Seismic Reliability of Steel Frames Systems Equipped with Viscose Dampers

Structures may undergo unexpected changes during the construction and assembly of materials and their sections, or may be affected by earthquakes of various magnitudes and mechanisms during their life time. Each of these changes may affect the possibility of structural failure. These variable parameters are examined as reliability. By the theory of reliability, uncertainties of the structural and non-structural parameters such as material properties, geometrical dimensions, and seismic inputs, etc. are taken into account. The theory of reliability with fragility curves shows which part of the model is more affected by uncertainties. These curves show the probability of passing a certain level of damage against seismic parameters.This paper presents a reliability analysis of the steel moment resistance structure equipped with viscous dampers applied by uncertainties in seismic input and structural properties such as ductility and fragility of beam and column, damping coefficient of dampers by obtaining fragility curves. Given the intensity and frequency of near-field earthquakes that cause large displacements in the structure and it is possible that the braces on which the dampers are mounted enter the nonlinear domain before activating or collapse of viscous damper, the analysis are examined only on the basis of far field earthquakes. Nonlinear incremental dynamic analysis (IDA) is applied to the 5 and 10-story frames modeled in OpenSees software under a set of 22 pairs of acceleration records. Also, to reduce the time and number of analyzes, the response level method has been used in this study. The number of scenarios required for the response level method is obtained from the box-Wilson method. According to the results obtained from the analyzes (mean and deviation from the failure level criterion), a second-degree surface procedure for mean and standard deviation has been internalized. The Monte Carlo method also simulated 10,000 fragility curves to determine the final fragility curve. The results show that increasing structural story has a significant effect on the uncertainty in the response of structures. Based on the results, considering uncertainties in 5 and 10-story structure reduce failure spectral acceleration (Sa) by 7.1% and 9.3% respectively. Besides, in spectral values corresponding to the first mode of 5 and 10-story structures, with considering the uncertainty, probability of failure increase about 52.4% and 74.7%, respectively. The results showed that considering the uncertainty in some parameters increases and others reduce the capacity of the structure; however, by considering uncertainty in all mentioned parameters simultaneously, it will reduce the capacity and increase the probability of collapse.