Abstract

In this paper, the concept of a semi active frictional damper called Adjustable Frictional Damper (AFD) is introduced. The clamping force of such damper is secured by hydraulic pressure, which not only reduces the manufacturing costs but also makes it possible to control the seismic response of the structure by changing the clamping force of the dampers.

The hysteretic behavior of AFD is studied by experimental means as well as by numerical model. Experimental process involves tests with various hydraulic pressures (which cause various frictional forces) at nearly static loading as well as dynamic loading with various frequencies. The results show that the proposed damper has significant energy absorption by stable hysteretic loops, which can be used for enhancement of the performance of structures subjected to earthquake loads with various intensities. Force–displacement characteristics of AFD such as slippage load, dissipated energy, effective stiffness and equivalent viscous damping for consecutive cycles of loading is calculated. The system is qualified based on the requirements for displacement-dependent devices according to ASCE/SEI 41-06 specification. Furthermore, the hysteretic behavior of AFD is studied by numerical method and a close agreement between the experimental and numerical results is observed.

Introduction

Seismic response control techniques involve addition of devices to the system in order to dissipate the energy imparted by earthquake motion (for a survey of such techniques see e.g. [1–۴]). Frictional based dampers are one class of such devices which dissipate the energy through frictional mechanism caused by two solid bodies sliding relative to each other. A conventional frictional damper compromises a frictional sliding contact surface and a clamping mechanism that produces normal contact force on the surface and heavily relies on coefficient of friction between surfaces. In a passive frictional damper, the clamping force of the damper and consequently the slippage force is a pre-determined constant value selected by design. If the axial force in the damper which is usually placed in a bracing system overcomes the static frictional force, the passive damper starts to slip and a considerable amount of mechanical energy can be transformed to heat energy and dissipated.