Design of a new passive energy dissipation system for earthquake resistant structures

Abstract

The basic principle of conventional earthquake-resistant design that has been applied for the last 75 years is intended to ensure an acceptable safety level while avoiding catastrophic failures and loss of life.Over the last half century, a large amount of research has been conducted into developing innovative earthquake-resistant systems in order to raise seismic performance levels while keeping construction costs reasonable.Those structural control systems are broadly classified into three categories asPassive and,Active control, andSeismic isolation system. Passive control systems have been considered as an effective and inexpensive way to mitigate earthquake risks to the structures.Among different passive energy dissipation systems available metallic dampers are popular (and inexpensive) choice for an energy dissipation device because of its relatively high elastic stiffness, good ductility and it’s high potential for dissipating energy in the post yielding region. One of the metallic dampers namelyAdded Damping And Stiffness (ADAS) is the most commonly used metallic dampers in seismic design. Usually, X-plates are chosen for mounted on a Chevron type bracing are usually chosen for ADAS. In principle, these devices dissipate energy through flexural yielding along the out-of-plane direction of the device, with an assumption of nearly rigid supporting Chevron bracing system along its in-plane direction. Clearly, these devices will be effective in resisting seismic excitation along one of the horizontal directions (in plane direction of the bracing). Other orthogonal components will be resisted by another set of devices installed in a frame spanning along the other orthogonal direction. This can be conveniently overcome if a device performing effectively in three dimensions is thought of. Three dimensional model of such a device has been proposed in this thesis. The shape of the proposed damper is in the form of an hourglass, and it is referred toHourglass Added Damping and Stiffness (HADAS) device. The HADAS device is capable of dissipating the input energy along both orthogonal lateral directions, provided the supporting bracing system is relatively stiffer. However conventional chevron bracings as used in supporting ADAS devices, have negligible stiffness along the out-of-plane direction. Therefore, a suitable bracing system, capable of providing stiffness along any two lateral orthogonal directions are required to be developed for receiving full benefit from the HADAS devices. Such a bracing system is also proposed in this thesis. In order to illustrate the improved seismic capacity of the building after installation of damper, a ten storey building located in seismic zone - IV of India is designed conforming to Indian Standards. Three seismic events recorded at the Large Scale Seismic Testing (LSST) array in Lotung, Taiwan are used for the purpose of illustration. The improved performance of building is assessed by comparing peak floor displacement, peak storey drift, peak storey shear force building without and with the devices.