Direction of Vibration
Friction Damper
A typical X-braced friction damper
Pinned Connections
Yielding Damper
Direction of Vibration
Installation of a typical viscoelastic (VE) damper
Tyler’s yielding steel bracing system
Semi-active Tuned Mass Dampers
Semi-active Tuned Liquid Dampers
Semi-active Friction Dampers
Semi-active Vibration Absorbers
Electrorheological Dampers
Semi-active Stiffness Control Devices
Magnetorheological Dampers
Semi-active Viscous Fluid Damper
Figure 8: Common semi-active control systems
Semi-active Control Systems
vibrations against winds and earthquakes, as Ability to well as ambient oscillations to improve structural Effective Suitability to Suppress Semi-active dampers possess some serviceability. These systems offer the advantages Adaptability to adapting Control Use for any Responses capabilities andon are often referred to as controllable Ground Motion of suppressing responses against a wide range Structure Control Against Wide Characteristics or intelligent systems. They have an additional Range of (figure 10). A typical fully Response Objectives of forcing frequencies Frequencies adaptive system which collects and process the adaptive active control system consists of three information about response of main structure types of elements (a) sensors (b) actuator, and and modifies the damper’s property based on (c) controller with a control system. The output this information (figure 9). A typical semi-active from sensors is feed in to controller (usually in control system comprises of vibration measuring the form of electrical signals) for processing the sensors, control computer, control actuator and information. The controller analyzes the data and a passive damper. The computer processes the generates suitable commands for the actuator, vibration measurements coming from sensors based on analysis. and generates the command for control actuator to modify the properties of passive damper Hybrid Systems according to requirement. In this way, semi-active dampers economically combine the advantage of Active control systems have two main limitations. both passive and active control systems. First, they require significant amounts of external power supply and complex sensing and signalActive Control Systems processing units resulting in high costs. Second, they require actuators capable of producing Passive systems are limited in their ability to large control forces. These limitations resulted adapt according to varying external excitations. in development of hybrid control systems Moreover, some passive systems (e.g. TMD and which combine the simple and reliable working TLDs) are only useful within a narrow range of mechanism of passive systems with the cuttingfrequency and may not be useful for response edge technologies for development of smart contributions from more than one vibration algorithms for active control. mode. On the other hand, semi-active devices are limited by the capacity of their component passive devices. Active response control systems meet these limitations by using electrohydraulic actuators which directly generate the optimum amount of control force based on actual Base isolation is a well-established technique of measured response of main structure. This passive control approach which tend to reduce control force serves as additional damping the energy transfer from ground acceleration force and helps in suppressing both response to structure. A structure mounted on a material
BASE ISOLATION SYSTEMS FOR SEISMIC RESPONSE CONTROL
Effective Control on Structure Response
Adaptability to Ground Motion Characteristics
Suitability to Use for any Control Objectives
Ability to Suppress Responses Against Wide Range of Frequencies
Figure 9: Advantages of active control systems Technology | December 2016 37