تحلیل تاریخچه زمانی

The behavior of a structure changes when it interacts with underlying soil, which acts as a flexible base, as compared to a rigid base condition. Given the importance of performance-based design, the direct method for soil-structure interaction (SSI) problem is essential for accurate characterization of the non-linear behavior of the soil and the structure. Using direct method in FE modeling of SSI problem poses several challenges. These include accurately representing the semi-infinite soil domain, accounting the inertia effects, radiation damping, and wave propagation, and properly applying earthquake ground motions at the boundaries, which coincide with the energy-absorbing boundaries. This article presents a precise and practical approach to tackle these difficulties, which is well-suited for implementation in FE software such as ABAQUS. This approach utilizes the combination of the domain reduction method (DRM) and Lysmer energy-absorbing boundaries. The accuracy of the model is assessed by some validations and compared by traditional Winckler's approaches; results showed the superior accuracy of the proposed approach. In addition, this method is used to demonstrate its efficiency in solving typical engineering issues. Furthermore, to demonstrate the capabilities of this method in solving engineering problems, seismic analyses of three types of concrete structures (low, mid, and high-rise) under various seismic scenarios are investigated. Seismic frequency content, soil type, and other parameters are examined. The analysis results demonstrate the substantial impact of mentioned characteristics on the structural reaction. In particular, the research findings suggest that low-rise structures show greater responses in comparison to other structures in this study.

The most comprehensive analysis methods are non-linear methods that require a lot of calculations. In this research, the endurance time method is used, that is a new dynamic method in which the need for calculations is reduced. In the endurance time method, the structures are subjected to specially designed acceleration functions and their response at different performance levels is estimated by each of the unit response history analyses, thus, significantly reducing the required computational demand. The design of rotational friction dampers in the studied structures was done based on the seismic performance index by endurance time method, and the sliding force of these dampers was uniformly distributed in the structure. The results of this research for two structures of 3 and 9 floors showed that the shear of the base is between 60 and 100%, as expected, considering that the structure was a moment frame at the beginning and had a different target time, and then braces were added to it. Increased. Due to the addition of the damper to the system, taking into account the relative increase in input energy, as expected, the amount of depreciated energy is between 10 and 97%. In relation to the study of drift, the reduction of the values in the floors was high, which was reported from 5 to more than 50% according to the results

This paper presents an efficient numerical analysis method called the Newton-Cotes-Hermite-Four-Point (NCH-4P) method for the time history analysis of structural systems with one and multiple degrees of freedom under earthquake effect. The method combines the numerical integration formula of the Newton-Cotes four-point method with the Hermite interpolation formulas to form a new algorithm for solving the vibration equation. The method can handle both linear and nonlinear systems, as well as different types of loading, such as external forces and earthquake excitation. The method is developed for the first time for the analysis of linear and nonlinear damped and undamped structural systems with one and multiple degrees of freedom. The method shows remarkable performance superiority in terms of accuracy, speed, convergence and simplicity compared to the pseudo-analytical Newmark-beta method and the semi-analytical Duhamel integral method. The method modifies the differential equation of motion to have a suitable form for numerical integration. Unlike the nonlinear Newmark-beta method, the method does not require an independent process such as Newton’s iteration to account for nonlinear effects; instead, a series of simple repeated calculations leads to the convergence of the response in nonlinear behavior. The numerical results demonstrate the efficiency of the method in estimating the response of systems under the famous EL-Centro record.

Despite the knowledge of steel shear walls for many years, not much attention was paid to it. Steel shear walls without stiffeners and with stiffeners have been used in America in recent years. This system is 50% cheaper compared to the bending frame. After the events of September 11, a number of scientists were thinking of creating resistant and impervious structures against explosive and seismic loads economically by combining this system and the concrete shear wall system. Steel shear walls are easier to implement. Also, the accuracy of the work is at the level of normal executions, and by observing it, the reliability coefficient is many times higher than that other types of systems. The execution speed of steel shear walls is high, and because of this, the execution costs are reduced. Also, the efficiency of the shear wall system is more and more suitable than all the advantages of centralized bracing systems such as X and V shape and off-center steel bracing systems. The resistance against the overturning anchor caused by the lateral loads and the horizontal load of the floor is the most important task of the steel shear wall. The constituent members of the steel shear wall system include a steel plate wall, two boundary columns, and a floor horizontal beam. Also, the horizontal beams of the floor are used as transverse stiffeners in the sheet beam. The goal of centralizing the steel shear wall system is that the beams and columns remain in the elastic range. In this article, five-, ten-, and twenty-story buildings with steel shear walls were designed using the strip equivalent brace method in ETABS, and then seven acceleration maps far from the fault were selected, scaled, and modeled in ABAQUS software. The five-class model was compared with the non-centralized model. According to the results of the push-over analysis of the five-story steel shear wall model, the beams and columns remained in the elastic range in the self-centering model, and according to the hysteresis obtained from the push-over analysis of the steel shear wall, they have more energy consumption. The results showed that the drift, maximum drift, maximum displacement, and the ratio of the maximum acceleration value of the roof to the acceleration of the selected records in the self-centering steel shear wall have increased compared to the non-self-centering ones.

A fast and efficient numerical scheme is presented for time-history analysis of single-degree-of-freedom (SDOF) structural systems undergoing seismic excitation (Chopra, 2003). The new method is called Newton-Cotes-4P-θ Method. It uses the most known 4-point Newton-Cotes quadrature in its body to solve the vibration equation. Nonlinear analysis is covered as well as linear analysis. Any arbitrary external loadings of type force or seismic signals are welcome. The significant advantages of the new formulation are its great simplicity, running speed, and appropriate precision level compared with its counterparts such as Duhamel integral and Newmark-β methods. The accuracy level of the Newton-Cotes-4P-θ is close to the semi-analytical method of Duhamel integration and its speed is similar to the Newmark-β algorithm. Notably, against the nonlinear Newmark-β method, the new method does not require a standalone procedure to handle nonlinear analysis; instead, it simply triggers iteration of the same computation used in its first processing round. Moreover, the Newmark-β method loses its performance dealing with stiff and near-conservative () systems; however, the Newton-Cotes-4P-θ method does not loos its accuracy and keeps its well-performed analysis in this case. Numerical results reveal the superiority of the Newton-Cotes- 4P-θ method against its counterparts such as the Duhamel integral, Newmark-β, and Wilson-θ methods (Babaei et al., 2021; Babaei et al., 2022; Babaei et al., 2023).

One of the uncertainties in the seismic evaluation of structures is how to select random seismic records and how to consider the orientation effects of horizontal components of ground motions in the time history analysis. The rotation of the recorded components can increase the seismic characteristics such as peak ground acceleration, response spectrum shape, or earthquake energy. Therefore, the effects of this issue on the most critical scenarios of seismic response of important structures are questionable. This study has evaluated three rotation methods proposed by previous studies, i.e., principal axes, maximum direction, and fault-normal and fault-parallel orientation, based on the data available in the Iranian Strong Motion Network. Then, the effects of these methods are assessed on the seismic response of two building types, low-rise and medium-rise regular steel moment frames, using the nonlinear time history analyses. According to the results, if the structure principal axes are along with the most critical orientation of the accelerometer installation, the magnification of the seismic response can be expected, especially in near-fault structures. So that for the studied structures, , two structural response parameters including the maximum base shear and maximum inter-story drift ratio are increased between 10 and 120 percent under different rotated ground motions, depending on the earthquake type and the applied method of record rotation and also depending on the building height and its distance to the fault. According to the results, the selection of the most critical rotation method was a complicated and time-consuming process. Based on this research results, it is proposed to give priority to the rotation method which maximizes the value of peak ground acceleration and specific energy density of the seismic record to reduce the calculations of identifying the critical scenario for the rotation method of seismic ground motions in the time history analysis method

The effect of the angle of incidence on the structural damage and the seismic demand in far-fault earthquakes has been taken into consideration by many researchers for several decades. However, this issue has recently received more attention from researchers and design codes for near-fault earthquakes. This issue is due to the pulse-type motion caused by forward directivity phenomena in near-fault earthquakes which increases the influence of the angle of incidence on the seismic demand. Due to the importance of the issue, several researches have been conducted in the past years to improve the design criteria for near-fault regions. For example, for Nonlinear Time History Analysis (NTHA), ASCE/SEI 7-16 design code recommended that the selected near-fault ground motions should be first rotated in the fault-normal/fault-parallel directions and then applied to the main axes of the structure. This paper aims to investigate the accuracy and efficiency of the proposed method for design of structures in near-fault regions. For this purpose, using nonlinear macro modeling of an Eccentrically Braced Frame (EBF) and applying near-fault ground motions with different angle of incidence, the seismic demands of structures were evaluated. The analysis results show that not only the direction of maximum response changes with the change of near-fault ground motions and the types of seismic demand parameters, but also it varies in different stories of a building. Nevertheless, the fault-normal response usually provides an acceptable estimate of the maximum response, which is suitable for design purposes. So that in almost 70% of the cases, the ratio of the fault-normal response to the maximum response is more than 0.75.

Diaphragms, beyond supporting gravity loads and transferring them to vertical structural elements, play a crucial role in collecting lateral forces and distributing them among lateral resistant systems. In some cases, due to architectural considerations in the design of braced steel building frames, structural designers are compelled to shift the braces in the structure's plan, classifying them under structures with out-of-plane offset irregularity. In such structures, the horizontal diaphragm between the shifted braces must effectively transfer the shear forces induced by earthquakes. Therefore, investigating the behavior of these diaphragms is imperative for the analysis and design of these structures. The objective of this research is to investigate the seismic behavior, drift demands, over-strength factor, and the degree of vulnerability of discontinuous concentrically braced frames (CBFs) when subjected to earthquakes. To achieve this goal, two three-dimensional CBFs of 3 and 6 stories, both with and without out-of-plane offset irregularity, incorporating inelastic diaphragm behavior, were taken into account through pushover and nonlinear time-history dynamic analyses using ABAQUS. The examination of the results indicated that the concrete diaphragm existing in the discontinuity region, with a thickness of five centimeters, has been damaged at a 45-degree angle. It lacks the ability to transfer the shear force resulting from the lateral load of the braces. This is in contrast to thicknesses of 10 and 20 centimeters, where the diaphragm in the mentioned area remains undamaged. Given the information provided, it seems that, with the minimum thickness specified in Iranian National Building Code (part 9), was vulnerable to the transferred shear forces. Additionally, it was found that the inter-story drift demands of the frames exceed the estimations proposed by the building code.

Today by increasing of earthquakes and population growth and development of building industry in city or country areas, building designing against applied loads especially earthquake load have regarded by engineers. Also for supplying of life and financial safety, buildings should have appropriate performance against applied loads. In this research work, influence of scaling of near-fault and far-fault records have been treated in 4 codes 2800 Iran, 4th edition, ASCE07, IBC 2006 and UBC 97 Simultaneously. In this study 3 buildings have been used in 4,7 and 10 stories as indicators of low-rise and mid-rise buildings. The results show that in low-rise and mid-rise buildings Iranian earthquake code scaling has stricter rules to other regulations. By increasing of stories in tall -building (10 story) every four regulations has their own performance and could be maximum according to the kind and characteristic of earthquake (PGA, Mw). In fact, regulation of 2800 Iran, 4th edition, requires separated scaling rules for low-rise and mid-rise buildings. Drift ratio in ASCE07-10 has decreased %94 to 2800 Iran. Also this value for IBC2006 %93 and for UBC %89 has decreased.

The computational complexity of performance based seismic design methods makes most engineers prioritize the use of simpler force-based methods. Having a practical relationship between force and performance methods can solve this challenge. The hybrid force/displacement method has the advantages of the design method based on the performance and computational ease of force design methods. In this research, frames with 3, 6, 9, 12, 15 and 20 story with 3 bays with a width of 5 meters have been considered. The length of the link beam is defined as another parameter affecting the response, 1, 1.75 and 2.50 meters. The studied models have been developed by designing the method of load and resistance factor design method, for 3 performance levels of immediate occupancy, life safety and collapse prevention, as well as the first occurrence of the plastic joint. The final models are analyzed under 20 pulse-type near-fault records using time history analysis. Finally, using the genetic algorithm, the corresponding experimental relationships are presented to determine the behavior factor, local and global ductility. The proposed relationships are influenced by geometric characteristics such as the number of stories, the stiffness ratio of the columns, the slenderness of the braces, the length of the beam and the ductility levels. The results of the hybrid force/displacement seismic design of structures outside the range of the defined database, in comparison with the force methods, show the accuracy of this method in estimating the seismic needs of divergent bracing frames.

In the present study, the effect of ice-shedding simultaneously at the transmission line's span and the wind was investigated using numerical modeling, and its results are presented. The transmission line has five transmission towers and six power transmission spans related to the 400 kV transmission line of the Khoy-Urmia power plant. The transmission tower's weaknesses have been identified using this study's results, which can be considered in strengthening existing towers and the design of new transmission lines.

From long time ago, various solutions have been proposed to reduce earthquake damages, including increasing ductility and reducing structural mass. New methods are based on separating the structure from the foundation, to reduce the shear force of the base of the structure. In other words, seismic isolation is a new method for designing buildings against earthquakes, which is based on reducing the forces entering the structure due to earthquakes, instead of increasing the capacity of the structure to withstand lateral loads. This paper is a focused on the study of the effect of the placement of rubber separators with lead cores in the behavior of reinforced concrete structures under the influence of remote earthquakes. Therefore, for rubber separators with lead core in two samples of concrete structures of 3 and 5 floors, a double damping of 10 and 15% has been considered. Separating structures and fixed base structures were modeled in “Opensees” software. Afterwards, under the influence of distant earthquakes, a time history analysis was performed on them. Finally, the results of time history analysis for designs by force and direct displacement method are exposed, which include, maximum drift of floors, maximum shear of base and period of structures. Results obtained from the analysis of time history show that with the increase of the rotation time, the shear of the bases and the maximum drift in the buildings with isolators designed by direct displacement method are more than the buildings designed by force method. Buildings with separators designed by direct displacement method have sections with less capacity than buildings designed by force method.

Buckling-Restrained Braces (BRBs) are one of the new seismic resistant systems. The cross-sectional area and length of the BRB brace is one of the most important characteristics of these braces that directly affects the cost of BRB frames. Since beams, columns, and connections are designed for the maximum forces developed in BRB, the decrease in cross-sectional area of the BRBs decreases the steel consumption in the whole structure.The main purpose of this study is to optimize the weight of the structure, BRBs weight while uniforming the drift profile by changing the cross-sectional area and the length of the BRBs using genetic algorithms and other multi-objective optimization algorithms. Optimization is based on the results of nonlinear time history analysis under seven earthquake records using OpenSEES software. For this purpose, the objective function and constraints were defined in the genetic algorithm NSGA_II, MOPSO, MOEA_D, PESA_II, SPEA_II, and the initial population produced was entered as the initial cross-sectional area and length of the braces in the OpenSEES software. The optimization results show that for all three objective functions, the optimization values with high percentages of structural performance were optimized in such a way that the weight of BRB can be decreased up to about 50%.

The seismic design of buildings ought to be done to decrease the expenses of building repairing after an earthquake. Self-centering systems such as the post-tensioned concrete wall can provide this purpose. In this study, to evaluate the seismic behavior of the post-tensioned concrete wall with friction-based damper (FBD), the proposed system, the post-tensioned concrete wall with energy dissipator (ED) bars, and the concrete shear wall are subjected to the cyclic and nonlinear response history analyses at three, six, and ten-story buildings using OpenSees software. Based on the cyclic analysis, the total energy dissipation coefficients for the post-tensioned concrete wall with FBD in three, six, and ten-story buildings are respectively 1.37, 1.40, and 2.02 times of that obtained for the post-tensioned concrete wall with energy dissipator bars system, and are respectively 1.15, 1.05, and 1.72 times of that achieved for the concrete shear wall system. According to the results of the applied seven earthquake records, the average of the maximum drift in the concrete shear wall system is less than the other systems in the lower floors, and the average of the maximum drift in the upper floors in the post-tensioned concrete wall with FBD is less than the other systems.

The formation of the short column phenomenon in reinforced concrete structures has caused design engineers to study the behaviour of such structures. One of the conditions that lead to the formation of a short column is the placement of the structure in a steep position. In this paper, two 8- and 16-story structures were modelled once on a flat surface and again on a sloping site, and their sections were designed using equivalent static analysis. Then, using nonlinear time history analysis, the behaviour of these structures in the plastic region was compared. Structures were modelled in Sap2000v20 software and SeismoSignal.v2018 software was used to scale the accelerometers used in nonlinear time history analysis. Examining the results, it was observed that the formation of short column phenomenon in reinforced concrete structures with special bending frame system has a negative effect on the seismic response of structures; It increases the displacement of the floors, increases the drift of the structure and also creates a mechanism (or the formation of plastic joints). For example, based on the results obtained from 8 and 16 storey structures with and without short columns, it was observed that the average drift of 8 and 16 storey structures with short columns was 19% and 7.1% in the X direction more than the structure, respectively. It has no short columns and also in the Y direction, the average drift of 8 and 16 storey structures with short columns is 7% and 12.8% more than the structure without short columns, respectively.

The inevitable occurrence of earthquakes and the infliction of great human and financial losses, especially devastating earthquakes that have occurred in recent years in different parts of the world, has emphasized the need to find a suitable and reliable solution to strengthen structures against this natural phenomenon. The use of dampers as one of the methods of passive control of structures due to reliable behavior, optimal strength and low maintenance has been considered by many engineers in recent years. Despite its relatively widespread use in buildings, the use of dampers in bridges is not common yet. The purpose of this study is to investigate the effect of using rotary friction dampers as an energy dissipation system in concrete bridges as a suitable solution to improve the seismicity of existing bridges against earthquakes. In this study, modeling has been performed on four bridge samples, with span dimensions of 20 meters and 30 meters and with three and five spans. Using time history analysis, the amount of base shear and maximum displacement have been calculated as the main parameters that have a significant impact on the failure of the stairs. According to the results, the shear force changes decrease by about 10 to 17% with increasing the span length from 20 m to 30 m. Moreover, the displacement of the bridge deck decreases about 4 to 15% by increasing the span length from 20 meters to 30 meters. In addition, by increasing the number of bridge spans from 3 to 5, a maximum increase of 11% is created in the above parameters.

Bridges are structures with great importance, and any interruption could cause financial damage and even life-endangering people's life. Based on the type of structure, bridges can be divided into conventional, cable, and movable bridges. Space limitations in urban areas and the establishment of the cities around the rivers attracted designers and engineers to these types of bridges. Considering the importance of the foldable bridges, seismic behavior of the bridge under subjection to near-fault ground motions has been investigated in this paper. Inheriting impulse effects in near-field contents is the main difference with far-field records. The total length of the bridge is 40 meters and consists of three movable spans, which are 3.65, 2.7 and 3.65 meters long. To study the seismic behavior of the bridge, at first modal analysis has been performed in ABAQUS built model and then under subjection to near-fault ground motions, which has been matched according to issue No.463 seismic time history analysis performed. The acceleration response, base shear, and vertical deflection of the bridge induced by perpendicular horizontal excitations were calculated and extracted. The destructive effect of the Varzeghan earthquake is more than other earthquakes, and the numerical value of acceleration response, vertical displacement, base shear, and tower drift is considerably higher than other earthquakes. The connection zone of the tower to the deck is vulnerable to seismic loads, and plastic hinges have been formed.

Passive control systems have always been used in civil structures due to the lack of external energy source, low cost, easy installation and simple design. The fluid viscous damper is one of the most advanced passive control devices that dissipates the energy input to the structure by converting mechanical energy into heat. In conventional viscous damping design methods, the required damping required to be provided by viscous dampers in the structure depends on the stiffness of the structure. In this paper, in order to distribute the viscous damping at the height of the building, the distribution method is used in proportion to the inter-story drift proportional distribution determined on the basis of the first mode deformations and five different methods for determining the stiffness of the stories are used to calculate the total damping. Finally, of the five methods, the one in which the responses of the controlled building to the viscous damper are more in line with the design goal would be the preferred method. Also, in order to evaluate the design cost to choose the appropriate method, a comparison has been made based on the total damping required (as a cost criterion) to achieve the desired design goal. The studied structures are 3, 9 and 20 story benchmark buildings of SAC project. In order to analyze the time history of buildings, four benchmark near field records with the effect of Fling Step and four benchmark field far records have been used. The results show the different effects of different methods of calculating the stiffness of floors in accordance with the design goal and therefore it is necessary to choose the appropriate stiffness method from different methods to determine the desired design goal.

Having a long history of seismicity and experienced destructive and deadliest earthquakes make Iran one of the vulnerable countries against earthquakes. Based on the seismic hazard zoning map presented in the Iranian seismic code (2800 provisions), more than 90% of Iranian cities are located in areas with high or very high seismic hazard zones. On the other hand expansion of urbanization in recent decades almost comprises reinforced concrete (RC) buildings. Many of these RC structures constructed in accordance with codes that did not mandate adequate detailing and reinforcement for seismic protection, may have already suffered damage since their erection, due to insufficient maintenance, earthquake activity, or other natural hazards. Therefore providing appropriate solutions for the rehabilitation of such structures has always been considered essential. Metallic energy dissipators have been grown experimentally and theoretically almost for steel structures. U-shaped metallic-yielding damper as one of the most well-known metallic energy dissipators has also developed as a lateral-load resisting system for strengthening existing steel frames. Experimental and theoretical results showed that U-shaped metallic dampers can operate with large displacements in the inelastic range and dissipate energy through the plastic deformation of the steel. The purpose of this study is to take potential advantages of this system to strengthen deficient RC structures. To the best of the authors’ knowledge, this issue has rarely been considered, most of which are limited to small experimental studies. Therefore, it can be useful to study this issue numerically at the real size structural level. In this regard, three RC intermediate moment frames in 4, 6, and 8 stories and irregular in elevation are considered. Irregularity is considered by a setback in elevation of the frames as a special type of irregularity with considerable effect on seismic performance. Frames were first designed deficiently by SAP2000 software according to the provisions of the Iranian national building code and Iranian seismic code for the intermediate reinforced concrete moment-resisting frames. Then the frames strengthen by adding U-shaped metallic-yielding dampers together with inverted V-braces. The nonlinear dynamic time-history analysis is performed on all frames subjected to three far source input motions utilizing PERFORM 3D software. Nonlinear specifications of beams and columns are considered by assigning plastic hinges to them in addition to defining nonlinearity for the dampers. The results of roof displacement, base shear, inter-story drifts, and performance of frames at the life safety structural performance level are monitored for both cases with and without dampers. The use of U-shaped metallic dampers has always reduced significantly the maximum lateral displacement of the buildings. On average, under the three records of Imperial Valley, Manjil, and Tabas, the reduction is obtained as 32, 33, and 22 for 4, 6, and 8 story frames, respectively. Such a significant reduction is also visible in the inter-story drifts.  . No major effect on the maximum base shear force is observed and even in some cases, it is increased up to 10%. Failure of frames reduced by transferring nonlinearity of elements to the dampers and seismic performance assessment indicates that dampers strengthen frames to almost satisfy the requirements of the life safety level.

In this paper, the seismic behavior of reinforced concrete (RC) high-rise buildings with frame-core tube systems as one of the lateral bearing systems are studied. In order to investigate the effect of the core tube system on the seismic behavior of the high-rise building, the structural model is evaluated in two cases with the inner core tube and without the inner core tube. Three methods of equivalent static analysis, dynamic nonlinear time history analysis and nonlinear static analysis (push-over analysis) are used. Also, a 25-story high-rise building with a frame-core tube system having voids in the last floors is implemented. The results showed that the use of RC core as a central tube significantly reduces the lateral displacement and drift of floors. Also, the results obtained from the nonlinear static analysis indicated that using the central RC core, the ultimate capacity of the building as well as the ductility of the building increase significantly. Finally, the results obtained from the nonlinear time history showed that the nonlinear static analysis have good accuracy in calculating the maximum displacement of the structure.