جستجوی مقالات مرتبط با کلیدواژه « soil-structure interaction (ssi) » در نشریات گروه « عمران »

The present paper aimed to evaluate the effects of soil-structure interaction (SSI) on the seismic behavior of base-isolated geometrically irregular steel sliding structures equipped with lead rubber bearing (LRB) isolators.To this aim, the behavior of the irregular system under nonlinear time-history dynamic analysis was assessed using numerical modeling based on the finite element method in ABAQUS. The study considered various factors including irregularity, number of structure floors, soil properties, isolation, and foundation stiffness to analyze their impact on the response of the structures. 3-, 5-, and 7-story structures with 20% and 40% irregularity were modeled to investigate the effects of irregularity and the number of floors. Additionally, models of five-story structures were used to study the impacts of soil-structure interaction (SSI) on three different types of soil: soft, medium, and hard. The results of the study demonstrated that the number of floors and the structure's irregularity have a significant impact on the seismic response of the structure in terms of displacement and acceleration. As the number of floors and irregularity increase, the maximum displacement response of the structure's floors decreases. The study also highlighted the substantial influence of soil type on the seismic response of isolated structures when considering the effects of SSI. Furthermore, the findings indicated that the presence of isolators on rigid foundations had a negligible effect on the dynamic response of the structures, compared to structures without isolators.

Process towers or vertical vessels are among the industrial structures that play a key role in the production process of petroleum products and their derivatives in refineries and oil and gas industries. Due to the vulnerability of these structures in past earthquakes, and the lack of valid regulations and methods for seismic analysis and design of these structures, a case study on a designed and constructed process tower 26.5 meters high, located in Qeshm Island Refinery, has been conducted in this research. Since considering a rigid foundation, without the interaction of soil and structure, may lead to wrong results, in this study, the tower has been modeled in Abaqus finite element software considering soil behavior. The Winkler model used for soil modeling and the seismic behavior of the tower was investigated using pushover and incremental dynamic analysis, and finally, the resulting fragility curve is presented to show the structure's vulnerability at different levels of seismic intensities. In this investigation, the probable failures, including the failure of the body and the skirt, as well as the overturning of the structure, have been investigated. According to the incremental dynamic analysis results, no buckling was observed in the body and the tower's skirt before the tower overturned. The results show that overturning was the predominant failure mode and the probability of this failure mode until PGA=0.1g is approximately equal to zero, and for PGA= 0.35g, this probability is less than 20%. But for rare seismic intensities, the overturning probability is considerable.

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.

 In the FEMA-P695 report, there is an applied method for evaluating the collapse of structures designed by seismic regulations under the most severely expected earthquake, in which the collapse of special concrete frames without considering the effect of soil-structure interaction is studied. In this study, soil-structure interaction analysis is used directly to evaluate the seismic performance of buildings. For this purpose, 4 and 8-storey reinforced concrete buildings with special bending frame system, on medium (D) and soft (E) soils classified according to ASCE7-10, have been modeled and analyzed by Opensees software. Incremental dynamic analysis has been used to accurately evaluate the collapse performance of the frames for both rigid base and flexible base. The results of the analysis show that the soil- structure interaction, especially with softer soil and increasing the number of building floors, can play a key role in the behavior of building frames including increasing system period, reducing floor drift, increasing performance and changing probability collapse of the structure. On the other, the results at first glance show an increase in the probability of collapse for frames placed on flexible supports at the same spectral acceleration, but using the modified flexible fragility curve, it is observed that the soil-structure interaction reduces the likelihood of collapse. Therefore, not considering the soil-structure interaction leads to unrealistic evaluation of the performance of structures.

During the past years, researchers have developed ideas to thoroughly investigated into the behavior of structural bracing systems. Accordingly, one of these emerging systems is the Strong Back Bracing System (SBBS) by which the inter-storey drifts are maintained constant to prevent occurrence of failure. This system is comprised of the components of conventional concentrically braced frames together with a strong truss whose presence is aimed at uniform distribution of drifts along height of the building. This truss precludes concentration of damages in one or several stories in the concentrically braced frames. On the other hand, the near-filed earthquakes differ from the far-field ones in terms of both amplitude and frequency content. Thus, it is required to study the effects of such earthquakes on behavior of the SBBS. In addition to earthquake, the soil underlying the structure can affect the structural responses especially in cases when structure rests on soft soils. This system is comprised of the components of conventional concentrically braced frames together with a strong truss whose presence is aimed at uniform distribution of drifts along height of the building. This truss precludes concentration of damages in one or several stories in the concentrically braced frames. On the other hand, the near-filed earthquakes differ from the far-field ones in terms of both amplitude and frequency content. Thus, it is required to study the effects of such earthquakes on behavior of the SBBS. In addition to earthquake, the soil underlying the structure can affect the structural responses especially in cases when structure rests on soft soils. Typically, the codes provide methods for structural analysis assuming that the structure is located on a rigid base whereas in reality, this assumption does not always hold true highlighting the need for inclusion of soil-structure interaction into the analyses. Accordingly, this paper deals with seismic behavior of the structures equipped with the SBBS considering the soil-structure interaction under near and far-field earthquakes. In this respect, 3, 6 and 12-storey structures resting on stiff and loose soil (soil type II and IV according to classification of Standard 2800) have been analyzed. To this end, nonlinear time-history analyses using seven far and near-field earthquakes for both cases of rigid and flexible base, have been carried out. The results indicate that maximum roof displacement of 3, 6 and 12-storey structures founded on stiff soils (soil type II) vary insignificantly under the far and near-field earthquakes. Conversely, in the case of soft soils (soil type IV), displacements have increased by 2.93 to 18.22%. Moreover, it was found that drift ratios for the structures on stiff soil, in the case of 3 and 6-storey structures, increases slightly and reduced by 6.75% for the 12-storey structure. In the case of soft soil, all structures under the near-field motion, incurred increase in drift ratios by 11.67% and in the case of far-field, 3 and 6-storey structures experienced 4.86% decrease and conversely, the 12-storey structure encountered 7.7% increase. In addition, ratio of residual drift of the 3, 6 and 12-storey structures under average of near-field earthquakes, has decreased and increased by 8.52 and 36.02 in the case of stiff and soft soils, respectively.

Unknown situations or factors in design of a structure such as underlying soil characteristics and presence of adjacent structures can affect the reliability, and consequently, the cost of the project. Therefore, the effects of soil-structure interaction as well as the simultaneous effects of this interaction in the presence of adjacent structures on the seismic response of 3, 9 and 20-story benchmark steel moment resisting frame structures are investigated, including six different adjacency cases of the structures in three different distances. The effect of soil-structure interaction is considered by using a hybrid method, in which the stiffness matrix of soil system is obtained through analysis of a two-dimensional model in Abaqus considering a plain strain condition. Then, the matrix is added to the nonlinear 2D model of the structure by using a set of pre-defined and a new developed element in OpenSEES. The results obtained from the time history analysis under ten far-field earthquake records show that the effect of soil-structure interaction on the response of a 20-storey high-rise structure is more significant than the other two structures and leads to a maximum increase of 9 percent in the maximum average drift ratio and decrease of 6.99 percent in the average base shear in this structure compared to fixed base. In addition, the presence of high-rise and mid-rise adjacent structures increase the maximum average drift ratio of low-rise structures by 10.44 and 9.36 percent and the average base shear in this structure by 2.87 and 3.93 percent, respectively.

Coupled steel plate shear wall (C-SPSW) is a relatively new system that has received less attention from research centers. This system benefits from a high ductility and stiffness, which are the two advantages that make this system superior to the other lateral load-resisting systems. This paper aims to study seismic response of the CSPSWs under near and far-field earthquakes, resting on soil types II and IV considering soil-structure interaction (SSI) effects using the 5, 10 and 15-storey frames in which length of link beams and frame bays is equal to 1.25, 2.5 and 3.75 as well as 2.4, 3.2 and 4.8m, respectively. Based on the analysis results, maximum roof displacement of the 5, 10 and 20-storet frames located on stiff soils (soil type II), does not experience remarkable changes under near and far-field earthquakes but to the contrary, in the case of soil type IV, changes are considerable. Roof acceleration of the structure located on stiff soil, is less than that of the structure on soft soil. In this paper, ratio of base shear to effective weight of the structure was taken into account and it was found that incorporation of SSI effects influences the base shear. Moreover, regarding behavioral modes of the coupling beam and coupling degree of the SPSW, the results indicated that this degree has a meaningful correlation with fundamental period of the structure and the short coupling beams that yield in shear, have a better performance.

In this study, the life safety and immediate occupancy of asymmetric-plan reinforced concrete dual structures under the simultaneous effect of torsion and soil-structure interaction in the near-fault pulse-like earthquakes were evaluated using a probabilistic framework. An 8-story R/C dual lateral load resistant building consisting of shear walls and moment-resisting frames was used. The sub-structure method was used to simulate the SSI effect. The impedance functions were calculated with the Novak semi-analytical method (DYNA5 software). The structure was modeled in the CANNY software considering the nonlinear behavior to perform the nonlinear time history analysis. All of the ground motion records were selected from the near-fault pulse-like records. Incremental dynamic analysis was employed to extract and fragility curves. To determine the life safety and immediate occupancy limit states, the strain of steel and concrete (as a micro index) were used rather than the usual macro indexes such as story drifts that lead to increase the accuracy of results. One of the most important of the conclusion is that neglecting the SSI effect in the life safety and immediate occupancy limit states for the plan-asymmetric structure is not in the safe side and lead to overestimation in the structural capacity. Also, an increase in the mass eccentricity leads to a decrease in the base conditions' importance and SSI effect. Another considerable observation is that an increase in the shear wave velocity of soil can lead to a decrease in the torsional response and the seismic response of asymmetric structure approaches to the symmetric one.