Viscous dampers (VDs) are effective and widely used passive devices for the protection of civil structures, provided that appropriate design is carried out. For this purpose, optimal design and optimum distribution of VDs method are presented for a shear building under the critical excitation by using random vibration theory in the frequency domain. In the optimization, by using Differential Evolution (DE) algorithm and the top floor displacement are evaluated as objective functions taking into consideration upper and lower limits of VDs damping coefficients, so that optimal damper placement and properties of the shear building can be determined. In this design, the VDs-shear building system is tested under the three different ground motions being compared to some methods in the literature and uniformly distributed VDs placed at each story. It is shown that the results of the study are both compatible and very successful in reducing the response of the structure under the different ground motions.
In this study, the absorption capability and the weight of various radiation-shielding materials were evaluated, for applications as alternatives to lead garments. Toxicity, atomic number, density, K-edge absorption energy and availability of elements that can serve as an alternative to lead, including tin, antimony, bismuth and tungsten, were considered. The attenuation coefficients of these elements were determined using the XCOM software package, and these metals were mixed with polymers at 50, 70, 80 and 85 % mass ratios. It can be concluded that all of the new shielding materials used in the study can be used for a diagnostic range of X-rays. However, they were compared with the commercial lead garments in terms of weight and attenuation coefficient; the 85 % samples were lighter than a 0.5-mm lead garment and provided superior radiation protection, which demonstrates its potential for commercial applications.
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