Amirkabir Journal of Civil Engineering
Year:2022 | Volume:54 | Issue:5|Papers Count:20

The damage observed after the earthquakes in Northridge, Kobe and Chi-Chi showed the importance of evaluating the elastic and inelastic behavior of structures against near-fault earthquake. Several studies have been carried out to evaluate the impact of the near-fault earthquake with fling-step motion effects. The obvious feature of such earthquakes is the existence of a pulse with a significant amplitude in the velocity accelerograms. In this article, in order to investigate the effect of pulse-type near-fault earthquakes on the elastic demands of steel moment frames, a 15stories was simulated. After verifying the modeling process, under the influence of 20 near-field and 2 far-field records, were analyzed. The relationship between effective cyclic energy, ECE, and the displacement, velocity and hysteretic curve of SDOF systems in near- and far-fault earthquakes was evaluated. Then, studying the energy of relative and absolute cumulative input energy with kinetic energy in one section and maximum inter-story drift for 4 different levels of nonlinear behaviors (R = 1.0, 2.0, 4.0, 6.0) in the other section, the effect of higher modes was evaluated. Studying the inter-story drift profile for two near-fault earthquakes, with and without accelerated pulses, indicates the formation of the maximum drift, IDRmax, in upper stories for low nonlinear degrees (R=1.0 and R=2.0) in Records with visible pulses that verify the participation of higher modes. However, in accelerated pulse-free records, in addition to intensifying the IDRmax in the upper stories, a large-scale demand is imposed in the lower stories. In other words, in the lower stories, the first mode is mainly involved in these records.

In the concrete repair industry, the adhesion between the repair layer and the concrete plays a decisive role in the successful composite performance of the repair layers. Due to the shrinkage and its effect on adhesion loss, in this paper, the effect of polypropylene fibers on the adhesion between mortar/concrete has been investigated. A new "twist-off" test has been used to perform the experiments. In all experiments, the results of the "twist-off" test were compared with the results of the "pull-off" test. X-ray diffraction patterns and scanning electron microscopy tests were used to further analyze the results. Also, the effect of fibers on shrinkage and mechanical properties of mortars and its relationship to adhesion between mortar and concrete were investigated. In this regard, the tests of "twist-off" and "pull-off" were used in the laboratory and compared with the outputs of computer modeling. Also, by examining the correlation coefficient between the results of in-situ tests and laboratory tests, calibration diagrams were presented to convert the readings obtained from the "twist-off" and "pull-off" tests into the compressive strength of mortars. The results indicate that for the fibrous sample, the peak intensity of Ca (OH)2 or calcium hydroxide is reduced, resulting in the production of more hydrated calcium silicate or C-S-H gel, which results in improved final properties of the mortar and increased adhesion. Also, on average, the shear and tensile bond strength of 90 days obtained from "twist-off" and "pull-off" tests with the addition of fibers increased by 49.5% and 43.1%, respectively.

Congestion is one of the problems that has bothered many countries in recent decades and has imposed huge costs on many countries. For this reason, many researchers are looking for ways to reduce congestion in transportation networks. On the other hand, it is predicted that the emergence of Automated Vehicles and Connected and Automated Vehicles can be effective in reducing congestion on the roads and increasing the capacity of the roads. For this reason, this study investigates the effect of Automated Vehicles and Connected and Automated Vehicles on the capacity of roads. In this study, a freeway network with the Merge section is used and the simulations are implemented using SUMO microscopic simulator software. In this study, to determine the driving behavior, the car following model for longitudinal movements and the lane changing model for lateral movements have been used. The Krauss car-following model and the LC2013 lane-changing model were used to determine driving behavior in this study. The simulation results show that Automated Vehicles can increase road capacity by up to 52% and Connected and Automated Vehicles can increase road capacity by up to 65%, which indicates the potential of these vehicles to increase capacity and reduce congestion. The results also show that these vehicles can have a significant impact on capacity when the presence of these vehicles on the road is significant.

To establish a system for managing road pavement, it is mandatory to prepare information components based on various perspectives of pavement management. One of the most significant information components in these systems is quality assessment regarding road pavement status. Accordingly, in this regard, data containing details of surface pavement failures and defects are of great significance. Apart from causing vehicle depreciation & damage, maintenance costs, and reducing the useful lifespan of the pavement structure, road pavement failures also lead to accidents and reduce road safety. Bearing in mind that the most important surface damages in road pavement are related to cracks with longitudinal, transverse, oblique, alligator, and block types, and as such cracks and defects can be visually and non-destructively assessed and evaluated, imaging-based approaches and techniques can provide details such as the type of defect, its severity, extent, and location and prove to be highly useful. In this paper, the Unmanned Aerial Vehicle (UAV)/drone photogrammetry has been proposed as a complementary approach aimed at providing information on defects caused by cracks in the country's road pavement management system. According to the author, the output of UAV photogrammetric products will significantly improve if the system parameters are adjusted. Consequently, through presenting a procedure to investigate the optimal parameters in the design of a UAV photogrammetric network, further, attempts were made for the implementation of an automated algorithm based on image processing operations & classifier decision tree which is independent of scale and image dimensions. Hence, after removing the road edges and determining the asphalt area, a pixel detection operation was carried out to reveal the cracks. Furthermore, after preparing the ground reality through selected orthophoto mosaic, the evaluation of crack pixel detection was determined using the proposed algorithm with three methods. An accuracy of 96% was determined for the main orthophoto mosaic. For the test orthophotos, which were the result of images taken by Phantom 4 Pro and Mavic Pro at different altitudes, an accuracy of approximately 82% to 91% was determined.

Increasing the population of large cities and the lack of construction area have increased tall buildings. In the present article, the overturning moment and base shear due to the along-wind and earthquake loads have been compared for tall buildings. The buildings are assumed to be located in Tehran city on type 2 soil and the structure is regarded as a vertical cantilever beam. The along-wind and earthquake loads are computed using the gust-loading-factor method and the linear spectral approach, respectively. First, an example of the 120-m high building is presented and evaluated, and then, the effect of the height and aspect ratio parameters are examined in the ranges 80 and 200-m, and 5 to 10, respectively, for the two square and circular cross-sections. For the primary example, the earthquake overturning moment and base shear were dominated respectively by the first and second vibration modes. For the square and circular sections, the ratio of wind-induced overturning moment to the earthquake effect were 1.1 and 0.81, respectively. For the parametric study, the wind and seismic overturning moments were equal to each other at the specific values of the studied parameters, and the wind effects were dominant for the higher values of these parameters. For instance, for the square cross-section, the equal point of the overturning moment and base shear were respectively 110m and 175m. Finally, by increasing the height and aspect ratio, the wind forces were dominant.

Short-term forecasting of streamflow is one of the most important goals in water resources management and flood control. However, one of the problems that researchers always face in this type of prediction is the Lack of an accurate and high-resolution database. The Fluvial Acoustic Tomography (FAT) is an innovative technology that acquires streamflow data. Therefore, by using the data collected from this technology with a suitable forecast model, accurate short-term streamflow forecasting can be achieved. In this research, the effect of FAT data on short-term streamflow forecasting by the Combinatorial GMDH Algorithm (CGA) has been investigated and compared with one obtained from the Rating Curve method. The k-fold cross-validation criterion has been used to prevent over-fitting. The results showed that the FAT data increases the accuracy of short-term forecasting. As an example, the Nash-Sutcliffe coefficient (ENS) for the 1, 6, 12, 24, 48, and 72 hours forecast horizons were 0.98, 0.96, 0.94, 0.88, 0.73, and 0.54, respectively. While these values for the Rating Curve ones were 0.97, 0.84, 0.61, 0.27, 0.12, and 0.11, respectively.

In pressurized water distribution systems, a constant speed pump is often used because of its simplicity. However, constant speed pipes are not easily able to deal with changing demands in water flows. When the demand for the discharge differs from the design discharge, the required demand (discharge and head) could be met by changing the pump speed without making any special changes in the system. Using an electronic drive circuit, the electrical frequency can be changed and the rotation speed of the pump motor can thus be modified. In this study, the application of variable speed pumps in pressurized irrigation systems is investigated. Two pumping station scenarios including a fixed speed pump and a variable speed pump are considered. The results show that using a variable speed pump increases the average pump efficiency by 18.7%. In addition, the variable speed pump system reduces the electrical consumption 57.6 % compared to a fixed speed pump. Therefore, the use of variable speed pumps in pressurized systems is recommended.

In this research, a method of probabilistic analysis of progressive collapse has been introduced based on the concept of fragility curves. In order to develop the fragility curves, the stiffness of two columns is considered as the random variable and the displacement at the top of the removed columns is considered as the Damage Index (DI). Based on these measures, the fragility curves of a 4-story steel structure with Intermediate Moment Frame (IMF) system were developed. Six scenarios of progressive collapse were investigated, including the removal of the corner, perimeter, and middle double-columns. The simulations were performed using OpenSees software. The structural analyses were performed using nonlinear time history approach in a three-dimensional framework. The results showed that the IDA capacity curve of the lower stories is weaker than the upper stories. According to the results, at each considered DI and assumed performance level, damage to the removed double-columns occurs at more stiffness in the upper stories compared to the lower ones. The results showed that considering the floor slab can reduce the probability of fragility of structures. The effect of the floor on the lower stories of the structure is more than on the upper stories. The increasing effect of the floor on the structural fragility corresponding to the first to fourth stories are 13, 9, 6, and 2%, respectively. The probability of exceedance of the performance levels of IO, LS and CP is almost zero until the reduction of the double-column stiffness is 50, 70 and 75%, respectively.

Considering the increase in intersection safety studies, the present study will review these studies using scientometric methods. To this aim, 744 articles related to intersection safety until April 1, 2021, were extracted from the Web of Science (WOS) research engine. In the current study, co-citation, co-author, and co-occurrence of words were presented with descriptive analysis methods using VOS viewer and Bibliometrix software, which provide a descriptive, social, and conceptual framework, respectively. Also, the growth and development of the publications, the most cited articles, the most influential authors, sources, institutions, and countries are analyzed. Results showed that according to the co-citation analysis, the conceptual structure of intersection safety is divided into five main clusters: accident frequency, accident severity, safety performance measures, safety of vulnerable users, estimation of safety level, and intersection accident data analysis studies. Moreover, using conceptual analysis of keywords in intersection safety articles, topics related to cyclist safety, intelligent transportation systems, driver simulation, driver behavior, segment analysis, and road intersections were identified as high density and high centrality in studies. Topics such as empirical Bayes, resource allocation, vehicle communication, automated safety analysis, countermeasures, old drivers, and intersections without traffic lights were identified as basic and transversal themes.

Steel structures are damaged for a variety of reasons including accidental loads, corrosion and reduced strength which need to be repaired and improved. In this investigation, local corrosion was applied to the steel circular columns and the effects of Carbon Fiber Reinforced Polymer (CFRP) for ‎strengthening have been studied. 19 specimens of steel Circular Hollow Section (CHS) column ‎with the same height and damage dimensions under compressive load were analyzed by ABAQUS software which six cases of them were performed experimentally. In laboratory cases, progressive corrosion was used to create damage to the specimens. In order to improve the accuracy of the analysis, a combined ‎method was used to study the post-buckling of the plastic zone. For this purpose, the ‎specimens were first subjected to elastic buckling analysis and then Riks non-linear analysis ‎with global and local imperfections was conducted. The results showed that the corrosion ‎reduces the bearing capacity and rigidity of the steel columns‏ ‏and complete destruction of the corroded area reduced the load bearing capacity by 40% for the column with corrosion in the middle and by 21% for the damage close to the base, which shows the former is more critical. Strengthening of columns retrofitted with carbon fibers restored ultimate load reduction by 33% and had a positive effect on controlling fractures and reducing stresses in the damaged area.

The purpose of this study is to find a method for obtaining all soil dynamic parameters numerically. Moreover, it is intended to predict the dynamic parameters after each impact and to obtain the predicted compaction as well as the desired dynamic parameters after a certain number of impacts. In the study, four hammers with different dimensions are modeled on sandy soil using ABAQUS. Additionally, the activated wave stiffness test is used to extract the dynamic parameters of each hammer for loose sand, and it is shown that which hammer under what conditions yields the highest efficiency. The peak particle velocity is obtained using the finite element technique for each hammer, and the results are used to determine the safe distance after each blow. The results indicate that the unsafe distance of the compactor from the location of impact increases with the weight of the compactor. In the study, a hammer with a mass of 875 kg, falling through a distance of 1 m. A safe horizontal distance of 3.80 m, and a safe vertical distance of 2.30 m are designed to deliver five blows to achieve the maximum stiffness with an improved depth under the foundation from 0.9 to 1.2 m in loose soil and a relative error of 5% is obtained. The improvement depth obtained numerically is in good agreement with the experimental results of centrifuge tests at accelerations of 1, 10, 20, and 30 g, as well as the field results of Parvizi and Merrifield, Allen, Maxwell and Briaud.

Glass powder is one of the increasing solid wastes in the world, and on the other hand, clay usually needs improvement to use in construction projects. In the present study, modification of clay soil strength parameters was studied by geopolymer based on recycled glass powder (RGP). For this purpose, uniaxial strength (UCS) and California load Bearing Ratio (CBR) tests were performed on the modified specimens. Processing time, the weight percentage of used-RGP and activator concentration (M) were the studied variables in the current study. For comparison, experiments were performed on samples modified with 10% Portland cement. The addition of the geopolymer to soil samples showed that 9% of RGP was the optimal amount. Also, despite of the 0day samples in the CBR experiment, other UCS and CBR samples had the optimal amount of activator concentration (NAOH), which indicates the effect of processing conditions on the behavior of the modified soil. The assessed scanning electron imaging (SEM) images showed the effect of the corrective method on soil mass. Analytical comparison of UCS and CBR experiments indicated a mathematical relationship between the results of UCS and CBR-7day experiments associated by a good relative correlation that was predictable due to the same storage conditions of the samples in the first 7 days. Due to the different processing conditions of both tests in the first 7 days, a slight correlation was observed in the results of UCS and CBR-0day tests.

The design of an urban storm sewer network is a costly task. Therefore, the design should be done so that the total cost becomes minimal. This requires modeling the problem in an optimization form. Floods are stochastic. Designing such a system is associated with risk. Thus, a project is optimal when both design costs and potential future risks are incorporated. This means that the selection of rainfall-runoff return period has to be based on risk analysis. SWMM software was used to handle hydraulic network simulation and the Network optimization was performed using a genetic algorithm in which the decision variables were the diameter and slope of the pipes. To calculate the cost of run-off damage, relationships for land uses, infrastructure and traffic were provided. The accuracy of the simulation-optimization model seeking the optimal design of the storm sewer network was approved by a benchmark network evaluation. The developed model was implemented in a region of Tehran city to determine the optimal design return period with a risk analysis approach. The results showed that the 10-year return period with is the optimal return period with an annual damage risk cost of 508.68 billion rials, an annual design cost of 943.78 billion rials and a total cost of 1452.45 billion rials. Therefore, the developed method in which the genetic algorithm and SWMM model are combined in addition to the risk-based design approach is an effective tool for the optimal design of storm sewer networks.

The block shear failure is a common limit state that governs the base metal strength in welded connections. The framework for block shear strength prediction adopted by current design specifications is originally based on research results on bolted joints. Also, in the past few studies conducted on welded connections, the mechanical properties of the steel used are distinct from the commonly applied steel in Iran. In this paper, first, a nonlinear finite element model with ductile damage capability was developed and validated against available test results on welded gusset plate connections. Then, a parametric study was performed on connection length, connection width, welding configuration, and gusset plate thickness, in which, the strain and stress distribution, as well as the block shear rupture path, were investigated. The results showed that the mechanics of block shear failure in welded connections is different from bolted ones for reasons like stress triaxiality development in tensile failure plane due to the existence of additional constraint against necking of base metal fibers adjacent to the weld. Evaluation of existing block shear strength equations revealed that the AISC block shear design equations provide so conservative capacities, on average 36%, for welded connections. Accordingly, a new block shear strength equation was developed, such that, the predicted nominal block shear strengths are, on average about 5% on the conservative side; however, using the LRFD load and resistance factors in the design along with this equation, the safety needed for this limit state is ensured.

Special concentrically braced frames achieve good seismic performance in the earthquake, these frames maintain the stability of the structure with linear behavior in weak to moderate earthquakes and with nonlinear behavior in extreme earthquakes. The design of structures is often based on linear analysis, so it is necessary to study the performance of mega-braced frames with different spans ratio by nonlinear analysis. In this study, the seismic performance of special concentrically mega-braced frames with different spans ratio is investigated. For this purpose, eight configurations of four and eight-story structures with special concentrically braced frame were designed in three dimensions, with conventional X and mega brace configurations with different spans ratio, then a braced frame of them was modeled in OpenSees in two dimensions, taking into account the second-order effects of the removed gravitational section, through a leaning column. Finally, in order to investigate the seismic performance of structures and perform incremental dynamic analysis, 14 far-field earthquakes were selected according to the characteristics of the construction site. Evaluation of analysis results according to NIST GCR 10-917-8 report and Hazus Technical Manual in maximum inter-story drift ratio, comparison of fragility curves and comparison of period and weight of structures indicates that in special concentrically mega braced frames, if the spans are equal, mega braces have a suitable and economic performance, and if the ratio of spans is different, the use of mega braces has a better performance than conventional X braces and is much more economical. For example, in eight-story structures with a span ratio of 1.5, the weight of the structure with the mega-brace is about 20% less than the similar structure with a conventional X brace. Also, the main period of frames with conventional X braces is about 20 to 30% longer than structures with mega braces, which indicates the higher stiffness of mega braces.

Leakage is one of the main challenges in the operation of water distribution networks. In the present study, leakage is detected using Feedforward Artificial Neural Networks (ANNs). For this purpose, two scenarios are considered for training the ANNs. In the first scenario, two simultaneous leakages with equal values, and in the second scenario, two simultaneous unequal leakages are applied to each pair-node of a network. The training data are analyzed by EPANET2.0 hydraulic simulation software linked with the MATLAB programming language. In both scenarios, first, ANNs are trained using flow rates of total pipes number. Then, sensitivity analysis is performed by Hybrid ANNs for the flow rates of different percent of pipes numbers. The results of the proposed Hybrid ANNs indicate that in the first scenario, by having the flow rates of 10% of the total pipes, the locations of two simultaneous leakages are successfully determined. However, for the second scenario, while the difference between the two leakages is less than 80% of the maximum leakage (up to ratio value of 10 and 90 % leakages), by having 10% of the total pipes flow rates, the locations of the two leakages are still successfully determined. However, for larger differences, only the location of the bigger leak could be detected. Despite the complexities of the second scenario, the proposed ANNs could successfully detect the location of the bigger leakage.

Researchers have recently considered ways to increase the strength of and damping of the structures against earthquake loads so as to reduce maintenance and maintenance costs while enhancing safety. These solutions include the combination of steel frames with viscous dampers as the most vital part. Additionally, one of the most powerful tools in passive control is viscous dampers, which absorb earthquake energy and reduce the structure's response to earthquakes. Therefore, we have undertaken this study to investigate the response of standard SAC frames, built-in three, nine, and twenty floors, by applying this structural system to seismic loadings. The issue was first investigated using the Abaqus software package's numerical model of the viscous damper. Then, the effect of applying acceleration of faults of far and near-field Imperial Vali, Lomaprita, and Northridge earthquakes on the behavior of this structural system is evaluated separately. The results include floor drift, load-carrying capacity (as maximum base shear), and energy absorption of the structure (in two External working modes and strain energy) are discussed. Applied viscous dampers resulted in an average 200% decrease in drift, a 30% increase in load-carrying capacity, and a 35% increase in energy absorption in SAC standard steel structures after the application of these dampers.

Although infill panels are considered as non-structural elements in the analysis and design process of building frames, these members may significantly affect the seismic performance of the frames. Nowadays, the tendency to design and construct irregular buildings has increased. Behavior factor (BF) plays an important role in the seismic design of buildings. Seismic codes usually present the same BF for the regular and irregular lateral load-carrying systems. In this investigation, the influence of masonry infill walls on the behavior factor of the vertically irregular moment resisting reinforced concrete frames was evaluated. To do so, 3-, 6-, 9- and 12-story moment resisting reinforced concrete frames with various types of vertical irregularities were considered. These frames were assessed with/without considering the influence of infill walls. The capacity curves of the frames were derived using incremental dynamic analysis using 14 acceleration ground motions and then the BFs were achieved. Outcomes demonstrated that infilled frames present higher BFs and more efficient performance in lateral load-carrying rather than bare frames. For the regular frames, considering infill walls effects increased the behavior factor between 18 to 25%. For the irregular frames, due to considering the influence of infill walls, the highest and lowest enhancements of BFs were 3 to 25% (for 3-story frames), 13 to 25% (for 6-story frames), 18 to 25% (for 9-story frames) and 14 to 22% (for 12-story frames). Furthermore, comparing the BFs of regular and irregular frames indicated that vertical irregularity made 14 to 32% reduction in the BF of considered moment resisting reinforced concrete frames. Eventually, two approximate relations were developed to acquire the behavior factors of bare- and infilled- vertically irregular moment resisting reinforced concrete frames. Comparing the behavior factors achieved using the developed approximate relations and an analytical method for three new irregular frames showed that the error of the proposed relations was lower than 7%.

Many attempts have been made to model the mechanical behavior of soil materials. The assumption that predicting soil plastic behavior in some engineering problems doesn’t present a significant relation with construction time has led to the neglect of the time effect in many constitutive models in geotechnical engineering. However, damage due to settlement or instability of excavations and many other such problems are caused by the time-dependent plasticity behavior of soil. Also, in some phenomena such as explosions, earthquakes, or consolidation, the issue of time is inherently raised. Therefore, it is important to install a time-dependent constitutive model in finite element codes that can properly predict the time-dependent behavior of structures in geotechnical engineering. In this study, an elastoplastic-viscoplastic constitutive model via UMAT subroutine was implemented in the ABAQUS finite element code. By considering the nonlinear elastoplastic-viscoplastic behavior with mixed (kinematic and isotropic) hardening mechanisms, this model removes most of the limitations of the constitutive models already installed in the ABAQUS code. The results of validation under laboratory paths such as creep, relaxation and rate effect indicate the high capacity and capability of the model in predicting the time-dependent behavior of soil.

The monitoring of fluvial suspended sediment transport plays an important role in the assessment of morphological processes, river behavior, identifying erosion and sediment loss zones and better watershed management. In order to eliminate information deficiencies and achieve a suitable database for suspended load, it is necessary to equip hydrometric stations with instruments for continuous and indirect monitoring of suspended sediment. The aim of this research is to construct and validate an optical sensor with a multi-beam ratio technology and artificial intelligence-based modeling (MLP & SVR) for suspended sediment measuring. After the implementation of the new technology, the performance of the device was evaluated in two stages, including calibration and validation. To attain this, various experimental tests were carried out in the hydraulic laboratory of the Water Research Institute of the Ministry of Energy. Reference turbidity meter and total suspended solids (TSS) were used to test the performance of the OBS technology. In the calibration stage, 70% of TSS data were used and the remaining 30% of data were used to validate optical technology. The plotted calibration curves show a very good correlation between the optical voltage recorded by the sensors and the suspended sediment concentration. Also, SVR & MLP models were employed to improve the results of suspended load prediction. The performance of the optical device and also optical device with intelligence models were evaluated through four statistical indices, namely, Mean Absolute Percentage Error (MAPE), Root mean square Error (RMSE), Nash–Sutcliffe coefficient (NSE), correlation coefficient (R) and coefficient of determination (R2). The results of this stage showed that the intelligence modeling could result in improvements in suspended load reported by optical technology. The best improvements were obtained by MLP-optical technology. The results showed that values ​​of validation indicators for MLP model are equal to 0.023, 7.608, 0.99, 0.99 and 0.99, respectively, which indicates the proper performance of the technology.