مجله پژوهش های زیرساخت های عمرانی
سال هفتم شماره 2 (پیاپی 13، پاییز و زمستان 1400)

Due to the fact that concrete is one of the most widely used construction materials and concrete has low ductility, tensile strength and flexural strength along with good compressive strength. To this end, in recent years, by adding fibers to concrete and making reinforced fiber concrete, these weaknesses have been greatly improved. In this study, four samples of reinforced concrete beams were made with recycled aggregate and one sample of beams was made with natural aggregate and in real scale with dimensions of 150×50×20 centimeters. Separate and hybrid types of steel and Kortta fibers were used in the manufacture of beams. In three beam specimens, steel and Kortta fibers were used separately and hybrids and no fibers were used in the beam specimen. In fiber beams and one of the beams without fibers, recycled aggregate was used in their concrete and in one of the fabricated beams, neither fiber nor recycled aggregate was used and it was used as a reference sample in the performed studies. Four-point flexural strength test was performed on the samples. Fracture mode, flexural behavior parameters of beams made with recycled aggregates were investigated. The results showed that the addition of hybrid fibers has a very positive effect on improving the flexural behavior of reinforced concrete beams and eliminates the weakness of recycled aggregates in flexural behavior compared to beams made with natural aggregates.

In this study, the potential of progressive collapse of a four-story steel structure due to the collision of an 8-ton truck with the ground floor columns was investigated. For this purpose, a 4-story steel structure ( with intermediate steel moment frame system and special concentric steel bracing in the x-direction and intermediate steel moment frame system in the y-direction ) was modeled and designed in ETABS software. ABAQUS finite element software was used to simulate the structure under collision scenarios. In this research, 6 scenarios of truck collision with adjacent columns of the structure have been considered by performing nonlinear dynamic analyzes. The vehicle speed is assumed to be 20 meters per second. The results showed that corner columns are more vulnerable to impact than perimeter columns. The presence of braces reduces the collapse and deformation in the desired scenario. The horizontal displacement in the impacted column in the direction of the moment frame was about 3 times that of in the direction of the dual system. this shows the positive effect of bracing system in reducing the structural responses to impact.

Strengthening breakwaters can reduce the damages that lead to hydraulic instability. Aiming to enhance the stability of reshaping breakwaters, this experimental study presents a method for controlling and reducing structural damages against waves by attaching a submerged obstacle to the structure toe and installing a floating wave barrier at a certain distance. In the tests, the breakwater was exposed to a total of 3000 random waves based on the JONSWAP spectrum. By generating an integrated 3D digital model of the structure using close-range photogrammetry, the displacement of armour units was recorded, and the damage parameter was calculated. Moreover, a comparison of the results between reinforced and simple breakwater indicated that the damage parameter was reduced by 37.19 and 34.14 percent by, respectively, attaching the submerged obstacle and installing the floating wave barrier, which confirms the good performance of the proposed models. Breakwater reinforcement with the submerged obstacle and the floating wave barrier simultaneously reduced the damage parameter by 51.79 percent, which was the highest efficiency among the different models. Also, the results show that with increasing the stability number, the damage parameter also increases, and the interaction between the wave steepness and the damage parameter indicates that the damage parameter decreases with increasing the wave sharpness values.

In structural analysis, P-Delta effect refers to the changes in internal forces due to P-Delta moment which can be found by multiplying gravity load (P) by the lateral displacement of structure for earthquake lateral load (Delta). The influence of P-Delta in elastic response of structures is ignorable, but P-Delta effect should be given more attention when the structure responds in inelastic range. On the other hand, the influence of ground motion duration is magnified when P-Delta effect is considered in the structural analysis. In this paper, to consider the simultaneous effect of ground motion duration and P-Delta effect, an algorithm is implemented in MATLAB which employs OPENSEES for linear and nonlinear dynamic analysis of elasto-plastic systems subjected to long- and short-duration records. The analysis results indicate that the frequency of structural collapse for long-duration ground motions is about twice of short-duration ground motions. The frequency of collapse also increases when ductility and stability index increase, but decreases when the period of structure increases. Furthermore, the increase of ground motion duration has no influence on the residual displacement of structures, but nonlinear behavior of structures and gravity load effect increase the residual displacements.

In previous studies, the effect of different types of polyethylene on the performance of asphalt mixtures has been investigated. In this research, the mixing design of asphalt mixtures containing high density polyethylene has been analyzed and modeled based on the conventional and the response surface methods for limestone and granite aggregates. For this purpose, the volumetric and strength behavior of laboratory-made samples have been measured and statistically analyzed. In the optimization process,, the optimal amount of binder and polyethylene has been extracted according to the criteria of the asphalt pavement regulations for Iranian roads and with the desirability approach. Experimental results show that the optimal conditions for limestone aggregate are 6.1% binder and 4% polyethylene with a desirability of 0.909. However, these values for granite aggregate are 5.9% binder, 4% polyethylene with a desirability of 0.962. The polyethylene additive increases the Marshall strength and specific weight of the samples for both materials. The higher percentage of additive has the greater effect on these parameters. Analysis of variance shows that polyethylene percentage has a significant effect on Marshall flow. By increasing the amount of additive from zero to four percent, the flow value decreases.

Reinforced concrete with steel fibers has been widely used in concrete and reinforced concrete structures in order to improve the properties of concrete. The reason for this widespread use is the myriad technical and economic benefits of using steel fibers in a concrete body. Due to these important advantages in concrete properties, the production and application of steel fibers in the industrialized countries of the world has a wide range, so that currently various types of steel fibers with various technical specifications and applications are mass-produced industrially. Reinforced concrete with steel fibers includes a concrete body composed of cement, stone materials, water as well as a percentage of short steel fibers that are mixed in a completely randomly and in different directions in the mixture that the presence of steel fibers determine the characteristics of concrete compared to pure Improves. Determining the optimal percentage of fibers is one of the important factors in terms of economics and efficiency of concrete. In this study, to determine the percentage of optimal fibers in different strength classes, 24 mixing designs were prepared and a mechanical laboratory and fresh concrete were performed. The flexural strength of samples containing 0.9% of steel fibers for categories C40, C50 and C60 was 1.91, 3.86 and 5.14 times higher than the control sample, respectively.

Excavation-induced displacements may cause damage to buildings and urban facilities. The displacement of walls is inevitable in soil nailing method to mobilize the tensile force in steel elements. FEM-based numerical analyses in MIDAS GTS NX were used to evaluate the response of a concrete building adjacent to deep excavation. The effect of various parameters of the concrete frame building, including the number of stories, distance to excavation, and the excavation stabilized by soil nailing at different depths was investigated in the building adjacent to the excavation. The design charts represent the foundation settlement, building rotation, excess axial stress in the concrete columns, and the excavation-induced shear strain in masonry infill walls. According to the results, the presence of a building can cause significant changes in the deformation profile of the ground surface. Results showed the adjacent buildings that are located at the excavation edge and a distance equal to the excavation depth experience the maximum displacement. The excess axial stress in the concrete columns of the building adjacent to the excavation was negligible. Furthermore, with increasing foundation depth, settlement and rotation of the building decreases. This study showed that the axial stress of the building column adjacent to the excavation due to excavation is less than 5% of the compressive strength of concrete. Most displacement in buildings adjacent to the pit occurs when the building is on the edge of the excavation. At a distance of 4 times the depth of the excavation from the edge, the settlement is insignificant.

Optimal use of materials in the construction of structures is one of the main goals in any design. Because the construction of building structures is costly for their builders, therefore, structures and buildings that are economically justifiable and appropriate and meet the requirements of the criteria are more welcome. On the other hand, maintaining the performance of structures in earthquakes plays an important role in ensuring safety and reducing earthquake damage. Optimization of frames reduces sections, stiffness, and strength of components, and as a result, the performance of these frames against earthquakes has been questioned by researchers. In this research, the performance level of optimized steel moment frames with metaheuristic algorithms has been evaluated. For this purpose, the seismic performance of five-story steel moment frames with different geometric characteristics has been optimized and seismically evaluated using Particle Swarm Optimization (PSO), Charged System Search (CSS)Ant Colony Algorithm (ACO) and Genetic Algorithm (GA). The results of studies show that the optimized frame based on the Charged System Search algorithm has lower weight and lighter sections, and the seismic behavior responses of the frames are obtained faster. In terms of performance levels, the total number of collapse plastic joints in the Particle Swarm Optimization (PSO) was higher than other methods. Therefore, this algorithm can also be proposed as a suitable proposal for the optimal design of similar frames.

Today, the need to apply project management knowledge as a key factor in success in project-based organizations is obvious. In order to increase the effectiveness of project management, increase the level of maturity of project management, and ultimately increase the success rate of the organization, it is necessary to establish a unit with centralization and project coordination function, which plays a role in the project management office (PMO). Adopting this approach is one of the effective measures in centralizing and integrating the organization's project management processes. With this in mind, organizations today have realized the need and importance of implementing project management offices to overcome problems and increase project management effectiveness. In this regard, in the present research, the challenges of implementing a project management office in the companies and projects of the oil and gas industries, with a case study conducted in the Oil Engineering and Development Company, have been identified and prioritized. For this purpose, in the first stage, to identify the challenges, interviews were conducted with experts in this field, which led to the identification of 36 challenges and were divided into three categories: organizational, managerial, and human resources challenges. Finally, in the second stage, these challenges were prioritized using the distribution of questionnaires among experts and the analytic hierarchy process (AHP). Managers with traditional thinking are some of the main and challenging issues in implementing project management offices in companies and executive projects of oil and gas industries.

Seismic base isolation is a practical solution to reduce the seismic demand on civil infrastructures. In this paper, the maximum displacements of friction pendulum isolators resulting from simplified method pre-scribed by ASCE7-16 are compared with the results from nonlinear response history dynamic analyses for near-field pulse-like and non-pulse-like earthquakes. The maximum displacements of the friction pendulum isolators with four different coefficients of friction and four effective radii have been determined using simplified methods pre-scribed by ASCE7-16. Nonlinear response history dynamic analyses are then performed for the 16 aforementioned cases using OpenSees under seven near-field pulse-like earthquake records and seven near-field non-pulse-like earthquake. Adjustment factors are finally developed for the simplified method of ASCE7-16 to update the predictions. The results show that the values predicted by the code are less than the values obtained from nonlinear time history analysis. In addition, the adjustment factors obtained for pulse-like near-field motions are larger than adjustment factors for non-pulse-like near-field motions.

Rail transport has unique advantages over other modes of transport, such as less environmental vulnerability, less pollution and more safety than other modes of transport. Due to the lack of lands with adequate load-bearing capacity, parts of the railway route are built on soft soils, which the possibility of creating instability and subsidence of railway lines in this type of soil is one of the main concerns of engineers. High-speed trains are now used in developed countries to reduce travel time, which can significantly increase the dynamic responses of components on railroad tracks, especially when the train is traveling at a critical speed. One of the ground improvement methods that has been widely used recently for the improvement of soft sediments and loose fine-grained soils is the rock column method. High-speed trains are two important factors in the operation and use of the railway complex. In this research, the performance of stone columns in the bed of high-speed trains to reduce soil subsidence and prevent the occurrence of asymmetric subsidence in different conditions and under the influence of various factors has been investigated. The results showed that with increasing column length Stone and its diameter decreases, asymmetric settling and subsidence due to high-speed train passage is reduced. Also, increasing the hardness of the geogrid reduces the subsidence.

One of the major uses of energy is in residential, commercial, and infrastructure such as educational buildings. One of the effective ways to reduce energy consumption in these buildings is before construction. But many buildings are already under construction and a solution must be found to reduce energy consumption in these buildings. One of the important solutions is to predict the amount of energy in these buildings. In this case, the energy consumption can be evaluated before and after some changes in the building. This article addresses the issue of energy prediction in existing school buildings in Mashad. For this purpose, a number of important physical characteristics of the building and its energy consumption based on consumption bills have been collected in the field. Then an artificial neural network is used for modeling. Using the results of the model, the energy of buildings in schools can be predicted. Finally, the effects of reducing carbon dioxide with respect to energy savings are discussed.