نشریه مهندسی عمران
سال پنجاه و چهارم شماره 7 (مهر 1401)

Sliding articulated isolators are well-known types of seismic control tools that extensive observations have shown their effective role in reducing seismic damages in structures. Although this tool significantly improves the performance of the structure at different seismic levels, but the existence of uncertainties in the limit behavior of this isolator in earthquakes with long return periods has attracted the attention of researchers in recent years to model their ultimate behavior. When the isolator reaches its displacement capacity, the sliding parts strikes the side edge of the sliding surfaces and the performance of the structure affects by this special condition. In this study, after implementing the equations governing the behavior of these isolators, we proceed to mathematically model their ultimate behavior and study its effects on the dynamic response of the superstructure. So, by designing and modeling a sample structure, we examine the superstructure dynamic response at different scales of several earthquake records. The results shows that the average ground acceleration at the beginning of the contact behavior under the studied records, is about 1.25MCE, the elastic base shear is about 0.48 superstructure weight and the maximum elastic drift of the superstructure is about 0.0038. By increasing the level of acceleration, the amount of base shear increases to the levels that the superstructure shows the nonlinear behavior. Also, by performing analysis on a model without ultimate behavior and comparing the results with the ultimate model, coefficients for converting the results of the non-ultimate model to the ultimate model are presented.

This research paper has been conducted with the aim of identifying the relationship between competency criteria of airport construction industry managers and project success criteria. The research method is exploratory and in this regard, the descriptive method of correlation has been followed. The statistical population consists of managers with experience in major Iranian construction projects in the airport construction industry. The sample size was 230 according to Morgan sampling table. Data collection tools were semi-structured interviews of managers and project success questionnaire. The data analysis method was to use the indicators of Kaiser Meyer, Olkin tests, as well as factor analysis and correlation tests. Data analysis and analysis showed that managers' competency criteria increased from the number of thirty initial proposals to 36 after credit from the sample group. The project's success criteria were reduced from the original 52 proposed cases to 38 after validation from the sample group. The success criteria of the project adapted to the local conditions were identified after factor analysis and their list was reflected in the results of the article. Thus, two types of localized tools were obtained separately to measure the competence of the management and the success of the project. The correlation test performed showed that there was a relationship between each of the competency factors of managers and the success factors of the project.

Nitrate removal from polluted waters is one of the most important environmental issues. The aim of this study was to remove nitrate from municipal effluent by activated carbon of orange peel modified with chitosan synthesized from shrimp peel and iron (ш) chloride. Identification of activated carbon functional groups by FTIR, the morphology of carbon cavities by SEM, and porosity properties were investigated by BET analysis. The characterization results indicate a porous structure with different functional groups of modified activated carbon. Pseudo-first-order, pseudo-second-order, intra-particle, and Boyd kinetic models were used to describe the kinetic data, as well as Langmuir, Freundlich, and Dubinin-Radushkevitch isotherms to describe the adsorption equilibrium data. The effect of pH and the amount of adsorbent was investigated and the results showed that pH = 2 and the amount of adsorbent 0.2 g in 50 ml of solution are the optimal conditions to achieve maximum nitrate removal. The results showed that the adsorption followed the pseudo-second-order kinetics (R2 = 1). Also, among the studied isotherms, Langmuir model described well the adsorption of nitrate onto synthesized activated carbon (R2 = 0.999) and the maximum adsorption capacity was 263.157 mg/g activated carbon. This behavior means the adsorption of the monolayer and the predominance of the chemical adsorption mechanism. Nitrate uptake increased with decreasing temperature, indicating that the reaction was exothermic. Nitrate removal efficiency with modified activated carbon was estimated to be 99.58%. In general, it can be said that modified carbon can be a candidate for use on an industrial scale.

Repairing damage caused by residual deformation after earthquakes in common structures is costly. Therefore, self-centering structures have been introduced by researchers to reduce residual deformation after earthquakes. In the typical design of these structures by force method, a constant behavior factor is used to calculate the base shear, which cannot consider the actual performance of the structures. On the other hand, the energy method has more accurate results than the force method by selecting the desirable yield mechanism and target displacement at the beginning of the design process. Since this method has not been used for the analysis of self-centering structures, in this study, for the first time, the energy method was used to determine the seismic response of the self-centering concentrically-braced frame (SC-CBF), and its accuracy was compared with test and analytical results. The results of the study showed that the energy method is a simple and fast analytical method without the need for software modeling and can provide an acceptable estimate of the structural response. By comparing the different ductility reduction relationships, it was observed that the equation presented by Lai-Biggs is the most appropriate relationship with an accuracy of over 80% because they used artificial earthquake records that are close to the design spectrum. Also, the results showed that with increasing the height of the structure, the final rotation and ductility of the structure decreased, which increased the accuracy of the energy method with other relationships to estimate the response of the structure.

Analysis of underground structures under blast has challenges due to the complexity of blast dynamic loading and soil behavior. Due to the role of underground structures as a shelter and the vulnerability of these structures to explosive loads, it is vital to investigate and analyze the effect of explosions on these structures. The aim of this study is to investigate the effect of explosive projectile distance from the underground structure and the diameter of the explosive sphere on the underground structure. For this purpose, using the finite difference method and dynamic analysis, the underground structure was simulated for different distances of the explosive projectile and different diameters of the explosive sphere. In this study, the propagation of explosion waves in a spherical manner was considered by applying an explosion pressure on the wall of the explosive sphere. The results show that with increasing the distance of the underground structure from the center of the explosion, the maximum soil pressure on the maintenance system as well as the bending moment and axial force in the canopy and wall of the tunnel maintenance structure decrease exponentially. In addition, after the explosion wave reaches the tunnel maintenance system, the displacement and vertical velocity of the storage system particles in the tunnel crown is the highest. As the diameter of the explosive sphere increases, the bending moment at the crown and wall of the tunnel increases almost linearly, which is three times the slope for the tunnel crown

One of the essential functional failures in concrete pavements is faulting. Predicting this failure can be used in various fields such as pavement design and pavement management systems. In this study, powerful tool of artificial neural networks has been used to predict this failure. Initially, using 32 input variables including traffic, weather and structural data, the artificial neural network architecture was determined by trial and error and then the specified architecture was properly trained. Among these 32 variables, in addition to the variables used in previous studies, new input variables that have not been studied so far, such as Poisson's ratio and elastic modulus of concrete slabs, have been considered. Then, with a new method, 19 important variables were identified and a new neural network model with 19 variables was constructed. The values of correlation coefficient, mean square error and mean absolute error for the model with 32 variables and 19 variables are equal to 0.97, 0.45, 0.43, 0.95, 0.54 and 0.6. Finally, using the random forest method, the importance of 19 variables was determined, of which the four most important variables are the annual cumulative number of days with precipitation greater than 12.7 mm (24%), elastic modulus (14%), Pavement life (12%) and base thickness (10%). elastic modulus is one of the most important input variables if this variable has not been studied in previous studies.

Investigating the performance of bitumen restored by recycling agents in maintaining or destroying the properties and characteristics of bitumen in the next period of pavement service is completely limited. The aim of this research was to evaluate the immediate and long-term effect of a naphthenic recycling agent in restoring the properties of aged bitumen. In this research, bitumen separation and infrared spectroscopy experiments to investigate the chemical properties of bitumen samples, Penetration, Softening Point, Rotational Viscometer, Multiple Stress Creep Recovery and Linear Amplitude Sweep were used to evaluate the physical and rheological properties of bitumen samples. To evaluate the long-term performance of the recycling agent, the restored bitumen was to long-term aged by aging simulation test. The results show that the use of naphthenic recycling agent in the optimal amount has restored the chemical, physical and rheological properties of aged bitumen to the base bitumen level. The naphthenic recycling agent results in a 38% reduction in the CI of aged bitumen, which indicates that the aged bitumen is softer and its colloidal structure is stable. It also reduces the rutting resistance of aged bitumen to the level of base bitumen. The limited increase in CI due to aging in restored bitumen indicates that the naphthenic recycling agent has performed well in maintaining the stability of the colloidal structure of bitumen in the long term. The results also show that the use of naphthenic recycling agent improves the fatigue performance of restored bitumen in the long term compared to base bitumen.

This research deals with the application of lead rubber bearing isolation systems in reducing the seismic risk of buildings located in Tehran metro city from technical and economic points of view. In this regard, first, three separate 5-, 10-, and 15-story buildings with the steel moment resisting frames system are considered. These models are designed in two separate scenarios: with and without the base isolation system. Next, all the active faults of Tehran and its sur-rounding area are considered to generate the probable earthquake scenarios in the 50-year life span of the buildings. This simulation contains the probable mainshock-aftershock event scenarios and the corresponding accelerograms for each of the generated events. Afterward, by adopting the Monte-Carlo simulation technique, an adequate number of random earthquake hazard scenarios are generated. Then, the buildings’ performances are evaluated under mainshock-aftershock sequences using the nonlinear dynamic time history analysis approach. In addition, by using the damage and loss models considering the fatality and injury, building physical damage, and time-dependent economic losses, the lifetime seismic risks of buildings are estimated. The outcomes highlight that the lead rubber bearing system is well capable of improving the building behavior and hence reducing the life-cycle cost of buildings tangibly which will be elaborated in this paper.

Fundamental period of a building plays a vital role in determining structural behavior during vibrations such as earthquake and estimation of building base shear in designing new structures or target displacement in the evaluation of existing buildings. Thus, having an appropriate estimation of fundamental period of buildings can have a considerable effect on design and evaluation results. As a result, after the November 2017 earthquake of Sarpol-e Zahab, ambient vibration tests were conducted on 22 reinforced concrete (RC) buildings to determine fundamental period. The obtained values for fundamental periods were compared with calculated values of proposed empirical relations by the first and fourth edition of Iranian Code of Practice for Seismic Resistant Design of Buildings (Standard No. 2800) and the first revision of Instruction for Seismic Rehabilitation of Existing Buildings (No. 360). The obtained results for damaged RC buildings with moment resisting frame show a significant difference between fundamental periods calculated by ambient vibration tests and empirical relations in such a way that in a building with a damage state 4, the obtained period from ambient vibration tests were 2.32 times of calculated value using empirical relations. Furthermore, in retrofitted RC buildings, fundamental periods calculated by empirical relations were up to 1.7 times greater than values determined using ambient vibrations. Therefore, two empirical relations for determining fundamental periods of damaged RC buildings with moment resisting frames and retrofitted RC buildings by adding shear walls are proposed by fitting curves on the obtained results of ambient vibration tests.

In recent years, studies on strength characteristics of unsaturated soils due to the importance of suction in these types of soils has been more focused on cohesive fine-grained soils or compacted sandy soils and limited research on liquefaction of loose unsaturated sandy soils and the effect of particle size on this behavior have been done. In this paper, it has been aimed to investigate the effect of particle size and degree of saturation on liquefaction resistance of loose unsaturated sandy soils by performing a series of cyclic triaxial tests at undrained conditions on three types of sand with different grain size distribution. The results show that variation of pore water pressure and liquefaction resistance in studied sands are largely dependent on particle size and intergranular voide ratio, so that #131 Firoozkooh sand has the lowest liquefaction resistance in saturated state due to its higher intergranular voide ratio. Also, according to the obtained results, increasing the size of sand grains reduces the matric suction created in the soil mass due to reduction in degree of saturation. Increase of number of cycles to liquefaction and consequently the liquefaction resistance of the stadied sands samples due to decrease of saturation, especially in sands with finer grains, is another result of this study.

Monopile is the most common type of foundation for onshore and offshore wind turbines. Wind load alternately applies in different directions during the life cycle of the wind turbine. In this paper, the influence of alternating change of wind load direction on the response of wind turbine piles is studied. The functional performance of soil-pile system is simulated with a bounding surface soil behavior model presented by Dafaliad-Manzari that is implemented in FLAC3D software. The softening and hardening effects of soils due to cyclic load patterns is incorporated in the model in a convenient manner. The results show that alternative change in the direction of loading results in the decrease in the maximum horizontal displacement and rotation up to 16% in comparison with the uni-directional loading mode. This difference in vertical displacement is about 100%. Residual displacement and rotation in the horizontal direction also decreases 13% and 18%, respectively. Alternating change of loading causes upward moves of the monopile; the pile moves upward from its original level. In general, the change of loading direction causes a significant change in the pile response, although the values of this difference vary in different parameters and for altered loading modes.

The compression behavior of structured soils after virgin yielding is nonlinear that can not be captured by a single line in semi- ogarithmic or fully-logarithmic stress-volumetric strain space. Increasing the stress level from the threshold stress of the virgin yielding initiates the crashing of the soil structure. Further crashing the structure of the soil and decreasing its void ratio increases the volumetric stiffness of the soil. Although this procedure is highly nonlinear, however it is a continuous phenomenon and can be formulated mathematically. Since the structure losing behavior of structured soils occurs between two known states, therefore, could be explained based on the disturbed state concept (DSC). According to the DSC, the behavior of complex phenomena between two reference states could be described based on their behaviors in two reference states using an appropriate state function.In this paper a constitutive model base on hierarchical single surface model (HISS) and the disturbed state concept was proposed to describe the stress-strain and the failure behavior of structured soils. The behavior of the soil at the beginning of the virgin yielding was considered as initial, relatively intact (RI), state and its behavior after fully crashed state was considered as fully adjusted (FA) state. A power form state function was proposed to describe the variation of the bulk modulus of the soil. The variable compression model was implemented in HISS model to capture the volumetric behavior of the structured soil. The proposed model verified based on the data from literature.

Shallow foundations such as strip foundations are widely used in transmitting loads from the superstructure to the supporting soils. In many cases, the ground materials are not uniform and may have thin layers, which are not usually detected in geotechnical site investigations. In this research, the effects of a thin layer on the ultimate bearing capacity of a strip foundation on the sand bed are investigated by small-scale physical models. Due to very limited research that has been carried out on the thin layer effect on the ultimate bearing capacity, it seems that further studies can understand the effect of this layer. The investigations were carried out by varying the material type, thickness, and depth of the thin layer. The results indicate that the weak thin layer decreases both the ultimate bearing capacity and stiffness of the soil-foundation system and the strong thin layer increases both the ultimate bearing capacity and the soil-foundation system stiffness. The amount of this effect depends on the thickness, depth of deposition, and material type of the thin layer. According to the results, the weak layer for the critical depth of 1.2B led to the most reduction in ultimate bearing capacity by 40%, while no effects were observed at the depth of 3.6B. The strong layer is also for the state where this layer is just below the footing, had the highest increase in ultimate bearing capacity by 76%, but at a depth of about 2.4B, it was ineffective.

Last-mile delivery is always one of the key issues in the field of transportation and the environment. Considering the rise in the online shopping rate, last-mile delivery has become one of the most important challenges for logistics service providers. In contrast to traditional delivery methods, new methods have been proposed, including sidewalk autonomous delivery robots (SADRs). These robots are a new generation of emerging technologies for the fast delivery of goods. The present study aims to investigate the factors affecting the adoption of SADRs by online shoppers in Iran. To this end, a model was proposed based on the diffusion of innovation theory (DOI). A total of 287 respondents were surveyed using an online questionnaire, and the partial least squares structural equation modeling (PLS-SEM) was employed for modeling. The results indicated that relative advantage, compatibility, and observability had a positive and complexity had a negative impact on consumers’ intention to use delivery robot. However, no significant relationship was found between trialability and intention. Also, The findings of the present study provide significant theoretical and practical contributions to logistics service providers and marketers.

Peridynamic theory with a new formulation in the equations of motion, replaces the partial differential equations with integral equations. Due to this capability, it is possible to model crack initiation in any direction without the need to consider crack-growth criteria. One of the main problems in peridynamic theory is its high computational efforts due to its dynamic nature. If the critical time step of the numerical integration is greater than the loading time step, it will increase the cost of calculations. In this paper, using wavelet transform, peridynamic problems under irregular and random impact loads are analyzed. The aim of this study is to increase the computational speed for these problems. The method presented in this paper is investigated on two material models, namely Prototype brittle material and micro-plastic material. In this regard, structures with linear and nonlinear behavior have been analyzed considering the effects of discontinuities (such as cracks) and without considering the effects of discontinuities. The selected structures include two beams. Each beam is subjected to two types of irregular impact loading. The beams are analyzed once with the main impact (wave) function and once with the approximate impact (waves) functions obtained using wavelet transform. Based on the results of linear and nonlinear analyses of this study, it can be judged that the presented method reduces the computational cost by 87% in perdynamic models with linear behavior. It also bring a 94% reduction in computational costs in predynamic models with nonlinear behavior.

Due to increasing population and urbanization and lack of suitable land in terms of bearing capacity, construction is performed on soft soils, especially clays with low bearing capacity and excessive conventional settling characteristics. In these types of saturated soils, the construction of structures, such as large buildings, will release pore-water-pressure and therefore create a consolidation. One of the ways to reduce consolidation to the permissible amount specified in the regulations is to use a preload method that will require soil and embankment operations and ultimately necessity the removal of those embankments. Vacuum combined with vertical drainage is an effective way to reduce the number of soil operations and associated costs, which in other words will accelerate the construction of structures and reduce costs. In this study, the effect of several parameters on the amount of consolidation was investigated by simulating soil consolidation via using the COMSOL Multiphysics and GeoStudio software. Based on the results, it was found that increasing vacuum intensity in vacuum chambers, increasing soil porosity ratio, and increasing bedrock depth, each of them accelerated the consolidation process. However, the number of vacuum terminals does not have a significant impact on this process.

Execution of construction projects despite safety regulations, there are always irreparable risks, including physical and financial accidents for human resources and the project, these events adversely affect the balance of cost, time and quality of projects. Therefore, the existence of safety management system can play an effective role in improving the project management process. This research includes identifying and evaluating the most important levels and safety criteria in construction projects, evaluating and developing a safety management maturity model in workshops based on a case study, statistical analysis of the data obtained from the questionnaire and applying the combined multi-criteria decision making method. It is based on combining Analytical Hierarchy Process techniques, Technique for Order of Preference by Similarity to Ideal Solution and Decision Making Trial and Evaluation. Based on the results of the study, twelve important safety criteria were identified and ranked according to the weighting performed and then among the three projects studied, one of them was selected as the project closest to the ideal solution and at the end, the most effective criteria were prioritized in four pillars. The main project, which includes the leadership and management of the project organization, project partners and stakeholders, key personnel and project staff, policies and strategies, was identified.

The advantages of reinforced concrete structures , in comparison with other structures, have made concrete one of the most widely used construction materials. However, concrete has brittle performance under flexural loads. Therefore, the present study investigates the influence of different fibers on the flexural performance of large-scale reinforced concrete beams. In order to achieve this goal, four reinforced concrete beams, with similar reinforcement details, measuring 150 cm long, 20 cm wide, and 30 cm high were made. The beams were reinforced using 0.5% by volume of steel, polypropylene, and korta fibers. Based on ASTM C78, four-point flexural test was performed and the parameters of flexural strength, energy absorption, ductility, and strain of the rebars were studied. The results indicated that reinforced concrete beam containing steel fibers shows better performance, in terms of flexural strength, energy absorption, and capacity of tensile rebars, in comparison with reinforced concrete beams containing polypropylene and korta fibers. In addition, this study showed that korta fiber reinforced beam has better ductility than polypropylene fiber reinforced beam.

Nowadays, the lack of suitable ground in urban areas has raised and solving the problems in loose areas is one of the main concerns of geotechnical engineers. In recent years, the use of polymeric reinforcements such as geocells in geotechnical engineering has increased significantly. In the present study, the effect of geocell on the bearing capacity of the shallow foundation located on sandy soil under inclined load has been investigated using PLAXIS 3D finite element software. Thus, after verifying the numerical model, the effect of parameters such as the presence of shear force as well as the optimal arrangement of the reinforcing layer on the bearing capacity of the foundation has been studied. The results of the analysis are plotted in the form of diagrams and based on that, the optimal dimensions as well as the optimal depth of geocell reinforcement layer are determined. The results of the analysis indicate that, with the addition of the geocell layer, the bearing capacity of the foundation under the inclined load increases 500 % and 210% in shear and vertical bearing capacity, respectively. The extent of this effect depends on the arrangement of the reinforcing layer. Also, the optimal placement depth, width and height of the reinforcing layer to obtain the maximum bearing capacity in the inclined load condition in the present study are equal to 0.025B, 4B and 0.6B, respectively.

Pile foundations are one of the most important foundation systems in geotechnical engineering. The design of pile foundations and the estimation of pile bearing capacity have been improved considerably over the years. However, due to inherent soil uncertainties and disturbances, most theoretical approaches have been mainly based on assumptions and simplifications. Resulting in a wide range of bearing capacity values, different design methods establish the existence of inherent soil variability and model error in bearing capacity prediction. The cone penetration test (CPT) is considered as one of the most useful in situ tests for the characterization of soil. Due to the similarity between the cone and the pile, estimation of pile capacity from CPT data is among its most common applications. This paper proposes a model for predicting the bearing capacity of piles in clayey soils using data that were collected from 62 practical cases of pile loading tests and the corresponding cone penetration tests. The reliability of proposed model was compared with other methods suggested in the literature. In order to evaluate the reliability of the proposed model, Monte Carlo sampling method was used. Results show that the proposed model in this research together with UniCone and Schmertmann methods have the highest accuracy and reliability.