Seismic response of building structures with mechanical damping devices.

Abstract

Increasing damping in structures has long been recognized as a means of reducing dynamic response amplification during earthquakes. Added stiffness also generally reduces displacement response. The added damping and stiffness (ADAS) devices which have been proposed as an economical means for increasing structural resistance to earthquakes are investigated. The ADAS device is constructed of X-shaped mild steel plates which are separated by spacer plates and clamped by bolts through end blocks at the top and bottom. The device is attached to the beam bottom and forced by interstory braces to bend cyclically in double-curvature curve. The plates effectively dissipate energy as the building sways in an earthquake. The mechanical characteristics of ADAS devices has been experimentally determined using two different moment frames to test the ADAS devices. Static cyclic loading with incremental displacements controlled by actuators applied at the floors of the moment frames was used to represent inertia forces which may occur during an earthquake. The ADAS characteristics can be represented by the Ramberg-Osgood hysteresis model. In the dynamic analysis of a building the ADAS device is modeled as a nonlinear horizontal stiffness element. A comparison of the analytical response and the experimental response of a three-story steel structure with ADAS devices subjected to shaking table tests at the University of California at Berkeley is used to show the adequacy of the analytical model. The response characteristics of buildings with ADAS devices subjected to earthquake ground motion are presented in the form of response spectra which were constructed using different device ductilities and stiffnesses. Comparisons with elastic systems with viscous damping are made to assess equivalent viscous damping factors. In addition, design criteria and a design procedure were proposed and illustrated by an example. Finally, the response performances of buildings with ADAS devices are compared with the response of concentrically and eccentrically framed structures. According to the experimental and analytical results obtained in this study, ADAS devices produce substantial increases in stiffness, strength and energy dissipation when compared to a moment frame. The system has excellent behavior with inelastic energy dissipation through yielding of the device material. The building vibration is controlled without brace or frame member damage.