فهرست مطالب سامان راحت دهمرده

Nonlinear time history analysis is recognized as the most appropriate tool for assessing the real behaviour of structures during seismic excitations. Validity rate of obtained results from this analysis significantly depends to the modeling, details and defined parameters. One of the main aspects of dynamic modeling is the consideration of natural viscous damping as well as value of damping ratio (ξ), which during last years evaluating the effects of these factors on nonlinear responses of moment-resisting steel frames has been limited, and Rayleigh damping model with ξ of 5% was used by researchers. Therefore, in this study attempt has been made to examine the impacts of value and modeling approach of natural damping on nonlinear responses of moment-resisting steel frames. For this purpose, a full scale 4 story steel structure which tested on shake table in 2007 has been considered as reference and modeled by OpenSees software. Natural damping has been defined with three methods; Rayleigh damping, mass-proportional damping and stiffness-proportional damping, for five different values of damping ratio (ξ=0.01, 0.02, 0.03, 0.04, 0.05). After conducting the nonlinear time history analyses, difference of obtained structural responses compared to the experimental responses has been investigated, and then errors of them have been extracted. Results indicate that reduce of damping ratio leads to the notable decrease of responses, specially, for story shear and overturning moment. The use of 5% damping ratio for nonlinear dynamic analysis of low rise moment-resisting frames is not appropriate and in most of cases leads to the underestimate and unreal results. Besides, it should be noted that the mass-proportional and Rayleigh damping models have higher accuracy in comparison with stiffness-proportional damping model, and these models show lower error.

Due to the lack of access to the data of three rotational components of earthquakes, seismic analysis of new buildings as well as assessment of the vulnerability of existing structures are usually carried out only by applying the translational components of earthquakes. Iranian Standard 2800 proposed an accidental eccentricity for considering the earthquake rotational component effect in the seismic analysis of building structures. The present investigation is focused on the effects of earthquake rotational excitation on the seismic response of buildings having various dynamic properties which situated on a rigid foundation. In addition, adequacy of the accidental eccentricity of 5% recommended by seismic design code for inclusion of the earthquake rotational component impact in the non-linear time history analysis of buildings is studied, as well. To achieve this, a large number of one-story torsionally stiff and flexible building models with a wide range of lateral vibration periods (T=0.05 to 2sec) and three different values of inherent eccentricity of 0, 15 and 25% were modeled. These models were once excited by the translational components of ground motions and once again by both translational and rotational components of ground motions. The building models were re-analyzed after applying the 5% accidental eccentricity based on the procedure presented by Standard 2800 (shifting the center of mass in the negative and positive directions by 0.05 of the plan dimension). For conducting the non-linear time history analyses, a number of earthquakes were selected and the rotational records for these events were generated by use of an indirect single station method based on the seismic wave propagation in an elastic and homogeneous medium. In total, over than 2600 nonlinear dynamic analyses have been conducted in this numerical research. In order to determine the role of earthquake rotational excitation in the seismic behavior of  buildings, the variations of displacement response for the left and right sides of diaphragm and the torsion of diaphragm about the mass center due to the effect of rotational component were evaluated. By comparing the results obtained in this study, it is found that the rotational component has a substantial influence on the structural responses, which this effect is a function of the fundamental dynamic characteristics of system such as uncoupled rotational to translational frequency ratio, lateral vibration period and irregularity. The displacement of diaphragm can be increased up to 50% when the rotational component of ground motion is included in the seismic load combinations. Decreasing the frequency ratio leads to increase of the rotational component effect for the stiff buildings with short periods, while in the other cases reduces the growth of displacement due to the rotational component. Furthermore, results indicate that the accidental eccentricity of 5% cannot increase the seismic responses as much as the earthquake rotational motion, and leads to unreal and underestimate results for the most of lateral vibration periods. Thus, the current Standard 2800 approach cannot be considered as an appropriate alternative for considering the accidental torsion induced by the rotational component of ground motion, and it seems that this approach needs to be re-evaluated.

Nowadays, based on the rapid growth of population, urbanization and industrialization of cities, the huge amounts of solid waste are generated daily in developing countries, which management of these wastes has become a serious challenge for environmentalists and municipal officials. A considerable proportion of the solid waste is related to the plastic waste, which just a little portion of them will be recycled. One of the alternative ways for recycling plastic wastes is to use these wastes in the concrete productions. So, assessing the engineering properties of this kind of concrete for using in different civil targets is essential. For this purpose in the current paper, attempt has been made to study the effects of adding various types of plastic waste on the fresh and hardened properties of concrete by evaluating the results of experimental data. Although results show that the addition of plastic waste particles in the concrete mixture leads to the decrease of mechanical properties, but this composite concrete can be used in the several structural and non-structural applications and also considered as a practical idea to entrepreneurship.

In the recent years, study on the gradual deterioration of concrete under effect of corrosive factors such as acid attacks has been one of the most important research challenges in the concrete technology. On the other hand, in order to achieving the sustainable development, recycled concrete production by using of building and non building wastes, is interest for researchers more than past. So in this experimental study, for assessing the performance of self compacting concrete containing glass particles under sulfuric acid attack, 9 mixtures comprising 0, 5,10,15 and 20% glass particles as fine and coarse aggregates were considered. To determine fresh and hardened behavior, Slump, T50, V-funnel, J-ring, L-box and compressive and flexural strength tests were performed. In addition, in order to specify the durability of concrete samples, after placing them in the corrosive sulfuric acid solution with PH=1.5 for 30 and 60 days, mass loss and compressive and flexural strengths tests were carried out. Results showed that with increasing glass particles, fluidity, passing ability and dispersion of self compacting concrete increased. After 60 days immersion in sulfuric acid solution, compressive strength reduced for all samples. By adding glass particles, durability of self compacting concrete improved significantly compared to the control mix. Mass of all samples decreased after corrosion, which samples containing glass showed better performance in the mass loss compared to the control sample.