Dynamic Response Control of a Building Model

Abstract

With the adevent of modernization and improved materials, use of lighter and exible structures have been increased in day to day construction. These structures are susceptible to the dynamic loadings like Wind, Ground Excitation, etc. Therefore, it is essential to determine dynamic properties of the structures like Natural Frequencies, Time Period, Mode Shapes and Damping to understand its importance and in uence on dynamic behaviour of the structures. Apart dynamic response of structure due to dynamic loading expressed in terms of Displacement, Velocity and Acceleration in the structure are also equally important to study as they are directly related to the damage of structure. Dynamic properties and dynamic response of any structure can be obtained by preparing a suitable model of the prototype structure and testing it using shake table facility. Dynamic properties of a model can be evaluated experimentally through Free and Forced vibration tests, while dynamic response of a model can be determined by Forced vibration test only. Structures with certain properties of mass, stiffness and damping leads to undesirable dynamic response which may eventually cause damage to the structure. It is important, in such cases, to control dynamic response of structure by some scietific way. Various researchers have evolved mechanisms to control structural response that are broadly catogerised as Passive, Active and Hybrid Systems. Passive systems are different than Active systems as earlier system requires no external power to control structural response while later system does. Hybrid systems exploits features of both passive and active systems. Passive sytem being economical were exploited first followed by Active and Hybrid systems. Good amount of research work have been carried out on "Passive Control if Structures" where in various types of passive damping devices like Viscous Dampers, Visco-elastic Damper, Metallic Yield Damper, Friction Damper etc. are used in the structure. Prior to these researcher has attempted Bracing systems and Base Isolation systems to the structural systems to control structural response. Present study is an attempt to assess efficacy of Passive Systems-Bracings and Tuned Mass Dampers attached to test model simulating Multi Degree of Freedom(MDOF) system, experimentally. A MDOF test model made up of aluminium is fixed to unidirectional shake table. Dynamic response of model is captured using Accelerometers, Data Acquisition system and LabVIEW on Computer system. A free vibration and forced vibration test is conducted on MDOF test model without passive systems(Bare) to determine dynamic properties as well as dynamic responses at oor levels. A MDOF test model with different types of bracings like V-type, Inverted V-type, Eccentric, Concentric, etc. used at each oor area tested for forced vibration test to assess efficiency of bracing systems to control structural response. Apart, Single and Mutliple Tuned Mass Damper are attached at various oors of MDOF test model to establish efficacy of Tuned Mass Damper systems subjected to excitations. Comparison among Bare test model and test model with different types of Bracings and Tuned Mass Damper are carried to establish the efficacy of the later systems. It has been found that Inverted V-type bracing configuration yields highest increment in damping value of MDOF test model and hence shows reduction in dynamic responses. A MDOF test model with single TMD shows maximum reductuon in responses when it is placed at roof level of the test model. A multiple TMD wherein TMD is placed at roof and immediate bottom oor level each yields maximum reduction in dynamic responses.