Response Analysis of Infill Walled Building Frame with Tuned Mass Dampers as Soft Storey

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IJSTE - International Journal of Science Technology & Engineering | Volume 3 | Issue 09 | March 2017 ISSN (online): 2349-784X

Response Analysis of Infill Walled Building Frame with Tuned Mass Dampers as Soft Storey Arsha G Fernandez PG Student Department of Civil Engineering Mar Baselios College of Engineering, Trivandrum

Dr. T Sundararajan Scientist/Engineer Department of Civil Engineering VSSC

Tisny D.B Professor Department of Civil Engineering Mar Baselios College of Engineering, Trivandrum

Abstract Tuned Mass Damper (TMD) is a passive control device which is simple, inexpensive and a reliable means for suppressing undesirable vibration of structures caused by harmonic or wind excitation. The effect of TMD with optimum parameters (frequency and mass ratios) is studied. In the present paper, a soft storey constructed at the top of a building is treated as a TMD and its usefulness in response reduction is evaluated. Analysis and modeling are done using FE software developed by VSSC, FEASTSMT and the building is subjected to an arbitrary acceleration as base excitation to record the response at top storey. TMDs with mass percentages of 2 and 3 are considered and the results are compared between buildings with and without TMD. Keywords: FEASTSMT, Response reduction, TMD, Soft storey, Infill Walls ________________________________________________________________________________________________________ I.

INTRODUCTION

The major goal in structural engineering is to maintain the structural stability against the effect of various forces acting on the structure. The objective of seismic analysis of structure is to mitigate or reduce the seismic risk. Seismic risk refers to various factors such as seismic hazard, exposure and vulnerability. TMDs are the simplest form of vibration absorbers which are relatively easier to implement. Tuned Mass Dampers are often used if the excitations are almost periodical and the structural response is dominated by its fundamental mode. By adding an auxiliary mass where the stiffness and damping are designed properly, the building vibrations can be substantially controlled. Hence to reduce the seismic response, optimum parameters needed to be considered for design. Mass ratio, frequency ratio and damping ratio are the criteria to be considered. TMD proves to be efficient in arresting acceleration and displacement responses of building when the optimum parameters are taken into consideration. For TMD to be effective in structures with high damping ratios, large mass ratios must be employed. Top floor with adequate stiffness and damping can be considered as a vibration absorber for the bottom floors. In order to obtain the optimum parameters of TMD single and multiple degrees of freedom structure are considered. For an un-damped structure, the tuning ratio: Tuning ratio, ‘f ‘= 1/ (1+Îź) Damping ratio, ‘Ξ’= √đ?œ‡/(1 + đ?œ‡) For a damped structure, f=

1

[1 − đ?›˝ √

1+đ?œ‡

Ξ=

đ?›˝ 1+đ?œ‡

+√

đ?œ‡ 1+đ?œ‡

]

đ?œ‡

1+đ?œ‡

For a MDOF system, tuning ratio ‘f’ is nearly equal to tuning ratio of SDOF system for mass ratio of ¾φ and damping ratio is equal to that of SDOF system multiplied by φ. i.e. f=

1

[1 − đ?›˝ √

1+đ?œ‡đ?œ‘

đ?œ‡đ?œ‘

1+đ?œ‡đ?œ‘

Ξ= đ?œ‘[

đ?›˝

1+đ?œ‡

+√

đ?œ‡ 1+đ?œ‡

]

]

where Âľ is mass ratio, β is damping ratio of structure and φ is the amplitude of first mode of vibration for a unit modal participation factor. By using the above formulas, optimum TMD parameters can be obtained which in turn results in considerable response reduction.

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