Scientia Iranica
Volume:29 Issue: 3, May & Jun 2022

A depth averaged 2D model is developed to study deposition and scouring in rivers. To calculate the bed load, different empirical formula were implemented. For suspended load, the two-dimensional depth integrated convection-diffusion equation is solved. In this study different widely used empirical relationships were implemented for determining the sediment exchange term with the bed in the suspended load equation. The model was utilized for calculating scouring and deposition in two complicated cases of scouring at a bridge location and scour-hole migration in an erodible channel bed. The results of the model were then compared with experimental measurements as well as 3D numerical model results cited in the literature. Based on these comparisons, the most appropriate combination of empirical formula for sediment exchange coefficient with bed and sediment load to be used for computing scouring and deposition is introduced. The results of numerical simulations show that this model can be used in river engineering for design purposes.

Knowing how a steel structure behaves under fire loading is of vital importance, given a large number of events in recent years have proved the vulnerability of steel structures under this type of hazard. Older concentrically braced frames have been widely used in buildings without observing seismic provisions and details. Although the vulnerability of this type of structural system, here referred to as non-seismic braced frames, has been studied under earthquake loading before, its behaviour under fire loading has not been investigated yet. This paper investigated the behaviour of global and local responses of the mentioned structural system under various uniform fire scenarios. The heating and cooling phases of fire were taken into account for different building stories using the finite element method. The results of analyses showed that the braces buckled at high temperatures due to the large compressive axial forces and expansion of lateral constraints. This phenomenon led to the early loss of lateral resistance of stories, which, in turn, resulted in the failure of columns. Consequently, the underlying floor collapsed under fire. The analysis results contribute to a better understanding of the behaviour of steel braced frames under fire conditions and the corresponding local and global responses.

Regarding the failures due to corrosion in later years, concern about corrosion damage has been intensified and some tests have been carried out in order to study the effect of corrosion on capability of bending and shear capacity of reinforced concrete beams. For as much as these studies is experimental commonly and using from its results subject to spend time and financial costs, this study is set to analyze behavior of corrosion found reinforced beams, using ABAQUS computer software. For this purpose, the sound reinforced concrete beams is modeled, first and simulating accuracy is confirmed by existing experiment results. Then corrosion found beams with different degrees are modeled by ABAQUS software and their results were compared with experimental results and finally, P-∆ charts are produced and provided for software models. In the way of simulations, effects of corrosion site, amount and intensity of corrosion, concrete compressive strength and bar yielding stress on behavior of reinforced concrete beams under corrosion is examined. In this investigation, the effect of different locations and different corrosion degrees is considered regarding changes which take place in cross section of steel, mechanical characteristics concrete and steel and integrity between steel and concrete.

The possible vulnerability of pipelines under propagating waves especially at bend area emphasizes the need of studying in this context. In the presented studies in this field the beam and beam-shell hybrid models were usually used but in this study a continuum model is examined. For this purpose, the bent pipe is modeled by shell elements and suitable boundary conditions are considered to simulate the infinite length of the pipe away from the bend. The soil around the pipe is modeled by 3D elements obeying the Mohr-Coulomb rule of behavior. Also, equivalent boundary conditions are used at the boundaries of the soil domain where it is truncated. By varying the properties of the pipe-soil model, it is investigated under seven different ground motions and the maximum axial strain is calculated at the bend area. Effects of different parameters including incidence angle of seismic waves, bend angle, pipe diameter to wall thickness ratio, and physical properties of soil are investigated. Using the results of analysis and regression, an equation is proposed for estimating the maximum normal strain of buried pipes at the bend area with good accuracy.

Wind-induced interference effects may result in a significant increase or decrease in the wind loads on the buildings constructed in groups due to modifying wind flow around, depending on the shape and relative location of the buildings. Experimental study of wind-induced interference effects on mean and root mean square (RMS) pressure coefficients between two tall buildings are investigated in detail for various interference conditions in this study. The Interference effects on mean and RMS pressure coefficients are presented as interference factors i.e. mean interference factor (MIF) and RMS interference factor (RIF). Results show that the interference effects on local wind pressure are significantly higher on the windward side's faces near the recessed corner. The full blockage condition generates suction on walls facing the gap. The half blockage and no blockage conditions create a more severe interference effect than the full blockage. The maximum value of MIF is 4, 9 and 13 in full, half and no blockage condition, respectively. Interference effects result in reduced wind load on side faces and faces at the leeward side. Suction at side faces reduced approximately by 65% in full blockage condition. RIF’s values less than unity are observed for all interference cases.

Nano-material as one of the stabilizer materials remains the central part of the improvement of soil characteristics. In the current paper, the wall of a real excavation, which is stabilized with the injection of Nano-clay, is studied to perceive how modern procedures affect soil slopes resistance like a real vertical cut. For this purpose, the samples extracted from different boreholes of the site are prepared for the tests with and without different percentages of Nano-clay for assessing the effects of Nano-clay on the soil parameters. To check the results in the laboratory, for stabilization of the excavation wall, 7% weight concentration Nano-clay is injected through nine different boreholes. The distances between the boreholes are adjusted from the results of the permeability test and SEM imaging. Increasing the excavation wall stability is evaluated by load-bearing capacity tests. The results of loading on stabilized and non-stabilized excavation walls show that adding Nano-clay affects the stability of the excavation wall significantly. Additionally, while an economical worth analysis shows that the use of Nano-clay can be rather more costly than soil nailing for stabilization of excavation walls, this method is still preferable due to numerous advantages.

Material quantity take-off is a necessary factor in estimating the cost of construction projects; accordingly, fast and precise estimations would better facilitate the overall construction process. In recent years, several Building Information Modeling (BIM) based applications (e.g., Autodesk Revit, Tekla Structure, Autodesk Navisworks Manage, and Solibri Model Checker) have emerged to assist in performing quantity take-off. Quantity take-off measurement using these applications is accurate when the elements length multiplies with their precise section area. Still, the process encounters errors when using element volumes or Industry Foundation Classes (IFC). In this study, the authors examined the embedded quantity take-off feature of these applications for sample steel and reinforced concrete structure and provided precautions in employing BIM properties. Consequently, an automated approach has been applied to facilitate an accurate quantity take-off by using an Application Program Interface (API) extracting information from a Navisworks model as well as database management systems. A case study is subsequently presented to demonstrate and validate the proposed methodology.

Liquefaction-induced lateral spreading has caused severe damages to pile foundations during past earthquakes. Micropiles can be used as a mitigation strategy against lateral spreading effects on pile foundations. However, the available knowledge regarding the possible efficiency of such a strategy is quite limited. In this paper, the effectiveness of a vertical micropile system as a lateral spreading countermeasure was evaluated using large scale 1g shake table tests on 3×3 pile groups. The results showed that the micropile system was not able to effectively reduce bending moments in piles while it reduced lateral soil pressures exerted on the upslope piles of the group by the upper non-liquefiable layer. The employed micropiles restricted lateral displacement of the upper non-liquefiable layer and partially that of the liquefiable layer, especially at upper depths. Solutions such as increasing the number of micropiles with a tighter pattern, using stiffer micropiles or fixing them in the underlying non-liquefiable layer can enhance their performance.

The effectiveness of fixed-time management systems dramatically decreases in case of fluctuated traffic demands at signalized intersection approaches. This leads to the waste of time in traffic and may cause material, psychological and ecological problems. Especially in recent years, to minimize the negative impacts of these problems, many researchers focus on Intelligent Transportation Systems (ITS). As it is known, one of the Intelligent Transportation Systems applications is called vehicle-actuated (traffic-actuated) management systems. Because the success of these types of applications is directly related to the created control logic, the selection of the most proper control parameters for the created control logic is an important issue. This study aims to create an effective control logic and flow chart for the vehicle-actuated management system. At the end of the analyses, it is seen that the created vehicle-actuated management system can adapt to fluctuations in traffic demands at signalized intersection approaches. Average vehicle delays, fuel consumptions and exhaust emissions can be reduced significantly by the created system. Especially, in case of fluctuations in traffic demands at intersection approaches exist, it is concluded that the performance of the intersection can increase enormously with the created vehicle-actuated management system.

Landslides are recognized as one of the environmental challenges that lead to land degradation, reduce fertility, and cause significant damage to the ecosystem. Therefore, proper identification of landslide-prone areas through modeling will be significantly helpful for land development managers and planners by providing them with appropriate management strategies to prevent land degradation. In this research, landslide susceptibility mapping was carried out for West Azerbaijan province in Iran using Frequency Ratio (FR), Shannon Entropy (SE), Random Forest (RF), and an ensemble of random forest and bagging (RF-BA) methods. Based on field surveys, local interviews, and review of similar studies, 12 factors influencing landslide occurrence, namely altitude, slope angle, slope aspect, distance from fault, distance from river, distance from road, drainage density, road density, rainfall, soil, land use, and lithology, were identified. In the field surveys, 110 landslides in the area were specified; 70% of the data (77 landslides) were randomly selected and utilized for modeling and the remaining 30% (33 landslides) for validation. The results of the ROC curve showed the accuracy of 0.92, 0.91, 0.89, and 0.88 with the RF-BA, RF, FR, and SE models, respectively.

Traffic short-term prediction helps intelligent transportation systems manage future travel demand. The objective of this paper is to predict the traffic state for Karaj to Chaloos, a suburban road in Iran. For this, two approaches, statistical and machine learning are investigated. We evaluate the performance of the multinomial logit model, the support vector machine, and the deep neural network as two machine learning techniques. The principal component analysis is used to reduce the dimension of the data in order to use the MNL model. SVM and DNN predict traffic state using both primary and reduced datasets (ALL and PCA). MNL can be used not only to compare the accuracy of models but also to estimate their explanatory power. SVM employing primarily datasets outperforms other models by 79% accuracy. Next, the prediction accuracy for SVM-PCA, MNL, DNN-PCA, and DNN-ALL are equal to 78%, 73%, 68%, and 67%. SVM-ALL has better performance for predicting light, heavy, and blockage states, while the semi-heavy state is predicted more accurately by MNL. Using the PCA dataset increases the accuracy of DNN but decreases SVM accuracy by 1%. More precision is achieved for the first three months of testing compared to the second three months.

The progressive collapse of the 16-story Plasco steel building induced by fire in Tehran on 19 January 2017 led to the death of dozens of firefighters. This paper presents the results of a comprehensive 3D nonlinear finite element analysis of a floor of the Plasco building under fire condition. The LS-DYNA program is used to investigate the cause of steel beam-to-column connection failure. Results of the nonlinear analysis of detailed numerical model confirms the failure modes of the structural elements such as columns, trusses, joists, beams, welds, and other structural elements investigated during the site visits. Design recommendations are provided based on the results from the fire analysis of the Plasco building.

Precise prediction of the structural capacity of lattice transmission towers under various loads is essential to assess the reliability of the transmission network accurately. In doing so, the uncertainties inherent in the modeling parameters of the towers need to be taken into account. In this paper, a probabilistic framework is developed to analyze the failure of a 230 kV double-circuit tower in full-scale type test accounting for the uncertainties including eccentricity at the connections, joint slippage, and initial imperfection in the members. Three loading patterns are applied to the manufactured full-scale tension tower. A finite element model of the tower with consideration of mentioned uncertainties is built and verified by the test results. The importance vectors derived from reliability analysis clarifiy the effect of each of these parameters on the target points' displacement, as well as the maximum load carrying capacity in towers' members for these load patterns. Besides, the additional moments due to eccentricity at the connections are considered by a proposed regression-based equation. The failure probability of the tested tower is determined for various load factors, and the results are presented in terms of fragility curves. Besides, the effect of eccentricity on the tower’s failure is quantified.

In the last few years, several major earthquakes in Indonesia have prompted an update of the building seismic resistance code. SNI 1726-2019 is the newest Indonesia seismic code. However, the change of PSHA results due to the 2018 Lombok Earthquake has not been accommodated in this code because it adopts the 2017 seismic maps from National Center for Earthquakes Studies. This paper studied spectral acceleration parameters according to the previous seismic codes (SNI 1976-2012) and current seismic code (SNI 1976-2019) and the PSHA results obtained after the Lombok earthquakes in 2018.The spectral accelerations were applied to a building structure located in Mataram City to analyze the seismic building responses. The results indicate that the seismic parameters of the PSHA result obtained after Lombok earthquakes lead to higher seismic demands structures than the codes either SNI 1726- 2012 or SNI 1726- 2019, especially for structures located in medium soil type. The current code needs to be immediate improved for the sake of earthquake mitigation resilience in this area.

In this paper a parametric study is applied to investigate the effect of the number of cells in optimal cost of the non-prismatic reinforced concrete (RC) box girder bridges. The variables are geometry of cross section, tapered length, concrete strength and reinforcement of the box girders and slabs that are obtained with ECBO metaheuristic algorithm. The design is based on AASHTO standard specification. The constraints are the bending and shear strength, geometric limitations and superstructure deflection. The link of CSiBridge and MATLAB software are used for the optimization process. The methodology is carried out for two-cell, three-cell and four-cell box girder bridges. The results show that the total cost of concrete, bars and formwork for two-cell box girder is less than three- and four-cell box girder bridges.