نشریه مهندسی سازه و ساخت
سال نهم شماره 10 (پیاپی 63، دی 1401)

Buried pipelines are vital infrastructures and are mostly used to transport energy and other essential commodities. One of the most important seismic hazards on buried pipelines is movement of faults crossed by them. In general, pipeline can be simplified as a beam, while pipe-soil interaction can be represented by soil springs in the axial, horizontal and vertical direction. Although this method has been implemented previously by ASCE and ALA guidelines the specifications of these springs are not well-defined. In this study, a full-scale tests were carried out on polyethylene pipe buried in dense sandy soil (with 120.5 mm of diameter). The response of the system (such as displacements and reaction loads) were recorded during the tests. A computer program was developed to optimize the specifications of the equivalent springs using Python scripts in MATLAB and ABAQUS environments. In this way, the deformation of the pipe along its length would have the highest level of congruence with the experimental results. Using the proposed approach, the initial stiffness and maximum soil-pipe interaction force have been calculated and compared to the criteria recommended by ASCE and ALA standards. The results showed that the value of yield force capacity and stiffnesses for the soil lateral equivalent springs, provided by ASCE and ALA codes, are determined to be in a great value of error. For polyethylene pipe at the condition of strike-slip faulting, these values were too smaller than the values put forth by ASCE and ALA .

Concrete is widely used as a building material all over the world, but it is not considered an environmentally friendly material due to environmental degradation and the use of large amounts of natural resources. Therefore, it is necessary to provide a solution to reduce the effects of recycled aggregate pollution. In the present study, the effect of the strength of recycled aggregates on the rheological and mechanical properties of self-compacting concrete is investigated experimentally and numerically. Hence, two types of recycled aggregates with known and unknown strength origins are utilized for the studied samples. The experimental design in this research is accomplished by the Box Behnken method, which is one of the response surface methods. Input variables in mixtures, including micro silica in the range of 5-15% as a percentage substitute for the weight of cement and recycled coarse and fine grains in the range of 0-50% for both series of recycled materials, are replaced by natural materials. The studied responses are slump flow, funnel V, compressive and tensile strengths. The results indicate that the increase in recycled aggregates reduces the rheological and mechanical properties of the mixtures, while micro silica effectively improves the mechanical properties. In addition, the sensitivity of most of the studied responses is related to recycled fine particles. It should be noted that recycled materials of known strengths are shown better results than recycled materials of unknown strengths. Some mathematical relationships are also provided using analysis of variance for all responses to predict the rheological and mechanical properties of mixtures.

Reinforcement of structures with concrete moment frame system by submitting metal damper with optimal cross section has been done in the present study. To investigate the effect of damping on the behavior of the structure, the structural system with the proposed damper was compared with three types of bearing systems of different structures of concrete moment frame, concrete shear wall and bracing with different number of floors 8, 14 and 20. In this study, 4 groups of concrete structures were studied and compared in terms of lateral bearing system, including medium concrete moment frame with behavior coefficient (R = 5), medium concrete moment frame with shear wall with medium ductility, concrete moment frame with Medium ductility with EBF steel brace and Medium ductility concrete moment frame with EBF steel brace Equipped with yielding metal damper. The studied structures have building frames with dimensions of 25 x 25 meters, which are modeled on 8th, 14th and 20th floors. Each dimension of the structure in the plan has 5 openings with lengths of meters. In modeling structures with dampers, four types of dampers modeled with 4, 6, 8 and 10 flowing plates in the damper have been used. By comparing them, it has been determined that the damping with 10 flowing plates has better performance and the results of that structure in Comparison with other systems was used. In 8-story models, the maximum final displacement in the brace was 17% higher than in the damper. The 8-story structure with dampers not only withstood the highest shear but also had the best performance compared to other systems. The results show that in structures with a low number of floors, the use of the system with the proposed damper is more appropriate and in medium structures, the shear wall system has a better performance.

Due to the complex behavior of materials containing gypsum, loading of structures containing these materials such as dams and bridges, etc. is very important. Therefore, it is important to pay attention to the deformability of these materials under different environmental conditions such as humidity and stress. The present study has investigated the effect of moisture and stress changes on the samples extracted from the Marash Dam site located in Mahneshan city of Zanjan province. For axial loading, a device similar to uniaxial device was designed and built and 9 samples were exposed to different loads in three modes of humidity percentage of 30, 50 and 80%. Loads were applied at different time intervals and sometimes up to 45 days for creep testing. The results showed that with increasing stress, the amount of creep strain increases and with the stresses approaching the uniaxial strength of the sample, the values of creep strain increase so that with increasing stress from 1.3 to 3.5 MPa, the values of creep strains sometimes Increases up to 2.5 times. According to the results, most creep strains occur in the early days. Also, with increasing humidity, the strain of the sample increases and the behavior of the sample changes so that in low humidity the strain is elastic and reversible and in higher humidity the strain is plastic. Increasing the relative humidity increases the deformation of these materials so that as they approach the saturation state, the sample showed a very large volume change. The results also showed that when the sample is placed in water for a longer period of time, water easily penetrates into the microcracks and joints of the sample and reduces the integrity of the sample and its loosening.

From long time ago, various solutions have been proposed to reduce earthquake damages, including increasing ductility and reducing structural mass. New methods are based on separating the structure from the foundation, to reduce the shear force of the base of the structure. In other words, seismic isolation is a new method for designing buildings against earthquakes, which is based on reducing the forces entering the structure due to earthquakes, instead of increasing the capacity of the structure to withstand lateral loads. This paper is a focused on the study of the effect of the placement of rubber separators with lead cores in the behavior of reinforced concrete structures under the influence of remote earthquakes. Therefore, for rubber separators with lead core in two samples of concrete structures of 3 and 5 floors, a double damping of 10 and 15% has been considered. Separating structures and fixed base structures were modeled in “Opensees” software. Afterwards, under the influence of distant earthquakes, a time history analysis was performed on them. Finally, the results of time history analysis for designs by force and direct displacement method are exposed, which include, maximum drift of floors, maximum shear of base and period of structures. Results obtained from the analysis of time history show that with the increase of the rotation time, the shear of the bases and the maximum drift in the buildings with isolators designed by direct displacement method are more than the buildings designed by force method. Buildings with separators designed by direct displacement method have sections with less capacity than buildings designed by force method.

In this study, different combinations of replacement of metakaolin, zeolite and fly ash in single, binary, and ternary mix designs were investigated in order to determine the optimal amount of suitable pozzolans. Fifty mix designs with constant water to cement ratio were made and the results of compressive strength, tensile strength, slump, specific gravity, water absorption, and volumetric electrical resistivity of concrete were recorded in order to evaluate the effect of type and amount of pozzolans and the effect of their compositions. The results showed that the highest amount of compressive strength was related to the ternary composition of pozzolans, and the amount of replacement was 3% (M3Z3F3). 3-, 7-, 28- and 90-days compressive strength increased by 14.8%, 24.1%, 41.1% and 54.1% compared to the reference sample, respectively. Compressive strength of samples containing single, binary and ternary mixes with a total of up to 45% will increase the compressive strength by different percentages and will have a further downward trend. The tensile strength of concrete in all samples containing binary and tertiary compounds of pozzolanic materials was higher than the reference sample with the highest increase related to M5Z5, M5F5, Z5F5 with 84.2%, and M3Z3F3 with 94.7%. The maximum reduction of water absorption is in the ternary mix designs M13Z13F13 and M15Z15F15 with a decrease of 75.8% compared to the reference sample. In all samples containing pozzolanic materials, the amount of electrical resistance has increased compared to the reference sample (from 1.3 to 9.1 times). The amount of electrical resistivity of concrete samples containing ternary composition was higher than binary and single. The maximum is related to M13Z13F13 and M15Z15F15 designs, which increased 9.1 times more than the reference sample. The presence of more than 40% pozzolanic values has almost no effect on the mechanical properties of concrete.

Rammed earth walls are known as sustainable and eco-friendly construction methods, constructed by the local soil in the temporary framework. Generally, the unstabilized soil does not have suitable compression and tension strength for construction. Ordinary Portland cement and lime are frequently used materials for soil stabilization. Regarding the environmental drawbacks of cement as a frequently used, affordable, and available material, it is essential to use eco-friendly material for soil stabilization. In this study, the mechanical behavior of the soil activated by sodium hydroxide, as an eco-friendly material, has been investigated, and the results compared with cement stabilized soil. Unconfined compressive and Brazilian tests for determining the compressive and tensile strength of the rammed earth were performed on the stabilized specimens. The specimens were prepared at different conditions of curing condition, curing time, and binder content. Results indicated that the slag stabilized specimens resulted in more compressive and tensile strength than cement stabilized soil. The superb improvement performance was observed at hot-dry condition, where is a suitable improvement strategy for the arid climate of Iran as well as water scarcity. The soil stabilizing with slag resulted in outstanding improvement efficiency; however, it increased soil brittleness which is not suitable for seismic behavior and may cause a sudden failure in the soil.

Seismic isolators are the common methods to improve the seismic performance of cable-stayed bridges. Roll-N-Cage (RNC) Isolator is one of the modern systems in recent years. In this paper, it is aimed to study the damage probility and reliability of cable-stayed bridges isolated with Roll-N-Cage (RNC) instruments. For this purpose, Bill Emerson Bridge is selected and based on the Monte Carlo method, damage probility assessment is performed under artificial seismic records and initial imperfection as cable loss. Artificial records have been produced with a proper distribution of random data based on the frequency content and duration of the earthquake and also according to the model of the spectral density function of the earthquake with the dominant Kanai-Tajimi frequency. Nonlinear time history dynamic analysis under the mentioned records are performed for 2000 random samples in accordance with the Monte Carlo method in the form of modeling in MATLAB and Opensees software. The results show that without initial imperfection, the bridge has proper vibration and isolator performance. The failure is observed only in the form of minor permanent deformations of the deck at the end of the vibration. The probability of failure of the cable-stayed bridge without initial imperfection is about 1%, which has a reliability index of 2.3263. By applying an initial imperfection in the middle cable of the middle span of the model, under some records, it experiences a complete collapse. In these conditions, the probability of failure is 2.81% and the reliability index of the bridge is 1.911.

The present paper aimed to develop a bridge management system using a combination of new fuzzy multi-criteria decision making methods. The developed system consists of a three-phase protocol. In the first phase, using past studies, personal intuitions and judgments and experts' experiences, a database containing critical factors affecting the critical condition of bridges was prepared, as well as identifying a number of urban overpass bridges in Tehran city with relatively similar characteristics and in need of maintenance. In the second and third phases, considering the uncertainties in the decision-making problem, by combining Delphi-SWARA-ARAS methods in a fuzzy environment, while screening and prioritizing more efficient and effective critical factors, the critical situation was assessed and the steps studied were selected. The results of Fuzzy SWARA method to determine the effective final factors showed that the factors of seam filling and discontinuity of the bridge related to the main structural index, average and duration of maximum annual rainfall at the bridge location of the main index of climate and hydrology, drainage, water discharge Surface and insulation of the bridge from the main index of safety, proximity and convenience of bridge access to adjacent arterial roads in terms of the main index of strategic (regional) importance, cost-benefit ratio for maintenance or reconstruction and replacement of the bridge from the main budget index and finally The volume of traffic passing over the bridge has gained higher ranks than the main index of traffic and pavement, respectively. Also, the results of Fuzzy ARAS method based on final critical factors (18 factors) showed that among the 24 bridges, Sheikh Fazlollah-SattarKhan, Hakim-Sheikh Baha'i, Hemmat-Africa, Lashkari-Aircraft industries bridges And Resalat-Haqqani with usefulness of 3.226, 3.171, 3.081, 3.080 and 3.077, respectively, are considered as the most preferred bridges in terms of the need for maintenance allocation.

There are several sources of uncertainty in the analysis and design of steel moment resisting frames, the random assumption of each of which can have a significant effect on the satisfiction of performance requirements of the structure. Among these factors, structural parameters can be mentioned, the most important of which are yield stress, modulus of elasticity, sections geometry and structural mass. Evaluating the impact of these factors depends on how the parameters are distributed and modeled. In this study, three common types of uniform, normal and log normal distributions for the parameters of mass structures, yield stress, modulus of elasticity and sections geometry that are random in nature are considered and using Monte Carlo method, the effect of uncertainty of these parameters is considered. The seismic performance of steel structures is investigated. Studies are performed on 4 structures of 3, 5, 10 and 15 floors of steel moment resisting frames with medium ductility, which are designed according to Iranian regulations. In order to model the structures and perform incremental dynamic analysis, Open Sees software was used .In order to evaluate the seismic performance of the structures, fragility curves were used. The results show that the type of distribution does not have a significant effect on the results of applying uncertainties. It is also observed that considering the mass uncertainty, increases the acceleration range in the Collapse Prevention (CP) and life safety (LS), which shows the significant effect of mass uncertainty compared to other parameters.

The containment structure of nuclear reactors is the most crucial barrier to releasing radioactive materials into the environment and protecting the reactor against external hazards such as earthquakes and floods. After the Fukushima nuclear accident, the safety of this structure in the earthquake has received much attention. Iran is also located in a region with high and very high seismic hazards and is essential. In this study, the seismic fragility curve of the containment structure of pressurized water reactors used in Bushehr has been determined by considering different failure modes. For this purpose, a computer model simulated in ABAQUS software and incremental dynamic analysis (IDA) have been used. The finite element model has been validated using a lumped mass model. Different failure modes are defined in terms of critical stresses in concrete, rebar, tendons, and steel plate attached to the containment body. Critical points of containment have been identified in terms of these failures. Concrete materials fail at a lower acceleration than other materials. At peak ground accelerations of less than 0.2 g, concrete remains elastic, and no cracks are formed; however, at peak ground accelerations of 2.2 g to 2.75 g, concrete cracks of more than 2 mm form, which allow the release of radioactive materials into the environment. The parameters of fragility, median acceleration capacity, and logarithmic standard deviation of median acceleration capacity were determined to be 2.251 and 0.155, respectively.

Engineered cementitious composites with polyvinyl alcohol fibers (ECC-PVA) are a group of cementitious composites, which not only provide high ductility and tensile strength but also control the crack width. The strain-hardening behavior under tensile and flexural loads and the formation of multiple shallow cracks instead of deep and concentrated cracks are among the main advantages of these composites, leading to their widespread application. In this paper, eight ECC concrete beam specimens, including four specimens containing 2% and the other four containing 1.5% PVA fibers, were tested and their load-displacement and load-crack mouse opening displacement curves were obtained. To determine the crack mouth opening displacement, four LVDTs were mounted around initial crack formed in the beam. As the displacement applied using the standard testing machine with a 500kN capacity increased, which were recorded using the LVDTs. Afterward, by averaging the recorded opening displacement recorded using LVDTs, the final crack mouth opening displacement was obtained. The results indicated that the ECC specimens with 2% PVA fibers had lower load-carrying capacity, and greater displacement, crack mouth opening displacement, and ductility values compared with the ECC specimens with 1.5% PVA fibers. Moreover, increasing the PVA fiber percentage elevated the flexural capacity of the beams by 10%.