for different types of isolated structures, such as hospitals, plants and residential buildings, since the 1995 Kobe Earthquake. Previous research has used static tests to estimate the performance of U-dampers. However, the ultimate plastic deformation capacities and hysteretic behaviors of full-scale U-dampers under dynamic excitations still remain unclear. In addition, it is unclear whether the initial temperature has an effect on the hysteretic behavior and plastic deformation capacity of U-dampers. In this paper, two series of dynamic loading tests of U-dampers were conducted to evaluate the issues described earlier. The major findings of the study are (i) the loading speed has little effect on the plastic deformation capacity of U-dampers; (ii) method to evaluate the ultimate plastic deformation capacities of U-shaped steel dampers of different sizes is established using a Manson-Coffin relation-based equation that is based on the peak-to-peak horizontal shear angle γt, which is defined as the lateral deformation amplitude (peak-to-peak amplitude) divided by the height of the dampers; (iii) the loading rate and the initial temperature have a minimal effect on the hysteretic behavior of the U-dampers; and (iv) a bilinear model is proposed to simulate the force-deformation relationships of the U-dampers. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]