This paper presents modal parameter identification results of two half scale reinforced concrete (RC) portal frames experimentally tested under quasi-static cyclic loading. One of the RC frames is without infill and the other one is with hollow-fired clay brick infill. The frames are progressively damaged in in-plane direction by applying increasing drifts by a displacement controlled actuator at the floor level. At each pre-determined damage states (levels), the actuator is detached from the specimen, and dynamic tests are performed. In-plane dynamic excitation used for modal identification is applied by an electro-dynamic shaker placed on the slab level. Besides, impact hammer and ambient vibration tests are also used. NExT-ERA, EFDD, and SSI-Data are the modal identification techniques used for modal parameter estimations. The purpose of the paper is multi-fold: (i) identify modal parameters of code conforming RC frames with and without infill walls at different damage levels, (ii) follow the evolution of damage level vs. associated damping ratio estimations which can potentially be used for reference-free damage level detection, and (iii) quantify the effect of broadband excitation provided by an offline shaker tuning technique on modal identification results.
Keywords Reinforced concrete frames • Infill effect • Modal parameters • System identification • Shaker tests
IntroductionCivil engineering structures are exposed to different external effects that change their dynamic characteristics. Damage can be defined as changes affecting the structural performance of a system. The fact that damage can alter stiffness, mass, and/or energy dissipation capacity of a structure, which in turn results in detectable changes in its vibration signature, is the underlying principle of vibration-based structural health monitoring (SHM) [1]. Operational modal analysis, which does not require measurement of input, is used as a technology to extract modal parameters as well as identifying damage in structures. Modal parameters to be extracted are natural frequencies, mode shapes, damping ratios. In the literature numerous surveys exist on the recent developments of structural health monitoring techniques applied to civil engineering structures based on changes in their vibration characteristics [2].An experimental study has been carried on two one-story one-bay half scale reinforced concrete (RC) frames with and without infill wall conditions under quasi-static lateral loads. At certain drift levels, the actuator was detached from the frames and a set of low level dynamic tests were conducted; the dynamic test program includes ambient vibration, impact and various white noise (WN) tests using a shaker. Using the dynamic data associated with certain damage levels, modal parameters of the RC frames were estimated. The aims of the study are to identify the modal parameters of code conforming frames with and without infill conditions as a function of different damage levels using three different output-only system identif...
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