جستجوی مقالات مرتبط با کلیدواژه « ساختمان بلند » در نشریات گروه « عمران »

In procedure for analysis, design and optimization of reinforced concrete buildings, for most or maybe all regular buildings, different parts of the procedure for different parts of the building, including main structure and its foundation, are usually carried out independently. This means that these structures are mainly analyzed and designed by supposing a fixed-base, and then, forces at the foot of columns are obtained and used to analyze and design the foundation. Thereby, no attention is paid to the effects of foundation settlements on the distribution of forces in structural elements. Interaction between the structure, the foundation and its subsoil (flexible-base), changes the actual behavior of the structure compared to the method in which the structure is investigated alone (fixed-base). In this paper, various RC buildings, including low-, mid- and high-rise types, with foundations and soil under their foundations in three different layers, with a depth of each layer equal to ten meters, are modeled using SAP2000. Also, all the frames are optimized using Artificial-Bee-Colony algorithm in MATLAB, subject to stress and drift constraints. The results show that, since in a structure with optimal design the values of stress in elements and drift of stories are usually very close to the maximum allowable limits, hence, a slight increase in structural response, induced by soil-structure interaction effects, may lead to the violation of optimal design constraints. Therefore, taking not into account such effects in design optimization of structure, may lead to not only a non-optimal but also an infeasible design.

Tuned mass damper(TMD) is an efficient tool to control wind-induced vibrations of tall buildings. Previous studies on the effect of TMD are generally limited to specific conditions. In the present study, the effect of the mass and installation height of TMD on the wind-induced vibration control of tall buildings are investigated. An example of tall building with the height 400 m and square variable cross section is presented. The analytical model of the building is assumed as a multi-degrees-of-freedom vertical cantilever beam with the masses lumped at the nodes. The wind-induced responses of the structure are computed using the frequency domain analysis and the random vibration method for a wide range of studied parameters. The results indicated that the vibrations of the structure and TMD system decreases with increasing the mass of the TMD. For instance, the 100 and 600-ton TMD installed at top-floor reduced the top-floor crosswind acceleration by 31 and 48 percent, respectively. By increasing the installation height, the control effectiveness of the system increases, while the vibration of the TMD does not change considerably. For a 300-ton TMD installed at 320 and 400 m heights, the crosswind acceleration reduced by 33.72 and 41.28 percent and the RMS displacement of the TMD at these heights were 58.68 and 54.92 cm, respectively.

Population growth, space limitation, economic and social factors are some of the reasons that led to the construction of tall buildings. However, the invention of light weight and durable materials has made tall buildings with low damping and high vibration period and sensitive to wind forces. Therefore, the study and analysis of tall buildings under wind forces seem necessary. The purpose of the present research work is to provide the necessary solutions for performance based design of a tall building having elliptic plan shape against the wind. In the present study, a tall elliptical building is exposed to wind interaction. Moreover, wind modeling and building specifications are performed in ANSYS.17 software. To simulate the atmospheric boundary layer in the software as a virtual wind tunnel, two parameters of the mean wind speed and turbulence includes length and intensity, are required. The results of software analysis were presented as a time history of longitudinal and transverse acceleration at three different heights of the building for four various mean wind speeds in short afterbody orientation for perpendicular to wind direction and 72 m/s in wind direction, then the standard deviation of acceleration was calculated and placed in standard curves of the regulation and interpreted. The effect of different factors on the performance of tall buildings against the wind is a type of response (alongwind or acrosswind), mean wind speed, orientation of the building, and the height of the desired point from the ground. Results show that the acrosswind response of tall buildings to wind does not follow a specific law and is a function of the mean wind speed, height of the building, and the alongwind and acrosswind response of the building ,i.e, displacement and accelerations .

Increasing the population of large cities and lack of construction area have increased tall buildings. In the present article, the overturning moment and base shear due to the along-wind and earthquake loads have been compared for tall buildings. The buildings are assumed to be located in Tehran city on the type 2 soil and the structure is regarded as a vertical cantilever beam. The along-wind and earthquake loads are computed using the gust-loading-factor method and the linear spectral approach, respectively. First, an example of 120-m high building is presented and evaluated, and then, the effect of the height and aspect ratio parameters are examined in the ranges 80 and 200-m, and 5 to 10, respectively, for the two square and circular cross-sections. For the primary example, the earthquake overturning moment and base shear were dominated respectively by the first and second vibration modes. For the square and circular sections, the ratio of wind-induced overturning moment to the earthquake effect were 1.1 and 0.81 respectively. For the parametric study, the wind and seismic overturning moments were equal to each other at the specific values of the studied parameters, and the wind effects were dominant for the higher values of these parameters. For instance, for the square cross section, the equal point of overturning moment and base shear were respectively 110m and 175m. Finally, by increasing the height and aspect ratio the wind forces were dominant.

Towers and tall buildings have been considered since the beginning of human civilization and providing the suitable stiffness and especially the lateral stiffness is one of the basic factors in the design of these structures. In this matter outrigger systems are very effective in reducing the response of the structure to lateral loads. Also, the occurrence of earthquakes and its destructive effects in recent years has increased the importance of applying the behavior and performance criteria to control the distribution of resistance and deformation in structural components. Therefore, it is necessary to provide an optimal design with economic justification capability, the main purpose of which is to achieve a reliable level of safety and performance against natural hazards. In this research, in two structures with 24 and 36 floors, using modified dolphin echolocation metaheuristic algorithm (MDE), the performance based design of steel structures equipped with outrigger system while layout optimization of the brace has been done. All performance design constraints are considered in accordance with FEMA regulations. The results indicate the appropriate behavior of structures with outrigger, the effect of outrigger position on its performance and the process of achieving optimal structure. as the 36-story structure in the optimal position of the outrigger installation, the weight of the structure has decreased by about 3.9% compared to the installation position at equal height distances. In both structures, the criterion of story drift and axial length change of bracing members prevails and the necessity to consider the effects of higher modes in studying the behavior of the structure is emphasized so that by increasing the number of floors and higher modes influence, the optimal position of outrigger is shifted to the upper floors.

In this numerical investigation, the effect of upstream and downstream interference of two identical tall buildings was evaluated using the computational wind engineering (CWE) method. In order to simulate three-dimensional turbulent wind flow with Reynolds numbers in the range of 1.4×〖10〗^4<Re<8×〖10〗^4, the Large Eddy Simulation (LES) model was used. Mean and fluctuating coefficients of drag and lift and pressure distribution were used as the main criteria to evaluate the aerodynamic response of the principal building in different conditions of interference. Streamlines and vorticity contours were presented and their relationship to aerodynamic results was interpreted to provide a better understanding of the physics of the problem. According to the results, the shielding effect of the interfering building in most interference cases led to a reduction of the mean drag coefficient of the principal building compared to the isolated case. Compared to the isolated building, depending on the location of the interfering building, the fluctuating lift coefficient either increases or decreases.Upstream interfering buildings with sufficient distance to the principal building lead to an increase in the fluctuating lift coefficient of approximately about 50 percent. While, the fluctuating lift coefficient of the principal building decreases up to 37 percent, due to the closely spaced tandem interference states. While the mean pressure coefficient at the windward surface is not significantly sensitive to the interference states, it is strongly influenced by the different states of the interference at the lateral and leeward surfaces. Aerodynamic parameters were less sensitive to Reynolds number variations due to the fixed position of the flow separation in the sharp corners of the rectangular section and the zero angle of attack in this study. Changes in the Reynolds number resulted in variations of about 4 to 10% in the drag and lift coefficients of the principal building.

Advantages of high-rise buildings with reinforced concrete cores include lower construction costs, higher construction speeds, and the possibility of creating a wider outdoor architecture compared to other high-rise structural systems. As the height of the building increases, the control of lateral displacement of these structures against seismic loads is challenged. The use of arm restraint in structures with cores is one of the welcomed solutions. In this article, first, tall structures with reinforced concrete cores with and without arm restraints are analyzed and designed. The arm restraint has a buckling type brace and the effect of its position on several different levels is investigated. Next, the core modeling is performed with the help of fiber elements with nonlinear behavior for the wall and arm restraint in software. Interclass relative, lateral displacement, anchor and shear are investigated. The results show that the lowest amount of relative lateral displacement between classes is related to the placement of the arm restraint at the level of 0.75 total height from the base level. Advantages of high-rise buildings with reinforced concrete cores include lower construction costs, higher construction speeds, and the possibility of creating a wider outdoor architecture compared to other high-rise structural systems. As the height of the building increases, the control of lateral displacement of these structures against seismic loads is challenged. The use of arm restraint in structures with cores is one of the welcomed solutions. In this article, first, tall structures with reinforced concrete cores with and without arm restraints are analyzed and designed. The arm restraint has a buckling type brace and the effect of its position on several different levels is investigated. Next, the core modeling is performed with the help of fiber elements with nonlinear behavior for the wall and arm restraint in software. Interclass relative, lateral displacement, anchor and shear are investigated. The results show that the lowest amount of relative lateral displacement between classes is related to the placement of the arm restraint at the level of 0.75 total height from the base level. Advantages of high-rise buildings with reinforced concrete cores include lower construction costs, higher construction speeds, and the possibility of creating a wider outdoor architecture compared to other high-rise structural systems. As the height of the building increases, the control of lateral displacement of these structures against seismic loads is challenged. The use of arm restraint in structures with cores is one of the welcomed solutions. In this article, first, tall structures with reinforced concrete cores with and without arm restraints are analyzed and designed. The arm restraint has a buckling type brace and the effect of its position on several different levels is investigated. Next, the core modeling is performed with the help of fiber elements with nonlinear behavior for the wall and arm restraint in PERFORM-3D software. Interclass relative, lateral displacement, anchor and shear are investigated. The results show that the lowest amount of relative lateral displacement between classes is related to the placement of the arm restraint at the level of 0.75 total height from the base level.

As the height of building increases, requirements of structural stiffness and stability become more important than the strength criterion. Each tall structure basically behaves like a vertical cantilever under lateral loads and the outrigger-braced system is a favorable system in tall structures (Taranath, 1998). This type of structure has a central core connected to outer columns by outrigger trusses or strong girders. The position of outrigger-braced system has a significant impact on the structural efficiency. Therefore, determining the position of outrigger braces is an important part of design process; it is mainly done experimentally and does not lead to good economic results. In this study, the particle swarm optimization (PSO), modified dolphin echolocation (MDE), Enhanced colliding bodies optimization (ECBO) and grey wolf optimization (GWO) algorithms are utilized to determine the optimum position of outrigger-braced systems in tall steel structures.

The need for adequate and appropriate living and working spaces and population density and the increasing cost of land and use of high-rise buildings requires growing research on these structures. The tube system is one of the most suitable structural systems for high-rise buildings. The purpose of this study was to obtain one of the most important dynamic properties, namely the natural frequency (ω) for a number of tall buildings with a pyramidal tube system. A tube-in-tube approximate method for analyzing and calculating the natural frequency of a combined pyramidal tube system with shear wall pyramid is presented. The size of the pyramid angle of the tube frame varies with the length (height) of the structure. The proposed method enables us to calculate the natural frequency of vertical and curved tall buildings with the help of computer programming. The models were analyzed using finite element form and mathematical analytical method. The results show that the investigated method correctly calculates the natural frequency and is in good agreement with the finite element results and has better compatibility with pyramidal angle structures with higher altitude, and the resulting computational error is much lower. The results of the proposed mathematical model provide an easy-to-use method for understanding the dynamic properties of structures and the effects of angle-frequency variations. Furthermore, this analytical method has the least error for tube systems with tube-in-tube and the highest error for shear wall pyramidal systems.

By increasing the height and slenderness of tall buildings, the wind-induced dynamic response especially crosswind response becomes the governing parameter in the occupant comfort requirement of tall buildings. In the present study, crosswind response of tall buildings has been investigated using the frequency domain analysis of multi-degrees-of-freedom systems based on the random vibration method. The tall structure has been modeled as a vertical cantilever beam with the masses lumped at the nodes. All the modeling and analysis procedure, including element meshing, determining the transfer matrix, calculating the matrix of crosswind force spectrum, and the numerical integration to obtain the root-mean-square (RMS) displacement and acceleration responses are carried out using MATLAB software. The effect of different parameters, such as basic wind speed, aspect ratio, side ratio for rectangle section and top to bottom width ratio for tapered tall buildings has been investigated. The results show that the slenderness ratio has an important role on the across-wind response. For tapered buildings, the crosswind displacement response decreases considerably with increasing the top to bottom width ratio.  For the studied tall buildings, the crosswind acceleration response is higher than the occupant comfort level and it requires to be reduced using an appropriate control strategy.

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.

forms of the outrigger or belt truss structure have high performance in reducing the response of tall structures against side loads. However outriggers system are not considered as a seismic system in design codes. In this paper seismic behavior of tall buildings with outriggers will be checked and the effect of adding outrigger on the seismic behavior of steel tall structures in term of capacity of seismic intensity corresponding to the level of performance of collapse, Distribution of seismic requirements in high of structures demand curves corresponding to the general instability of structures and Fragility curves will be studied. Therefore, in the first three buildings of 20, 25 and 30 floors in three dimensions are designed so that the effects of outriggers not considered in the initial design and in terms of members resistance and the relative displacement (drift) have passed some regulations.
To do this, the three structures is designed using 3D model So that the effects of outrigger are not considered in the initial design and in terms of resistance members as well as the relative displacement of stories have passed limits of design code. and then one of main frame of structure is analyzed using “Opensees” software and moment frame structural system and CBF with regard to inelastic behavior in both the presence and absence of outrigger checked by IDA analysis. The results show

Tall buildings with Cor wall are growing in the structural industry. Generally, occurring one plastic hinge in the base of the structure is acceptable. In this research,20, 30 and 40 story buildings are designed according to the practice and response spectrum analysis. Then, the base of the structures are modeled by inelastic elements and seven earthquake records are applied to the models.The results show that the moment demands around the mid-height of the reinforced concrete core walls are more than expected values.This matter result in more reinforcement than the amount required from respons spectrum analysis.Another approach is to use another plastic hinge in the mid-height of the core wall.Nonlinear time history analysis of the model with capability of two plastic hinge shows that the moment demand will decrease more than 30 percent for the studied buildings.A third approach is the extended plasticity in which the core wall can have plasticity in anywhere along the height of the core wall. The results show that the interstory drift of such models is not satisfactory. The behavior of the wall will be studied in each approach.