Friction-based structural control is an available strategy for reducing the seismic response of buildings. The friction dampers in such systems can be operated using passive and semiactive control. Passive dampers with constant, pre-defined capacity are effective and simple, but their adaptability to a broad range of frequency excitations is limited and their optimal configuration is complex. Semiactive control provides a means to vary the dampers’ capacity to their optimum levels in real-time, but time delays in the control action may affect their performance. In this investigation, a passive system is initially introduced in a multi-storey steel frame to identify a threshold of optimum control force demand related to the limits of the building’s elastic response. A new semiactive algorithm is then introduced to adjust the dampers’ capacity based on the current deformation state across the building. From simulations of the non-linear response of the frame, the semiactive system reduced the structural response to levels similar to the optimum passive control, with more uniform distributions of storey drift. The control system had optimum performance when a range of time delays was included to simulate different regulator mechanisms.

Introduction

A mechanism for dissipation of the seismic energy exerted in buildings during strong earthquakes is through damage at specific locations in the structure. The damage, in the case of moment resistant frames, develops in the form of plastic hinges at the ends of beam elements. This may induce degradation of the structural resistance, with associated costs of repair and aesthetic degradation. As an alternative mechanism, passive and semiactive control systems are of particular interest due to their high energy dissipation capability. By using such systems, the dissipative capacity of the structure is increased, without modifying its original design strength. An extensive description of control systems can be found in Housner et al. [1]. Symans et al. [2] give a good treatment of passive control and its applications, and Parulekar and Reddy [3] present the state-of-theart of passive systems. Description of semiactive systems and examples of applications are described by Morales-Beltran et al. [4], Casciati et al. [5], Spencer and Nagarajaiah [6], Symans and Constantinou [7], and Spencer and Sain [8]. Amezquita-Fuentes et al. [9] present a review of control laws implemented in semiactive systems. Passive control systems are activated by the action imposed by the main structural system. After the control device is installed, it has no ability to regulate itself under different ground motions. Control systems with frictional mechanisms (e.g., [10–۱۴]) are simple and costeffective. However, the optimum performance of friction-based passive control is given by a unique configuration of slip-load capacity and placement of the dampers [15]. Filiatrault and Cherry [16] noted different performance between systems with slip-loads that were either proportional to the inter-storey shear force or uniformly distributed, and proposed a design slip-load spectrum to determine the optimum slip-load directly. Dowdell and Cherry [17] proposed a proportional distribution of the dampers’ slip-load based on the structural deformation of the fundamental mode and the mass of the building. Apostolakis and Dargush [18] used genetic algorithms to identify the optimum capacity and placement of friction dampers in low-rise moment resistant steel frames. Min et al. [19] proposed the design of a single storey structure with friction damper based on a target equivalent damping ratio derived from the frictional hysteretic mechanism into a viscous damping mechanism at the steady-state response condition in the structure, which was subjected to harmonic ground motion.