مجله علوم و مهندسی زلزله
سال هشتم شماره 1 (پیاپی 26، بهار 1400)

The continental suturing in Zagros was mainly occurred between the Arabian Plate in the southeast and Central Iran in the northeast along the Main Zagros Thrust. During the Pliocene time, the suture zone was reorganized and the belt-parallel component of the Arabia – Central Iran convergence has been localized along the Main Recent Fault (MRF). The Main Recent Fault is a major active strike-slip fault system on the border between the northern Zagros belt and Central Iran. Both geometry and kinematics of the fault system is rather well known along its central part and at its SE termination, while its possible continuation to the northwest is ambiguous. Moreover, less regard has been paid to possible relationships between this major intracontinental fault system and other strike-slip faults in NW Iran – SE Anatolia. The aim of this study is to describe both the genesis and evolution of Quaternary extensional basins in relation with the present-day geometry and kinematics of the NW continuation of the Main Recent Fault between SE Anatolia and NW Iran. We have used a combined approach including fault-slip data analysis and tectonic geomorphology to investigate active faulting of the MRF in NW Iran. Our results indicate that, to the north of latitude 37°N (NW from Piranshahr town), the main zone of the Main Recent Fault continues northwards along a less known branch of the Neotethyan suture up to the sinistral Khoy – Baskale fault zone in SE Anatolia. The recognized fault network in addition to the well-known NW part of the Main Recent Fault is divided into three distinct southern, central and northern structural zones. The almost 200 km long active fault system affecting the central and northern structural zones is transtensional dextral in character and is constituted by several strike-slip and normal faults and fault zones. The structural linkages of different zones occur through direct structural connections or soft linking releasing fault relay zones between overlapping fault strands. Our results also reveal that the NW continuation of the MRF clearly terminates to a NE-striking sinistral fault zone. At that place, the intracontinental dextral shear dies out and active deformation is transferred to N-S normal fault zones at the intersection zone of the NNW-SSE dextral and NE-SW sinistral faults. The crustal-scale ESE extension induced to these N-S fault zones has produced elongated extensional basins which, in the west of Lake Urmia and SE of Lake Van, resolve the space problem at the termination of the intracontinental dextral shear. These large elongated extensional basins show significant differences in both geometry and structural pattern with respect to the usual pull-apart basins formed in releasing fault relay zones of the dextral Main Recent Fault. According to our observation, the Marivan, Piranshahr, and Sardasht tectonic depressions are among the pull-apart basins formed in this kind of fault relay zones, while the Silvana – Serow and Başkale depressions are the result of crustal extension at the end of the dextral system. Considering the evolution stage of all the investigated extensional basins, those are classified into three distinct groups of active, transitional and inactive basins. Active basins are undergoing active extension and deposition, while inactive basins are transected by shortcut strike-slip faults and have entered the erosional stage. Basins in the transitional stage are filled by recent deposits affected by retrogressive erosion and incision. Active extension ended in the mature basins due to a direct structural connection of the overlapping main fault segments through a shortcut fault zone. This erosion – deposition balance in the extensional basins (whatever their genesis) suggests that the extensional basins are more evolved southwards along the Main Recent Fault implying a probable northwards propagation for the dextral fault system. The distribution pattern of extensional basins described in this study reveals the importance of strike-slip faulting in producing special tectonic geomorphology features that are usually seen in extensional tectonic settings, while a dextral transpression is prevailing over the region.

Soil dynamic properties play fundamental roles in the analysis and design of various earth structures. Shear modulus and damping ratio are two important dynamic properties. In particular, shear modulus, especially at the level of very small strains typically denoted as Gmax, is a dynamic property of great significance, which is frequently implemented in the seismic design of geo-structures against the destructive earthquakes. The shear modulus reveals the resistance of geo-structure to the deformations imposed by the external loading. On the other hand, one of the commonly used methods to increase the strength and stiffness properties of soft soils is to stabilize them using either cement or lime. Addition of these stabilizing agents to the parent soil strengthens the bonding among particles, thus resulting in the overall increase in the shear stiffness of the mixture. Therefore, the stabilization technique is always considered as an efficient method of soil improvement. In the current study, the small strain shear modulus of soft clay stabilized with various lime contents is thoroughly evaluated using the results of a comprehensive series of bender elements tests under isotropic stress states. Bender element is a nondestructive experiment commonly used to estimate the velocity of shear waves propagating through the soil samples. Using the shear wave velocity obtained, the small strain shear modulus of the specimens could be easily evaluated with a simple equation in soil dynamics. The applicability of the bender element test to measure the shear wave velocity for the stiff stabilized samples in this study was extended using a new innovative method. The influence of input frequency on the shear wave velocity measurements was also rigorously examined and it was concluded that it barely affects the received signals. Based on the bender elements experimental results, the influence of lime inclusion (5%, 10%, 15% and 20%), water content (45%, 65% and 85%) and curing time (28 and 56 days) on the small strain shear modulus is thoroughly investigated. The amount of water in the soft clay-lime mixture was selected to be about 1, 1.5 and 2 times of the liquid limit moisture of the parent clay. According to the experimental results, it is observed that the small strain shear modulus decreases dramatically with the increase in the water content over the liquid limit. The addition of lime to the clay, up to a particular level, leads to a considerable increase in the small strain shear modulus. However, beyond this optimum value, the shear modulus shows a declining trend with the increase in the lime content, which is an indicative of the inefficiency of the stabilization process. Thus, it is a common practice to limit the lime content to a specific percentage so as to obtain the maximum possible value of shear stiffness. The general trends of shear modulus variation for the samples stabilized at different curing periods are also observed to be quite similar. In general, the small strain shear modulus increases with the increase in the curing time, as more chemical reactions could occur within the mixture. Finally, a microstructural analysis was also conducted using the scanning electron microscopy (SEM) images of the treated specimens so as to somehow justify the trends of variation in small strain shear modulus obtained from the bender element experiments. Utilizing the results obtained in the course of this study, useful information is provided for the prediction of the small strain shear modulus of the clays stabilized with lime using deep mixing or grouting methods. Indeed, the results of this study could be effectively used in different geotechnical construction projects to improve the parent soil strength and stiffness properties and ensure about the serviceability and efficient performance of the underlying soil deposit.

Determination of seismic response of geotechnical structures is important for safe design in a seismically active area. The dynamic behavior of geotechnical structures is complex, and therefore the use of different methods helps to understand this dynamic behavior. Numerical methods allow to well describe the complex dynamic behavior of geotechnical structures. However, the time-consuming, determination of several different parameters, radiation conditions, and difficulty in interpreting the results are the reasons for limiting the use of these methods in the technical community. The pseudo-static method is the most common method for analyzing seismic stability in geotechnical engineering. This method is independent of time and does not consider the dynamic nature of the earthquake load. Also, some soil parameters such as damping or compressive and shear wave velocity are not considered. To overcome these drawbacks, the pseudo-dynamic method was developed by Steedman and Zeng [1]. Sarangi and Ghosh [2] used the pseudo-dynamic method to determine the seismic stability of nailed vertical excavations in medium dense to dense sand. However, the boundary conditions are not included in the pseudo-dynamic method. Therefore, the pseudo-dynamic method has been modified again to satisfy the boundary conditions [3]. Recently, Kokane et al. [4] using the modified pseudo-dynamic method presented a solution for nail tensile force and inertial forces acting on failure wedges. However, the formulation used in this article is very difficult to develop. In this paper, the modified pseudo-dynamic method is used to analyze the seismic stability of nailing soil walls. Because the modified pseudo-dynamic formulation has been formulated to calculate the seismic pressure of a nail-free wall, the modified pseudo-dynamic formulation first is rewritten for the wall system with nail reinforcement, to calculate the seismic active pressure. Using pseudo-dynamic acceleration components derived by Belleza [3] and conducting an analytical process, the proposed formulation is obtained for the active seismic soil pressure coefficient and the safety factor corresponding to the general stability of soil-nailed walls. In the proposed formulation both Qh and Qv as horizontal and vertical inertial forces of the failure wedge are considered. Then, using the try and error iteration method, the critical angle of failure, seismic active pressure, and seismic safety factor are obtained. The main innovation of this study is to apply the modified pseudo-dynamical method for a nailed soil wall, however, as another innovation, seismic pressure on the wall is calculated taking into account the tensile force of the nails. It should be noted that in the available analytical methods, the seismic pressure of the wall has been calculated without regard to the nail tensile force. In the following, to validate and verify the proposed analytical method, a comparison between the presented analytical results with the results of the shaking table and the available analytical methods is carried out, which shows the high accuracy of the proposed method than other analytical methods. Finally, with a numerical example, a parametric study is carried out to verify the effect of various soil and nail parameters on the seismic stability of the nailed walls, and the coefficient of seismic active pressure. References 1. Steedman, R. and Zeng, X. (1990) The influence of phase on the calculation of pseudo-static earth pressure on a retaining wall. Geotechnique, 40(1), 103-112. 2. Sarangi, P. and Ghosh, P. (2016) Seismic analysis of nailed vertical excavation using pseudo-dynamic approach. Earthquake Engineering and Engineering Vibration, 15(4), 621-631. 3. Bellezza, I. (2015) Seismic active earth pressure on walls using a new pseudo-dynamic approach. Geotechnical and Geological Engineering, 33(4), 795-812. 4. Kokane, A.K., Sawant, V.A. and Sahoo, J.P. (2020) Seismic stability analysis of nailed vertical cut using modified pseudo-dynamic method. Soil Dynamics and Earthquake Engineering, 137, 106294.

Liquefaction is the primary cause of most earthquake-induced damages in saturated loose and medium-dense deposits. The literature on liquefaction potential has mainly focused on clean sand, and it has been assumed that liquefaction can take place only in sand, and fine- or coarse-grained soils cannot generate water-pore overpressure. However, after the occurrence of multiple earthquakes, it was found that non-plastic fine soils also have a significant liquefaction potential in addition to sands. A review of earlier literature showed no study on the effect of the cyclic stress ratio (CSR) on the critical silt content in the study of the liquefaction potential of sand with a fines content of equal to greater than 40% to 100% pure silt content. In other words, the mutual effects of CSR and non-plastic fine aggregates on liquefaction potential of sands with high fine aggregate content, especially pure silt, has not been studied up to this moment. Moreover, discrepancies exist between the results reported on the liquefaction potential of sand and silty sand containing 40% fines. This study investigates the effects of CSR and non-plastic fines on the liquefaction potential of silt and silty sand at a constant confining pressure through undrained cyclic triaxial tests. The test was repeated under the same conditions and steps at different cell pressures (CP) and bottom back pressures (BBP) to investigate the effects of pressure application steps in the saturation phase (Bvalue) of different soil types, from sand to slit, on the liquefaction potential and resulting strains, which had not been investigated before. The cyclic triaxial test was performed on non-plastic slit and Firuzkuh sand 161 according to ASTM D5311. The specimens with a diameter of 5 cm, a height of 10 cm, and a density (Dr) of 30% were prepared by wet tamping According to the results, the liquefaction resistance of sand decreased as the silt content increased up to 30% and then increased when the silt content increased to 60%. A relatively uniform behavior was observed when the slit content increased to 100% (pure slit); because, when the slit content of clean sand is increased to 30%, the fine slit particles fill the empty space between the coarse-grained sand particles, leading to a decrease in the soil drainage capacity during earthquake-induced vibrations or cyclic loading. Therefore, the liquefaction potential increased under these conditions; but the sand behavior was dominant until the particle content was increased to 30%. The soil behavior changed when the slit content exceeded 30%, and the fine-grained soil behavior was observed, declining the liquefaction potential. On the other hand, the CSR affected the liquefaction behavior of all soil specimens so that the fines content generating the maximum pore-water pressure (PWP) varied by increasing the CSR. The liquefaction curves were presented for different soil types. Four specimens with different silt contents showed different strain behaviors at different CSRs so that the strain path taken by the four soil types to reach ru = 1 is more uniform at CSR = 0.15 than CSR = 0.2. The effect of pressure applied to the soil structure in the saturation phase (Bvalue) on the liquefaction results and respective strains was insignificant for pure slit; but more tangible in silty sand and sand.

Brittle failure can prevent structural connections from reaching their peak performance. It is therefore considered as one of the most destructive forms of failure. The prevalence of different failure in rigid connections of steel frames in the aftermath of the Northridge and Kobe earthquakes brought the performance of these connections under question. Research into rigid connections with complete penetrating welding revealed that it is highly probable for the welds to undergo premature brittle failure at low drifts. To address this problem, the use of Reduced Beam Sections (RBS) was recommended by the scientific community after the Northridge earthquake. In this connection, the beam’s flanges are cut (reduced) so that it can take on the form of a fuse, making it possible for the plastic hinge to be driven toward the inside of the beam, thereby preventing the panel zone from failing. RBSs, which are categorized as “prequalified connections”, have been the subject of extensive investigations and have suitable energy absorption and ductility under cyclic loadings. They are not, nonetheless, without flaws and are accompanied by problems such as the need for replacement after average or severe earthquakes due to severe inelastic deformations in the reduced area. This problem is compounded by the connection of secondary beams to primary beams in the ceiling of the structures in which they are used. The objective of this investigation is the numerical evaluation of RBS connections with replaceable fuses. Numerical simulations on three models – namely, a conventional reduced beam section connection (RBS), a reduced-flange connection with a replaceable fuse (RBS-F), and a reduced-web connection with a replaceable fuse (RWS-F) – were carried out using ABAQUS, with material and geometric nonlinearities having been considered. Also, the materials of the columns, beams, and plates, stiffeners, doubler and continuity plates, seat plates, and bolts have been defined based precisely on experimental data. Loading and support conditions of the numerical models were the same as those of the experimental samples. In the numerical models, the bolts were first pre-stressed to a sufficient degree. Then, lateral cyclic loading was applied to the beam of each model. The hysteretic curves of the numerical models are in good agreement with those of the experimental samples, indicating that the numerical models can reliably be used for the evaluation of other sections. Seven different profiles were selected from IPB sections (IPB140 to IPB340) for the beam. Suitable columns and endplates were designed for every beam size. For every set, three RBS, RBS-F, RDS-F, and RWS-FR models were constructed, bring the total analyzed models to 28. The dimensions of the RWS model were selected so that its plastic section modulus would be the same as that of the RBS sample. Similar to the tests, the analyses continued until a draft of 8% and the hysteretic moment-rotation diagram of each sample was obtained. Since in tall buildings beams and columns with variable dimensions are used in the experiment was carried out for beams and columns with one size, performing extensive numerical analyses can offer a better comparison of the performance reduced-depth sections and reduced-flange sections. The results of more than 28 numerical analyses showed that in the RBS and RBS-F models, increasing the size of the beam reduces ductility. However, for the RWS-F sample, not only does increasing the size of the beam maintains the beam’s ductility, it also keeps it, noticeably, above those of the other two samples. The ultimate strength of the sample, however, is less than the other two samples. By increasing the web’s thickness and its plastic section modulus, an ultimate strength on par with those of the other samples can be achieved. Therefore, the modified RWS-F sample can be a suitable replacement for RBS connections.

Masonry bridges are vulnerable structural systems to the ground motion excitation that their survival in case of such incidents has to be studied in detail. In this work, a simplified model for dynamic analysis of masonry arch bridges based on rocking motion of rigid blocks is proposed. Using this model, nonlinear time integration analyses on these bridges can be done with ease and in a short time. Later, acceptance criteria for three cases of un-cracked, fully-operational and collapse-prevention pier sections are developed for such bridges. The accuracy of proposed model in representing the behavior of a rocking system has been verified using the results of experimental studies on rocking motion of a masonry-concrete block reported elsewhere. The results show the suitability of the proposed model in representing rocking motion of rigid blocks. In a case study, the proposed model for masonry arch bridges was used in evaluation of seismic performances of a monumental masonry bridge subjected to both horizontal and vertical seismic actions. The study shows the importance of vertical component of ground motion in determination of internal forces and shear-sliding deformation at the bottom of the bridge’s pier. The proposed model has also shown its ability in defining the effectiveness of a seismic retrofit approach for the same bridge system in a comparative study. According to this investigation, seismic performances of the bridge can be significantly improved in case of adding ductility to its deck assembly. To understand the capacity of bridge system in dealing with earthquake demands, a series of Incremental Dynamic Analyses (IDA) have been carried out on the rocking-pier model of the bridge system using earthquake records. Considering the simplicity of rocking pier model, all the analyses on above-mentioned bridge system have been carried out with ease and in a very short time. According to results, a bridge system subjected to bidirectional seismic actions (vertical and horizontal) has, unexpectedly, more capacity in dealing with seismic demands if it is compared with the same bridge system with unidirectional horizontal seismic excitation. Conversely, the sliding breakdown of the pier in case of bidirectional seismic actions is much higher than that in the case of unidirectional one. Moreover, significant reductions in the level of rotational pitch and shear sliding at rocking joint of the pier is expected in case of adding ductility to the deck of the bridge assembly. As it was expected, ductility in the bridge system also decreases the discrepancy of bridge responses with respect to different earthquake actions, which is attributed to the systems with higher energy dissipation potential.

Overpopulation in metropolises has led to a space reduction in the cities and a tendency to use underground spaces. Different solutions have been proposed for traffic problems; there are many cases in science research in recent years that show the significance of earthquake destruction effects on these structures. Regarding seismicity of the Kermanshah city, we have tried to study the effects of earthquake on the site effect of Kermanshah subway tunnel by using ABAQUS software and finite element method. Each one of BH-7, BH-8 and BH-9 bore holes have been analyzed in three different steps: first, frequency analysis, then free field analysis (without tunnel), and finally the main model. The results derived from the time historical analysis of the three BH-7, BH-8 and BH-9 bore holes show that the maximum amplification occurs in the BH-9 borehole, which is the most critical borehole in terms of amplification received waveforms on the earth surface. Although the maximum amplification occurs in the BH-9 borehole, the highest maximum stress occurs in the tunnel cover at the site of the BH-8 borehole due to the location of this borehole, which is near the bedrock. According to this study results, the type of damage in tunnels cover depends on the geotechnical characteristics of the layers, the content and intensity of the earthquake record, the amplification that occurs in the soil profile, the amount of tunnel overhead load and the strength of materials that covers tunnel with concrete.  1. Introduction Nowadays, underground structures such as subway tunnels, water and sewage transfer tunnels, utility tunnels, subway stations and underground parking are among the vital infrastructures of the new urbanization. This kind of structure especially in crowded cities is built to resolve different needs. The study of destructive earthquakes that have occurred in recent decades has clearly shown that geological conditions and site effects play an important role in amplification of the strong movement of the earthquake. Soil type and local geology can play an important role in seismic movement’s amplification and the type of damage caused by strong earthquakes.  2. Specifications of Materials Used in Numerical Analysis 2.1. Geometry and Tunnels Cover One of the effective parameters in studying the seismic responses of underground tunnels is the geometric dimensions of the tunnel section. The cross section of Kermanshah City subway tunnel is horseshoe type with an average radius of 4.3 meters. In this case study, two-dimension modeling has been used for modeling with plan strain conditions. The thickness of the concrete cover of the tunnel is 30 cm. Behavioral model of damaged concrete has been used to define the nonlinear characteristics of concrete tunnel cover. This behavioral model is the most comprehensive and widely used model for concrete in Abacus software. In the damage mechanism, it is assumed that the decrease in stiffness is due to the creation and expansion of small cracks in order that the decrease in stiffness can be measured and determined with a parameter called damage.  Conclusion        In this study, we have tried to study the effect of earthquake on the site effect of Kermanshah subway tunnel by using ABAQUS software and finite element method. According to study results, the type of damage in tunnels cover depends on the geotechnical characteristics of the soil layers, the content and intensity of the earthquake record, the amplification that occurs in the soil profile, the amount of tunnel overhead load and the strength of materials which covers tunnel with concrete.

Buildings should be designed to resist earthquake-induced deflections and internal forces. The experience of recent earthquakes illustrates that the amount and extent of damage in irregular buildings are far more significant than the others. Irregularities in the structural system may amplify structural response leading to significantly more severe damage compared to regular structures. In fact, when irregular structures are subjected to lateral seismic loads, they will experience lateral motion accompanied by torsional rotations, which is due to an eccentricity between the center of mass and the center of stiffness. In other words, structural irregularities decrease the seismic performance of buildings significantly, and they will be heavily damaged as a result of torsional effects on structural elements. Many studies have been conducted on reducing torsional effects on structures. One of the approaches is to apply control systems. In this study, efficiencies of some passive damping controls are investigated to reduce the torsional irregularities in building structures. One type of passive control system is tuned mass dampers (TMD), which usually have a significant mass. Having a great mass can be a drawback for these types of systems and limits their application in practice. Therefore, to eliminate this issue, a new type of tuned mass damper called Whirling Tuned Mass Damper (W-TMD) has been recently introduced in the literature. This type of tuned mass dampers has a smaller mass compared with ordinary TMDs. In the present study, the seismic performance and behavior of ordinary TMD and W-TMD have been investigated and compared. For this purpose, the seismic behavior of three similar buildings, with different controlling systems, having five story steel moment resisting steel structures are compared. The first building does not have any controlling system; however, the last two ones are equipped with TMD or W-TMD. Nonlinear time history analysis results of these buildings under five earthquake records are compared. The applied records are for Northridge, Loma Prieta, Kobe, Imperial Valley, and Chi-Chi earthquakes. The obtained results show that buildings with controlling systems are much better; however, W-TMD has a better performance in reducing the story drift and structural torsional modes, compared to TMD. Moreover, a sensitivity analysis is carried out on the properties of a W-TMD by changing the method of supplying the required inertia. Two different methods are chosen: the first one has a solid disk but the second has a ring section. The results showed that when W-TMD is fitted with the ring cross-section, not only it has a smaller mass, but also it has a better performance in decreasing the irregularity response of the structure. To be exact, the higher the ratio of the radius of the inner circle to the outer circle of the ring, the greater the amount of inertia will be, and therefore W-TMD requires less mass. Since a W-TMD applies less mass to the structure, it can be an excellent alternative for TMD. If the W-TMD is equipped with a disk section, it has 66% the mass of TMD, while using ring section, it can have 42% of the TMD mass. The obtained results of the sensitivity analysis of W-TMD confirm that the damper mass can be reduced up to 50% without significantly reducing its efficiency. Some damage indices, including drift story, torsional rotation of floor and torsional irregularities coefficient, are considered for evaluating the performance of each model equipped with TMD and W-TMD. It can be concluded that the model equipped with a W-TMD has a much better performance in reducing all damage indices.