نشریه مهندسی عمران
سال پنجاه و پنجم شماره 7 (مهر 1402)

The accumulation of coal waste from industry has made these materials available and economical to use in ground improvement reducing environmental pollution. Research has shown that adding cement to coal reduces coal pollution. Therefore, coal tailings of different sizes can be mixed with cement and the resulting mixture can be used to stabilize and improve sandy soil in road construction or construction of stone columns. The main idea of this study is to investigate the effect of particle size of coal tailings and coal leachate on fine sand stabilization with cement. Therefore, different weight percentages of cement and coal tailings of different sizes have been mixed and the physical and strength characteristics of the resulting mixtures have been investigated with several tests such as standard Proctor compaction and unconfined compression tests. To achieve the optimal mixing ratio, the effect of the weight ratio of cement to coal tailings (0/100, 10/90, 20/80, 30/70, 40/60, 50/50) and the effect of the particle size of coal tailings including passing Sieve No. 40, Sieve No. 200, as well as coal waste solution were examined. The results show an improvement in the strength of soils mixed with finer particles of coal tailings. The results of unconfined compression tests show that by increasing the ratio of additives from 2.5% to 7.5%, the compressive strength increases and the optimal mixing ratio of additives is equal to 90% of cement and 10% of fine coal waste particles.

This research, investigates the behavior of 3, 5, and 8-story steel structures with medium bending steel frames in four cases without considering interaction (A), considering interaction (B), using damper (C), and in Damper usage mode considering soil and structure interaction (D) and the performance of pal dampers, fragility curve, has been discussed under seven acceleration maps of the near-pulse area. The innovation of the research is in the use of a pal friction damper and considering the effect of soil-structure interaction (SSI) to investigate the dynamic and seismic behavior of low and mid-rise intermediate moment steel.Modeling has been done in ETABS software and Incremental Dynamic Analysis (IDA) by LRFD method in Opensees software.Vulnerability levels introduced in HAZUS MH-MR4 have been used to investigate different failure modes of the models. The studied frames with dampers have been subjected to nonlinear analysis in three damping levels 5%, 10%, and 15%. The obtained results showed that: for the state (B) in short structures, the order of displacement of floors remained almost constant and had no difference compared to state (A); But in case (C) it caused a decrease in the movement of floors and on the other hand in case (D) the movement of floors has been relatively reduced; And the pattern of displacement reduction in different records is different.Also use of a damper has no effect on the amount of base shear of structures, but the amount of base shear has decreased in structures with more floors.

Seismic progressive failure refers to the early fracture of some key structural elements during an earthquake due to explosions or design and construction defects. It results in the elimination of these elements from the structural frame, leading to a rise in stress in the adjacent elements followed by large-scale failure in part of the structure. The study of this phenomenon is of utmost importance and constitutes the topic of this research. So, the present research evaluated seismic progressive failure potential in steel frames with various structural systems. In the present study, the 3-story steel frame was modeled by non-linear beam-column elements with wide plastic, which are available in the archive of Apensis software. Then the models were subjected to nonlinear dynamic analysis and the results related to earthquake stimulation and progressive failure in Excel and MATLAB software were examined and compared in the form of graphs and numbers. The structural systems considered in this study were flexural, cross braced, eccentrically braced, and knee braced frames. In order to examine the seismic progressive failure potential, the El Centro, San Fernando, and Kobe accelerograms were selected, and two scenarios, namely the elimination of the side and middle columns at the first level were considered. According to the results, elimination of the side column resulted in larger responses since only one beam contained the upper node of the eliminated column.Moreover,frames with a larger number of levels were less affected by column elimination.

Steel shear wall is one of the most suitable common systems for the strength and stability of the structure against lateral loads. In this system, vertical boundary elements around the shear wall, in addition to being part of the lateral load-bearing system, are responsible for bearing the weight of the structure during and after the earthquake, and therefore in designing this system, the border elements are tried to be remained in the elastic state after complete yield of the web plate. Also, to provide uniform stress along the length and height of the wall, vertical and horizontal boundary elements must have high flexural stiffness. Code provisions in this case sometimes lead to the selection of non-economic sections in the beams and columns attached to the wall. In this study, in order to reduce the demand for vertical boundary elements attached to the wall and to make the design economical, vertical and inclined stiffeners are predicted inside the wall. These stiffeners direct the plastic deformations mainly into the wall and away from the columns. To evaluate and compare the behavior of the proposed model, 30 finite element models were studied under lateral monotonic and cyclic loading. The results show that the addition of stiffeners, in addition to increasing the stiffness and lateral resistance of the system, increases the ductility of the lateral bearing system and reduces the required flexural stiffness of horizontal boundary elements.

This paper describes the development of a ductile fuse system to reduce Seismic demand in steel frames with knee element connections. In these types of structures, connections often require reinforcement to withstand the tensile capacity of the brace to comply with the capacity design process.To overcome this problem, it is necessary to think of a solution to prevent the premature failure of the connection.For this purpose, in this research, different models of ductile fuses consisting of a reduced cross-sectional area are placed on the brace of the knee element in a braced frame.The fuses are designed to reduce the tensile capacity of the knee element braces to the capacity of the joints. The results show that the braced frame with fuse can be used to reduce the seismic load demand to the connections sufficiently, to prevent the strengthening of the connection caused by the application of capacity design principles. It was also observed that the properly designed fuse system in braced frames shows a stable hysteretic response under cyclic loading and maintains sufficient ductility with a reasonable reduction in the compressive strength of the braced members. Also, the results showed that the failure of all samples occurs in the fuse, and as a result, by using the fuse, it is possible to use the full capacity of the connection and brace. Finally, based on the results of the study, the best fuse models that creates both Sufficient ductility and compressive strength to an acceptable level were identified for design applications.

Although about four decades have passed since the development of self-compacting concrete (SCC), its replacement with ordinary concrete, there are still problems in quality control and construction in large dimensions. These problems are partly due to the lack of complete understanding of the properties of SCC and partly due to the extreme sensitivity of the performance of this type of concrete to changes in the design parameters, climate, physical and chemical characteristics of the components of the mix design, the need for expert workers, the lack of design suitable and safe mixtures are contractors' reluctance and maintainability. In this research, in order to investigate the effect of the amount of stone materials in order to achieve the optimal mixture design, the first step is to prove that concrete can be made with local materials of Behbahan, located in Khuzestan province, in the laboratory and then in a site. This stage was done by making 28 mixes in a trial and error manner on all concrete components to keep them stable, concrete tests in fresh and hardened conditions were carried out according to the standards of "Federation of European National Unions of Concrete Representatives" and "Japan". Finally, after reaching a reference mix design, new mixes were made by changing the amount of fine aggregates from 30% to 70% with a rate of 5% increase. Based on the results and statistical analysis, the optimal mix design is determined and introduced as a design with 65% fine aggregates compared to the total aggregates.

In today's world, Environmental life cycle assessment is recognized as one of the complete methods for assessing the environmental impact of buildings. This study aimed to select the best way for assessing the environmental impact of life cycle in high-rise construction with full coverage of environmental impact classification. In this study, seven important categories of environmental impacts were analyzed in eight widely used life cycle assessment method using SPSS software, and finally, the ReCiPe method was selected as the most appropriate method. This method has then been studied for 16 high consumption materials in a residential building of construction phase in Tehran. Conclusion In this study, after comparing the midpoint and endpoint approaches using the ReCiPe method, the midpoint results are comprehensive while the endpoint results are brief. However, the endpoint approach provides more information on the environmental damage that should be considered to use a midpoint supplement. This study's findings can help project designers and builders before the construction of high-rise residential projects by estimating the environmental impact at the level of two approaches in selecting environmentally friendly materials. It should be noted that any misuse of these two approaches may affect the evaluation results and lead to misleading findings.

In recent years, engineers have faced many structural problems, such as buckling, corrosion and excessive loading in damaged steel structures. The labor force's mistakes during welding and the destruction of the weld are among the many problems in steel structures. Therefore, strengthening and repairing the welding place in steel structures is inevitable. In this article, the influence of polymers reinforced with carbon fibers for strengthening steel studded double columns with defects caused by welding has been investigated. For this purpose, seven steel columns were modelled in Abaqus finite element software. A CONTROL column was modelled as the first sample with no defects and welded all over. The rest of the defective samples were reinforced using CFRP fibers. On the other hand, strengthening using CFRP fibres to improve the location of the defect was investigated in detail for three samples. Reinforcement of these sections using CFRP fibers is not only an effective method to increase the maximum axial force in these columns, but it has also helped to improve resistance and delay local buckling in them. According to the results, it was observed that among all the samples, the maximum bearing capacity is related to the 2UW3 model, and it has increased by 29.9% and 21.7% in the laboratory sample and numerical modelling, respectively, compared to the 2UW3C1 sample. In addition, 2UW3C1 and 2UW1C1 samples have the highest hardness among laboratory and numerical modelling samples, respectively.

Industrial steel fibers (ISFs) are the most widely-used fibers for the purpose of concrete reinforcement. The industrial production of these fibers is costly, and it contributes to Greenhouse gas emissions. The present study, therefor, aims to explore the ways in which these fibers can be replaced by recycled steel fibers (RSFs) made of scrap vehicle tires. To this end, the present study examined 13 mixtures containing different volume percentages (0%, 0.5%, 1%, 1.5%, and 2%) of ISFs, RSFs, and their combinations. The examinations included rheological properties of the fresh self-compacting concrete (J-ring, L-box, U-box, and V-funnel tests), mechanical properties of the hardened concrete (compressive, Brazilian tensile, and flexural strength tests), environmental characteristics (global warming potential (GWP)), and economic characteristics. Results showed that RSFs had a poorer performance than ISFs in terms of mechanical properties. The use of 2% ISFs increased the splitting tensile and flexural strengths by 114% and 82%, respectively, while the same amount of RSFs increased these parameters by 80% and 44%, respectively. On the other hand, RSFs showed better performance than ISFs in terms of rheological, environmental, and economic characteristics. Replacing ISFs with RSFs in mixtures containing 2% fibers could improve the rheological, environmental, and economic characteristics by 8%, 30%, and 65%, respectively. Finally, given the multi-criteria optimization results, RSFs were superior to ISFs in terms of rheological, mechanical, environmental, and economic characteristics.

The conventional approach to River Basin Flood Management (RBFM) focuses on increasing the safety and security of drainage systems against heavy rainfalls. Recent floods in urban catchments have highlighted the need for a more resilient approach that also considers the floods consequences. Resilience of a RBFM system refers to a systems ability to withstand various precipitation events, reduce flood damage, and restore normal conditions. This study proposes a framework for selecting flood management options in a hierarchical system based on social resilience indicators, focusing on social aspects. In this study, behavior of RBFM systems in response and recovery from varying rainfall events defines the resilience. To operationalize the framework a set of social response, social recovery capacity, resistance point, and warning point-related indicators have been defined. A hierarchical fuzzy system has been developed to quantify the indicators, considering the uncertainties in social variables and avoiding dimensional incosistency. Using this approach in the Gorganrood river basin demonstrated the effectiveness of selected flood risk management options in terms of resilience, by considering various social resilience indicators, as compared with traditional decision-making methods. Comparing the response-recovery curves for different management options has highlighted the importance of defining different resilience indicators to determine the behavior of the RBFM system after performance failure. Finally, the results of this study suggest that the proposed indicators can be employed as decision-making criteria in selecting various management options based on the behavior of the river basin system under rainfall events with different return periods.