BULLETIN OF EARTHQUAKE SCIENCE AND ENGINEERING
Year:2018 | Volume:5 | Issue:2 |Papers Count:10

Using 48016 synthetic maximum Wood-Anderson amplitudes read from waveforms of 2650 events recorded by stations of Iranian Seismological Center (IRSC, irsc. ut. ac. ir), Iranian National Seismograph Network (INSN, www. iiees. ac. ir) and temporary seismic networks belong to Institute for Advanced Studies in Basic Sciences (IASBS, iasbs. ac. ir), the empirical attenuation curve ( 0  log A ) for local magnitude of Iran has been calculated as follows: 0 log (1. 556 0. 06) log (0. 001637 0. 0009) ( 100) 3 100 R A R              where R is hypocentral distance in km and 0 A is maximum displacement amplitude of shear wave in millimeter. The empirical attenuation relationship is valid for hypocentral distances equal or smaller than 800 km. ML amplitude is the maximum amplitude observed on a Wood-Anderson (W-A) seismogram. We manually picked the maximum amplitudes on the shear window of synthetic W-A seismograms having S/N of larger than 5. We calculated synthetic W-A seismograms by removing the instrument response of each record and convolving the resulting signal with the response of the standard W-A torsion seismograph. We assumed a static magnification of 2080 for the W-A instrument. The selected ML amplitudes are belonging to events at hypocentral distance of 10 to 800 km. Except for the Makran and South Caspian Basin regions, the ray coverage of the ML amplitude covers properly the whole Iranian Plateau. To reduce the scatter of magnitude residues and ensure a reliable calculation of the attenuation curve, the selected events belong to 45 precisely relocated seismic clusters with location uncertainties of 5 km or less. The cluster approach produces redundancy in amplitudes arriving from a cluster to a given station. The redundancy will facilitate easy recognition and removal of possible outliers and thus provide a reliable estimate for the magnitude station correction. The magnitude station corrections attempts to absorb the regional attenuation difference relative to that dictated by average attenuation relationship derived in this work. The calculated attenuation curve shows a larger geometrical spreading for hypocentral distances closer than 100 km, representing a super-spherical geometrical spreading, and a smaller value for intrinsic attenuation for distances farther than 200 km once compared with the currently used ML relationship of Hutton and Boore (1987). Excluding amplitudes with hypocentral distances smaller than 60 km results in a geometrical spreading coefficient close to spherical spreading, emphasizing the importance of near distances data on accurate estimation of the geometrical spreading value. The difference in the attenuation parameters between our results and those of Hutton and Boore (1987) relationship clearly indicates the crustal disparity of Iranian Plateau and southern California. This necessitates using the new attenuation relationship for Iran. We calculated the local magnitude empirical attenuation relationship by inverting the amplitude data set for the geometrical spreadin]g and intrinsic attenuation. We did not consider magnitude station corrections in our inversion to avoid any tradeoff between the station corrections and attenuation parameters. We have shown that the magnitude residuals calculated by our local magnitude empirical relationship do not vary systemically versus hypocentral distance or magnitude. Due to the cluster-wise approach in selection of our events and partially because of the precise location of the selected events, the standard deviation of magnitude residues is about 0. 19, significantly smaller than those reported by others. We calculated the station corrections by averaging the magnitude residual in each station. The station corrections vary between-0. 44 to 0. 32. Generally, stations located in Zagros, Alborz and north west of Iran have negative station correction representing amplitude amplification in these regions relative to central Iran and north east of Iran. The new attenuation relationship provides better estimates for the attenuation parameters and especially provides precise magnitudes at close hypocentral distances. By time, the expansion of Iranian seismic networks reduces the average distance spacing of Iranian seismic stations and thus usage of better local magnitude formula such as ours becomes more important.

Introduction Generally, topographic effects are mostly introduced by hills, canyons, basins, and slopes. Besides, the topographic features produce significant seismic site-effects and can apply a crucial influence on the severity of building damages and its spatial distribution during earthquakes. Some experience observation such as Tarzana hill in the 1994 Northridge earthquake and the Kushiro Meteorological Observatory in the 1993 Kushiro-Oki earthquake, revealed the effective role of surface topographies such as hill and ridges on the seismic damage on the crest and hillsides. Reviewing the technical literature can deduce that the most studies about the effects of topography and the amplification patterns are limited to the linear behavior of the medium. However, the use of linear models to estimate amplification patterns of waves can lead to misleading results than the actual behavior of the soil, especially in the soft soils. The non-linear seismic behavior of the hill topographic features unknown in comparison with other types of topographic irregularities, e. g. basins or alluvial valleys. Hence, in this study, the effects of non-linear behavior of the hill type-discussed. In this regard, the trapezoidal-shaped hill has been taken into account for parametric study with four shape ratio (SR=0. 1, 0. 3, 0. 5 and 0. 7). Besides, in order to evaluate the effect of topography geometry, the semi-sine and semi-elliptical shapes of the hills have been studied. The constitutive model used herein is based on non-linear Kinematic Hardening model with Von-Mises failure criterion. Parametric Studies In this research, the finite element method (ABAQUS software) is used to evaluate the hill-type Topographies behavior due to the vertically in-plane propagating incident SV waves. The hill-type Topographies has been excited vertically by Ricker-type pulse excitations. In this regard, two center frequencies (fp) of low (i. e. 1. 4 Hz) and high (i. e. 4. 3 Hz) have been considered to cover all frequency responses with a maximum acceleration equal to 0. 3 g. The constitutive model used herein is based on non-linear Kinematic Hardening model, which is suitable for clay materials. The results are presented as horizontal component amplifications (direct component) or vertical (indirect component). Spectral amplifications have been defined with respect to the free-field motion, based on the maximum Fourier amplitude of the horizontal or vertical component, to the maximum Fourier amplitude of the Free-field motion. In this research, the horizontal and vertical component amplifications are shown, with AH and AV-Moreover, the obtained results provided for the dimensionless distance (X/L) in which X is points from the center of the hill and L is half the width of the hill. All results have been compared in two linear and non-linear soil behaviors. Concluding Remarks The obtained results indicated that considering the non-linear soil behavior can reduce seismic response of topographic effects in comparison with linear behavior. Furthermore, the maximum amplification appears on the crest of the hill in both linear and non-linear behaviors. The non-linear amplification values reduced about 15 percent at the Extended Abstracts سال پنجم، شماره دوم، تابستان 9317 lower frequencies for the trapezoidal-shaped hill with shape ratio (SR) of 0. 7 compared with linear behavior. The seismic response of topographic irregularities tends towards free-field ground motion with far from surrounding hills. Besides, in this research the PGA values versus depth and the impedance ratio between inside of hill and its base materials have been studied. The results of this research can be used in seismic hazard and microzonation studies of various urban areas and to point out this the hills with softer materials than the bed, where soil behavior can be non-linear and using linear models, can lead to misleading results than the actual behavior of the soil.

In this study, the impact of passing traffic and temperature reduction on the stability of the frozen soil wall is studied. Design geometry and mechanical properties of the frozen and unfrozen soil have been simulated according to the line 2 of Tabriz Subway. In order to numerical modeling, in all stages of the present study, the ABAQUS finite element software has been used. For modeling of unfrozen soil, mechanical properties resulted from experimental tests on the samples obtained from boreholes, then the Mohr-Coulomb constitutive model has been used. Since the frozen soil is an unconventional material, there is no reasonable constitutive model for that. Taking into account the actual site conditions (including unit weight, water content, void ratio and lateral earth pressure), more than 60 triaxial compressive tests were conducted on the frozen soil samples. Results from triaxial tests on the frozen soils showed that shear strength of frozen poorly graded sand increases with temperature reduction. Thus, by modeling the triaxial test on frozen soil in ABAQUS software, Mohr-Coulomb constitutive model was verified according to the experimental results of triaxial tests, so that it can model the strain-softening elasto-plastic behavior of frozen sand. The geometry of metro station excavation with the length of 104 m and the depth of 10 m was simulated according to the cut and cover method, consequently. Analysis results showed that lateral displacement of the frozen soil wall into the excavation due to the cut at middle section of the wall is greater than the supports section. Besides, the effect of passing traffic load on the middle section of the frozen soil wall is greater and it leads to larger lateral displacement into the excavation in this section. The reason of this fact is the friction between unfrozen and frozen soil at the place of abutments. Therefore, in close section to abutments of frozen soil wall, thin and warmer (subzero) temperatures can be used. It is worth mentioning that the decrease in temperature has no significant effects on lateral displacement reduction of the frozen soil wall at abutments (about 2-3%), while, this value is up to 13% at the middle of the frozen soil wall. Eventually, the method of artificial ground freezing for supporting the excavations in this study (subway station of line 2, Tabriz subway) is recommended, which is adjacent to the main road and heavy vehicles traffic is possible.

The destructions of earthquakes in Turkey and Taiwan (1999) have increased the interest of investigation on structures behavior in surface fault rupture propagation. Therefore, many studies have been accomplished to investigate the fault rupture and shallow foundations interaction. Based on the fact that a lot of structures are constructing and they have the possibility of facing fault emergence hazards due to the uncertainty in exact locating of surface fault emergence, the investigation on surface fault rupture hazards can give a better insight to explicit this issue and mitigate the damage to constructions adjacent or in active fault zones. In this research, numerical investigations on surface fault rupture hazards based on the evaluation of earthquake's field studies and seismic codes limitations for constructions in active fault zones have been employed. Based on field studies observations, four different fault zones with different levels of hazard possibility for structures have been obtained. Some of the field studies results have been reviewed in this paper. For numerical studies, the two-dimensional, finite element software (Plaxis) was employed to study the surface fault rupture mechanism beneath the foundation in four different locations. In the mentioned Plaxis model, a rigid foundation with breadth, B=20 and embedment depth, 𝐷 = 0 𝑚 was used. The model height was 25 m, and in order to model the bedrock, 5 m layer with Vs= 1000 m/s was considered beneath the model. It should be mentioned that the fault has a dip angle, α =60 ° at the rock– soil interface, the length of fault propagation upward from the bedrock is 25 m and the fixed part of the model is 75 m. After locating the fault rupture trace on the ground in free-field condition, the foundation was located in four different positions in respect of free field and bearing pressure, q=90kpa (9-storey building) was imposed on all of them. Foundation rotations were calculated in these models and compared together. By moving the foundation toward the foot wall, the rotation amount decreased. In the following, to investigate the effect of load on reverse faulting, the bearing pressure was increased to 360 kpa for two foundation locations and the results discussed. Decreased foundation rotation and soil uplift in surrounding area were really noticeable. In order to investigate the seismic code limitations, two different models were made. The foundation was located in hanging wall at the distance of 15 m from free field location. In these models, bearing pressure of 90 and 360 kpa were examined. In this case, by increasing the bearing pressure, the amount of foundation rotation increased. The field studies results indicate, foundation location and structure weight have important impact on structure damages during surface fault ruptures. As mentioned, these results have been achieved in this paper. Briefly, the results of numerical models demonstrate that seismic codes limitations such as setback do not have necessarily safe construction outcome.

Because of the importance of the dam safety and to overcome the damages caused by the failure of the concrete dams under the earthquake, the seismic performance assessment of concrete dams needs more attention. This study deals with the investigation of the effect of the near-fault velocity pulse type ground motions and their effective parameters on the structural response. For this purpose, the Morrow Point arch dam has been considered as the case study. The dam is modeled in the SOLIDWORKS software and analyzed in the finite element ABAQUS software, considering the dynamic interaction of dam-reservoir-foundation and nonlinear behavior of concrete. In a nonlinear seismic analysis of dam-reservoir-foundation system, the crack propagation and the dam failure due to the low tension strength of concrete is necessary to be considered. Therefore, this study uses the concrete damage plasticity (CDP) model to consider the nonlinear behavior of concrete in tension and compression. Generally, near-fault ground motions have short effective duration and contain long period pulses with big pulse amplitude. Three types of pulses have been introduced in the literature to show the velocity pulse type ground motions. Pulse A is a onesided type (one half cycle pulse) that results in fling step in its displacement time history. Pulse type B represents for the forward directivity effects and contains a two-sided pulse (a pulse with two half cycles), which has a long period and amplitude in its velocity time history and its displacement time history includes just a one-sided pulse. Nevertheless, all the near-fault ground motions do not follow the forward directivity or fling step patterns; hence, another pulse type named C has been introduced. These pulses have at least three half cycles in their velocity time histories, more than those of pulse types A and B. These pulses result in at least two half cycles in the displacement time history. In order to consider the effects of near-fault ground motions on the dam response, a collection of ground motions with B and C pulses in their velocity time histories have been selected and used in this study. For comparison purpose of the near-fault pulse like records, one should keep some of the effective parameters constant in the analysis process in order to study the effects of the other parameters. Unlike previous studies that only consider the peak ground acceleration (PGA) as the constant and common parameter of the records, the similar energy of the records is also taken into account in this study. The records are divided into two categories according to their specific energy density; so that, after scaling their PGA to 0. 3 g, the specific energy densities of each category of the records are relatively similar. In the first group in which the maximum velocity, the Arias intensity and maximum displacement are relatively similar, the results indicate that the records which contain pulse type C, show more destructive responses. The difference is due to the shape nature (more half cycles) of this pulse type. In the second group, generally, the surveys also show more destructive responses of the records with pulse type C. Further investigations also present relatively much more effects of the "Arias Intensity" and "Pulse Duration” on the response for the records with relatively the same specific energy density. Besides, in the case of the relatively the same values for the above-mentioned parameters, other parameters such as the maximum displacement are effective. The results of this study could be useful for the structures designed and constructed for the near-fault regions.

Since Iran is located in a seismic region and due to the existence of trapezoidal or triangular terrains, because cities were not constructed based on a grid format in the past, in addition to the interest of contemporary architecture in designing irregular structures and structures with non-parallel lateral resisting system as defined in the 4th edition of the Standard 2800, thus this paper studies the seismic behavior of such structures. In this paper, three-dimensional modelling of steel structures with five different plans, each representing a percentage of irregularities of the lateral resisting system and three-dimensional modelling of a completely regular plan is presented for comparison. Besides, the torsional behavior of structures with lateral resisting systems is studied and compared with regular structures. The letter alpha is used with indexes indicating the level of anomaly of the carrier systems. The value of the alpha index is obtained by dividing the length of the removed openings by the length of the entire structure. In order to investigate the effect of height, the structures were modelled and studied using two, four and twelve floor models. The modelled structures are made of steel and possess a specific steel converging bracing system in line with Y and a modular steel folding frame along X. Moreover, the soil on the land is of type 2 in accordance with the 4th edition of the Standard 2800, and the structures are in accordance with articles six and ten of National Building Regulations. To analyze the structures, pushover analysis and dynamic linear analysis were implemented. In the pushover analysis, a load was analyzed in line with X and another load was analyzed in line with Y. Furthermore, for dynamic linear analysis, the peak acceleration recorded for Tabas, Iran and El Centro, USA earthquakes were used. The final point is that loading in a state of non-parallel lateral resisting system (Y) will entail more unpredictable and disastrous results.

In this paper, vertical seismic isolation (VSI) of a building for seismic response reduction by partitioning its structure into two different dynamically behavior substructures and linking them together by viscous or visco-elastic links was investigated. To have a better understanding of the VSI features, study of a sample one-story single frame was supposed to be helpful. The Kelvin model was employed to represent the visco-elastic damper for which the stiffness and the damping coefficients are 𝑘 𝑙 and 𝑐 𝑙 respectively. In the vertically isolated structures (VIS) by using viscous or visco-elastic dampers, the influence of system dynamic characteristics, including natural frequencies and modal damping ratios in response reduction was of interest. In a comprehensive study, eigenvalue analyses of non-classically damped system were performed. These analyses were also carried out for different parameters of the connecting link. In this study, color contour graphs were employed for presenting the results. The more important advantage of this representation is creating the possibility to observe results of both stiff and flexible isolated structures in one individual graph. This graphical representation was called Vertical Isolation Contour Graph (VICG). Various ratios were considered for mass and stiffness of either of the two substructures to the mass and stiffness of the original structure to find out which ratios or range of ratios result in maximum seismic response reduction. Depending on these mass and stiffness ratios, three states of Mass Isolation, Interactional State, and Control Mass were differentiated in isolation behavior. To study the seismic performance of the one-story VIS, its response histories subjected to different earthquake excitations were obtained by a series of time history analysis (THA) cases. In these analyses, the aim was examining the effects of different parameters on the efficiency of the VSI. In the VSI, one of the main goals was the determination of an appropriate range of mass and stiffness ratios and the associated interconnecting link parameters to achieve the maximum possible seismic response reduction. To solve the governing differential equations of motion numerically, a program, developed by the authors in MATLAB environment based on Runge-Kutta method, was employed. Response ratios that Compare maximum displacements of each substructure of the isolated structure with that of the original structure were taken into account as the VSI performance assessment. The results of numerous analyses on different earthquakes excitation, performed in this study, implied that employing appropriate link parameters, proportional to mass and stiffness ratios, can lead to satisfactory levels of seismic response reduction. To investigate the advantage of the VSI in low-rise multi-story buildings, the seismic performance of a five-story building with the VIS was also studied. Based on the VICGs, it was observed that response ratios are satisfactory in the short multi-story buildings for both short-period and long-period earthquakes. The following remarks can be stated as the conclusions of this study: By applying the VSI technique to low rise multi story buildings in Interactional State, up to 40% decrease in the seismic response of flexible substructure and even more in the stiff substructure is achievable.  In the Mass Isolation state of the VSI, it is inevitable to use relatively large values of practical link damping as 15 to 20% to achieve the reliable response reduction. Link stiffness in the practical range less than 10% of the original structure does not affect response reduction of the flexible substructure. In the Interactional State of the VSI, it is practical to select a wide variety of mass and stiffness ratios with different link damping values.  The values of inter-story drifts in low-rise multi-story VSI buildings is less sensitive to input earthquakes characteristics.

In recent years, various studies have been performed on the nonlinear responses of steel moment resisting frames under the near-fault earthquakes. Due to the event of near-fault earthquake, a significant amount of energy is exerted upon the structure, in a very short time. For this reason, the nonlinear distribution of demands differ with respect to those of the far-fault earthquakes. Investigating previous damages due to near-fault earthquakes indicated that significant inter-story drift demands are formed within the structure, which endanger its safety and stability. Near-field earthquakes containing forward directivity effects, due to the pulse in the velocity record, cause significant demands on the steel frames with respect to the ordinary earthquakes. Therefore, investigating the steel frames behavior as well as the higher modes effects under near-fault earthquakes is essential. For this purpose, five intermediate (ductility) steel moment resisting frames with 4, 7, 10, 15 and 20 stories under 20 far and near-fault accelerogram have been investigated. Finally, by examining the elastic responses of the single degree of freedom structure (SDOF) under considered accelerograms, the coefficients for transforming response of the SDOF structure to that of the MDOF structure are presented. The results of this research show that higher modes effects under the far-fault earthquakes are greater in comparison to those of the near-fault earthquakes. Besides, for about 30%-50% of the height of upper stories of the structures, the drift angle resulting from the near-fault earthquakes with the forward directivity effect is greater than that of far-fault earthquakes. RESEARCH METHOD Validation of analytical models is one of the most important steps of a study. In numerical studies, especially when a considerable database should be prepared for the extraction of the empirical expressions, lack of certainty concerning the validity of that created model could lead to inaccurate results. To avoid this issue in this article, all models are validated. In order to investigate the higher modes effects, 4, 7, 10, 15 and 20 stories 5-span 2D frames selected. Each model has 4 m story height and 5 m span length. The frames are intermediate (ductility) moment resisting frames. The structures being investigated in this research are designed completely based on the ANSI/AISC 341-05 and ASCE/SEI7-05 codes for gravity and seismic loads. Both the equivalent static lateral force and the modal response spectrum analysis were used for the models. ST37-type steel is used in design of the structures with the yield stress of 2400 KgCm2 and the ultimate stress of 3600 KgCm2 and the Poisson's ratio is 0. 30. The lateral drift values in all the structures are compared with the allowable value in the ASCE/SEI7-05 code. All elements have been chosen as compact sections (limiting local buckling) assuming enough lateral supports. Extended Abstracts سال پنجم، شماره دوم، تابستان 9317 15 km from the fault. All chosen accelerograms in this research have the moment magnitude greater than 6. 5 and the soil properties are of the Class D soil type based on the Fema 356 classification guidelines and are taken from the PEER website. The elastic response spectrum created by Seismosignal software. Besides, all acceleration time history has been normalized to their peak ground acceleration (PGA) before being scaled. All used accelerograms in this research are scaled according to the method presented in the Iranian Seismic Code (Standard 2800) and used in the NTHA method. Nonlinear time history analysis is also conducted by OpenSEES. CONCLUSION  The higher modes effects under far-fault earthquakes are greater than those of the near-fault earthquakes with the forward directivity effect.  By an increase in the structure height (period), the difference in seismic demands values of structures under the far and near-fault earthquakes decreases.  Investigating the drift angle over the height of various structures shows that for about 30%-50% of the height of structure, at the upper stories, the response obtained from the near-fault earthquakes with forward directivity effect is greater than the response obtained from the far-fault earthquakes. The buildings’ lateral load-resisting system is steel special moment-resisting frame. All buildings are 15 m in width.

Introduction design. frames. Research Procedure masonry. Results the vertical load turns into a destructive factor in combination with the lateral load effects. Ductility of the specimen with vertical loading of 200 kN is less than that of the specimen without the vertical loading.

Earthquake is one of the most destructive natural events that threats human society and cause the loss of lives and assets. In the past decades, extensive efforts have been conducted to reduce the damages caused by the earthquake and various technical papers, guidelines and codes are published trying to achieve this goal. Observations indicate the formative influence of these efforts and reduction in losses. However, despite these progresses, the main problem is why there are significant differences in performance of communities in the face of the earthquakes. This issue is properly mentioned by Ambraseys (2010) that compares death toll caused by two different earthquakes with the same magnitude in New Zealand (3/9/2010) and Haiti (12/1/2010). Considering the Corruption Perceptions Index (CPI) and the number of deaths resulting from the earthquake (DRE) for shallow earthquakes occurred during the period 1980-2009 of 6. 8