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Volume 0, Issue 0 (2-2024)
Abstract
Writing assessment literacy(WAL) for second or foreign language (L2) teachers, which refers to teachers’ knowledge, conceptions, and practice of writing assessment in L2 contexts, has lately received attention from scholars. Although there has been significant debate about the impact of contextual and conceptual factors on teachers’ assessment literacy, studies focusing on how such factors influence teachers’ WAL are lacking. The purpose of this qualitative study was to explore the way Iranian English writing teachers' conception of assessment, and macro, meso, and micro contextual variables impact their writing assessment practice. It also looked at how writing teachers make assessment decisions in order to negotiate and find a compromise when their assessment views and beliefs diverge from the assessment policies in their local contexts. The data was collected through semi-structured interviews with ten in-service l2 writing teachers in Iran. The findings show that participants had positive conceptions about formative writing assessments but they stated that they mostly used summative assessment in writing classes. Macro level contextual factors turned out to mostly impacted teachers’ writing assessment practices and conceptions. The results underscored the role of school and work experience in shaping and changing writing assessment conceptions. The findings of this study contribute to our current understanding of WAL development and provision of more efficient assessment training for language teachers in teacher education programs.
Volume 0, Issue 0 (2-2024)
Abstract
This study investigates the impact of translational contact on use of epistemic modality in Persian translations and originals in the genre of education. Our findings show that the frequency and distribution of epistemic markers (especially, hedges) in the English texts is considerably higher than those of the Persian translations and originals. However, this has changed in the period of some sixty years, and Persian texts have become noticeably similar to English texts. Upon investigation of the ways translators rendered the epistemic uses of English modal auxiliaries (e.g., may, must, etc.) we found that translators in the 2006–2015 time farme have omitted fewer epitemic modals and translated fewer of them into Persian modals of higher confidence than translators in 1957–1968 time frame. These findings suggest that as the translational contact between English and Persian prolonged translated and original Persian texts have relatively converged towards the communicative preferences of English and have become more addressee-oriented. In fact, the addresee orientation of has first leaked into Persian translations and then has found its way into Persian originals. Weakening of cultural filtering in Persian translations has facilitated this process.
Volume 0, Issue 0 (2-2024)
Abstract
در نشانه – معناشناختی ، نشانه ، گونهای منعطف ، سیال ، پویا ، تغییر پذیر ، متکثر و چند بعدی است . همهی اینها معنا را تعاملی ، فرایندی ، تحولپذیر ، پویا و چند وجهی میسازند . از این دیدگاه ، نشانه – معناشناختی نویدی است برای شناخت چگونگی کارکرد ، تولید و دریافت معنا در نظامهای گفتمانی ، زیرا فرایند معناسازی خود تحت نظارت و کنترل نظامی گفتمانی قراردارد . و دارای سطوح مختلفی است تا بتوان با توجه به وسعت حضور نشانه – معناها ، کارکردهای متفاوت معنایی آنها را ارائه داد . کارکردهای مختلفی با توجه به حضور نشانه - معناها در گفتمان وجود دارد که مهمترین آنها عبارت است از : کارکرد مقاومتی ، ممارستی و مماشاتی که مبنای شکل گیری بسیاری از گفتمانها به شمار میروند . از این دیدگاه ، نظام اسطورهای ، نظام نشانه - معنایی است که چارچوبی کیهان شناسانه و ادراکی برای تبیین پدیدههای پیرامون انسان ارائه میدهد که دقیقا در کارکرد ادراک معنایابی و تفسیر آن نوعی نگاه به جهان مطرح است که منجر به ایجاد نوعی التفات به جهان میانجامد که متاثر از زیست جهان انُسانها شکل گرفته است . در این پژوهش مساله مهم این است که نظامی جهت تبین جهان بینی و ایدئولوژی اسطورهای خود از چه شگردها و راهکارهایی بهره برده است ؟ همچنین کارکردهای ویژه اسطوره در گفتمان هفت پیکر چیست ؟ این پژوهش نشان
Volume 0, Issue 0 (2-2024)
Abstract
The present case study had as its aim to uncover the diagnostic and instructional potential of dynamic assessment (DA) in the context of L2 writing during asynchronous computer-mediated communication (ACMC). More precisely, the study investigated the role of ACMC-based DA through e-mail in diagnosing and promoting low-proficiency L2 learners’ writing abilities in an Iranian EFL context. To this end, a case study design was adopted and three low-proficiency students of English as a Foreign Language (EFL) were selected to participate for a time span of ten weeks. The error analysis of learners’ performances in the pretest and posttest sessions led to the detection of a number of writing problems including the content, structural organization, grammatical accuracy, lexical appropriateness, and mechanics. A posterior examination of computer-mediated offline interactions led to the detection of a number of mediational strategies namely ask to revise, identify a problem area, specify the problem area, clarify the error kind, offer a choice and provide an explicit explanation as well as reciprocity patterns including unresponsive, growing autonomy and full autonomy which together helped diagnose the students' writing problems and trace their developmental trajectories. On implication side, it is argued that the ACMC-based DA serves as a strong diagnostic tool that makes a genuine understanding of L2 learners' writing abilities.
Keywords: dynamic assessment, sociocultural theory, asynchronous computer-mediated communication, writing
Volume 0, Issue 0 (2-2024)
Abstract
Transfer of learning from English course to other contexts is one of the most fundamental objectives of EAP instruction. Providing opportunities to transfer the acquired knowledge from the ESAP writing course to writing tasks of specialized disciplines as well as analyzing students’ perceptions of transfer catalysts and barriers might suggest a foundation for future educational planning. This study examines how engineering graduates learning ESAP assessed the four constructs of learning transfer inventory that might facilitate or inhibit the transfer of learning in discipline-specific academic writing programs. 60 engineering graduate students participated in this study. During the ESAP course, collaboratively designed discipline-specific writing tasks were presented and practiced through multimodal input. The catalysts and the barriers to the learning transfer act were identified by administering the Learning Transfer System Inventory (LTSI). Results indicated that the students could obtain significant levels of academic writing skills and finally transfer their acquired instruction to authentic discipline practices. Furthermore, data analysis demonstrated that transfer of writing outcomes will be increased if more consideration of work-related factors is considered in higher education. All participants reported personal capacity as the main impediment induced by the work-related construct. Students’ positive attitudes toward three ability factors and all motivational factors suggested that an auspicious foundation for future educational planning exists if disciplinary and institutional considerations are embraced.
Volume 0, Issue 0 (2-2024)
Abstract
The intricate connection between teacher support, academic burnout, grit, and psychological wellbeing is a compelling area of research that has recently garnered second language (L2) education researchers' attention. This study aims to investigate such complex relationships with undergraduate English-major students in Iran. To this end, a sample of 318 undergraduate English-major students from various universities in Iran was selected through convenience sampling. The data were analyzed using IBM SPSS version 26 for descriptive statistics and correlation analysis, while LISREL software was employed for Confirmatory Factor Analysis (CFA) to validate the measurement models. The findings revealed that teacher support showed a positive and significant correlation with students' L2 grit and L2 psychological wellbeing while demonstrating a negative and significant correlation with students' L2 academic burnout. Furthermore, the simple linear regression analysis indicated that teacher support significantly predicted a 13% increase in students' grit and psychological wellbeing and a 0.03% in academic burnout. This suggests that measures to reduce the academic burnout of students in higher education should be prioritized in second language education through positive teacher support and positive psychology. The study provides valuable insights and recommendations for English language teachers, students, and policymakers and outlines future research directions.
Volume 0, Issue 0 (2-2024)
Abstract
Among the L2 skills, writing is considered one of the most emotion-wrought aspects of language learning due to the high level of students’ engagement and investment in the composing process. Nevertheless, many L2 teachers have neglected the psychological aspects of writing which can be traced to the profession’s history of emphasizing cognition over emotion. Positive Psychology principles highlight the fact that the students’ success in accomplishing educational tasks such as writing depends not only on their knowledge, effort and perseverance but also their psycho-emotional status. Accordingly, the present study, adopting a correlational design, investigated the associations between 40 Iranian EFL learners' writing performance and their perceptions of a set of positive psychology constructs. The required data were collected based on the students' performance on two essay writing tasks and their responses to the items of L2-specific academic buoyancy, L2 writing mindset and willingness to write questionnaires. The correlation coefficients indicated no statistically significant relationship between the students' writing performance and the positive psychology constructs investigated; nevertheless, there was a significant positive relationship between academic buoyancy and willingness to write variables. In addition, the multiple regression analysis showed that among the subscales of the positive psychology measures, the positive acceptance of academic life and regularity adaptation could best predict the writing performance of the students. The MANOVA results also indicated no statistically significant differences among more-skilled, moderately-skilled and less-skilled student writers in terms of academic buoyancy, mindset and willingness to write.
Volume 0, Issue 0 (2-2024)
Abstract
Over the past decades, empirical studies regarding the application of data-driven learning (DDL) and its’ role in second and foreign language learning have increased. At the same time, several studies have investigated the association between working memory (WM) and different aspects of L2 and found that WM plays a significant role in the language performance of L2 learners, as SLA processes rely on cognitive resources. Nevertheless, the findings of such research are inconclusive. The role of WM in the relationship between DDL and second/foreign language learning is also a neglected area. Drawing on data from 84 Iranian female EFL learners, aged between 20 to 24, on three different measures of WM capacity (digit span, number-letter, and flanker), the findings of the present study showed that first, DDL was a significant predictor of English academic lecture comprehension. Second, regardless of which WM measure to use, WM was not a significant predictor of English academic lecture comprehension; and the interaction effect between DDL and WM was not a significant predictor of the students’ English academic lecture comprehension. That is, WM did not moderate the effect of DDL on the students’ comprehension of English academic lectures. Altogether, the results suggested that learning L2 at high levels of English academic lecture comprehension was mostly contingent upon automatic processing. The findings of this study may have implications for research and practice in second/foreign language teaching and learning, and more specifically in the application of DDL for L2 learners.
Volume 0, Issue 0 (2-2024)
Abstract
In this study, Virtual Reality (VR) was employed in an English course intended to promote oral presentation skills in Iranian academia, and the possible impact of the course on learners’ self-efficacy regarding presenting, Foreign Language Anxiety (FLA), and speaking skills was investigated. Eight participants attended a 6-session course, and practiced academic oral presentation in a virtually simulated environment. Prior to the course, semi-structured interviews were administered; in addition, participants’ weekly reflection notes and self-assessments were gathered throughout the course. Moreover, post-course semi-structured interviews and written follow-up interviews were conducted afterward. The findings revealed that the learners reported higher levels of self-efficacy regarding presenting after the course, due to a perceived improvement in their presenting style, as well as their presentation content and slides. Additionally, the course had contributed to lowering the learners’ FLA due to presence in the Immersive Learning Environment (ILE), ample practice opportunities, and collaborative avatar interactions. Moreover, the learners mentioned that the course had helped them to improve their speaking skills due to academic vocabulary expansion, pronunciation enhancement, fluency upgrade, and grammatical adjustment. The findings can provide insights for language educators with regard to the use of virtual reality for simultaneously fostering language and academic skills, as well as facilitating internationalization in higher education.
Volume 0, Issue 0 (2-2024)
Abstract
Learning French as a foreign language presents unique challenges that may sometimes reduce students' motivation and academic performance. This study aimed to examine the relationship between cognitive and metacognitive strategies, mental vitality, and academic buoyancy among French language students. A mixed-method approach (quantitative and qualitative) was employed in two phases. In the quantitative phase, data were collected using standardized questionnaires on academic buoyancy, mental vitality, and cognitive and metacognitive strategies. The statistical population included all 61 French language students at Hakim Sabzevari University, who participated in the study through a census sampling method. In the qualitative phase, semi-structured interviews were conducted with 10 French language professors from Iranian universities to explore their perspectives and experiences regarding academic buoyancy and its influencing factors. Quantitative data were analyzed using descriptive and inferential statistical methods, while qualitative data were examined through inductive content analysis. The quantitative findings revealed that the use of cognitive and metacognitive strategies, along with mental vitality, positively influenced students' academic buoyancy. Furthermore, qualitative results indicated that various factors, including social variables, family, educational emotions, learner goal-setting, learning strategies, cognitive functions, communication skills, cognitive and emotional skills, academic behavioral motivators, educational content, teacher-related personal variables, teaching skills and techniques, and the teacher's motivational approach, significantly impact students' academic buoyancy.
Volume 0, Issue 0 (1-2024)
Abstract
Tomato is attributed as a global host for root-knot nematode (Meloidogyne incognita) soliciting ponderous damage. Using biocontrol agents to control plant parasitic nematodes is a well-established, green approach in advance of synthetic nematicides. The role of Bacillus spp. in inciting physiological and biochemical alterations in nematode infestation is discussed in the present study. The susceptible (PKM-1) and resistant (Hisar Lalit) tomato cultivars treated with Bacillus pumilus augmented the shoot length, root length and biomass of plants compared to the standard check, Pseudomonas fluorescens, followed by B. megaterium. Accordingly, all the biocontrol agent-treated susceptible plants showed reduced galling and exhibited a root gall index of 3 (moderately resistant). Contrarily, all the resistant plants showed highly resistant reactions. B. pumilus showed the topmost expression of all the biochemical enzymes like peroxidase (PO), polyphenol oxidase (PPO), catalase (CAT), phenylalanine ammonia-lyase (PAL) and total phenols. Conclusively, B. pumilus was found to be the most potential in reducing nematode infestation by embellishing the plant growth and enhancing defense-related enzymes in tomatoes.
Volume 0, Issue 0 (1-2024)
Abstract
This study shows the integration of e-commerce and advanced algorithm-based learning to establish a sustainable economic system and foster cultural education. The research also investigates the impact of rural aging on the utilization of several different land types, including arable land, forest land, and transportation land. The incorporation of e-commerce platforms offers advantages such as resource consumption reduction and efficient supply chain management, enabling broader market access and sustainable production and consumption. However, challenges related to data privacy, algorithm bias, and the digital divide need to be addressed for inclusive access. An artificial neural network (ANN) was constructed to analyze the impact of resource consumption and cultural exploration on market access, ethical practices, and data privacy. The ANN predictions showed that cultural exploration is most prominent with restricted market access, while data privacy is inversely related to ethical practices and market access. Regardless of consumption levels, resource consumption leads to increased data privacy. The study also found that rural aging has a significant negative impact on urban, industrial, and transportation land, but no significant impact on arable, forest, and garden land. The impact varies between towns and townships, with rural aging reducing urban and industrial land in towns but promoting the expansion of forest and grassland in townships. The results show the promising avenues for sustainable economic development and cultural education through the integration of e-commerce and advanced algorithm-based learning, while emphasizing the need to address key challenges and the implications of rural aging on land use for sustainable development.
Volume 0, Issue 0 (1-2024)
Abstract
Entomopathogenic fungi, Beauveria bassiana and Metarhizium anisopliae are important and effective biocontrol agents against arthropod pests. Compared to chemical insecticides, insect pests do not easily develop resistance against these fungi. In this study, the mortality and phenol-oxidase activity of the Helicoverpa armigera 3rd instar larvae were evaluated after exposure to the B. bassiana and M. anisopliae. The LC50 values for B. bassiana and M. anisopliae were 0.795 ×106, and 5.972 ×107 spore ml-1, respectively. LC30 and LC10 of either entomopathogenic fungi were injected into body of larves, then, 24 and 48 hours after injection, their hemolymph was extracted. After 24 h the highest and lowest phenol-oxidase activity was observed in LC30 of M. anisopliae, and LC10 of B. bassiana, respectively. After 48 h of infection, phenol-oxidase activity increased in all treatments. At the LC30 of M. anisopliae, the highest phenol-oxidase activity was recorded, and other treatments also showed a significant difference compared to the control. Five types of hemocytes including prohemocytes, plasmatocytes, granulocytes, onocytoids, and spherulocytes were identified in the hemolymph of larvae. The highest total hemocytes count (THC) was recorded in LC30 M. anisopliae at 9 h after initial infection. Our results showed that both fungi have the ability to affect phenol-oxidase enzyme activity. These microbial insecticides exhibited high potential for controlling the pest.
Volume 0, Issue 0 (1-2024)
Abstract
The present study was conducted to identify the empowerment dimensions of female-headed households in rural areas and their effects on food security in Iran country. Statistical population was including 495 women based on the data collected from Statistical Center of Iran. 216 women were selected by using Cochran’s formula. A questionnaire was designed by researchers and its validity and reliability was confirmed by confirmatory factor analysis and Cronbach method, respectively. Structural equation modeling was used to compare associations. The results confirmed that grouping work and communication skills, creativity and solving problem, commitment and responsibility, information and specific knowledge, technical skills and operational work, psychological factors, social factors, political factors, economic factors, managerial factors and educational factors had significant effects on food security. Commitment and responsibility, economic factors and grouping work had highest effects on food security, respectively. Job empowerment predicted 75.00% of variance of food security and it is suggested considering job empowerment of female-headed households in rural areas for decreasing food insecurity.
Volume 0, Issue 0 (1-2024)
Abstract
Microcredit plays a vital role in the food security of rural households. However, to the best of our knowledge, the effects of microcredit on improving the food security of households have not yet been well studied and understood in Iran. Therefore, this study aims to investigate the success of microcredit programs on enhancing the food security of rural households in Zehak county using the propensity score matching method and bootstrap algorithm. For this purpose, two food security indices, including the Household Food Insecurity Access Scale (HFIAS) and the Food Consumption Score (FCS), are used. The results revealed that 100% of the households face food insecurity. The prevalence of food insecurity was 20.0%, 42.5%, and 37.5% for mild, moderate, and severe food insecurity, respectively. In addition, 30% of households are in poor status of food consumption. Our findings emphasize the positive and significant role of microcredit in improving food security. The results showed that microcredit decreased the HFIAS index of the recipient households by 24.31-27.81% and increased the FCS index by 25.87-31.45%. Therefore, policy-makers and decision-makers should promote and strengthen governmental and non-governmental organizations providing microcredit. It is also recommended to provide information and reduce collateral restrictions to increase households' access to microcredit.
Volume 0, Issue 0 (1-2024)
Abstract
Pear is one of the most important pome fruits in the world fruit market with a high nutritional value. This study was performed to determine the phenolic compounds and some chemical properties of the flesh and peel of 12 Asian and European pears. Chlorogenic acid and rutin were found the important phenolic compounds in the peel which were measured using HPLC. Fruit titratable acidity (TA), total soluble solids (TSS), firmness, color, nutrient elements, and total phenol contents were measured across the various cultivars. Potassium was the most abundant nutrient, followed by nitrogen and calcium, respectively. As the total phenol increased, so did the amount of rutin. Principal components analysis (PCA) of all data showed that European and Asian pear cultivars were categorized and placed into two distinct groups. In general, the different European and Asian pear studied cultivars were different in terms of most of the studied biochemical traits, and significant relationships were observed between some traits.
Volume 0, Issue 0 (8-2024)
Abstract
Aluminum nano-films are one of the functional elements that have various applications in different fields such as strengthening cement base materials, improving the performance and efficiency of concrete, and enhancing the mechanical and volumetric properties of clay. In this study, the mechanical responses of aluminum nano-film are investigated under uniaxial tensile and compressive tests using the molecular dynamics (MD) method. The initial configuration of the nano-film is constructed based on a 3D aluminum core—alumina shell model that provides a suitable description of surface oxidation in the nano-film. This model is useful to determine the influence of surface oxidation on the mechanical behavior of nan-film. Because of the accuracy and competency, the inter-atomic interactions are evaluated using the EAM+CTI potential, which is a hybrid potential consisting of two components, i.e., EAM and CTI potential, such that it can also take into account the electrostatic interactions between the atoms. After establishing the initial configuration, the energy minimization process is performed on the nano-film, and then its temperature and pressure are adapted to the environmental conditions through the relaxation process. The MD analysis is accomplished by the open-source LAMMPS software, and the visualization of outputs is performed by the open-source OVITO software. The periodic boundary condition is imposed on the lateral sides of the nano-film to eliminate the free surface effect of the atomistic analysis. The tensile and compressive tests are applied to the nano-film in accordance with the experimental tests, and the stress—strain curves are determined. The concept of Virial stress is employed to calculate the stress of the atomic model, which is equivalent to the conventional Cauchy stress in classical mechanics. In order to diminish the dynamic effects, deformation is incrementally applied to the nano-film, such that at each increment, a small strain is gently imposed, then the nano-film is relaxed under the deformed conditions, and finally the stress and strains are evaluated. The numerical simulations are verified by comparing them with experimental data, which demonstrates the acceptable accuracy of the obtained numerical results. The influence of various parameters such as the thickness and the percentages of oxide layers are investigated on the mechanical response and stress-strain curve of aluminum nano-film under the uniaxial tests. It is demonstrated that the thickness of the oxide layer significantly impacts the mechanical behavior, such that the hardness and energy absorption capacity of the nano-film is increased considerably by increasing the percentage of the oxide layer thickness. However, increasing the total thickness of the nano-film leads to a decrease in the Young’s modulus and elastic limit of the specimen. It is because of the decrease in the percentage of oxide layer thickness by increasing the total thickness of the nano-film. Point defects are one of the important imperfections in the crystal structures of atomic configuration that have a significant effect on the mechanical behavior of materials. In order to investigate the influence of point defects, different percentages of voids are generated by randomly omitting some atoms in the nano-film domain. The generated specimens are analyzed under the uniaxial tests, and their mechanical characteristics are evaluated. The numerical simulations demonstrate that the hardness of the nano-film is significantly reduced by increasing the point defects.
Volume 0, Issue 0 (8-2024)
Abstract
Masonry infills are generally assumed as non-structural elements in structural calculations and are not modeled. However, observations after past earthquakes have shown that masonry infills have significant effects on the seismic performance of structures and their seismic behavior should not be neglected. Additionally, the absence of masonry infills in the first story, which is common in structures for commercial and architectural reasons, has led to the occurrence of the soft story phenomenon in past earthquakes. The maximum interstory drift ratio (MD) is the most important criterion for assessing seismic damage and the occurrence of collapse in structures. In this study, the seismic performance of 3- and 9-story steel moment resisting frames (MRFs) with masonry infills was evaluated using a probabilistic framework considering the record-to-record variability. Two configurations were considered for the masonry infills including fully infilled and open ground story configurations. The seismic performance of the MRFs with these two configurations was compared to that of bare MRFs. The OpenSees software was employed for nonlinear modeling of the structures and masonry infills were modeled using single compression-only struts. The fundamental periods of structures with masonry infills significantly increase after the failure of the masonry infills. To evaluate these effects, Rayleigh damping was modeled using the conventional method and a modified method, which considers the severe elongation of fundamental period due the failure of infills, and the responses obtained from the two methods were compared. By performing incremental dynamic analyses using 78 far-field ground motion records, drift margin ratios (DMRs), drift fragility curves and mean annual frequencies of exceeding four MD levels of 0.7%, 2.5%, 5%, and 15% (λMD) were obtained for the structures. The MD levels of 0.7%, 2.5%, and 5% correspond to the performance levels of immediate occupancy, life safety, and collapse prevention, respectively. The MD level of 15% corresponds to the seismic collapse of the structures. The results indicate that the presence of masonry infills improves the drift performance of the MRFs with the fully infilled configuration. However, since the masonry infills experience failure at higher drift levels, their effectiveness decreases at these drift levels. Furthermore, the absence of masonry infills in the first story leads to the soft story phenomenon at lower drift levels, and therefore, the performance of the structures with the open ground story configuration is worse than that with the fully infilled configuration. It should be mentioned that at higher drift levels, due to the failure of masonry infills, the structures with the two configurations for infills have almost the same performance and close to the performance of the bare MRFs. The amplification of the soft story phenomenon in the 9-story structure causes the performance of the structure with the open ground story configuration given some drift levels to be even worse than that of the bare structure. For example, by using the modified damping method for the 3-story structure with the fully infilled configuration, the masonry infills reduce the λMD value given MD = 0.7% by 43%, but the reduction in the λMD given MD = 15% is 19%. Based on the results obtained, the conventional Rayleigh damping method in the technical literature underestimates the responses.
Volume 0, Issue 0 (8-2024)
Abstract
Horizontally curved bridges have been observed to suffer severe structural damage during past earthquakes so determining the seismic performance of curved bridges is crucial due to the complex dynamic behavior of these structures because of their irregular geometry and non uniform mass and stiffness distributions. Analyzing and plotting the capacity curve of these structures can be costly and time-consuming. As a result, many efforts have been made to simplify the structural models of these bridges and reduce the computational workload required for their analysis. This article presents a straightforward method to convert the multi-degree-of-freedom system of these structures into an equivalent single-degree-of-freedom system, ensuring that the capacity curve of the equivalent structure closely matches that of the original structure with minimal error. In this study, the OpenSees program was used to extract the stiffness and mass matrices of a curved bridge structure. These matrices were then condensed into one-by-one matrices for mass and stiffness using dynamic condensation equations. The characteristics of these matrices were applied to a single-degree-of-freedom stick model. In this model, the obtained mass is placed at the top of a stiff rod (stick), which is connected to the ground by a spring (zero-length element) with the equivalent stiffness obtained. A nonlinear static pushover analysis of the bridge structure was performed to obtain the capacity curve. An equivalent bilinear curve was then drawn, and the yield shear force and yield displacement were determined. The nonlinear behavior of the single-degree-of-freedom structure was modeled using the Steel02 material available in the OpenSees library by zero length element utilizing the yield shear force and yield displacement magnitudes of the curved bridge. The capacity curve of the stick model, which has a single degree of freedom, showed an error percentage of 7% compared to the bridge's capacity curve. This indicates acceptable compliance with the capacity curve of the main structure, making the stick model a viable alternative for repeated analysis of the curved bridge structure. This study also included a sensitivity analysis to investigate the effects of increasing the curvature radius and decreasing the curvature angle of the bridge on its capacity and effective mass. Due to the dynamic condensation of the curved bridge structure, the influence of all degrees of freedom was considered in the stiffness and mass matrices, unlike methods that rely solely on the first vibration mode for dynamic condensation. Comparing the capacity curve of each structure with that of an equivalent single-degree-of-freedom system revealed that the structure's capacity increases with a larger curvature radius. In contrast, the lowest capacity was observed in the straight bridge scenario. Additionally, modal analysis of the studied models showed that increasing the bridge's curvature radius leads to a longer structural period, while a decreasing curvature angle has a similar effect. However, the period of the straight bridge was longer than all the other models. Furthermore, as the curvature radius increased, the mass contribution percentage of the first mode in the translational x-direction decreased, whereas the translational mass contribution percentage in the y-direction and the rotational mass contribution around the z-axis increased.
Volume 0, Issue 0 (8-2024)
Abstract
Damage of both building and non-building structures (including the space structures) against earthquake is of great importance for civil engineers, because collapse of such large structures may have significant casualties and economic losses. Space structures are classified as large-scale structures and can cover a large space without columns. Seismic behavior of these structures is different from building structures. There are different types of space structures considering the geometrical aspects, which are effective in the damages causing economic and life losses. A space structure has three-dimensional behavior, and their higher-mode effects are remarkable. On the other hand, the weight of these structures is relatively low that may cause an unrealistic reduction in the calculation of seismic force in a static analysis. Therefore, the static analysis cannot capture their structural response effectively. Traditionally, the dynamic analysis is utilized for seismic design of space structures due to their complex structural behavior. Thus, in this paper, seismic design of two single-layer domes is performed using two dynamic analyses: time history analysis and response spectrum analysis. Although there are some studies on seismic design of domes, further investigations are required due to the structural diversity of different domes and the difference in their seismic behavior. Here, the ribbed and Schwedler domes under gravity and seismic loads are analyzed dynamically. The parameters of the design response spectral acceleration are based on ASCE7-16, and the site class (based on the soil type) is selected as “D”. Both horizontal and vertical components of seismic excitations are utilized in the dynamic analyses, because all these components are effective in design of a dome structure. The damping ratio is assumed to be 2% in the dynamic analyses based on the relevant literature. In the response spectrum analysis, the vertical seismic load is expressed in terms of dead loads in the response spectrum analysis. In the time history analysis, seven ground motion records are selected based on the seismic zone. These ground motion records are scaled using both amplitude scaling and spectral matching approaches. The vertical components are scaled to the specific vertical design spectrum obtained from ASCE7-16. In this study, seismic design of the ribbed and Schwedler domes with a span of 36 meters and a height of 6 meters are carried out with some limitations on the member stress ratios and top nodal displacements. The structural designs based on the time history analysis and the response spectrum analysis are compared. The same cross-sectional areas are used in designs of the dome structures to compare the effects of these dynamic analysis methods better. In general, the top node displacement and stress ratios of the dome obtained using time history analysis is larger than that obtained using spectral dynamic analysis. Accordingly, the results indicate that the structure designed with the time history analysis is heavier than the structure designed with the response spectrum analysis. Obviously, although the time history analysis provides a better understanding of the dynamic behavior of the structure, it requires much higher computational cost than the response spectrum analysis.