فهرست مطالب alireza mortezaei

Many abilities of Monte Carlo simulation methods have led to their increasing use in solving various reliability problems of structures. These methods are based on generating random samples in order to simulate events and estimate their results. Achieving certain accuracy requires a significant number of simulation operations. Acceptable accuracies can be achieved with a smaller number of samples by adopting different approaches. In this article, for the first time, symmetric structures are analyzed using the theory of graphs and canonical forms, the frequency of the structures is calculated, and their reliability is also checked using these theories. Also, the study and investigation of the calculation of frequencies and eigenvectors corresponding to symmetric structural models from the point of view of the decomposition of the stiffness matrix in probabilistic reliability analysis, which we will achieve this goal by using the proposed theories. In this article, in addition to obtaining all canonical forms, the relationship between all canonical forms is obtained. Finally, a new Rayleigh-based theory called the proposed improved Rayleigh theory is presented, which is used to extract the natural frequencies of structures. Also, in this research, several samples of different frames and structures were presented using the proposed method and finally, numerical results were presented and the solution of the three-story frame with 24 degrees of freedom was presented. It can be seen from the results that the proposed method has a much higher speed and accuracy than the Monte Carlo method.

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.

In this research, the progressive collapse of the reinforced concrete frames following the middle column removal has been investigated based on the sensitivity and robustness indexes. At first, the numerical model of the reinforced concrete frame was simulated and verified with Li et al. model in SeismoStruct software. After developing the numerical model, the performance levels and the number of plastic hinges in the frames were obtained. The frames were subjected to the column removal in the first story and their vulnerability to progressive collapse was investigated under nonlinear static push down analysis. In the present research, parametric study including change in the number of stories, span length, story height, concrete compressive strength, rebar yield strength, poisson's ratio and damping ratio of the structure in the progressive collapse of the frames was performed based on the sensitivity and robustness indexes. The results showed that increasing the number of stories from 5 to 20 story, reducing the span length from 5.5 to 3 m, reducing the story height from 4.45 to 3.20 m, increasing the concrete compressive strength from 21.3 to 51.3 MPa, increasing the rebar yield strength from 234 to 350 MPa, increasing the Poisson's ratio from 0.12% to 0.25% and increasing the damping ratio from 5% to 15% decreases and increases the sensitivity and robustness indexes, respectively. Thus, the condition of the frames in progressive collapse improves. Finally, the effect of simultaneous removal of several columns in the progressive collapse of the frames showed that the case 5 of the column removal has the lowest sensitivity index and the highest robustness index, thus having better conditions in progressive collapse.

Non-ductile reinforced concrete frames are commonly found in older buildings in many parts of the world. These structures designed for gravity loads, have limited lateral strength and ductility, are prone to excessive one-way lateral movement and soft-story mechanism. This paper focuses on the retrofit of an existing reinforced concrete frame, using steel X-braces by indirect internal connection method. The main purpose is the analytical study of general behavior and response of large scale vulnerable frames. An experimental study was used to validate the numerical modeling performed in ABAQUS. Next the base samples were retrofitted with X-braces and four proposed indirect internal connection methods. Furthermore, in a separate parametric studies, the effect steel frame profile type, connection type and use of high strength grout in the boundary zones between steel and reinforced concrete frames were investigated. The results indicated that the stiffness and bearing capacity of the reinforced concrete frame by using steel X-braces increases up to 3.7 and 2.8 times, respectively. It also reduces the final displacement and drift by 50%. Moreover, bracing acts like the first defense system against lateral loads, such as structural fuse with its yield, increases the amount of energy dissipation. It also removes the plastic hinges by reducing the ultimate displacement and stress of lateral load in the panel zone.

Nowadays, concrete is known as one of the most used building materials in the world. Being economical, the availability of constituents, good resistance under the fire and atmospheric factors, the ability to fit in shapes and molds, and also the high compressive strength are factors that have made public acceptance in the use of concrete as a building material. The use of fiber in concrete has increased dramatically over the last few decades. The use of fiber in concrete causes the concrete to become flexible to a considerable extent and the resulting concrete is highly homogeneous. Since the concrete specimens are used worldwide to determine the mechanical properties of concrete, in this study, 160 samples of fiber concrete containing 64 cube samples with dimensions of 5×5×5, 10×10×10, 15×15×15, 20×20×20 cm for testing of compressive strength, 64 cylindrical cylinders with dimensions (diameter × height) of 15 × 30 and 10 × 20 cm for compressive strength and tensile strength tests and 32 samples of beam with dimensions of 10×45×10 and 15×60 ×15 were used for flexural strength testing. Furthermore, in this study, 4 concrete ranges of 20MPa, 25MPa, 30MPa and 35MPa were tested. Of each concrete grade and each dimension, four samples were made; one of which was non-fibrous (as the base sample) and three samples with fibers. The steel fibers used were two-end hooks of 3.5 cm in length and 0.8 mm in thickness, with 0.5% of the volume of concrete used. The results showed that the flexural strength, tensile and compression strength of the concrete increased with the presence of fibers and some new conversion factors were proposed for the fiber-containing specimens.

This study aims to investigate the effectiveness of engineered cementitious composite (ECC) as a ‎means to enhance the seismic performance of short columns. Eleven ECC short columns and one reinforced concrete (RC) short column were ‎designed and tested under lateral cyclic loading with different fiber volume fractions(0 -1.5%) and shear ‎aspect ratios(3-7). The influence of fiber volume ‎fraction, and shear aspect ratio on crack pattern, hysteresis behavior, energy dissipation, failure ‎modes, and length of yielding region is presented and discussed. The test results show replacing ‎conventional concrete with ECC can effectively improve the seismic behavior of short columns. ‎Further more , ECC short columns show excellent ductility and damage tolerance. Results shows ‎larger plastic hinge lengths were obtained with an increase of aspect ratio and fiber fraction‎.The influence of fiber volume ‎fraction, and shear aspect ratio on crack pattern, hysteresis behavior, energy dissipation, failure ‎modes, and length of yielding region is presented and discussed. The test results show replacing ‎conventional concrete with ECC can effectively improve the seismic behavior of short columns. ‎Further more , ECC short columns show excellent ductility and damage tolerance. Results shows ‎larger plastic hinge lengths were obtained with an increase of aspect ratio and fiber fraction‎

Insufficient separation distance between two adjacent buildings can cause to collision when large lateral displacements are accrued due to seismic excitation. The impact force between structures induces many serious damages, which is called building pounding. In this study, pounding between two dynamic models is investigated and the impact force is numerically calculated. The impact is simulated based on special elements, including spring and dashpot, and the impact force and dissipated energy during the impact are determined. Both mentioned parameters depend significantly on the impact velocity, spring stiffness and the value of damping. For this purpose, the impact velocity of collision is parametrically measured and subsequently, coefficient of restitution is automatically determined. Furthermore, the impact damping ratio and nonlinear stiffness of spring are calculated to evaluate the impact between models. Finally, a new equation is presented to determine the value of damping and the accuracy of formula is confirmed, which is verified by three various approaches. In the first stage, an experimental test is considered and the peak impact force is extracted when a concrete ball is dropped on a rigid concrete surface. On the other hand, a numerical simulation is similarly assumed and the suggested formula is used to determine the peak impact force during collision. Then, the results of the peak impact forces between experimentally and numerically analyses are compared, which shows both are close to each other. Secondly, an estimated impact between two bodies has been studied. The results of the analysis are also compared between the dissipated and kinetic energies during impact. The comparisons indicate relatively low errors between the calculated and assumed values of the coefficient of restitution when the proposed equation is used. Finally, a value of the coefficient of restitution is selected and an impact is simulated to show hysteresis loop. The enclosed area of each loop is calculated as the dissipated energy and compared with the energy absorption. The above three comparisons show that the proposed formula is very effective and the accuracy of the impact force, calculated by the suggested formula as a parameter of the impact force model, is also acceptable.

Historical sites and remnant monuments from different eras in Iran are the main reasons of tourist attraction. One of the factors that endanger existence of these monuments is earthquakes and it is well known that Iran is located on the Alpide seismicbelt and earthquakes are inevitable. Understanding the structural behavior as well as possible weaknesses and then seismic strengthening under the earthquake are the ways of mitigating hazard in architectural heritage. Minaret of Tarikhanehmosque which is one of the oldest minarets and most precious historical monuments in Islamic world was built between 130 and 170 AH (750-760 AD). In the present study, this minaret is first modeled via ABAQUS finite element software considering geometric details and different seismic analysis such as pushover, modal and nonlinear time history analysis is conducted under the different earthquake frequency contents. After realizing the current state and weaknesses of the minaret, seismic strengthening is done via three different methods including FRP sheets, Ferro-cement (welded wire mesh with micro-concrete/mortar), and fiber reinforced cementitious matrix (FRCM) material. Finally, results of these three strengthening methods were evaluated and the most appropriate method was selected. According to the results, it was observed that Ferro-cement strengthening method is the most effective one among the proposed methods; so that, in comparison to the FRCM strengthening method, this method is effective by up to 100 %.

With the increase in the population of cities and the lack of spaces for construction, the creation of diverse uses, architecture and beauty of structures, ،he performance of a magnetic damper with a fuzzy controller to reduce the vibrations of an irregular hard structure under near and near earthquakes has been investigated. In the present study, the performance of a magnetic damper with a fuzzy controller reduce the vibrations of an irregular stiffness structure under near and far field earthquakes has been investigated. The capacity of the introduced magnetic damper is equal to 1000 kN, which is installed in the first floor between the floor level and the ceiling level of the first floor. Three different types of irregularities in height, including hardness irregularities with a coefficient of 60%, are used in a 10-story structure and are modeled in the OpenSees software. These irregularities have been investigated in three different elevation locations including the lower half of the structure height (floors 1 to 5), the lowest floor (1st floor) and the middle floor of the structure (5th floor). Based on the numerical analyzes performed for these structures under the excitation of near and far field earthquakes, the residual displacement is reduced by an average of 23.15% and 45.64%, respectively. In addition to improving criteria such as maximum displacement, shear, and base anchorage in both types of earthquakes, the most improvement occurred for the irregular structure on the first floor and the least for the irregular structure in the middle floor.

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.

One of the most important structural features is fundamental vibration period which depends significantly on the inherent characteristics of structures. Seismic codes and some researchers estimate experimentally and mathematically fundamental vibration period using the number of stories or the overall height of the building. The consequences of evaluating the various relationships have been resulted based on structural height, mass, stiffness and number of stories. As the overall height and the number of stories do not make difference between regular and irregular structures, so it seems that mass and stiffness of each story is so important in zone of building vibration period. Considering the importance of irregular buildings, a new relationship proposed to determine fundamental natural period of vibration for elastic regular and irregular buildings in height using artificial neural network. The accuracy of the proposed relationship is perfectly validated and confirmed by numerical calibrations and matrix analyses.

Undoubtedly, bridges have substantially effect in metropolitan areas and are usually built to connect between two roads in order to decrease traffic. Pounding, is one of the important parameters to design different bridges Pounding, is one of the important parameters to design different bridges as this structures should be controlled during seismic excitation to provide safety conditions in order to organize and support unpredictable situations. During very strong earthquake, bridges may experience large horizontal relative displacement, which may lead to pounding if sufficient gap size is not considered between adjacent slabs of bridge. Insufficient separation distance is naturally caused to collide between two slabs and, subsequently, stiffness of bridge is decreased and finally, collapse is occurred. In order to determine critical distance between two slabs, a mathematical program is used based on neural network to coordinate the result of analyses in order to calculate sufficient separation distance for avoiding collisions during earthquake.

The significance of the seismic rotational components have been overlooked in the seismic evaluation of structural behavior. As researchers have measured seismic components more accurately using sensitive rotational velocity sensor, it was observed that the magnitude of rotational components is considerable and could not be neglected. Hence, some parts of seismic damage or failure of structures cannot be exclusively attributed to the translational components. In this regard, this paper used seven accelerograms in which rotational components were measured by advanced sensors. The considered RC buildings which designed as per intermediate moment-resisting frame system were analyzed using OpenSees in nonlinear dynamic domain. In the numerical modeling, lumped plasticity model was used to simulate the behavior of RC component members considering the rotational motions and soil-structure interaction as main parameters. The results of numerous nonlinear time history analyses showed that the contribution of rotational components to the seismic behavior of RC frames is considerable and should be included in the seismic design codes.

The present study examines the behavior of concrete coarse-grained and fine-grained (raw concrete and concrete mortar) containing tungsten oxide Nanoparticles as well as the performance of concrete beams repaired with concrete mortar containing tungsten oxide Nanoparticles. For this purpose, two types of designs, including primary concrete and concrete mortar containing 0.5, 1.5 and 2.5 weight percent of cement were used. The compressive and tensile strength tests 0f 3, 7, 28 and 63 days specimens and 1 , 3, 7 and 28 days specimens were carried out on the primary and mortar concrete, respectively. Four-point bending strength tests on the primary concrete by 28 and 63-day duration and concrete mortar was performed on 28 day. For the repair of concrete beams, the contact surface of concrete and concrete mortar were prepared in a smooth and coarse manner and subjected to a four-point bending test in order to evaluate compatibility between the repair materials and the primary concrete. The results showed that with the increasing presence of nanoparticles in raw concrete and mortar, increase compressive strength, flexural tensile, by compared to the control samples and about the repairing beams with rough surface samples have a flexural strength more than the sampler with a smooth surface that part of this increase in flexural strength can be used to increase the compressive and tensile strength of mortar and other restorative effect of tungsten oxide nanoparticles.

It is important to obtain accurate information about the preferences of people for measuring quality-adjusted life years (QALYs), because it is necessary for cost-utility analysis. In this regard, mapping is a method to access this information. Therefore, the purpose of this study was to map Functional Assessment of Cancer Therapy – General (FACT-G) onto Short Form Six Dimension (SF-6D) in breast cancer patients to provide appropriate conditions for a detailed cost-utility analysis. This descriptive analytical study was conducted on 416 patients with breast cancer. The SF-6D and FACT-G questionnaires were completed for patients selected by consecutive sampling from the Imam Khomeini Cancer Institute in Tehran in 2018. The Ordinary Least Squares model was used to estimate the value of utility and the models' goodness of fit was evaluated using R2. In addition, models' predictive performance was assessed by Mean Absolute Error (MAE), Root Mean Square Error (RMSE), and Minimal Important Difference (MID) conducted between the observed and predicted SF-6D values. Models were validated using a 10-fold cross validation method. Given the criteria of goodness of fit, model 2 was the best (R2 = 41.19 %). Moreover, findings of the predictive performance of models showed that model 2 was the best (MAE = 0.06943, RMSE = 0.09031, and MID = 0.0003). Findings showed that the developed algorithm had a good predictive ability. So, it can enable the policymakers and researchers to convert cancer-specific health-related quality of life instruments to preference-based instruments.

Cylindrical liquid storage tanks are contemplated as vital structures in industrial complex whose nonlinear dynamic behavior is of crucial importance. Some of these structures around the world have demonstrated poor seismic behavior over the last few decades; consonantly a major improvement is required to reach their level of applicability. There are several methods and techniques for rehabilitation and reducing damages in these structures which among them the devices for passive control, particularly base isolators, are perceptible. Friction Pendulum System (FPS) is the most popular base isolation system which its period does not depend on the structural weight. In this research work, the efficiency of FPS is examined on decreasing the seismic responses of base isolated steel storage tanks as well as the impact effect of slider to the side restrainer. To this end, the whole mass of liquid storage tank is contemplated as three lumped masses known as convective mass, impulsive mass which is connected to tanks with corresponding spring, and rigid mass which is connected rigidly. By means of state space method the time history analysis is done applying 60 earthquake records to acquire dynamic responses under the various hazard levels i.e. SLE, DBE and MCE ground motions. The results show that the normalized base shear force in squat tank decreased 59%, 62% and 33% respectively under SLE, DBE and MCE ground motions. The reduction of normalized base shear force in slender tank is 53%, 49% and 35% under the aforementioned hazard levels. Examining the effect of side restrainer’s stiffness on the maximum responses exhibit that the impact effect must be considered particularly when the system is excited by MCE’s ground motions.

Liquid storage tanks are important industrial structures that must continue their performance under severe earthquakes. The induced damages caused in the past earthquakes shows their poorly behavior of these structures. One of the most effective methods to retrofit and reduce the induced forces is to use base isolation. Friction Pendulum System called FPS has better performance compared to other base isolation systems, due to its period does not depend on the weight of the structures above it.
The aim of this paper is to investigate the effect of FPS under three different hazard level earthquakes (SLE, DBE and MCE). It is also, the impact effect due to contacting the slider with the side restrainers is investigated. For the required analysis, two different liquid storage tanks are considered and their responses are compared in Fixed, Isolated without considering impact and isolated with considering impact conditions. The obtained results show, increasing the hazard level of ground motions leads to decreasing the performance of FPS. It is also observed, compared to SLE and DBE earthquake ground motions the MCE has the maximum probability of impact. The results also show that, the impulsive mass displacement, overturning moment and base shear increases when the impact occurs, while the impact has no special effect on convective displacement

Previous earthquakes have shown that a strong ground motion is followed by some aftershocks that are smaller than the main shock, but often produce moderate to high aftershocks in the affected areas. Hence, the structures constructed in seismic areas are not only affected by a single seismic event, but this event also includes foreshocks, main shock and aftershocks. For example, the 2012 East Azerbaijan earthquake (August 21, 2012), with a magnitude of Mw = 6.4 occurred in the northeast of Tabriz, had an aftershock with a magnitude of Mw = 6.3 that happened approximately 11 minutes later. It is known that aftershocks can cause significant failure to the structures damaged by mainshock ground motions. In other words, during aftershocks, there are structures that have already been damaged by an earthquake and have not yet been repaired, which may be damaged or collapsed under the aftershock seismic event. Literature review shows that most existing codes are limited to choose a single event called "design earthquake", while the effects of aftershock earthquakes have been ignored. Despite the qualitative knowing of this issue, limited studies have been reported in the past studies on sequence earthquakes. The plastic hinge area in reinforced concrete buildings is an area where an RC member experiences a moderate to severe plastic deformation under the moderate to strong ground motions. The occurrence order and position of plastic hinges plays a key role in the seismic rehabilitation of old buildings as well as the design of new structures. Contrary to the subject importance, most studies have been limited to the steel structures, and no studies have been conducted on the occurrence order and position of plastic hinges in the reinforced concrete buildings under the mainshock-aftershock seismic sequences. Therefore, in this paper, three-dimensional models with 4, 7, 10, 13, 16, and 20 stories are evaluated under the seven single and seven mainshock-aftershock earthquake records by nonlinear time-history analysis. The formation and average rotation of plastic hinges as well as the performance level of the structures are calculated and compared by nonlinear time history analysis. The results show that the buildings suffered serious damage under the aftershock earthquakes. Number of plastic hinges that pass through LS level increase significantly, so that this number is 31 times in the 13-story building and the building collapse after mainshock earthquake. In all the structures except the 4-story building, under the mainshock-aftershock earthquake records, plastic hinges are formed in the columns of some stories.

In many studies on the evaluation of seismic behavior of RC buildings with a box-type structural system, link beams are not included in models simulation in order to reduce the time and effort of calculations. In addition, in spite of early failure of the link beams to the shear walls, the system faces challenges because of dimensional limitations as well as design and construction of detailed specifications for the link elements as seismic fuses. The present study, while presenting a proposal for replacing reinforced concrete link beam with a replaceable steel type, investigates the effect of these elements on the seismic performance of box-type systems in the framework of relationships related to the strength reduction factor. According to the results, link beams have a significant effect on the system capacity and stiffness enhancement; and the model does not yield acceptable results by eliminating them. Replaceable steel link beams, while increasing the reliability of the system, have no effect on the performance level of the buildings under the design and maximum credible hazard levels. Due to the replace-ability of these elements, in order to compensate for the constructional weaknesses available, their usage is suggested.

In recent years some studies have been done on the moment rredistribution in buildings and new methods offered for calculating of redistribution. Observations demonstrated that the combination of moment and shear force is important in analysis of reinforced concrete structures. But little research is done about the effect of redistribution by using moding in software. In order to study the effect of moment redistribution on the stability of RC moment resisting frame structures, four buildings with 4, 7, 10 and 13 story have been considered. In these models, the nonlinear behavior of elements (beam and column) is considered by the use of interaction PMM hinges. The average plastic rotation was calculated by performing pushover analysis and storing stiffness matrix for 5 points and then the buckling coefficients were obtained by conducting buckling analysis. By the use of modal analysis natural frequency was calculated and it was attempted to be related the average plastic rotation with the buckling coefficients and the natural frequency. It could be concluded that increase in the plastic rotation reduce the buckling coefficients to about 96% which this amount of reduction is related to the average plastic rotation. Moreover, the buildings experience instability state when the average plastic rotation reached to 0.006 radian.

In this study, the effect of deep excavation on the seismic response of RC moment resisting building systems has been studied. Deep excavation can cause significant changes in the stress and strain levels of soil environment and also changes in the propagation of seismic waves. This leads to permanent displacements in the foundation system. In this study, three RC building systems, i.e. 5, 10, and, 15 stories, were modelled considering the nonlinear behaviour of soil and structural material as well as the soil-structure interaction effect. Nonlinear dynamic responses of buildings were evaluated before and after excavation and also with a rigid base (without soil modelling) under the seven earthquake records. Analysis results indicate an increase in seismic demands and responses in the vicinity of the excavation. So for 15-storey buildings near the excavation, 35% increase in the base shear, 70% increase in maximum drift, 26% increase in the story shear force, and a 30% increase in the maximum story acceleration was observed. As a result, considering the effect of excavation on the seismic response of RC building systems is inevitable.

The increase of effective period of structures results fromthe increase of foundation movement due to changes of soil stiffness. In high-rise buildings, due to the seismic motions, the bending moment in sub-structure will cause foundation rotation. The increase of rotation in the sites with different shear wave velocity will cause different behaviors. The increase of the site stiffness leads to the decrease of settlement and generation of uplift condition in the foundation. This circumstance will ultimately lead to the increase of structural movements and seismic response. Applying the circular micropile group as foundation will reduce and control the rotations of foundation. In this paper, by means of FLAC3D software and by parametric study of the inclination angles, distance ratio, and slenderness changes in circular micropiles group, a new equation is developed. Developed expression is used for showing how to affect the decrease of foundation rotations in sites with high shear wave velocity and to decrease structural seismic responses by presenting necessary diagrams.

One of the strengthening methods in reinforced concrete frame buildings is improving seismic behavior of such structures by means of steel bracing. When influenced by compressive stresses، traditional steel braces would buckle and are free of any ductility. As a result، efforts in order to restrain buckling problem for steel braces has led to creation of steel unbonded brace. In these braces، Eulerian buckling of central steel core is controlled by placing in a steel tube full of mortar. In this paper، RC buildings of 6، 12 and 18 stories are first designed based on standard 2800 and then controlled based on the rehabilitation regulation and the third edition of standard 2800. After analyzing and in order to improve seismic behavior، these buildings are strengthened by the use of common braces and steel unbonded braces and the columns of braced frames are also reinforced by concrete jacket. Totally، 42 models were analyzed by nonlinear static analysis (pushover analysis). The results indicate that structures with traditional braces have weakness in high level of drifts due to buckling of compressive braces and the energy absorption in 12 and 18 stories structures is even lower than non-strengthened structures. Nevertheless، this defect is removed by applying unbounded braces because of somehow identical behavior in extension and pressure as well as utilizing total capacity of these kinds of brace. Also، in comparison with structures with traditional braces and non-strengthened structures، a high level of energy absorption will be obtained. One of the strengthening methods in reinforced concrete frame buildings is improving seismic behavior of such structures by means of steel bracing. When influenced by compressive stresses، traditional steel braces would buckle and are free of any ductility. As a result، efforts in order to restrain buckling problem for steel braces has led to creation of steel unbonded brace. In these braces، Eulerian buckling of central steel core is controlled by placing in a steel tube full of mortar. In this paper، RC buildings of 6، 12 and 18 stories are first designed based on standard 2800 and then controlled based on the rehabilitation regulation and the third edition of standard 2800. After analyzing and in order to improve seismic behavior، these buildings are strengthened by the use of common braces and steel unbonded braces and the columns of braced frames are also reinforced by concrete jacket. Totally، 42 models were analyzed by nonlinear static analysis (pushover analysis). The results indicate that structures with traditional braces have weakness in high level of drifts due to buckling of compressive braces and the energy absorption in 12 and 18 stories structures is even lower than non-strengthened structures. Nevertheless، this defect is removed by applying unbounded braces because of somehow identical behavior in extension and pressure as well as utilizing total capacity of these kinds of brace. Also، in comparison with structures with traditional braces and non-strengthened structures، a high level of energy absorption will be obtained.

During past decades, many control algorithms with some advantages/weaknesses have been proposed. However, the most famous and historic algorithm which has found widespread applications in different fields of science, is the family of optimal control method (OCM). Today, this family includes many different approaches using various performance indices in continuous or discrete domain of consideration. The main stem of OCM is rooted in a simple definition, say performance index (PI), which should be minimized with respect to the main independent variables of the system. Although, different proposed algorithms are employed various performance indices besides simple or stable weighting matrices, their performances are noticeably similar. Extensive analysis shows that the main aspect, which results in reasonable similar performances in spite of their assumption for determining control force, arise from solving the Riccati matrix equation (RME) during their procedure or their stability criteria. This idea is examined by introducing a new simple but unusual assumption, named the simplified LQR (SLQR), via considering seismic behavior of an eight-story shear type building structure.