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Abstract
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Non-structural components (NSCs) in the majority of the FE models are commonly considered as a concentrated/
distributed mass, and their stiffness along with damping ratio is ignored. Likewise, NSCs have significant efficacy
on the accurate vulnerability assessment and select an appropriate structural system versus the seismicity of the
area. The chief aim of this research is to present a simple theoretical method in conjunction with a practical
empirical technique for assessing the influences of NSCs on the modal properties and vulnerability of buildings,
exclusively steel structures. In this regard, the ambient vibrations were measured on four buildings with
concentrically steel braced frame structural system under the construction process in three independent stages:
(1) after the erection of the structural and skeletal systems; (2) after the construction of the interior and exterior
partition walls; (3) after the installation of the facade and parapet elements. Utilizing two signal processing
techniques (i.e., floor spectral ratio and random decrement method), the acquired microtremors were analyzed to
extract the modal properties and compute the vulnerability indices of the structures. It is perceived that the
values of the modal properties of the steel structures, namely, natural frequency and damping ratio, have
considerably increased during the construction process with taking the influence of NSCs into account. In
addition, the obtained results disclosed that the vulnerability index has significantly decreased in the second
stage over the first one. However, it has not noticeably fluctuated in the third stage over the second one.
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