جستجوی مقالات مرتبط با کلیدواژه "حوزه دور" در نشریات گروه "عمران"

To make structures resistant to earthquakes, various systems are used, one of the most important of these systems is a steel Moment frame with a steel shear wall, which has been used as one the systems since the 1970s. Steel shear walls are usually made in two types, stiffened and unstiffened. The idea of corrugated steel shear walls was proposed as a replacement for stiffened shear walls. These plates have high buckling resistance due to their out-of-plane stiffness. This research investigated the seismic behavior and vulnerability of steel structures with horizontally and vertically corrugated steel shear walls using ABAQUS nonlinear analysis software. For this purpose, after validation of the modeling by controlling with an experimental study, 280-time history analyses were conducted. Then fragility curves were produced on 3 and 10-story structures.7- acceleration records of the far-Fault earthquakes and 7 acceleration records of the near-fault earthquakes were used to generate the fragility curves. The results showed the 3-story structure suffered damage at a lower acceleration compared to the 10-story structure. The structure was more fragile under near-fault rather than far-fault earthquakes. The highest percentage of damage reduction in the far-fault earthquakes compared to the near-fault occurred in the 10-story structure at the life safety performance level (LS). Further in trapezoidal samples, by changing the direction of placement of corrugation plates from horizontal to vertical, the probability of wall failure decreased at different PGA levels.

Recent growth in the construction of wind farms with concrete piles in seismic areas with liquefaction potential has necessitated the evaluation of the seismic performance of these structures. In this paper, the effect of liquefaction on the seismic response of wind turbines supported by reinforced concrete mono-pile is investigated. Nonlinear dynamic analysis has been performed by finite element method in OpenSees software. Beams on a nonlinear Winkler foundation method was applied. The responses of reinforced concrete mono-pile foundation was studied for two sets of far and near field earthquake record and four different groups were considered for liquefied sandy soils with different coefficients of internal friction, shear wave velocity, relative compaction percentage and porosity. The results showed that with increasing the coefficient of internal friction and soil compaction rate, the amount of excess pore pressure of the soil adjacent to the RC mono-pile decreases. Also, as the thickness of the liquefied layer increases, the pressure of the extra pore water around the mono-pile will decrease but the displacement of the mono-pile will increase

In this study, the effect of isolators positioning at three Levels and different arrangements on seismic response of RC buildings are investigated. For this purpose 18 RC building of 4, 8 and 12 story with and without lead rubber bearing (LRB) isolators were selected. The LRB isolators positioned at three Levels and five different arrangements were modeled in Opensees software. The near field and far fault earthquakes were added to the frames and incremental dynamic analysis was performed. The fragility curves base on inter-story drift ratio as well as the IDA curves base on maximum inter-story drift ratio, maximum base shear, maximum roof displacement and acceleration versus peak ground accelerations (PGA) were plotted and compared. The results showed that among the isolated structures, the isolator positioning at the level of below the first floor (type 1 and type 2) had the best performance in reducing responses. The positioning type 1 (MSI-1) resulted the best decreasing in inter-story drift ratio and base shear. In addition, this type of isolator had the best increasing the PGA according to median fragility between the different types of the positioning levels. The recommended type of isolator had the best performance, especially in high rise buildings in severe damage levels.

The appreciation of buckling restrained brace systems has increased over the past two decades. The relatively high energy losses and optimal ductility are the characteristics of this system and the l displacement control as well as the residual displacement is challenging issues under the earthquake. In this paper, the behavior of simple frame structures with buckling restrained braces with and without viscous dampers in intermediate and high rise buildings under the influence of   near fault and far fault records was investigated. Initially, the structures were analyzed using a spectral dynamical analysis method and valid regulations. Then nonlinear model of structures was developed in PERFORM-3D software and nonlinear time history analysis was performed. The response of the structures was examined and compared. The results show that the inter-story relative displacement in the structure with buckling restrained braces and fluid damper under far fault earthquakes compared to without damper case decreases by about 30%, with the corresponding value under the near-earthquake of about 15%. The maximum resistive force of the liquid damper appears at the moment of the most inter story relative velocity, and this is evident in the buckling restrained brace in the most inter story relative displacement. Due to the phase of relative inter story displacement and relative inter story velocity, the use of a hybrid system can lead to better control of structural responses.

The unpredictable nature of earthquake has led to engineers to the statistical and probabilistic studies for investigating of the effects of earthquake phenomenon problem. The movement recorded of the ground under influence of earthquakes in near fault zones are different from far fields. The pulse phenomenon in the history of acceleration, velocity and displacement is one of the characteristics that distinguishes near and far field earthquakes. In this research, after scaling the time histories of accelerations, structural analysis of reinforced concrete bridge with four 22 meters openings has been performed by dynamic analysis of liner history. Then, the results in the form of internal forces of the members and displacements in a particular joint under the time history of accelerated incidents are presented. The result of investigating the effects of bridge distance from faults on internal forces of columns due to earthquake showed that axial forces including compressive, tensile and torsional moment in columns have the highest value when near field earthquake occur. Also, the result of evaluating the effects of bridge distance from faults on internal forces of deck due to earthquake showed axial force and bending moment at time of far field earthquake happen have highest value. Although, this amount is dependent on severity of earthquake.

In regions that are susceptible to earthquake occurrence, designing large and engineering developed structures such as tall buildings, dams and bridges most often requires quantitative dynamic analysis. Engineers discuss important questions on possible magnitude of earthquake in the zones under construction and require knowledge on the movements or the spectrums enforces and/or defining parameters. Time history analysis is the most natural analytical method compatible with the physical behaviors in the course of earthquake in a way that structures are performed by including the effects of earth acceleration as a function of time being applied in the structural base. The accelerograms which are used in analyzing the chronological history in determining the impacts of earth movement must reveal the actual movements of earth in the construction site of the structure during earthquake; As a result, selecting accelerogram is very important in analyzing the chronology. Unfortunately, the point that suitable records must be selected with respect to the conditions that govern seismic source, the geological characteristics, tectonic distance from fault and the largeness of the zone is usually neglected. Our country is located in one of the most active seismic regions in the world. According to the scientific information and documents, Iran is one of the riskiest regions of the world and is exposed to serious damage from earthquake. In the recent years, there has been an earthquake with large physical and financial casualties in one of the regions of the country once every five years in average. Presently, Iran is on top of the list of countries where earthquake is associated with life casualties. It is very difficult to fully prevent damages caused by high magnitude earthquakes. This is especially important in the city of Tehran with the very large population that lives in it, and is encircled by several active faults. The main goal of this research is to prepare a suitable list of remote range strong motion accelerograms to be used in nonlinear analysis in Tehran. The main focus of this research is to study all parameters that are effective in selecting suitable strong motion accelerogram in Tehran and for this purpose, 1000 strong motion accelerograms from earthquakes that occurred in Iran between 1978 through 2007 were studied and the entire parameters effective in selecting suitable strong motion accelerograms for the city of Tehran including distance, magnitude, frequency contents, earthquake mechanism, soil and specifications of earth strata were reviewed. Ultimately, a suitable list of strong motion accelerograms is presented to be used in nonlinear three-dimensional analysis. To achieve this goal, the geological and geotechnique features of the region were studied. In addition, the mechanism of active faults in the region were studied as well and by considering the parameters of magnitude, the focal depth, the distance of registry stations to the earthquake place, the geology studies of the records registry stations, mechanism and the frequency contents of a series of the accelerograms are suggested to reveal the actual movement of earth in Tehran as much as possible; if modeling and chronological history analysis are bi-dimensional, it will be possible to use 28 categories alongside and orthogonal with the faults in the suggested list. It should be noted that to analyze the chronology, only those accelerograms were used which could be scaled with the spectrum of the standard plan of the region and prove compatible with the frequency period of the structure. Minimum moment magnitude in the mentioned list is equal to 5.6 and maximum moment magnitude is 7.4. The mean magnitude in this list is 6.45. The mean maximum earth acceleration for the list was equal to 0.191g. The dominant mean period in the list is 0.64 seconds. The dominant frequency in this collection of accelerogram includes a large frequency range; therefore, suitable stimulation could be anticipated from this list for various structures.

Reinforced concrete structures are one of the most commonly used structures all over the world. However, the high nonlinear behaviour of this kind of structures still needs more research, e.g to shed light into the effects of nonlinear modelling and the structure characteristics. One of the most common methods to predict the nonlinear response of concrete structures is the simplified nonlinear spectra. The nonlinear spectra have been widely used in the seismic design and rehabilitation procedures e.g, ATC40 and FEMA 274. A set of closed-form formulas have been proposed in this manner to predict the strength reduction factor for a given period and ductility. The design and rehabilitation procedures can significantly simplified by using this kind of closed-form formulas. The aim of this paper is to evaluate the seismic behaviour of a set of 4620 single-degree-of-freedom (SDOF) oscillators, which was taken into account based on their period, damping and nonlinear backbone curve parameters. Eleven different periods, three damping ratios, five cracking states, seven ductility ratios, five hardening slopes and two collapse negative slopes were taken into account to cover a wide range of nonlinear behaviour of oscillators. The all combination of nonlinear characteristics with eleven periods and three damping ratios produces 4621 different oscillators to be investigated.The SDOF oscillators were analyzed for two sets of ground motion records which are representative of far and near field records. The far-field records contain 30 strike-slip records with moment magnitude of 6.5 to 6.9. The records are corresponding to the firm soil without any directivity effects. The near-field set contain 31 strike-slip records corresponding to four different earthquake events. They were all recorded within 16 kilometre of the earthquake epicentre. The incremental dynamic analysis was employed to calculate the system demand ductility in a wide range of earthquake intensity levels. The relationship between the strength reduction factor and the ductility factor was then derived for all considered SDOF systems. The results show that the natural period of vibration as well as the primary concrete cracking can significantly influence on the predicted strength reduction factors.The incremental dynamic analysis was employed to calculate the system demand ductility in a wide range of earthquake intensity levels. The relationship between the strength reduction factor and the ductility factor was then derived for all considered SDOF systems. The results show that the natural period of vibration as well as the primary concrete cracking can significantly influence on the predicted strength reduction factors. The incremental dynamic analysis was employed to calculate the system demand ductility in a wide range of earthquake intensity levels. The relationship between the strength reduction factor and the ductility factor was then derived for all considered SDOF systems. The results show that the natural period of vibration as well as the primary concrete cracking can significantly influence on the predicted strength reduction factors.