جستجوی مقالات مرتبط با کلیدواژه « steel structure » در نشریات گروه « عمران »

In this research, the progressive collapse of braced frames with knee braces in steel structures under fire load was investigated based on the software modeling method. In order to carry out the research 3, 6 and 9-story steel frames with coaxial and off-axis knee bracing systems were considered in the shape of inverted-V and were analyzed and analyzed using the software method and ABAQUS and SAP software. In this regard, at first, the frames were analyzed and designed by modeling the frames in SAP software, and the sections of the frames were determined. In the following, the frame was analyzed in ABAQUS software under the fire load. the frame without and with the removal of the critical elements was analyzed successively under the fire load in the SAP software to check and compare the energy of the frame samples in each case based on the results obtained from the analysis. Based on the study conducted on the frame with off-axis and coaxial knee bracing, it was determined that the bracing type of off-axis had a significant effect on reducing the energy of the frame compared to the coaxial bracing system. The 3,6 and 9-storyframes with off-axis knee bracing had 35%, 50% and 65% less energy than the frames with coaxial knee braces during the fire and in the entire time period.

Isolators and dampers are devices that dissipate energy and reduce the seismic response of structures during strong earthquakes. Lead Rubber Bearings (LRBs) and Tuned Mass Dampers (TMDs) are two common types of these devices. Studying non-linear behavior and seismic properties of structural systems equipped with this type of isolators and dampers can significantly enhance understanding of their behavior against lateral forces caused by strong earthquakes. In this study, a 9-story steel structure was analyzed using the Endurance Time Analysis (ETA) method in SAP2000 software with fixed and isolated bases, along with a tuned mass damper with different mass ratios and without a tuned mass damper. The analysis results indicate that the tuned mass damper is highly effective in reducing the displacement of the isolator level, drift ratio, and story shear forces. This effect is more significant with higher mass ratios of the TMD. This effect is more pronounced with higher mass ratios of the TMD. However, reducing the absolute acceleration response of the structure has not been effective, and increasing the mass ratio of the TMD only reduces the performance of the control system in improving the absolute acceleration response compared to the isolated state.

Seismic waves of structural vibrations propagating through the soil and transmitting to other structures, and the effect this has on seismic performance, have recently come up due to the result of recent ground movements originating in soft soil zones like Mexico City. In regions with densely built structures, this vibration may have a significant impact on structural responses. The purpose of this research is to evaluate the seismic performance of a single structure on soil (Soil-Structure Interaction, or SSI) vs. that of a pair of similar structures with differing soil conditions (Structure-Soil-Structure Interaction, or SSSI). Recent research suggests that damage risks may increase due to the SSSI impacts. The studied structure is a three-dimensional, six-story steel building with a foundationally sound moment and braced frames lateral force resisting system. To account for the non-linear behavior shown by SSSI and SSI models, a three-dimensional steel structure is presented in OpenSEES. For simulating the soil easily under the foundations and between structures, the nonlinear Beam-on-Nonlinear-Winkler-Foundation (BNWF) model is employed. There is a meter of space between structures. Therefore impact between buildings is prohibited. The SSSI and SSI systems are examined using 11 horizontal components. Ground motion magnitudes ranges from Mw = 5.0 to Mw = 8.5, soil shear velocity varies from Vs30=185 m/s to Vs30=365 m/s, and distance from faults goes from 10 km to 50 km. The two orthogonal horizontal components of selected seismic ground motion stimulate the system. Inter-story drift ratio, roof displacement, and plastic hinge rotations of structural elements are among the reactions of importance. In the SSSI and SSI models, the Park-Ang damage index is utilized to calculate the local and global damage index. This damage indicator is divided into two categories: deformation and energy-based indices. The current study's findings show that the SSSI model increases the roof displacement response by up to 58%. When the SSI and SSSI cases are compared, it is discovered that the SSSI case increases the inter-story drift ratio by 118% in the moment frame and by 53% in the braced frame. In addition to this, it is shown that,  in general, a second structure may have a significant impact on the frequency amplitude of a system that is adjacent to it. According to the data, the amplitude of the power spectrum density in the SSSI model is more than 44.6% higher than that which is found in the SSI model. According to the findings, the damage index predicted by SSSI models is 32% greater than that predicted by SSI models. It is important to keep in mind that constructing a second building next to an existing one is often counterproductive and raises the possibility of damage occurring in both of the structures. As a result of the findings, it is clear that more study into SSSI phenomena and their influence on structural seismic risk is necessary. This is because it has been shown that adjacent buildings may significantly increase a structure's vulnerability to earthquakes.

According to the American Building Loading Code, progressive failure is defined as the spread of failure in a structure from one element to another, which ultimately leads to the failure of the entire structure or a large part of it. Lead to this type of failure are: car impact, gas explosion, aircraft collision, construction error, fire, accidental overloading of members, explosion, etc. Most of these accidents have a short impact time that in The result leads to dynamic responses. In this research, 100 types of models will be considered and the progressive collapse reference codes will be used for analysis and the application software will be used to achieve the answer under nonlinear static analysis by removing the column and performing nonlinear static analysis. The behavior of structural members against this phenomenon will be evaluated and finally the results will be controlled by the rules in the regulations and the final behavior of the structure against this phenomenon will be examined. Artificial neural networks have been used as a powerful tool in various fields of engineering and their use is increasing. Civil engineering and the study of the behavior of structures are no exception to this rule and neural methods have been used in it. In this study, three types of neural networks have been used to investigate the phenomenon of progressive collapse. Input and output parameters are selected and modeled with the help of evaluation indicators of this phenomenon. Finally, by comparing the performance of artificial neural networks, the most successful type of neural network has been proposed.

The degree of control of the response and performance of structures under external loads is one of the most important issues in structural and earthquake engineering. Today, the use of modern systems to control structural vibrations has expanded significantly. Viscous dampers are one of the most common tools for controlling structural vibrations against external loads. One of these foreign burdens could be an explosion caused by terrorist attacks. In this research, it has been tried to investigate the behavior of structures with viscous dampers based on energy balance under explosion load. For this aim, two 10-story structures with Moment Resistance Frame (MRF) system and steel Moment Resistance Frame with viscous damper under different explosion scenarios have been analyzed and the dissipated and absorbed energies in the energy balance due to external work have been evaluated. First, to better understand the behavior of these structures, the performance of the structures is evaluated based on the plastic hinges and the relative displacement of the studied stories and finally the effect of viscous damper in reducing the damage of structures using energy balance concepts. The results show that in general, viscous dampers can reduce the damage to an acceptable level and control the behavior of the structure.

Recent earthquakes have shown that, besides the seismic forces, the interaction between faults and structures could cause extensive damage to the surface and underground structures. Field observations showed that the need for design measures and regulations for fault loading due to fault movement in areas with active faults seems necessary. In this study, the three-dimensional finite element model in Abaqus finite element program to study the behaviour of a 9-story steel structure with a moment frame system based on three types of mat foundations, piles group, and diaphragm walls was used on sandy soil. The performance of the structural-foundation system was evaluated taking into account the structural and geotechnical performance goals such as the drift ratio of floor levels, displacement of the foundation and distribution of bending moment and shear force along with the pile and foundation. In this study, the position of the foundation relative to the fault line and the foundation type were considered as key parameters. The results of the analysis showed that the best performance in reducing the ratio of the permanent drift ratio of the floors related to the structure with the diaphragm wall system. This was in the case that the edge of the foundation is tangent to the fault line, this value reaches 1.62%. Also, in most cases, in small amounts of fault movements, the mat foundation system had a smaller difference than the other considered foundation system in this study.

Behavior coefficient is one of the important parameters in calculating the loads affecting the structure in structural analysis. In this research, different aspects of behavior coefficient have been identified and have been raised as the main issue of the present study. Eccentric Bracing Frames (EBF) braces are also used as a useful tool in steel structures. One of the important issues in steel structures with EBF braces is the problem of link beams. The main purpose of this study is to investigate the coefficient of behavior of steel frames with link beams and different heights by considering the effect of soil-structure interaction, which were studied based on increasing nonlinear static analysis in four, eight and twelve floor structures. The variable of link beam length along with the effect of soil-structure interaction has been evaluated. In the study of the effect of soil-structure interaction on the cover curve, it was observed that considering the effect of soil-structure interaction, the displacement in the pushover curve increases but the base shear force decreases. It is also observed that the values of behavior coefficients decrease in the presence of the effect of soil-structure interaction, which can be due to the decrease in base shear values and increase in displacement values. The general trend of determined graphs has been to increase the values of the coefficient of behavior due to the increase in the length of the link beam. Also, the values of behavior coefficients have been reduced by considering the effect of soil-structure interaction.

History of past earthquakes and the destruction caused by them show that irregular structures have the vulnerability potential more than other structures. Reinforced concrete (RC) walls are commonly used as the primary lateral-force-resisting system for tall buildings, although for buildings over 49 m (160 ft), IBC 2006 requires use of a dual system. Use of nonlinear response history analysis (NRHA) coupled with peer-review has become a common way to assess the expected performance of tall buildings at various hazard levels to avoid the use of a backup Special Moment Frame for tall buildings employing structural walls. Modeling of the load versus deformation behavior of reinforced concrete walls and coupling beams is essential to accurately predict important response quantities for NRHA. The design of tall buildings essentially involves a conceptual design, approximate analysis, preliminary design and optimization, to safely carry gravity and lateral loads. New developments of tall buildings of ever-growing heights have been continuously taking place worldwide. Consequently, many innovations in structural systems have merged. The design criteria are strength, serviceability, stability and human comfort. The strength is satisfied by limit stresses, while serviceability is satisfied by drift limits in the range of H/500 to H/1000. Stability is satisfied by sufficient factor of safety against buckling and P-Delta effects. The factor of safety is around 1.67 to 1.92. The human comfort aspects are satisfied by accelerations in the range of 10 to 25 milli-g, where g=acceleration due to gravity. The aim of the structural engineer is to arrive at suitable structural schemes, to satisfy these criteria, and assess their structural weights in weight/unit area in square feet or square meters. This initiates structural drawings and specifications to enable construction engineers to proceed with fabrication and erection operations. The weight of steel is often a parameter the architects and construction managers are looking for from the structural engineer. This includes the weights of floor system, girders, braces and columns. The premium for wind is optimized to yield drifts in the range of H/500, where H is the height of the tall building. In this paper, the seismic behavior of steel frames with reinforced concrete core in the duplex and common high rise building are investigated. In this research, linear analysis under 3 kind of earthquake loading (equivalent static, spectral dynamic and dynamic time history) and wind load on structures with 20, 40 and 60 stories have been accomplished and different parameters, such as structure’s base shear and effect of increasing height on seismic behavior have been discussed. Based on results, making structures duplex, causes changes in modal shapes and mass participation percentage of modes. For this reason, there is no change in linear static methods and wind load of common structures and duplex structures response but it has seen changes in structure’s response for 12 far and near earthquake records. In some earthquakes, base shear has been increased maximum 32 percent of common structure’s base shear and also there is no change in base shear in some of them. In some structures, base shear has been decreased maximum 16 percent of common structure’s base shear.

The occurrence of terrorist attacks and bombings in recent years has shown the importance of constructive safety against blast loading more than ever before. Blast is one of the rare events that can cause many damages to the buildings during their lifespan. Investigating the behavior of structures under blast load can help to make managerial decisions for the safety of structures. In this research, the behavior of steel structures with seismic isolation of LRB type in different explosion scenarios was investigated using the concept of energy balance. Two types of 10-story steel structures with isolated and fixed-bases have been subjected to 12 types of blast loadings after designing. Initially, the performance of the structures under these loadings and the rotation of the plastic joints and drift of structures were evaluated and then, using the time history curves the depreciated and absorbed energies of the structure, balance of energy in each scenario are studied and the role of isolators in the creation of energy balance is investigated. The results show that the existence of depreciated plastic strain energy in seismic isolators reduce depreciated energy in other members and the amount of their damage will be decreased. Also, the percentage of internal energy in the energy loss caused by the explosive charge has also been evaluated.In structures with a seismic separation, the energy loss ratio of the elements of the beam and column is less than that of the fixed foot structure.

There are several methods for structural analysis and design, one of which is equivalent to static analysis. There are limitations. 4 models are examined in this research, the general shape of the plan of a five-story frame, in the first sample is a regular frame, the second sample is a mass irregularity in the first floor, the third sample is a mass irregularity in the third floor and the fourth sample is a mass irregularity in the fifth floor and Its seismic loading has been studied using the standard design spectrum of 2800 fourth edition. Mass irregularities in the first floor with a difference of 45% were higher than other classes and mass irregularities in the third floor were 15% less than the regular sample. Dynamic time history analysis was performed using different near and far fault earthquakes. Responses of lateral and relative displacement were calculated for different stories and compared with the allowable values of the regulations. As a deductive result of this study, we can point to the conservatism of the equivalent static method in estimating the incision and the inability of this method to consider the shape of the load. The results show a decrease in the seismic capacity of structures with mass irregularities in height and therefore it is recommended to avoid creating mass irregularities in height as much as possible.

Nowadays terrorist attacks on civilian facilities have increased.Paying attention to the design of construction sites against the impact loads due to the explosion is important. Identifying the nature of explosive loads and their impact on the structure is one of the important issues to be studied. The explosion is one of the complex phenomena including high strain rate which highly affects the structural elements behavior. Regarding the fact that existing steel structures are typically designed based on conventional gravity and seismic loads, it is required that the performance of these structures be investigated under the explosion load. In this study, the evaluation of simple steel frame behavior with different dampers against explosive load and earthquake is investigated. Nonlinear dynamics analysis is performed on models with 3, 5 and 10 floor structures and in accordance with UFC 3-340-02 at two different levels of explosive charge, in the SAP 2000 software. The results show that between XADAS, friction dampers, Viscose in diagonal system, in the seesaw system, U-shaped with flexural and shear performance and proposed pipe dampers, The displacement dampers have the greatest impact in reducing the structure response. From this Friction damper and pipe and U-shaped with flexural function is more effective.

Optimization is one of the most important issues in civil engineering. In this research, artificial neural network (ANN) has been used to optimize the structure of steel structures. The multilayer neural network of perceptron, one of the most widely used neural networks, has been used. Different structures of artificial neural network with different number of hidden layers and number of different neurons have been modeled to achieve the best architecture of artificial neural network model. Neural network models have acceptable success in the optimization process. Dimensional properties of structures have been used in all these models. Models used for optimization have four input parameters, one output parameter is used. A large set of structural models has been used as a database. In the perceptron neural network, networks with different architecture with one and two hidden layers have been used to determine the most accurate network. Extracting and presenting the relationships governing a neural network model gives the user more confidence in using such models, thus facilitating the application of such models in engineering work.

Concentrically braced frames (CBFs) have become prevalent as a lateral load resisting system due to their rigidity, low lateral displacement and ease of implementation over the last three decades. These advantages encourage the increasing utilization of this system in the construction industry. Despite the advantages of CBFs, the lack of ductility and buckling of the bracing element before yielding is the main disadvantage this lateral system. In the last three decades, studies have become focused on the ductility and energy dissipation of the CBFs that were modified in terms of using dampers and fuse segments. The current study aims to presents an innovative Composite Buckling Restrained Fuse (CBRF) to be used as a bracing segment. CBRF with relatively small dimensions is an improvement on Reduced Length Buckling Restrained Brace (RL-BRBs) as a hysteretic damper with different performance in tension and compression. Extra tensile elements in a novel configuration were used to compensate for the limitation of tensile strength that exists in bracing elements containing ordinary fuse segments. Here, some key design parameters of CBRF such as length and cross-sectional area of the core are discussed theoretically. Two specimens were designed and tested under cyclic loads. Moreover, the hysteretic response of the specimens was evaluated to calculate their strength adjustment parameters. The results indicate that the proposed CBRF has a ductile behavior with an average strain of 5% and high energy absorption capacity along with sufficient tensile strength.

The tuned mass damper is one of the latest structural control system that helps the structure to damp the dynamics loads. So far using the Tuned Mass Damper (TMD) on the roof or a few dampers was installed at several points at the height of the building or other levels of the building was popular, but this system has some disadvantages like considering a significant mass as overhead which requires special material and enough space to install. Therefore, in this research the efficiency of Multiple Tuned Mass Damper (MTMD) in tall building is investigated. Also the effects of MTMD on regular and irregular tall moment resisting buildings are studied. The 10,15 and 20 story buildings with regular and irregular U and L shapes are modelled,analysed and designed, using the SAP 2000. Then the models equipped with MTMD and analysed in nonlinear dynamic mode under the earthquake records of the near and far fault , using OPENSEES. Afterwords, the models compared considering different earthquake records.finally the results showed the MTMD on the roof had seismic performance with 40% reduction of the base shear , 30% reduced absolute displacement of the stories and 35% smaller acceleration, which increased the efficiency of the models and the situation have improved their seismicity.

By reviewing previous studies in the field of roof’s collapse, an efficient analytical method is required to simulate the impact mechanism and failure procedure. Hence, the purpose of present study is mainly to analyze the beams' impact. Consequently, upper and lower beams are considered to survey the collision effects of upper beam’s equivalent concentrated mass to the lower beam’s midspan in a way that an initial impact caused by mass is taken into account. At first, the maximum bending moment at the midspan is calculated by assuming linear behavior and employing the relations which involves the kinetic energy of concentrated mass and potential energy of the lower beam. Then, studying a conventional steel frame demonstrates that the bending moment is about eight times greater than the bending moment capacity of lower beam, therefore it would lead to formation of a plastic hinge at the midspan. In continue, the mentioned relations are solved by using the equations of motion including inertial effect. The results are used to calculate velocity in different sections of lower beam. Subsequently, the equilibrium equation is employed in the middle of lower beam and a virtual hinge at an arbitrary section which is tending in a wave form to supports is considered. Due to mentioned assumptions by investigating hinge formation behavior, the time of hinge tendency to the supports is calculated. Additionally, displacement values along the lower beam are obtained. Finally, the diagrams and tables are represented by using the obtained equations and compared with the lower beam's displacement capacity. The results demonstrate that the lower beams will collapse due to the collision of concentrated mass of upper beam and progressive collapse occurs in lower stories. Finally, for more accuracy of present study, the effect of secondary impact of upper beam on the lower beam is considered.

Today, many elements are used to control vibrations and reduce structural damage. Pall friction damper is one of these elements. This energy-dissipating damper can help to reduce structural damage. Various loads such as seismic and blast impose significant amounts of energy on the structure. This energy must be absorbed or dissipated by structural elements to create a new energy balance in structures. In this research, tried to investigate the performance of a ten-story building with a pall fraction damper under blast loads using the concept of energy balance in a structure. Tow ten-story steel MRF structure whit Pall fraction damper are exposed to 12 blast loadings and their performance has been investigated using the concepts of plastic hinges, drift and strain energy of plastic. The results of the study show that the plastic hinges, the story drift and the strain energy in structural elements in the model with a frictional pallet damper are less than the model without a damper. The dissipated energy in the pall friction damper reduces the contribution of plastic strain energy to other members, and reduces structural damage.

One of the most important and fundamental issues that civil engineers always deal with today due to its importance is the study of the performance and behavior of structures under different conditions. In addition, in many cases, buildings are analyzed and designed separately and without considering the effect of other elements, including the foundation and soil of the infrastructure, which in many cases creates irreparable risks; Therefore, it is necessary to study and evaluate the effect of soil-structure interaction on the performance and design of buildings in order to manage the cost and time of construction projects. In this study, the performance of steel structures with concentric brace of 5, 10 and 15 floors by considering the interaction of soil structure in three different soil modes using nonlinear dynamic analysis of time history under 3 near-fault earthquakes has been done. The results show that considering the interaction of soil and structure increases the accuracy of structural responses.