BULLETIN OF EARTHQUAKE SCIENCE AND ENGINEERING
Year:2023 | Volume:10 | Issue:3|Papers Count:8

Design spectrums are used to compute seismic demand in structural design process. Therefore, seismic designcodes try to provide safety margin in performance of structures by developing appropriate design spectra. Thedesign spectra in Iranian seismic design code (Standard No. 2800) were developed via the analysis of differentearthquake response spectra. In Standard 2800, a mapped PGA value for 10% in 50 years used as an anchor point toproduce the design spectrum at a desired point. Meanwhile, this approach fails to provide a quantitative safetymargin as claimed in design code. Furthermore, their accuracy have not yet been examined by conventionalapproach such as uniform hazard spectra (UHS), which is conventionally employed by many design codes such asEurocode 8 (1998). Spectral ordinates of UHS have equal probability of exceedance (PE) across all periods ofvibration. Therefore, designed structures with recent design spectrums have the same imposed seismic hazard level.An attempt was made in this study to directly examine the accuracy of proposed design spectra in Standard 2800by those of UHS derived in Tehran Megacity as a case study. For this purpose, the area under study is divided into632 grids with a 1 km × 1 km area. The hazard curve was calculated by considering the soil type at each grid pointas defined in Standard 2800 from hard to soft (I to IV). The number of grids fall at each soil type are 10, 465, 150and 7 points for I, II, III and IV soil types, respectively. Hazard curves at the grid points were calculated and wereused to compute uniform hazard spectra for 2% and 10% PE in 50 years (return periods of 2475 and 475 years,respectively). For each soil type, the mean of uniform hazard spectra at different grid points with the same soil typewere calculated, which were used as a representative uniform hazard spectrum for that soil type. The derivedrepresentative uniform hazard spectra for 10% PE in 50 years were compared with those proposed in Standard 2800for different soil types. Furthermore, spectral acceleration ratio of uniform hazard with respect to those fromStandard 2800 at periods of 0.2 s and 1.0 s were computed and were compared for the whole points according totheir soil types. The outcomes reveal that the spectral acceleration in design spectra of Standard 2800 are larger thanthose in UHS for all the periods, especially for the periods larger than 0.5 s for soil types I and II. Meanwhile, thespectral accelerations of Standard 2800 become almost the same at periods lower than 0.5 s, and again becomelarger than UHS at periods larger than 0.5 s for soil types III and IV. In general, it is found that the proposed designspectra in Standard 2800 are conservative. This may need further examine by more recent approach such as uniformrisk, and then being considered in future revision of Standard 2800.

Seismic resonance assessment of the site and its relationship with ground structures play an important role inearthquake engineering and risk assessment. Seismic waves can be exacerbated by sudden geometric changes due totopographical effects, significantly. Various parameters can be involved in the evaluation of topographicalcomplications. Finally, the effect of all these factors should be summed up and considered in seismic designs. Boorewas the first to use the Finite difference method to examine the triangular hill under SH waves. In this paper,FLAC2D software is used to analyze the topography of semi-sine hill under Landers earthquake record. FLAC2Dsoftware is a Finite difference program of Itasca software that is used for continuous environments. Each topographyis drawn to investigate the effect of layering of complication materials at angles of 15, 30, 45, 60 and 75 degreeswith a height of 20 m layered and to investigate the effect of height at heights of 10, 20 and 30 m and also withchanging the angle from 15 to 75 degrees. Also, increasing the number of layers in topography with different anglesof 15 to 75 degrees and investigating the effect of placing layers with loose and dense materials is considered. Mostof the time, numerical analysis of a new problem always begins with the simplest behavioral model. Materialbehavior here is assumed like most previous studies that considered the behavioral model of materials as linearelastic model. An important factor that affects numerical results is the layering angle of the hills. Therefore, semisinehills with different layering angles (15 to 75 degrees) exposed to the Landers earthquake with alluvialfrequency related to each model are modeled with layers that have different properties in terms of density and shearwave velocity and Poisson ratio. The ratio of maximum displacement of the desired point in the model withtopography to the maximum displacement of the desired point in the reference model here is expressed asamplification (ah). Increasing the angle of the layers increases the topographic displacement amplification. Thepresence of layering with impedance difference in the site causes seismic waves to be caught and increases theeffects of the site. At each layering angle, the height increase is equivalent to an increase in amplifications. In thisway, a model with a height of 30 m, in all angles, has the most displacement response. At all angles, as the numberof layers increases, the amplification of the topography is added. In the three-layer hills with increasing angle, awider surface area of the hill is composed of materials with the lowest shear wave speed, which along with thecomplexity of layering these hills, has increased their amplification. The impact of how to place loose and densenon-horizontal layers on seismic motion intensification is the last parameter studied in this paper. It can be said thatthere is a relationship between topographical and stratigraphy resonance, and in particular, stratigraphic effects havea greater impact on the characteristics of earth's motion than topographical effects. By comparing the obtainedresults, it was found that each of the parameters of layering angle of topographic materials, height, and number oflayers and the positioning of loose and dense layers in semi-sine geometry are the components affecting the seismicresponse of the site.

The seismic collapse capacity of a structure is a critical factor in earthquake risk assessment within engineeringpractices. Conventionally, evaluating this capacity involves intricate and time-consuming incremental dynamicanalyses. However, recent progress has brought forth alternative, streamlined methodologies grounded in the use ofstructural behavior curves. This study employs the application of these innovative approaches to comprehensivelyassess the seismic collapse capacity of structures. Embracing advancements, it strives to enhance the efficiency andprecision of seismic risk assessments in engineering practices.In addition to the efficiency of assessment methodologies, it is imperative that the calculation of seismic collapsecapacity aligns with the specific demands of the construction site. This ensures that the seismic risk falls within theestablished allowable limits. This consideration becomes particularly critical for construction sites located in closeproximity to fault zones. In such areas, the presence of directivity pulses heightened attention to seismic collapsecapacity. Recognizing that structural ductility and the pulse period ratio in the near-fault are primary factorsinfluencing seismic collapse capacity, which is demanded in site, this study delves into a detailed numericalinvestigation of these critical elements. Subsequently, the seismic collapse capacity demanded in the near-fault ismeticulously estimated based on these considerations.The extensive investigations undertaken in this study yield insightful revelations. It is evident that heightenedstructural ductility correlates with an augmentation of seismic collapse capacity, both in the near-fault and far-faultscenarios. Conversely, a reduction in seismic collapse capacity in the near-fault is discerned as the pulse period ratioincreases concerning the fundamental period of the structure. To conduct a comprehensive evaluation, the ratio ofseismic collapse capacity in the near-fault to that in the far-fault is calculated, taking into account both ductility andpulse period ratio. This derived parameter, denoted as γ, is then employed to estimate the seismic collapse capacitydemanded in the near-fault. This analysis contributes valuable insights to the understanding of seismic behavior inboth near-fault and far-fault regions.For the assessment of seismic collapse capacity demand at construction sites, the study recommends theutilization of a lower bound of the ratio of near-fault to far-fault seismic collapse capacity. This lower bound,associated with lower ductility and a higher pulse period ratio, is not just conservative but also robust. Importantly,this cautious approach ensures that an increase in this parameter does not significantly escalate the demand at theconstruction site. Such a calculated and conservative estimation of seismic collapse capacity demanded contributesto a more resilient seismic risk assessment for structures situated in near-fault zones.In conclusion, the results indicate that for the assessment of seismic collapse capacity that is demanded atconstruction sites in near-fault zones, utilizing a lower bound of the ratio of near-fault to far-fault seismic collapsecapacity, associated with lower ductility and higher pulse period ratio, is sufficiently conservative. Moreover, anincrease in this parameter does not significantly escalate the demand at the construction site.This approach ensures a cautious estimation of seismic collapse capacity demand, contributing to a more robustseismic risk assessment for structures in near-fault zones.

Turning to clean energy is inevitable, among which wind energy is one of the most common and available. Theuse of wind energy due to its known advantages over other renewable energies has caused the technology of windturbines to grow more, and this has led to the increase in the capacity of wind turbines and the commercialization oflarger sizes. By increasing the capacity of wind turbines, the size of the rotor and consequently the height of thetower necessarily increase. Therefore, the design of wind turbine towers more goes complex day by day, and mustbe done specifically on a case-by-case basis. For this purpose, wind turbines should be modeled completely with alldetails. One of the most expensive parts of wind turbines is its tower. Considering the whole applied forces anddesign criteria and fatigue base on the regulations and guidelines is necessary to achieve a safe performance. Inaddition to these factors, in seismic prone areas the dynamic earthquake forces should be considered in analysis anddesign of towers. Therefore, in this study, we have tried to study the seismic behavior of a real tower model incomparison with other dynamic forces, in order to obtain the amount and manner of effect of each force. Standardsgenerally specify design load combinations for ultimate load and fatigue load analyses. The speed of 11 m/s is thespeed at which, according to the power generation diagram of the studied turbine, the speed of the turbine reaches itsmaximum power, and it is assumed that the turbine will be installed in a site where the wind will be at this speedmost of the time, and the probability of earthquake occurrence at this speed is more than other modes.Therefore, considering the emphasis on considering the earthquake force in seismic areas along with other forcesacting on the wind turbine in the new versions of the regulations in this field, and the seismicity of Iran, acomparative analysis of seismic load with other forces acting on the wind turbine based on Standard GL, chapter 4,Table 4.3.2 for turbulent wind of 11 m/s, in the state of zero deviation angle for the 2 MW national wind turbine ofIran, with an 80-meter steel tower and a 55-meter 3-bladed rotor, in a complete and practical model, with themodeling of the steel tower structure and concrete foundation and soil layers in the case construction. The commenthas been analyzed and investigated by the dynamic finite element numerical method using Abaqus software.Considering the location of this wind turbine, with soil layers 6 meters deep, the maximum change in the location ofthe tip of the tower by considering the seismic load increased by about 7%, but the significant increase in theequivalent stress at the height of 50 meters of the tower, despite the low depth of soil layers. The lack of significantacceleration of the earthquake from the rock bed to the earth's surface was obtained, amounting to 36%. Therefore,the necessity for simultaneous consideration of earthquake load along with the wind load was well concluded.

This study is divided into two main parts. In the first part, the behavior of four groups of connections that arecommonly used in the construction of the country has been investigated, because of which their hysteresis behaviorhas been determined. In the second part, the behavior of connections damaged in Sarpol-e Zahab Earthquake hasbeen investigated, and finally the changes in the stiffness, strength and ductility parameters of the connectionsdamaged in the earthquake have been determined.Connections used in buildings may be categorized into rigid, semi-rigid or pinned-end connections. Theassumption of perfectly pin or rigid behavior for a connection may not always be reliable in the design of astructure; therefore, in this study, an attempt was made to investigate the real behavior of connections that arecommonly used in the country's constructions.In experimental studies, due to the existence of some limitations, assumptions are always considered that mayaffect the results of a test. Therefore, the best experiment is to determine the behavior of the members of a buildingafter an earthquake. One of the earthquakes that can be used to investigate the behavior of the members of a buildingis the Sarpol-e Zahab – Ezgeleh earthquake. Because the buildings built in the city of Sarpol-e Zahab were generallyafter the war between Iran and Iraq (1367-1359), which can represent engineering constructions in the country.Although several years have passed since the construction of these buildings, this type of connection is still commonin many constructions in Iran. For this purpose, in this research, the damages caused to this type of connections andtheir performance have been investigated.Based on field observations, the connections related to steel buildings in the earthquake-affected areas ofKermanshah province can be divided into four groups: 1- connection with top and bottom cover plates along withstiffeners; 2- simply supported seat angle connection with stiffener; 3- simply supported seat angle connection withstiffeners and shear plates; 4- like No. 2 or 3 together with gusset plate. In this study, in order to understand thebehavior of these connections during an earthquake, the experimental model of each group was made with full scale,and their moment-rotation curves were extracted under cyclic loading. Based on the results obtained from theexperimental studies, connections No. 1 and 4 of these groups were classified as rigid connection, and No. 2 and 3were evaluated as semi-rigid connection with brittle behavior.Another scope that has been addressed in this study is to determine the behavior of damaged connections in anearthquake. This issue, which is the result of observing the trend of the connection hysteresis curve during loading,makes it possible to determine the remaining capacity of the earthquake-damaged buildings. The remaining capacityof the damaged building is one of the important and crucial parameters in the decisions that to decide whether thebuilding should be repaired or demolished. For this purpose, the hysteresis curve of the tested connections has beeninvestigated and analyzed. As a result of these analyses, the curves that show the modifications in stiffness, strengthand ductility have been extracted for all four types of connections investigated in this study.Finally, two levels of damages were considered for each of the four connection groups. Then their performancecurves in each of the two levels of damages were presented along with the performance curve of the connectionwithout damage. The results of the studies showed that stiffness and ductility, unlike strength, are the parametersthat are most affected by the damage caused in the connections.

Traditional bazaars, as cultural and economic centers of historical cities, are among the most vulnerable urbanfabrics in Iran. Therefore, natural hazards may destroy historical and cultural assets in these areas, disrupt thebusiness of many people and cause significant casualties and economic loss. Considering that such bazaars havemany differences with other urban fabrics, thus, applying conventional risk and resilience assessment methods formeasuring the resilience of traditional bazaars may not provide appropriate results, and new models should bedeveloped for resilience assessment in such urban fabrics. Accordingly, in this paper, a new model to estimate thesystem performance of these urban fabrics that have historic and commercial value against earthquakes isintroduced. The proposed model provides a comprehensive approach based on the system performance to be used inearthquake resilience assessment of traditional bazaars. For this purpose, some indicators related to differentdimensions of earthquake resilience were classified into physical, economic, social and organizational dimensions,based on the relevant scholarly articles. In addition, a new aspect entitled the cultural-historical dimension (which isvery important in assessment of the resilience of traditional bazaars) was introduced, and indicators related to thisdimension were also added to the framework. Then, a questionnaire-based survey was conducted to assess theweights of parameters and their relevant indicators. Finally, the new model was developed based on integration ofdifferent parameters and indicators considered their weights and values.In order to test the applicability of the proposed method, Tabriz Traditional Bazaar (as a World Heritage) wasselected as case study and the overall system performance of this bazaar against earthquakes has been calculated.For this purpose, the values of different dimensions and indicators were integrated based on their weights. Bycalculating the average of the total performance at each section, the total performance of Tabriz bazaar wasestimated to be 54%. This shows that currently the bazaar does not have good condition and in case of anearthquake, different physical damage, socio-economic loss and cultural consequences are expected and recoveryneeds a long time. By using this model, the effectiveness of different interventions in the bazaar for improvingresilience can be also estimated. This will help decision makers to implement the most efficient approaches toreduce the potential impacts of earthquake in this bazaar and select the areas for intervention based on cost - benefitanalysis. The proposed model can be utilized in similar old urban fabrics in other cities, after calibrating theparameters and their weights based on local conditions.

AbstractThe seismic response of alluvial valleys is strongly influenced by the geometry, mechanical characteristics and the sedimentary layers of the valley. Seismic waves that enter the site from the source may be greatly amplified due to the variation of wave velocity between different layers. One of the most important reasons for evaluating site response analysis is the difference in the seismic response of structures with various frequency that are located on the ground. Many studies about seismic behavior of topographic effects are linear or equivalent linear and there are few non-linear analyses. In this article, the results of different parameters and their effects on nonlinear seismic behavior of alluvial valleys have been investigated. Also, the difference between the various methods available in the literature and their results have been identified .finally the effects and importance of each of these parameters have been summarized.a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a aa a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a aa a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a aa a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a aa a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a a aa a a a a a a a a a a a a a a a

In modern societies, the importance of financial and temporal resources is evident and has received attention inrecent decades, and it is predicted that such importance increases with time. Structural health monitoring and crackdetection are two topics in the field of civil engineering, which two areas have a key role and is considered almostnew knowledge in civil engineering. In this project, we will try to use basic structural dynamics relations andstrength of materials to achieve a better understanding of structural damage. In fact, this project offers a practicalmethod that uses natural frequency to help identify the rate of damage to the support, which can help structuralimprovement. In this method, the only requirement is to obtain frequency from the structure and there is no need forstructural control and permanent presence of manpower. As you will see, dynamic parameters have a strong role inthis regard. What makes structural health and crack detection in particular both interesting and hard is significantuncertainty of structural damage. In fact, much uncertainty is involved in formation of structural damage and itsdetection and repair, which makes it a hard task with a high computational cost. Despite all these problems, due toimportance of structural health monitoring and attempt to make most of available resources, many researches havebeen done in this regard and certainly the costs of knowledge of structural damage is much less than the material andnon-material damages of incidents in communities.Although we studied a sample model of structure, given this discussion is newly emerged, this elementary modelwill be needed in future for much more complicated models that are closer to real structures. Besides the above said,we saw in this project that despite study of damage to supports is very important in overall stability of structure andseems a difficult problem, a good knowledge of damage can be obtained using simple and reliable relations. Thestructure studied in this project that had three damaged supports can provide a better model, compared to previousones, which were mostly in form of console or single-opening beams. However, addition of openings and use ofcharacteristic coefficients matrix equation to obtain shape function will be very hard and requires that we look for asimpler alternative method in this section. The other points of this project include direct study of level of damage.What has been sought so far rather in the area of damage detection includes an interpretation of the level of damagethrough variations of frequency or study of trend of variations of mode shape. In this project, having obtained thefrequency of damaged structure using the said method, we obtained level of stiffness reduction.As for direct solution, which is aimed to find proper shape function, acceptable results were obtained. But thetrend of results shows that error of this method increases as difference of stiffness of supports increases. It can beinferred that, given Rayleigh’s opinion, difference of stiffness cause the main mode to take distance from the firstmode and such difference results in error. In fact, if stiffness of supports is symmetric, the main mode of thestructure, which unveils the main structure of the shape function, gets closer to the first mode, which makes theinitial assumption for shape function more acceptable.In the second part, which is derivation of frequency function with the aid of Rayleigh method, as is the case withdirect solution method, the effect of factors of the main mode of structure changes the error level of the results. Inthis part, by addition of test mass at points on the main mode. In direct solution, we obtained the shape function inabsence of test mass, which causes error to increase with test mass.