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    A capacity curve model for confined clay brick infills
    (Springer, 2016) Ozkaynak, H.; Surmeli, M.; Yuksel, E.
    Experimental studies have proven that clay brick infills, confined with carbon-fiber-reinforced polymers (CFRP) in reinforced concrete (RC) frames, have some advantages in terms of stiffness, strength, energy dissipation capability and damage intensity. Owing to these advantages, existing infill walls in RC frames may be retrofitted with CFRP strips, especially in low-rise buildings in earthquake-prone areas. There is a gap in the literature concerning their behavior model, for use in structural analysis. A piecewise linear capacity curve model called DUVAR'' is proposed here, which estimates the envelope of force-vs.-displacement hysteresis, depending on the data compiled from the literature and the completed experimental studies. A nonlinear shear spring element is utilized in the model to represent the bare and retrofitted infills. The ultimate shear strength and the corresponding displacement, the ratio of cracking stiffness to initial stiffness, the ratio of ultimate strength to cracking strength, and the ductility ratio are the five key parameters of the model. The model is validated against the experimental results of two sovereign studies. Finally, the model is employed in the performance evaluation of an existing three-story RC building to exemplify its straightforward application.
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    Evaluation of Integration Techniques Used in PsD Testing Methodology
    (European Assoc Structural Dynamics, 2014) Ozkaynak, H.; Guney, A. K.; Yuksel, E.
    Pseudo dynamic testing (PsD) methodology is used to simulate earthquake effects on the structures or structural components and it consists of both the analytical and experimental parts with a coupled interaction. The dynamic equilibrium equation is generated and the displacement vector to be applied to the specimen in the next step is calculated by using an appropriate numerical integration technique. The overall success of pseudo dynamic tests not only depends purely on the resolution of the measurement devices but also highly depends on the sensitivity and convergence of the integration techniques used for the solution of the dynamic equation of motion. In this study, the success of the central difference method, operating splitting method (OSM) and alpha-operating splitting methods (alpha-OSM) are evaluated by means of several PsD simulations performed on a steel single degree of freedom (SDOF) system having three alternative constitutive models. The main parameters are the integration technique, time intervals and constitutive models. The advantages of the techniques are compared in terms of the test duration and convergence capability. In conclusion, for all behavior types CDM and OSM methods can be used with the time interval which is equal or larger than the input earthquake data. This means great saving of time during the PsD test and it increase the overall success of the experiment.
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    Masonry infill walls in reinforced concrete frames as a source of structural damping
    (Wiley-Blackwell, 2014) Ozkaynak, H.; Yuksel, E.; Yalcin, C.; Dindar, A. A.; Buyukozturk, O.
    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 formulation 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, respectively. Copyright (c) 2013 John Wiley & Sons, Ltd.