steel buildings

Use of passive control systems causes reduction in seismic demand and prevents damage to the main components of the structure. Yielding dampers are among the common tools used for dissipation of earthquake energy entering the structure. The main goal of the present research is introduction of a novel pseudo elliptical yielding damper for improvement of the seismic performance of the existing steel structures. Considering the impact of geometric parameters of the pseudo elliptical damper on its stiffness and strength, a precise numerical study was performed on the ratio of diameter to thickness and other dimensions of the damper in this research.  For evaluating the impact of proposed damper on the seismic performance of existing steel buildings, use was made of three benchmark structures with 3, 9 and 12 stories which were retrofitted by this type of dampers. Also, the nonlinear time history analysis has been performed using the near field and far filed accelerometers to evaluate the analyses results at different seismic states. The results of numerical analyses indicated the good performance of propose pseudo elliptical yielding damper in terms of dissipating the earthquake energy entering the structure and reduction in the seismic responses of retrofitted benchmark buildings by this type of dampers. It was found that on average, the maximum inter-story drift in the 3, 9 and 20 story benchmark buildings were reduced by 66, 69 and 67%, respectively.

The fragility curves are used to indicate the probability of damage to buildings during the earthquakes with different intensities. The main objective of this study is to present a new design procedure for exploring the effectiveness of using viscous dampers in the seismic rehabilitation of steel structures using the seismic fragility analysis. In addition, a straightforward formula is presented to determine the effectiveness of seismic rehabilitation of steel structures with viscous dampers. The inter-story drift as one of the effective parameters for assessing the safety of buildings after an earthquake is used in this study as a damage index. To compare the damage probability of buildings with and without damper, three 3, 9 and 20-story benchmark buildings are used. Furthermore, the earthquake records corresponding to three levels of seismic hazard are used for the nonlinear dynamic analysis. Comparison of the fragility curves between the steel structures controlled and the buildings without the damper shows a significant decrease in the damage probability after the rehabilitation with the viscous dampers. The results of numerical analysis showed that although seismic rehabilitation in all benchmark buildings led to the improved seismic performance, the decrease in the response of the 9-story structure is higher compared to the other buildings.

The first and the most important step in preparation of seismic retrofit plan for existing buildings is the analysis of their vulnerability by conducting retrofit studies. However, most of the existing buildings in Tehran are in urgent need of retrofit studies due to reasons such as high seismicity, upgration of building and seismic codes, the abundance of old buildings and so on. In these studies, it is very important to identify the seismic status of the buildings which are in the first priority of seismic retrofit, especially the ones with public use like schools. A seismic risk prioritization technique for steel buildings is proposed in this paper, using a risk assessment hierarchical structure and fuzzy inference system. Afterward, this technique is applied in a case study, validating the results obtained for the steel buildings of the schools in Tehran. At the first of the prioritization process, the required information of the buildings is classified according to the designed hierarchical structure; Then, after quantification of the qualitative data and the fuzzification, the data are modeled, evaluated and defuzzificated based on the fuzzy inference system; This process is performed for all stages of the hierarchical structure to obtain the seismic risk parameter. After the qualification, this parameter indicates the risk of buildings and their requirement for retrofit or rehabilitation. The results that are distinguished by urban districts, determined the high-risk steel school buildings requiring retrofit studies and have shown the role of each effective parameters on the seismic risk of the buildings.