Experimental evaluation and characterization of yielding and viscous devices for the seismic protection of structures.

摘要

Advances in the field of earthquake engineering and the ever-increasing cost of the built environment has resulted in a shift from the primary goal of life safety in a seismic event to one of achieving higher performance levels. This dissertation focuses on two innovative energy dissipating devices gaining wide acceptance in the United States and throughout the world---the buckling-restrained brace and the viscous fluid damper. A buckling-restrained brace dissipates energy through the hysteretic yielding of the steel core, while a viscous fluid damper dissipates energy through the shearing action of the fluid within the damper.; In addition to the need for an accurate representation of their behavior, there are important issues relating to the sustained performance of the devices under cyclic loading. For buckling restrained braces it is necessary to ensure brace stability and cumulative plastic ductility capacity; whereas, for viscous fluid dampers the issue of viscous heating is of importance as moderate heating of the internal fluid has shown to reduce the force output, while excessive heating may compromise the integrity of the internal seals.; The results of an extensive experimental testing program established that buckling-restrained Unbonded Braces(TM) deliver stable and repeatable behavior with nearly symmetric hysteretic behavior in tension and compression. The braces showed no sign of degradation with the plastic deformation capacity of the brace exceeding the specified requirements both in terms of ultimate deformation and cumulative plastic deformation.; The behavior of the Unbonded Brace is characterized at the macroscopic, force-deformation level with the Bouc-Wen model which is found to predict the brace behavior with fidelity. The parameters of the macroscopic model are derived from the geometric characteristics of the brace and the mechanical properties of the steel and can be used with confidence to characterize the behavior of the braces.; Subsequently, this dissertation summarizes the results of a comprehensive experimental program that investigates the performance of three viscous fluid dampers---a 3 kip, a 15 kip and a 250 kip damper. As the force-velocity characterization of viscous fluid dampers is well established, this dissertation focusses on the problem of viscous heating under seismic loading.; Temperature was continuously recorded at multiple external locations along the damper casing and within the internal fluid during dynamic loading. The data suggest a two parameter law of cooling that allows the dependable estimation of internal fluid temperature when the external temperature on the damper casing is known.; It was observed that under long-stroke motions (more than two times the piston diameter), four to six cycles are sufficient to raise the temperature of the internal fluid by approximately 100°F at the mid-stroke location, while the temperature rise at the end-of-stroke location---the location of the internal seals---is relatively small.