مجله علوم و مهندسی زلزله
سال دهم شماره 4 (پیاپی 37، زمستان 1402)

The old bridges were mainly designed for gravity loading with partial consideration of seismic or lateral loads, which were vulnerable to seismic effects. There are many examples of damage to the elements of superstructures and underground structures of bridges and in some cases complete collapse. Recently, researchers have proposed the concept of a rocking foundation for column-foundation in bridges. A rocking foundation uses soil failure to protect the structure during seismic loading. In this way, this foundation can act as a fuse and partially isolate the bridge system from serious earthquake damage. Previous research has mainly focused on the behavior of rocking foundations located on sandy soils, and in a few cases, sandy clay soils or clay soils, while not much attention has been paid to the performance of foundations constructed in fine-grained non-plastic silty soils. In this research, the seismic performance of rocking foundations that constructed on silty soils has been investigated using physical modeling on a small scale and by shaking table tests. The experimental tests in this research consist of an "SDOF superstructure-foundation" system that is used to model the behavior of a bridge pier. To this aim, eight series of shaking table tests were carried out in different conditions, including different frequencies of input motions and different A/Ac values. Four different values (1.81, 2.37, 2.52 and 2.69) were employed to investigate the effects of the A/Ac parameter. To this aim, the concentrated masses of 60, 30, 25 and 20 kg are used in the model. In addition, to achieve rigidity against static and seismic loads and avoid any deformation, the thickness of the used steel plates was selected at about 4 mm, which ensures sufficient rigidity of the pier with respect to induced loads. The embedment depth ratios (D/B) were considered equal to zero, and the superstructure was constructed directly on the surface of the soil media. The results of the experiments show that the foundation settlement and the rotation of the structure are rate-dependent parameters and increase with the decrease in the frequency of the input motion. In addition, it has been shown that increasing the ratio of the critical contact area leads to a decrease in settlements and an increase in the rotation of the structure.

Knowing the factors that increase or decrease the effects of seismic waves is one way to minimize the damage caused by earthquakes. In recent decades, many researchers have studied these factors, including one of the most important ones: topographic effects. The effect of surface features on ground motions, known as the topographic effect, has been studied using various methods that have emerged in the last few decades. Most studies on topographic features focus on single features, while nature shows more complexities in surface features. Therefore, this research aims to investigate the effect of the neighborhood of homogeneous semi-sine hills on seismic response. Semi-sine features are the most common form of topographic features in nature, making them important in the application of study results. The research uses the boundary element method and HYBRID code for 2D numerical modeling. In the first part, the seismic behavior of a semi-sine hill with a shape ratio of 1, height of 500 m, and half-width of 500 m is studied. Then, the number of hills is increased to five to investigate the effect of adjacency. The seismic behavior of the hills in three models M1, M3 and M5, and for two groups of stations located on the crest and foot-hill are compared with each other in the time and frequency domain. Finally, the impact of the angle of the incident wave on the adjacency effect and the seismic response of the adjacent features is investigated.The following are the results obtained from this research:As the number of hills increases, the incident wave propagates in the domain by re-reflecting from other features. According to the presented time domain results, the wave reflected in the adjacent hills generates a new peak in the S1 stations. In the frequency domain graphs, an increase in the value of the spectral amplification ratio is observed along with the frequency shift towards higher frequencies.The crest of the middle hill in the M5 model, specifically the S1-M5 station, had the highest value of spectral amplification. This indicates that as the number of hills increased from one to five, the amount of amplification increased at the crest of the middle hill.Adjacent hills also cause intensification in the amplification and de-amplification values at the bottom of the hill.The comparison of the graphs of the spectral amplification ratio of the two models M1 and M5 under vertical and oblique incident waves with an angle of 30 degrees shows that the angle of the incident wave has an effect on the “adjacency effect” and causes an increase in the spectral amplification ratios.The results for station S1 in both models under oblique and vertical incident waves indicate that the frequency shift in the peak of the spectral amplification graphs decreases under oblique incident waves with an angle of 30 degrees.Due to the population growth and urban expansion, settlements around cities have increased, especially in mountainous areas around cities such as Pardis City in Tehran province. It is important to pay attention to the effect of adjacency and its impact on seismic response in the design of buildings, both on the crest and heel of hills. The results of this research show that the crest of hills in the adjacent state has a significantly higher spectral amplification ratio than a single hill. However, building codes only briefly reference the effect of topography

The presence of liquefaction in the soil has a great impact on the condition of the structures built in that area; therefore, studying and evaluating liquefaction is of great importance. Liquefaction of the sand lens can cause changes in the force and shape of the tunnel lining. These issues have been evaluated and investigated in this article. Asymmetric deformations and distortions in the tunnel lining lead to an increase in the ratio of dynamic torque to static torque and distance to diameter. The presence of this phenomenon causes changes in the state of effective stresses, pore water pressure, and settlement. In this thesis, the effect of the sand lens around the tunnel is investigated. Soil-structure interaction is also considered between the tunnel and the sand lens. To put it more simply, a sand lens is a piece of soil in the environment that has high liquefaction properties, so its investigation and evaluation is an important matter that has not been extensively studied so far. Estimation of peripheral and structural soil parameters in tunnel lining always requires software simulation and bulky and time-consuming studies. Providing a method to be able to present these parameters with appropriate accuracy and small computational effort in the fastest possible time has always been an engineering challenge. Therefore, the present study aims to present a machine learning-based method to predict some important properties such as liquefaction event, maximum bending stress of tunnel cover, settlement of subsurface tunnel, and pore water pressure under near- and far-field earthquakes. Hence, first, the three-dimensional finite-difference software with parameters such as soil-structure interaction between tunnel cover and sand lens has been used to simulate the tunnel cover model exposed to ground stimuli. Mohr-Coulomb and Finn models have also been used to consider clay sediment and sand lens liquefaction evaluation, respectively. Then, an extreme learning machine (ELM) is used to predict and estimate the quantities mentioned. The main purpose of this study is to introduce a new method using extreme learning machine to predict some important characteristics such as liquefaction event, maximum bending stress, settlement, and pore water pressure. The results of the studies indicate the proper performance and accuracy of the proposed method in estimating the mentioned parameters so that in the worst case, the estimation error was less than 6%. Also in this study, the effect of a liquefiable sand lens in a non-fluidic environment with different seismic waves and the results of the high influence of bending moment in the tunnel lining, effective stress, pore water pressure and the settlement along the axis of the tunnel in the presence of sand lens has been evaluated. The results demonstrate the great influence of the presence of the sand lens in bending moment parameters in the tunnel lining, effective stress, pore water pressure, and settlement along the tunnel axis. In the final part of the study, all the results obtained from the software are compared with the machine learning outcomes. Also, in the presence of a sand lens, the ratio of bending moment to the state without of sand lens in some cases is over 50%, which is a very significant value, and the maximum settlement occurred in places close to the tunnel axis.

Earthquake is one of the most important natural phenomena that causes economic damages and human losses due to the damage and breakage of structures. The unfortunate economic and social consequences caused by earthquakes, determine the importance of evaluating and improving existing buildings against earthquakes. This issue is particularly important for schools and educational buildings. School buildings, due to their demographic structure, are important buildings whose safe design, implementation and control of behavior and performance are of great importance. Experience of past earthquakes shows that damage to schools can lead to high casualties and human catastrophe; therefore, design regulations also provide stricter rules and regulations for the design of educational buildings. Seismic performance control of existing educational buildings is also of special importance and various methods including linear and nonlinear analysis have been recommended by different regulations and instructions. On the other hand, there are many uncertainties in the study of structural performance that prevent a definite achievement of the structural performance response. Some of these uncertainties are inherent, such as the impossibility of predicting the intensity of future earthquakes, and some are due to errors in analysis and calculations, so the probabilistic expression of structural performance is a logical way to study structural performance. There are several methods to check the reliability of the structure that are different in terms of hypotheses, methods and accuracy, so the effect of uncertainty in each method should be considered appropriately. A review of past research shows that many studies have been conducted on the possible evaluation of the seismic behavior of concrete structures, but there are few studies on the behavior of real examples of such buildings. In this study, two repetitive types of Kermanshah concrete structural schools are non-linearly modeled and analyzed and evaluated using time-history dynamic analysis under the effect of 12 possible earthquake records, appropriate to the type of land and distance from the fault. In order to evaluate the seismic reliability of these schools, based on the specific levels of intensity, the probability of reaching the response to the corresponding values ​​is determined at different levels of damage. The maximum structural drift is considered as the response, and the performance levels defined in the FEMA356 guideline are considered as the failure criterion. The fragility curves of the studied schools have been compared and verified with the behavior of a sample of these schools in a real earthquake, as well as the fragility curves presented in the technical manual of the Hazus earthquake model. In this study, the non-linear behavior of important structures such as schools, which are designed in a linear way, is evaluated and compared. Also, expressing the probability of vulnerability of such structures for possible earthquakes can provide the performance of important structures in each region. The results show that the probabilistic expression of the structure's performance is a suitable method to express the behavior and performance of the structure. The type of ground of the school building and the distance of the building from the fault has a significant effect on the seismic performance and response of the structure. With the increase of storeys, the probability of reaching the school drift to different functional levels is always higher and by increasing the earthquake intensity this proability increases as well. Also, the structures of the studied schools, despite the irregularity in the plan, have a good performance in order to take into account the effects of earthquake intensity, site ground and site distance from the fault. This information can be widely used in crisis management, urban management decisions and future planning of the region.

In general, determining the seismic behaviour of a building damaged by an earthquake is a difficult and complex task. This issue is important and practical in today's world because demolishing of all the buildings damaged by the earthquake is very expensive and time-consuming. For this purpose, in the first step of the reconstruction of an earthquake-stricken city, it should be determined which buildings are useable and safe, which buildings are repairable, and which ones should be demolished. The repairability, destructibility or usability and safety of a damaged building is effective when the seismic behaviour of that building can be determined after the damage. To determine the seismic behaviour of the building damaged by the earthquake, some methods have been presented by other researchers. However, most of these methods need to spend a lot of time to check the behaviour of the structure. The purpose of this research is to provide a new analytical method for the seismic evaluation of steel moment frame structures damaged in an earthquake, which can determine the force-displacement curve of a steel structure for different levels of damage. Also, in this research, with the benefit of SPO2IDA's approximate analysis, a method for classifying damaged structures based on the percentage of damages has been presented. For this purpose, a three-story steel moment frame structure was subjected to nonlinear static analysis in OpenSEES Software. Then, using the proposed method to analyse the damaged structure and considering the cyclic deterioration of the damaged members and elements by modifying the behaviour curves of the structure, non-linear static analysis curves were extracted for different levels of damage. In the method of cyclic deterioration of damaged elements, based on the amount of rotation or deformation occurred in the member during the earthquake, the performance curve of the member changes in such a way that these changes include stiffness, resistance and ductility. According to the initial back-bone curve, four levels of damage were meant for the damaged structures, and each of these damage levels is dependent on the amount of reduction in resistance that occurred in the initial back-bone curve of the structure.Also, using the SPO2IDA method, the approximate curves obtained from incremental dynamic analysis were extracted for the analysed structure. Then, by using these curves, the proposed procedure was evaluated in order to classify the structures after the earthquake. At the end, the results of this method are compared with the methods proposed by others in each step, and the crucial differences in response are fully explained. It was shown that at different performance levels, by not considering the effects of cyclic distortion, between 30% and 50% of the structure's capacity will be estimated higher. According to the obtained results, in the event of an aftershock with a magnitude close to the main shock, it can be concluded that not considering the cyclic distortion in the behaviour of the damaged members and elements can lead to many mistakes in decision and classification of the structures which result to irreparable consequences.

The occurrence of the Northridge earthquake in 1994 and its effects on structures and infrastructures drew attention to the philosophy of damage-avoidance design (DAD). One of the most damaged lateral load-resisting systems during that earthquake was the steel moment-resisting frame which had more than 130 cases with connection failures. In lots of cases, brittle fractures were started in the connection at low levels of plastic demand, and in some cases while the structures remained elastic. After earthquakes like Northridge and Kobe, many efforts have been made to improve the ductile behavior of the connections. Since that time, different details have been proposed. The beam sections near the column face are either reduced or enhanced with various components, such as cover plates, side plates, slit dampers, annular stiffeners, ribs and diaphragms. However, permanent deformations and residual drifts can be seen after an indestructible earthquake, which is difficult to investigate and repair. To eliminate or reduce inelastic deformations as a DAD, self-centering (SC) mechanism has been considered seriously for moment-resisting frame connections. These types of connections are supposed to be composed of columns, beams, energy dissipation elements, and post-tensioned cables or bars to return the structure to its initial position and generate SC behavior. Different types of details have been suggested since the start of investigations. However, one of the most used details comprises bolted top and seat angles and high-strength steel strands that are post-tensioned after installation energy dissipators. Contact stresses develop at the interface of the beam and column under the action of strand force and the resulting surface provides notable moment resistance. Strands are tied up at the outer surface of the column. The shim plates and reinforcement plates are also used in the connection area. The resulting connection is not required for field welding and has initial stiffness almost identical to a common welded connection. An important phase in the performance-based design of moment frames with SC connection is to assess the structural performance and obtain engineering demand parameters EDPs by conducting nonlinear time history analysis. When it comes to the decision-making phase, compression between the results of EDPs for the conventional welded moment frames and frames with SC connections can be meaning full and important for the final SC connection details. Thus, in this study, two designed four- and eight-story steel moment frames are considered, and their connections are modeled with both SC and welded details. The lateral resistance of both structures were supposed to equal. Nonlinear time history based on 22 far-filed records which are scaled based on codes are conducted and results are compared. Values of the median for maximum drifts in stories are increased for first and second floors in, four-story SC model by 2.10, 2.44 and decreased by 0.31 and 9.00 percentage, respectively, for third and fourth stories; also for 8 story SC frame, results are shown, decreasing values for first, second, fourth, seventh and eighth stories by 6.65, 1.52, 9.90, 12.58 and 12.97, while for third, fifth and sixth stories increased by 3.69, 12.71 and 3.11 percentage, respectively. For story acceleration, it can be seen an increase of median values for both 4 and 8 story SC models which are 7.73, 24.40, 24.34 respectively for stories 1 to 3 of four-story SC model, and 20.65, 13.91, 32.81, 12.91, 18.65, 23.28, 7.05 percentage respectively for stories 1 to 7 of 8 story model and only for roof stories of 4 and 8 story models, it decreases by 7.21 and 10.20 percent, respectively. Finally, significant decreases are shown for median values of maximum residual drift for both in the 4 and 8-story SC models, which are 71.98, 91.47, 72.54, and 84.35, respectively, for stories 1 to 4 of the four-story SC model, and 55.65, 87.00, 93.13, 87.11, 87.23, 83.54,73.12 and 61.63 respectively for stories 1 to 8 of 8 story SC frame. Also, results of the nonlinear static analysis show that frames with SC connections have the same strength compared to welded moment resisting frames.

Planning for housing construction after a probable earthquake in big cities has received less attention due to its complexity and ambiguity in urban settlements like Tehran. Since reconstruction is an opportunity for development and better construction, using up-to-date and suitable technologies in the building is inevitable. The new technology used in the construction of housing after earthquakes must have these features: high construction speed, lower cost, low energy consumption, compatibility with the environment, appropriate stability and strength, seismic resistance, and consequently higher useful life of buildings. Due to the wide dimensions of construction technologies, high implementation costs and the need to have executive knowledge and cognition of post-disaster conditions, the use of suitable and appropriate technology in all dimensions and components of the building requires a correct understanding of the indicators. The current research aims to identify and prioritize the indicators of permanent housing construction technology after the earthquake in Tehran using the Delphi method and Shannon's entropy technique.The research methodology applies a combination of qualitative and quantitative methods based on analytical and exploratory strategies. After reviewing the articles, documents and specialized texts as well as examining the experiences from previous studies, indicators were extracted and classified using the Delphi method then approved by the experts and ranked using Shannon's entropy technique. After that, the opinions of ten experts, senior managers, officials, and eight university professors aware of the field of housing in Tehran were used. By referring to the qualified specialists and experts in the field of housing construction technologies after the earthquake and by visiting the relevant departments and organizations, senior managers, and officials in person, questionnaires were completed by experts in the field of housing and university professors knowledgeable in the field of housing who made up the target statistical population. Then, to achieve the indicators, the research background, publications and published documents related to the subject were reviewed.For this purpose, the indicators obtained through interviews with experts were examined, and among dozens of cases, after combining similar cases and including overlaps, removing unrelated and ambiguous cases, and making necessary corrections, 78 variables were selected as the indicators in the field of housing construction technologies were identified after the earthquake in Tehran.In the first step, a questionnaire was designed under the title of weighting indicators of housing construction technology after a possible earthquake in Tehran, which included 12 components and 90 sub-components and was given to 18 experts to rate each index based on a 5-point Likert scale. It is worth mentioning that the experts were asked to mention, in addition to the determined indicators, if they consider another influencing factor. In the research process, the majority of experts agreed, some added new components, and some did not express an opinion. Then, in the second round, items with an average of less than 3.5 were removed and new items were added. Thus, during two stages and using the Delphi method, various items of post-accident housing construction technologies were extracted. The meaning of housing in this research is permanent and conventional housing of 5 to 7 floors with an area of 70 to 90 square meters in Tehran, which is usually assumed to start construction after the stages of emergency and temporary housing. Twelve effective components in housing construction technology after the Tehran earthquake have been identified in previous studies. These factors include construction and execution management, cost, housing construction components, type of materials, time, prefabrication, energy consumption, safety, cultural and social characteristics, environmental conditions and compatibility with the architectural design, which are categorized into four managerial, economic, social and cultural sectors.The results show that among the refined indicators, "quality, durability and high resistance of housing construction materials", "application of existing standards of the construction industry in building systems", "main structure of housing", "supplying space light", "minimum required energy for climate adaptation" and "considering different areas of Tehran" were recognized as the most important indicators of housing construction technology after earthquakes.The criteria with high priority in housing construction technology can be analyzed from the structural and non-structural points of view.A Scrutinizing look shows that there are factors in the construction technologies considered by the respondents, which are mostly non-structural and architectural and the view of builders and designers from the scope of structural and physical issues of housing to other categories in the construction process, including Management, architectural and social factors have been focused in Tehran.

In this article, the Jennings method has been improved by using the third-order spline interpolation function. In this research, in order to be able to compare the advantages and disadvantages of the Jennings method, which is based on exact relationships and the assumption of linear changes of the excitation, compared to the spline interpolation method, a damped one-degree-of-freedom linear system under sinusoidal harmonic loading is considered has been taken. Exact values of the deformation response coefficient of this system are available for different excitation frequencies. The approximate values of the deformation response coefficient of this system for different excitation frequencies were calculated assuming linear interpolation of excitation and also assuming interpolation with spline function and were compared with their exact corresponding values. This work was done for two, five, ten and twenty percent damping. The results of the work indicated that when the number of points by which the sine wave is approximated is small and also the amount of damping is low, the interpolation with the spline function has a significantly higher accuracy than the linear interpolation mode. Another noteworthy point is the high sensitivity of the cubic spline interpolation to the level of system damping, so that for a certain number of divisions, the error value is highly sensitive to the damping value. Thus, with the increase of damping, the sign of the error changes and its value increases strongly for the number of large divisions.  This phenomenon is not seen at all in linear interpolation.Therefore, considering that in interpolation using the spline method, the continuity of the slope and the second derivative are maintained in the internal points, it is suggested to use this method to calculate the dynamic response of linear systems and the results obtained with the results of Jennings' method should be compared and appropriate decisions should be made if there is a significant difference in the analysis results obtained from these two methods.It is important to mention that the execution time of the computer program related to the cubic spline interpolation method is longer than the Jennings method. Because in the spline interpolation method, it is necessary to solve the system of linear equations with the number of unknowns equal to four times the number of intervals, while in the excitation linear interpolation method, it is not necessary to solve the system of equations at all and simply by having the velocity and displacement at the beginning of the step and assuming that the excitation is linear during the desired time step, the coefficients A, B, C, D, A', B', C', D' were calculated and using this eight coefficient, velocity and displacement at the end of the time step are obtained. It should be noted that if the time interval between different accelerogram points is constant, it is sufficient that the coefficients A, B, C, D, A', B', C', D' are calculated only once.