نشریه مهندسی سازه و ساخت
سال نهم شماره 2 (پیاپی 55، اردیبهشت 1401)

Liquid storage tanks are very important structures for storing various types of fluids in urban and industrial areas. Therefore, designing, manufacturing, and evaluating their performance for different conditions is very important. In this study, the behavior of steel tanks with changes in the ratio of height to diameter of the structure under the effects of far and near field earthquakes has been analyzed and studied. For this purpose and for better analysis of these structures, 4 models of steel tanks with different height to diameter ratios and in empty and 90% full states have been subjected to seismic analysis using modeled ANSYS finite element software. To better investigate the trend of seismic effects on steel tanks, selected far and near-field earthquakes have been scaled to the same amount of 0.5g. The results showed that in empty tank conditions, by increasing the ratio of height to diameter to more than 1, the maximum values of displacement in the far and near-field earthquake are close to each other. The results also show the extraordinary importance of adding water to the response of steel tanks due to far-field earthquakes for a height to diameter ratio of more than 1. In most cases, by increasing the ratio of height to diameter of the structure and adding the fluid to the analysis, the values of the first main stress and the maximum reaction of the horizontal abutment in the two modes of analysis under the effects of the far and near-field earthquakes get closer to each other. The results show that in order to analyze and investigate steel tanks affected by earthquakes, in addition to near field earthquakes, far-field earthquakes should be studied and analyzed.

Given the increasing importance of time, cost, and resource management, organizations are pushing for a knowledge base consisting of all the knowledge acquired during a project, and with the prior knowledge being put in place to maximize productivity. The purpose of this research is to investigate the effect of knowledge management on the delays of road construction projects in project-oriented organizations. The present study, after explaining the concept of knowledge management and identifying the causes of delays in road construction projects, examines the components of knowledge management and the impact of each of them on reducing the time latency of road construction projects through a questionnaire study method. Then, one of the sub-criteria of delay factors and its effectiveness from knowledge management was investigated. For this purpose, a statistical population consisting of active employers, consultants and contractors in the road construction sector of Southern Khorasan province was considered and parametric tests were used for inferential analysis. Findings show that there is a significant positive two-way relationship between knowledge management and reducing project time latency. This means that the more knowledge management is used in road construction projects, the greater reduction in project latency we will see. Among the components of knowledge management, knowledge creation has the greatest effect (17.42%) on reducing delays and based on the calculated results, it can be said that about 96.8% of delays in projects can be controlled by knowledge management. Also, according to the descriptive statistics obtained in the general case, it can be said that the most important factor affecting the delays are the contractors at the rate of 21.35% and then the employers at the rate of 20.76%.

Soil-cement is a mixture of cement, water and soil that by compaction and hydration of cement , its components are joined together to form a compound with very low permeability , durable and abrasion resistant . Considering that the main applications of soil-cement as a base layer in road paving are sealing elements in earthen and concrete dams and foundation improvement, and since in recent years the addition of cement on mechanical parameters and The soil-cement physics has been investigated . In this study , the effect of adding different weight percentages of hemp fibers, polypropylene fibers and nanosilica to the soil-cement before and after successive melting and freezing cycles in shear and behavioral strength parameters . In this research, the sample soil of Nazarabad industrial town of Karaj was used . The measurement parameters in this research are different enclosing stresses, different processing times, different weight percentages of hemp fibers, propylene fibers and nanosilica and after successive melting and freezing cycles . This study is in Unreinforced non-drained triaxial test . The results indicate the improvement of behavioral and resistance parameters in all materials and increased durability after successive cycles of melting and freezing in samples containing nanosilica .

Operational modal analysis typically requires the physical attachment of a sensor to measure the structure vibration. As a non-contact method, digital cameras are relatively inexpensive, fast, and providing high spatial resolution results. The aim of this study is to identify the dynamic parameters of structures (frequency and damping ratio) by using video measurement (output only) based on the phase. For this purpose, it was only used mobile smartphones to identify modal parameters. The accelerometer sensor in the 3 attached smartphones was used to extract vibrational information. Video recorded by another mobile smartphone simultaneously identifies the dynamic parameters. In video measurement, the steerable pyramid transform is applied to frames that were extracted from the video to identify the local phases encoded in the image. After that, blind source separation (complexity pursuit) and single value decomposition techniques were applied to the image phase. Frequencies and damping ratios are extracted by the Fourier transform and logarithmic reduction technique. Thus, to validate the proposed method, two samples of 3D wall sandwiches panel, including a concrete sample and a straw sample that were already loaded and their stiffness was reduced by an average of 90%, were used. The results showed that the proposed method was able to extract the frequencies and damping ratios of the panels with an error of less than 2%.

Reinforced concrete members form the main structure of a structure. The risk of corrosion of rebar is considered as an effective factor in determining the life of these structures, so identifying and investigating its destructive factors is very important, especially corrosion of longitudinal rebar; Because the weakness of concrete in tensile increases the possibility of cracking of tensile concrete and the formation of a bed to start the corrosion process in longitudinal rebar. The beginning of the corrosion process leads to a decrease in the cross-sectional area of the rebar and an increase in the corrosion products; This increase in volume due to the products causes tension around the rebar, which ultimately creates cracks in the concrete, reduces the adhesion between the concrete and the rebar, exfoliates the concrete surface and reduces the compressive strength of the concrete. Due to the fact that the adverse effects of rebar corrosion have been less studied in deep reinforced concrete beams, in this study, the corrosion effect of longitudinal rebar by applying elements such as: reduced cross section, reduced rebar yield strength, reduced concrete compressive strength, reduced adhesion The connection between concrete and rebar in ABAQUS finite element software on the stiffness and strength of deep reinforced concrete beams has been investigated. The results show that with the increasing percentage of corrosion of longitudinal rebar, the strength and stiffness of deep beams are significantly reduced so that when the longitudinal rebar reach 50% corrosion, it loses 51.38% of its strength and A reduction of 43.57% is difficult. Beam behavior has also changed from shear to bending due to corrosion and the stress-strain diagram shows the decrease in stress and strain with increasing corrosion percentage.

The most important issue in developing countries is the lack of proper infrastructures to facilitate the welfare of society and deal with problems in a desirable way. Due to the nature of infrastructures, the implementation of such projects requires significant funding, which, especially in developing countries, governments do not have enough capacity, so we must pay close attention to attract the new methods to finance projects. Therefore, it is necessary to use methods or models to determine the appropriate financing method for each organization according to its risk endurable level. The present study intends to provide a framework for determining the level of risk of financing methods in order to select the appropriate method in each project. In the first phase of the proposed framework be developing the qualitative method called content analysis, coding of interviews with experts and applying the Fuzzy AHP method, 17 risk criteria in the form of 7 main criteria including financing costs, risk of timely provision of resources, repayment structure The risk of interest rate fluctuations, the risk of exchange rate fluctuations, the risk of non-timely realization of project revenues and the risk of macroeconomic variables were identified and weighted. In the second phase, a fuzzy expert system was presented to predict the level of risk of financing methods. The results of the research in identifying the criteria showed that the risk of non-realization of project revenues in a timely manner, the economy risks and financing costs had the highest priority in the risk of project financing methods. Also, in the part of fuzzy expert system, firstly, in the development of the model, a new method was used to limit the number of rules in the knowledge base, and secondly, according to the validation performed, the accuracy of the model was determined to be 88%.

During the recent years, the use of cold formed steel structures has expanded all over the country in housing industry, and they are employed in mass constructions and great projects. Apart from the advantages of this construction system, like high speed execution and lightness, lack of proper performances in different construction’s stages of design, constructions and installations have caused many difficulties and problems in use of this modern structural system. Hence, there is a concern that this opportunity would be converted to a threat for the country’s construction industry. In this paper, an attempt is made to identify the barriers and problems existing in cold formed steel constructions. It is hoped that by precise planning and the efforts of the authorities, these problems will be minimized.In the present study, while conducting a case study on a large number of buildings which constructed by LSF, interview with some expert executives, engineers, professors and beneficiaries were performed. The answered questionnaires then analyzed by network analysis process, Dematel and Delphi methods. After that, the most effective factors in lowering quality of this kind of structural systems were identified and ranked. Finally, some suggestions were made in order to improve the quality of this system.

Value engineering is one of the most important and effective items in the field of cost and time optimization in construction projects and industries such as oil and gas. As in developing countries such as Iran, which also face limited equipment and resources, this issue and cost and time management have become essential. It is worth noting that in some projects, due to obstacles, value engineering is not done. In some projects, despite doing so, issues such as cost increases are encountered at the time of implementation, part of which is due to improper implementation of value engineering. In line with the above, in this study, using semi-structured interviews, value engineering factors in the field of benefits, obstacles, solutions, and promotion have been identified. The obtained reliability and Cronbach's alpha have been calculated equal to 0.834. The Kolmogorov-Smirnov test was also used to normalize the data, and the Friedman test was used to rank the data. The results obtained in the field of value engineering benefits, elimination of unnecessary functions and upgrading of construction projects, and improvement of executive plans have the highest score. In the field of value engineering obstacles, resistance to change due to its risks and lack of awareness of brokers and culture, the most important factors and in the field of effective solutions to upgrading value engineering, the level of management support for value engineering proposals and performance and the use of specialized consultants, have the highest score and impact from the statistical community and a case study in engineering and development gas company of Iran in order to identification and classification of existing benefits and obstacles of implementation of value engineering upgrades in civil projects.

Recent earthquakes have shown that, besides the seismic forces, the interaction between faults and structures could cause extensive damage to the surface and underground structures. Field observations showed that the need for design measures and regulations for fault loading due to fault movement in areas with active faults seems necessary. In this study, the three-dimensional finite element model in Abaqus finite element program to study the behaviour of a 9-story steel structure with a moment frame system based on three types of mat foundations, piles group, and diaphragm walls was used on sandy soil. The performance of the structural-foundation system was evaluated taking into account the structural and geotechnical performance goals such as the drift ratio of floor levels, displacement of the foundation and distribution of bending moment and shear force along with the pile and foundation. In this study, the position of the foundation relative to the fault line and the foundation type were considered as key parameters. The results of the analysis showed that the best performance in reducing the ratio of the permanent drift ratio of the floors related to the structure with the diaphragm wall system. This was in the case that the edge of the foundation is tangent to the fault line, this value reaches 1.62%. Also, in most cases, in small amounts of fault movements, the mat foundation system had a smaller difference than the other considered foundation system in this study.

In this research, optimized intelligent models were developed to design optimal sustainable concrete containing recycled Polyethylene Terephthalate (PET). For this aim, evolutionary Artificial Intelligence (AI) approach was implemented based on the integration of the Multivariate Adaptive Regression Splines (MARS) and Extreme Learning Machine (ELM) integrated with particle swarm optimization algorithm to investigate the strength behavior of sustainable concrete containing recycled polyethylene terephthalate-based fine aggregate. The experimental database consisting 273 records comprising mixture components at different ages are collected from published papers and optimal variables are identified using principal component analysis. The capability and efficiency of proposed model are validated through standalone MARS and ELM. Performance metrics indicated that proposed evolutionary formula-based models (MARS-PSO and ELM-PSO with the ((R= 0.902, RMSE=4.836 MPa and RSE=3.5) and (R= 0.900, RMSE=4.881 MPa and RSE=2.24), respectively) outperformed than other standalone AI models for CS prediction. Uncertainty analysis of the standalone and hybridized models is also applied using Monte-carlo simulation to prove that the hybridized multiscale model has less uncertainty in the prediction of the compressive strength compared to those benchmark models. The findings of the present paper presented the superiority of the model’s development in constructing reasonable and robustness evolutionary Model for formulation of CS of eco-friendly concrete containing recycled PET.

In this study, the capacity, rupture and ductility of circular reinforced concrete columns reinforced with glass-fibre reinforced plastic pipes and carbon- fibres reinforced plastic, under eccentric load was checked. The effects of eccentricity, casing, twist and number of layers on the behaviour of the columns were evaluated. Eighteen circular columns with and without casings, with diameters and heights of 150 and 600 mm, respectively, were subjected to axial loads with eccentricity of 20 and 50 mm, and the effects of GRP and CFRP as the enclosing factors of the columns were investigated. The results showed that the use of casing and twist separately and simultaneously causes a significant increase in the compressive capacity of the columns. On average, the addition of one layer and two twisted layers with and without casing, increased their capacity by 24%, 34%, 6.3% and 12%, respectively. The number of twisting layers did not have much effect on the ultimate compressive capacity in the columns with casing; while the casing increased the compressive capacity of the columns by 3.5 times on average. Rupture occurred in columns without casing mostly locally and gradually, and in columns with casings completely; the cause can be attributed to the very high degree of enclosure caused by the casing. The use of casing increased the ductility of reinforced concrete columns by a large amount, so that the average increase in axial displacement in columns with casing compared to similar columns without casing, was 399%.

A large part of the dynamic force applied to the dam is the hydrodynamic force generated in the reservoir due dam and reservoir interaction. The nature and method of applying this force in near and far fault earthquake records on structures was different and structures behave differently against each of these types of records. One of the solutions to control the seismicity of the concrete gravity dam is to use seismic dampers at the interface of the dam and the reservoir to reduce the hydrodynamic pressure on the dam. Therefore, in this study to investigate the effect of damping on the seismic performance of a concrete gravity dam, two near fault and two far fault earthquake records were used for the analysis. Output responses including maximum response of dam crest displacement and 1st principle stress at heel have been selected as critical responses. Ansys software, based on finite element method, was selected for dam modeling and seismic analysis and Newmark method has been used to solve the dynamic equation. The results of the analysis show the positive effect of the isolation layer in reducing the seismic responses to the dam in both far and near earthquake fields. In addition, it can be said that rubber damper performs better in the near fault than in the far fault.