Masonry infill walls in reinforced concrete frames as a source of structural damping H. Ozkaynak 1 , E. Yuksel 2, * ,† , C. Yalcin 3 , A. A. Dindar 4 and O. Buyukozturk 5 1 Department of Civil Engineering, Beykent University, Istanbul, Turkey 2 Faculty of Civil Engineering, Istanbul Technical University, Istanbul, Turkey 3 Department of Civil Engineering, Bogazici University, Istanbul, Turkey 4 Department of Civil Engineering, Istanbul Kultur University, Istanbul, Turkey 5 Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA SUMMARY This paper presents the results of an experimental study on the determination of damping characteristics of bare, masonry infilled, and carbon fiber reinforced polymer retrofitted infilled reinforced concrete (RC) frames. It is well known that the masonry infills are used as partitioning walls having significant effect on the damping characteristics of structures as well as contribution to the lateral stiffness and strength. The main portion of the input energy imparted to the structure during earthquakes is dissipated through hysteretic and damping energies. The equivalent damping definition is used to reflect various damping mechanisms globally. In this study, the equivalent damping ratio of carbon fiber reinforced polymer retrofitted infilled RC systems is quantified through a series of 1/3-scaled, one-bay, one-story frames. Quasi-static tests are carried out on eight specimens with two different loading patterns: one-cycled and three-cycled displacement histories and the pseudo-dynamic tests performed on eight specimens for selected acceleration record scaled at three different PGA levels with two inertia mass conditions. The results of the experimental studies are evaluated in two phases: (i) equivalent damping is determined for experimentally obtained cycles from quasi-static and pseudo-dynamic tests; and (ii) an iterative procedure is developed on the basis of the energy balance formula- tion to determine the equivalent damping ratio. On the basis of the results of these evaluations, equivalent damping of levels of 5%, 12%, and 14% can be used for bare, infilled, and retrofitted infilled RC frames, respec- tively. Copyright © 2013 John Wiley & Sons, Ltd. Received 6 August 2012; Revised 13 September 2013; Accepted 20 September 2013 KEY WORDS: masonry infilled frames; CFRP retrofitting; damping; equivalent damping; energy methods 1. INTRODUCTION Past earthquakes and research demonstrated that the masonry infill walls have advantages in the improvement of energy dissipation as well as increase of stiffness and strength properties of reinforced concrete (RC) structures when they are placed regularly throughout the structure and/or they do not cause shear failures of columns, [1]. Damping in RC structures arises through energy dissipation by various mechanisms such as cracking of concrete and sliding between structural and nonstructural elements. Because it is very difficult and also unpractical to directly calculate the damping, experimental research is essential in order to determine a range of such energy dissipation characteristic. A review is given in the following: Buttmann [2] conducted an experimental study on the specimens with the dimensions of 100 × 200 × 11.5 cm and 24 cm. The horizontal sinusoidal excitation applied to the specimens was *Correspondence to: Ercan Yuksel, Faculty of Civil Engineering, Istanbul Technical University, Istanbul, Turkey. † E-mail: [email protected] Copyright © 2013 John Wiley & Sons, Ltd. EARTHQUAKE ENGINEERING & STRUCTURAL DYNAMICS Earthquake Engng Struct. Dyn. 2014; 43:949–968 Published online 14 October 2013 in Wiley Online Library (wileyonlinelibrary.com). DOI: 10.1002/eqe.2380
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