جستجوی مقالات مرتبط با کلیدواژه « Stability » در نشریات گروه « عمران »

Various geosynthetics reinforcements used to stability of soil slopes and geocells due to the three-dimensional nature of cells proposed by many researchers. Most current researches of reinforced soil analyze are two dimensions, which is inefficient for modeling the 3D geocell element. In this paper, the static and dynamic response of reinforced soil studied by three-dimensional modeling.For this purpose, Plaxis-3D finite element software has been used to modeling with different geometric characteristics. The results of this study show that tVarious geosynthetics reinforcements used to stability of soil slopes and geocells due to the three-dimensional nature of cells proposed by many researchers. Most current researches of reinforced soil analyze are two dimensions, which is inefficient for modeling the 3D geocell element. In this paper, the static and dynamic response of reinforced soil studied by three-dimensional modeling.For this purpose, Plaxis-3D finite element software has been used to modeling with different geometric characteristics. The results of this study show that the geometry of the wall including the height and angle of the embankment as well as the arrangement of geocell cells at different level (height) and the length of the penetration affect the lateral displacement and the embankment stability coefficient.he geometry of the wall including the height and angle of the embankment as well as the arrangement of geocell cells at different level (height) and the length of the penetration affect the lateral displacement and the embankment stability coefficient.

Due to expansion of population and construction, also due to lack of space, weakness of ability to respond to the traditional method, the need to introduce and investigate the industry in the building is more evident. For this reason, due to the ineffectiveness of traditional systems in mass production, it seems necessary to pay attention to the industrial methods of building production. For decades, plans for the industrialization of building production have been started in the country, but they have not been successful because by importing a few manufacturing plants that are largely dependent on industrialized countries in terms of technology and there are no regulations and technical knowledge corresponding to it in the country, it is not possible to Industrialization goals achieved. Industrialization should begin with a careful examination of the world's leading technologies and ensure the possibility of responding to cultural, environmental and climatic needs, as well as its ability to adapt to the construction patterns in the country and continue with cultivation to strengthen this technology. In this research, firstly, by conducting library studies, a list of effective factors in increasing the stability of launching industrial construction projects was prepared, and through questionnaires based on the Likert scale, the opinions of experts in the field of industrialization of construction in Kerman city were collected, and after checking validity and reliability of the questionnaire, The grouping of factors was done using specific assumptions, according to the results, then the decision matrix was made based on indicators and options, the formation and classification of points in fuzzy intervals was done, finally, using the weighted least squares method and Yager method, the importance coefficient of the indicators according to Base on the findings of the research, "economic", "social and political", "management", "qualitative" and "environmental" indicators have the highest impact respectively.

One of the most important issues in traffic safety is assessing the stability of the fatalities trend. In order to evaluate the effectiveness of the road safety plan to achieve a specific goal or policy objective, it is necessary to measure the stability of the number of fatalities and injuries. The purpose of this study is to study the changes in trend of the fatalities in the provinces of the country, to investigate the ability to model the optimal trend in road safety and also to identify provinces with poor performance with the aim of investigating the causes of a steady upward trend in casualties. In this study, in order to evaluate the safety stability of rural roads in the provinces of Iran, the development of simple trend lines and exponential trend lines has been considered. These trends were developed for the number of casualties on the rural roads of the province, as well as due to the shocks and fundamental changes in the volume of road traffic in recent years for the number of fatalities to the exposure (multiply the length of the road and the volume of traffic) in the province. Based on the results and findings, the provinces of Khorasan Razavi, Kurdistan, Gilan, and Hamedan are the provinces that have had a good performance in terms of reducing the number of casualties caused by accidents on rural roads. Therefore, the best experiences, plans and, documents of the mentioned provinces can be used in order to strengthen and improve the level of road safety in other provinces. Sistan and Baluchestan province also has a steady increasing trend in fatalities due to rural accidents and therefore needs special attention and detailed planning to investigate the causes of this trend.

Due to economic efficiency, members with variable cross-sections are widely used in steel structures, especially industrial sheds. But with the increase in temperature caused by thermal changes, the strength and hardness characteristics of industrial frame members decrease rapidly. It is necessary to check stability (thermal buckling) in industrial frames for a safe and complete design. In this article, thermal buckling and vibrations caused by thermal changes of non-radiative elastic columns are investigated by the Rayleigh-Ritz method. In the next step, the weak form of the differential equation is calculated and the Chebyshev series is used as the transverse displacement function and the weight function. In the last step, after extracting material stiffness matrices, geometric stiffness, and mass matrix, the eigenvalues of the equation are checked. The results show that the simultaneous increase of the slope of the section and the coefficient of thermal changes significantly affect the effective length coefficient and reduce the buckling load capacity in all the boundary conditions of different supports. Also, the simultaneous increase of the slope of the cross-section and the coefficient of thermal variation, depending on the type of boundary conditions of the support, cause an increase or decrease in the dimensionless natural frequency. Aligned curves are used to present results and display graphs to apply results in engineering calculations. The results of previous research are used for validation. There is an acceptable agreement between the present results and previous studies.

Real-time hybrid simulation (RTHS) is a form of testing where the physical component of structure communicate with numerical model which simulates the behavior of the rest of the structure. Interface forces between the experimental and computational substructure are imposed by an actuator. The resulting displacement and velocity of the experimental substructure are fed back to the computational engine to determine the interface forces applied to the computational and experimental substructures for the next time step. In this paper, the RTHS technique is used to conduct experiments with a numerically simulated structure and physically tested tuned liquid damper (TLD). One very important factor which causes instability in RTHS is the actuator's inability to perform the commands from the simulator in real-time. In RTHS, an actuator dynamic is approximated by a pure time-delay, and the time-delay in the closed loop system causes inaccuracy results or even instability. Therefore, Delayed Differential Equation (DDE) is used to determine the critical time-delays depending on the TLD parameters. Then, the compound stability condition is investigated for a general case and the results show that the mass ratio has a lower limit for low delays and upper limit for high delays to remain stable. As frequency and amplitude ratios increase, the margin of stability for the mass ratio increases.

The incidences of fire and earthquake are the two serious hazards to buildings that jeopardize the safety of occupants. Much research has been carried out on the effect of seismic loads on structures, but little is known on the concomitant impact of these threats, specifically fire before an earthquake. Besides, many buildings are currently in use after a fire event without any particular retrofitting, which are exposed to future earthquakes like undamaged structures. In this research, the behavior of a moment-resisting steel frame is studied in two cases of damage by fire before an earthquake as well as the post-fire earthquake damage. Accordingly, the structure under study was designed following the Iranian Standard for Seismic Resistant Design of Buildings (Code 2800, 3rd Ed.). A set of ten fire scenarios was considered for thermal analysis. The results indicate that the structure remains stable after seismic loading in the case of post-fire earthquake, given that a maximum temperature of 600-700 °C is experienced in different fire scenarios based on the Eurocode standard fire curve. However, in the case of post-earthquake fire, the maximum stability temperature after seismic loading lies in the range of 600-800 °C for different fire scenarios, according to the ISO 834 fire curve. In the former case, deflection of the beams increases downward rapidly upon reducing the stiffness and strength of steel as temperature exceeds 600 °C, while in the latter case, the beams deflection increases downward sharply in the temperature range of 650-800 °C.

Strengthening breakwaters can reduce the damages that lead to hydraulic instability. Aiming to enhance the stability of reshaping breakwaters, this experimental study presents a method for controlling and reducing structural damages against waves by attaching a submerged obstacle to the structure toe and installing a floating wave barrier at a certain distance. In the tests, the breakwater was exposed to a total of 3000 random waves based on the JONSWAP spectrum. By generating an integrated 3D digital model of the structure using close-range photogrammetry, the displacement of armour units was recorded, and the damage parameter was calculated. Moreover, a comparison of the results between reinforced and simple breakwater indicated that the damage parameter was reduced by 37.19 and 34.14 percent by, respectively, attaching the submerged obstacle and installing the floating wave barrier, which confirms the good performance of the proposed models. Breakwater reinforcement with the submerged obstacle and the floating wave barrier simultaneously reduced the damage parameter by 51.79 percent, which was the highest efficiency among the different models. Also, the results show that with increasing the stability number, the damage parameter also increases, and the interaction between the wave steepness and the damage parameter indicates that the damage parameter decreases with increasing the wave sharpness values.

The steel moment resisting frames (SMRF) are the most common type of structural systems for bearing the gravity and lateral loads while this system is one of the more vulnerable structural systems under fire loading due to rapid descent of stiffness and strength properties of steel with temperature. In this regards, many researchers experimentally investigated the behavior of steel structural elements (e.g. Column, Beam, Connections) when exposed to fire. Most of these researches are limited to a sole element. Therefore, in this paper the entire behavior of the Steel moment resisting frames with intermediate ductility under different fire scenarios and for several gravity load ratios are studied through the numerical models. Three steel moment resisting frame with different stories and gravity load ratios in this study are considered. The analytical models of the studied frames are modeled in ABAQUS software. The results show that in different cases depending on the ratio of the gravity loads, different failure modes occur. In cases with the normal gravity loads, progressive collapse does not occur while with increasing the gravity loads; the vulnerability of structures increases and the potential of progressive collapse are increased.Fire loading, Steel moment resistant frame, Progressive collapse, Numerical models

Due to heavy rainfall, underground water level and pore water pressure increase each year, which can cause failure of the earthen slopes. Retaining wall is one of the main structures that is used to increase the earthen slopes stability. In the present study, the stability of earthen slopes relative to the critical hydrological cases was simulated by Slope/w software and the pore pressure behind the retaining walls over 10 meter height which causes to instability was simulated using Seep/w software. The studied parameters are: precipitation intensity, soil type, position and the diameter of drainage. Also the kind of drainage has been considered as a variable parameter and horizontal and chimney drainages were used. Results showed that for fine grained soils with intensive rains condition, using of one horizontal drainage could not provide the stability of retaining wall. While in the same conditions, for coarse grained soils, the retaining wall will be stable by using of one horizontal drainage and drainage will be able to discharge all of the excess water behind the retaining wall. Also the chimney drainage system provided the best results and the stability of the retaining wall did not face any danger under the worst circumstances. For overturning moment and water pore pressure behind the wall, linear and non-linear regression relations were produced in dimensionless form. The accuracy of the regression relations were proper and the acceptable results could be expected.

This research deals with the buckling analysis of cracked column with fixed-fixed conditions. The crack is modelled with a unilateral elastic bending-stiffness behaviour, represented by a unilateral rotational spring. This model takes into account the crack closure effect on buckling behaviour of column. The governing equation of the problem is introduced by the variational approach based on energy arguments. Using the variational approach, the governing equation can be formulated as a function of damage index. Damage index is the stiffness of the equivalent rotational spring associated with the crack. A one-crack and a tow-crack are theoretically investigated to illustrate the effects of the crack on the buckling load. For the one crack column, the buckling load increases with the stiffness of the crack section. When the crack-stiffness parameter tends towards an infinite value, the structural model is reduced to the classical Euler column. It is observed that the buckling load increases as the crack get closer to the supports, for constant damage value of the crack parameter (constant crack depth). For the two crack column, the crack closure phenomenon is investigated. In order to two cases are considered. In the first case, the two-crack are located on the same side of column, and in the second case, the cracks are located on the opposite side of the columns. Comparison between two cases show that the crack closure influence on the buckling load. In other words the crack-closure phenomenon tends to increase the buckling load.

In this paper, various methods of linear and nonlinear stability analysis of simple steel frames are introduced. In the following, based on moderately large rotations and small strains, nonlinear stability analysis of a non-prismatic simple steel frame with semi-rigid connection and flexible supports is performed, which is subjected to a concentrated vertical load eccentrically at its joint. Accordingly, firstly, the accuracy and capability of suggested formulations will be verified by comparing with the results of other researchers. Then, the effects of eccentric axial load factor, shape factor of non-prismatic column, rotational stiffness of elastic support, translational stiffness of lateral support, rotational stiffness of beam-column connection and slenderness ratio of members on the pre-bucking and post-buckling behavior of a steel frame will be investigated. The results show each of these factors has a significant effect on the equilibrium path and buckling load of the structure. In other words, by increasing the slenderness ratio of members, shape factor and stiffness of connections, increases the nonlinear buckling load of the structure. Accordingly, the translational stiffness of lateral support and slenderness ratio of members have the maximum and minimum effect on this increase, respectively. Moreover, by utilizing the non-linear stability analysis, the buckling load of the simple steel frame reduces with respect to linear stability analysis.

Retaining walls are walls that maintain the pressure caused by the existing state of the difference in levels caused by embankment, excavation or natural factors. In this study the stability of the flexible walls and the type of reinforced soil walls are evaluated to examine the stability and design the retaining walls with reliability method which gives more realistic results than other design methods. Reinforced soil wall is a special material that is formed by the combination of the soil and the reinforcement member. Basically the soil is weak in stretching and cutting and the idea of reinforced soil wall is in fact the solution to this problem. There are many uncertainties in civil engineering and in particular in the geotechnical discussions the discussion of the uncertainty of the parameters is much more evident because the anonymity of the soil behavior. The traditional methods of evaluated the stability of reinforced soil walls which are usually based on empirical judgments such as the concept of a coefficient. Efforts to quantify uncertainties causing genesis of probabilistic methods. Probabilistic analysis in comparison with definite analysis the uncertainties in the calculations and instead of using the confidence coefficient in the project safety level it usually uses the probability of failure or the reliability index

The SPSWs have been enthusiastically applied in some of the tall buildings across the world as a novel lateral load-bearing system and due to their proper stiffness, strength, ductility, and energy absorption, as well as remarkable reduction in buildings’, weigh compared to the concrete cases, they are deemed as an efficient alternative for the traditional load-resisting systems. fire-related hazards and their impacts on the structural systems have been of major concern for practitioners which is of utmost significance for special structures and tall buildings. Accordingly, in case of thin steel plate shear walls, fire is most likely to leave detrimental effects on the lateral stability and strength of them due to their small values of thickness. To better understand the behavior of such systems in the event of a fire, this paper aims to investigate the impact of heat caused by a fire on the stability, elastic stiffness and yield strength of a 3-storey frame equipped with SPSW system. Based on the results derived by connected stress-heat analyses, thickening the wall results in substantial reduction in the column’s deformations. Moreover, increase in thickness and yield strength of the steel plate plays an effective role in less reduction in yield strength and elastic stiffness of the system after fire events although, while the plate thickness is kept constant, the system’s elastic stiffness does not vary as the yield strength raises. In addition, simple relations were achieved to estimate the post-fire elastic stiffness and yield strength of the SPSW system.

Various uncertainties exist in the engineering problems, so it is necessary to study these problems from probabilistic point of view. This paper aims to evaluate the interactions between new tunnel over – crossing the underlying existing tunnel. Metro line-6 tunnel above-crossing line-7 tunnel in Tehran was chosen as a case study project. In this study the numerical investigation was performed using the FLAC3D software and cohesion and friction angle of third layer and the surcharge on the ground level were assumed as random variables. Generating the random numbers and fitting the probabilistic distributions to the geotechnical variables was done using the Monte – Carlo method. The displacements at four points of existing tunnel (line 7) were recorded due to new tunneling and the appropriate probabilistic distribution was fitted according to the mean, median and skewness of each set of random numbers. According to these probabilistic distributions the probability of occurrence of the displacements more or less than a specific displacement can be determined. The results indicated that although input parameters have normal distributions, not all the outputs have symmetric or normal distributions and the results of deterministic method aren’t as the same of mean values of stochastic approach. For all random parameters the probability of displacements greater than the mean value at the bottom and right side of the existing tunnel due to the new tunneling is 56 % and 55/5 %, respectively.

Real-time hybrid simulation (RTHS) is a kind of simulation where an experimental component of a structure is tested within a numerical model describing the remainder of the system. In this paper, a multi-story structure is partitioned into numerical and experimental substructures, and vibration behavior of the experimental stories are evaluated within the real-time simulation of the rest of the system. An electro-hydraulic actuator is employed to apply static and inertial forces to the experimental structure due to the forces calculated by the numerical substructure. An actuator dynamic is approximated by a pure time-delay, and the time-delay in the closed loop of simulation may causes inaccuracy results or even instability. Thus, the approach of delay differential equation (DDE) modelling is used to determine the dependence of the critical delay on the parameters of the system. The results demonstrate the influence of non-dimensional parameters and partitioning effects in stability of the hybrid simulation.