نشریه مهندسی عمران
سال پنجاه و دوم شماره 1 (فروردین 1399)

Estimating seismic demands of structures has acquired renewed importance as a result of recent interests in performance-based seismic design. Consequently, in recent years, different equivalent nonlinear static analysis procedures have been developed to estimate structural seismic demands. However, just a few studies have been conducted to examine the accuracy and adequacy of these developed methods. Thus, it is necessary to conduct thorough investigations of these methods’ limitations, possible shortcomings, and their performance. In this paper, the accuracy of CSM-DAP method in comparison with FEMA356 method has been evaluated for estimating seismic demands of low-rise steel moment resisting frames with geometric irregularity in elevation. The CSM-DAP method is an equivalent displacement-based adaptive nonlinear static analysis method combined with the FEMA440 capacity spectrum method. The CSM-DAP and FEMA356 methods are used to analyze 44 five-story moment resisting frames subjected to 14 far-field earthquake ground motions and their results are compared with the results of nonlinear dynamic analyses. The selected sample includes wide range of geometric irregularities in elevation for low-rise structures. The estimated demand responses are namely roof displacement, inter-story drift ratio, and base shear. This study shows that considering the CSM-DAP computational effort, this method does not present significant advantages with respect to FEMA356 method at least for low-rise structures with geometric irregularity in elevation.

Gates in dams and irrigation canals are used for control of discharge or water surface regulation. To determine the discharge under a gate, discharge coefficient (Cd) should be determined. This study investigates the effect of sill shape under the vertical sluice gate on Cd. Both of sill shape and sill height are investigated. Investigated shapes comprise polyhedral and non-polyhedral sills. Results showed that circular sill is the most effective and triangular sill is also proper shape of polyhedral in increasing Cd. Circular sill increases Cd at least 23% up to maximum of 31%. In addition of shape, sill height is also important in determination of Cd. Using dimensionless parameters and regression analysis, an equation for prediction of Cd in free flow condition with and without sill is presented. The developed equation coincides with the published previous researches.Suggestions is for determination of Cd in submerged gate condition, and using FLOW3D or FLUENT software for more information about velocity and pressure distribution. Future experiments for producing more data set, can improve the accuracy of the developed equations.

It was believed that adding fines grains to a base coarse-grained soil would result in shear strength increase due to filling up the voids among coarse content and reducing global void ratio. However, this belief was against following experiments. New variables referred to as the equivalent intergranular and interfine void ratios, have been proposed to resolve this problem. In this paper, by using Discrete Element Method, several soil samples were created by mixing two coarse- and fined-grained soils. Simulations were performed in two-dimension in which, the particles are circular. After the soil sample preparation, it was consolidated under isotropic confining pressure followed by biaxial compression loading. The loading condition was continued until the samples reached the critical state. Based on the simulated results, the required parameters to estimate the portion of coarse- and fine-grained parts in the global soil behavior, were obtained. Comparison of the results of the this study with those of experiments shows good agreements. The threshold fines content, which indicates the government of either of coarse or fine-graind parts was also derived. The two-dimensioanl simulations indicate that for each sample with a specified fine content, the corresponding critical state line can be obtained. If the definitions of equivalent intergranular and interfine void ratios are used, unique critical state lines are reachable.

In this study a new hybrid energy dissipation device is developed by combining two friction dampers (auxiliary and main fuse) in series to be used for seismic control of two different earthquake intensities. Compared with the conventional friction dampers, the new hybrid damper has an advantage in that only auxiliary fuse (with low sliding force) is activated for moderate earthquakes and both fuses work simultaneously for strong earthquakes. Cyclic loading tests of the combined hybrid dampers are carried out to evaluate their seismic energy dissipation capability. The obtained experimental force- displacement indicates proper details of the new damper to create two performance level. Finite element analyses of the test specimens are also carried out for comparison, which had good agreement with the test results. Force displacement characteristics, Energy dissipation and equivalent viscous damping are also derived and good agreement has been found with code requirement for displacement dependent dampers. Also, it is demonstrated, engaging the main fuse with non-loaded pretention bolts, strength losses of hybrid damper in subsequent cycles are limited compared to the common friction dampers which can be called “resurrection-type” behavior of the main fuse in the main shocks.

Nowadays, strengthening of column by using fiber reinforced polymer (FRP) composites is considered as the strengthening technique of these loading elements in a structure. In this technique, increasing the surrounding pressure on radial levels of the concrete column increases the compressive and tensile strengths of the concrete element, reduces slenderness, and increases the buckle load and ductility of this element. Moreover using glass-fiber reinforced plastic pipes (GRP) as the concrete column casing in addition to the independence of the need for framing leads to confinement effect on the concrete, high ductility and energy absorption, reduction in shrinkage and creep of concrete, lack of contact of the concrete with the corrosive factors, high construction speed, and proper loading capacity. In this research, compressive capacity test was conducted on 6 cylinder reinforced concrete columns (RCC) of 150 mm and diameter 600 mm height, with and without GRP casing, and the effect of FRP wrapping was studied on them as the confining factor. The research results showed that using FRP wrapping and GRP casing improves the compressive capacity and ductility of RCC. Adding one or two FRP wrapping layers increased the compressive capacity by 18.5% and 26.5% on the average, while using GRP casing increases the compressive capacity up to 300% on the average and this shows that although FRP wrapping and GRP casing are both confined, GRP casing is more effective in increasing the compressive capacity due to its higher confinement and similar ductility with RCC.

Contaminant transport in groundwater has been growing concern during last decades, since pollution can leach through the soil and reach the groundwater. The present research has been investigated solute migration through saturated porous media by the physical modeling laboratory, result in practical graph, determining the general pattern of contaminant plume in both homogeneous and heterogeneous layers. Three types of sand are selected for experimental model, which include both coarse and fine aggregate. The results indicate that in the coarse aggregate medium, the movement of pollution is 10 times faster than the fine aggregate containing 10% silt and 1.5 times faster than the fine aggregate sand without silt. The ratio of the length to width of the contaminated area in the coarse-grained soil in comparison to the fine-grained soil containing silt, and without silt increases 110 % and 40% respectively. In the heterogeneous fine- coarse model, Darcy velocity magnitude in coarse aggregate medium is much greater than fine aggregate result in more advection. In this case, because of the significant difference in velocity values in the two layers, the pollutant is rapidly transferred to the downstream after reaching the border of the two areas. Also, in the frontier of the coarse- fine medium, pollution is dispersed more for the fine aggregate medium acts as though it were the wall.

Stabilization/Solidification (S/S) is an attractive technology which helps to reduce the toxicity and facilitate the disposal of sediments containing heavy metals, industrial wastes, and contaminated soils. The efficiency of the S/S technology can be enhanced by the use of clay nanoparticles. The S/S process incorporating Montmorillonite nanoparticles can be employed to prevent the dissemination of heavy metals effectively. Although many studies have addressed the stabilization of contaminant by the use of cement, few have discussed the microstructural interactions between montmorillonite nanoparticles, heavy-metal contaminants, and cement in different time intervals. In addition, there are not enough researches on the impact of montmorillonite nanoparticles in the efficiency of solidification process. Therefore, this study aims to investigate the interactions between montmorillonite nanoparticles, heavy metals, and cement in different time intervals from microstructural point of view and to determine the impact of clay nanoparticles on toxicity leaching from solidified/stabilized contaminants. To achieve the above mentioned objectives, different concentrations of heavy metal (zinc) and different percentages of Portland cement were added to nano-montmorillonite. The contaminant retention mechanism was then experimentally analyzed through monitoring the changes in pH, evaluating microstructural changes (using X-Ray Diffraction), and Toxicity Characteristic Leaching Procedure (TCLP) measurement. The results indicate the role of clay nanoparticles in retaining the heavy-metal contaminant and the lack of linear relation between the quantity of cement content of the specimen and the contaminant retention efficiency.

The bond strength between fiber reinforced polymer (FRP) laminates and concrete is the main factor affecting the behavior of concrete members strengthened by externally bonded reinforcement (EBR) method. The bond strength depends on several factors, such as surface preparation, concrete strength, FRP stiffness and thickness and effective bond length. According to previous studies, using a bond length longer than the effective bond length, will not increase the connection load carrying capacity. Most existing theoretical models estimate bond strength based on the effective bond length. So, in order to achieve a satisfactory connection, it is important to determine the accurate value for the effective bond length of the lap joint. In this study, in order to evaluate and compare the effective bond length of fiber implantation method and the conventional EBR method, 12 concrete specimens were prepared and tested. Then, the effective bond length and the bond strength of the specimens were obtained by using single-shear pull test and using particle image velocimetry (PIV) method and compared with the existing specifications such as ACI and fib. The results showed that, using fiber implantation method instead of the conventional EBR method, would reduce the effective bond length by 20% and increase the bond strength between FRP and concrete substrate by 34%.

Nowadays, civil engineers are looking for novel approaches to develop structural performance and the speed of building construction simultaneously. One of these approaches is using of rectangular spiral stirrups instead of traditional stirrups in manufacturing of RC beams. Based on recent experimental studies, these beams have shown some advantages in performance when compared with beams reinforced by traditional stirrups and in some cases, the results were much better. In this study, at the first stage, two types of RC beams with rectangular spiral stirrup and traditional stirrups were simulated in the ABAQUS software and verified under monotonic loading. The shear capacity was measured and based on the experimental force-displacement curves, validation was performed. Then, at the second phase of this research, another RC beam with traditional stirrups was simulated and was verified against push-over curves and force-displacement of monotonic loading and failure mode obtained from an experimental study. A cyclic loading was applied to the beams with continuous rectangular spiral and traditional stirrups. Then, the performance of those simulations was compared by envelop strength curves. But in the cyclic loading phase, in most cases, the performance of beams with these two transverse reinforcement methods is equivalent and in some cases, the traditional one has shown even better results.

Flow with intermediate relative roughness (the ratio of roughness height to water depth higher than 1/80 and lower than 1/40) is common in most of mountainous streams. Despite this fact and numerous studies on flow with intermediate relative roughness, it is still unclear that how profile of the streamwise velocity varies along water depth. In this study, instantaneous velocity of flow in an open-channel with rough bed has been measured using Particle Image Velocimetry (PIV). In order to analyze profile of streamwise velocity, double averaging method (spatial averaging of time-averaged values in a thin slab parallel to the channel bed) is used. It was observed that near the rough bed, vectors of instantaneous velocity showed strong spatial variations that makes extraction of unique behavior for velocity profile impossible without double averaging. Results also showed that values of double averaged velocity is not sensitive to priority in averaging (i.e. time and then spatial averaging or spatial and then time averaging); thus double averaging regardless of priority can be used. To investigate double averaged velocity profile, three approaches including logarithmic profile with variable parameter, linear profile and mixing layer profile were employed. Results showed that all three profiles could be fitted properly to our experimental data. However, logarithmic profile with variable Von-Karman constant and integration constant which is supported by strong scientific background is the most suitable profile and is therefore recommended.

Numerical modeling is a strong tool for soil deformation in deep excavations. There are some kind of method such as finite element, finite difference and etc. Finite element method help to select the appropriate constitutive soil model with high accuracy. The controversy between simplicity and accuracy is an important issue always has been intrested in by the researchers. By using physical modeling the accuracy of each constitutive soil modeling could be asset. In this paper, four models of geotechnical centrifuges have been uesd to investigate the effect of the overburden distance from the edge of the excavation and the results of various constitutive soil models in the soil nailing wall. The results showed that the overburden distance from the edge of the wall is so effective on the value and pattern of wall deformation. By increasing the overburden distance from the edge of the excavation, the greatest amount of horizontal deformation of the wall leads to the bottom of the excavation. However, the basis of numerical solution, without the overburden distance from the edge of the excavations, this deformation always occurs in the top of the excavation. Also, based on the comparison of the results of centrifuge models and the results obtained from different behavioral models, in order to predict the vertical deformation of the top of the excavation, the result of hardening soil small strain model (HSS) is nearer to real than other investigated constitutive soil model.

Looking for of increased pollution and environmental concerns, as well as rising fuel and energy prices, the Warm Mix Asphalt (WMA) technology has been introduced as an environmentally friendly technology, and Nowday the direction of the pavement industry has become more widely used. WMA asphalt technology, despite the reduction in production and compaction temperature and density and other advantages comparing to Hot Mix Asphalt (HMA), has a weakness in moisture damage, which is one of the main concerns of this technology, and the use of Anti-stripping additive is one of the most widely used methods to reduce this damage. Asphalt mixtures of WMA are composed of different materials such as bitumen, aggregate and WMA additives, and the study of the effect of each of these materials on the reduction of moisture sensitivity less attention has been investigated. Therefore, in this study in order to aware of road engineers to improve this problem with this type of asphalt mixture will be discussed. Studies have shown that the type of aggregate (characteristics of acidity or alkalinity), the type of WMA additive, and mixing and compaction temperature are among the most important factors affecting the WMA asphalt mixture resistance, which indirectly affects the pavement.

Tomography is a technique in order to display a representation of a cross-section through solid objects using x-rays, gamma rays or ultrasound waves. The purpose of this paper is to provide a non-invasive technique for creating a CT image and detecting air holes in a concrete structure using gamma-ray tomography technique.In this work, the concrete column with a cross-section of 40 cm × 40 cm and length of 3 meters has been considered as the desired structure. There are two air holes in the concrete column. Also, the isotope Cs-137 was regarded as a radioactive source. One NaI(Tl) scintillation detector was used to measure the rate of gamma-rays emitted by the radioactive source. This structure was simulated using MCNPX code. Then, the image of cross-section was reconstructed using the obtained data of MCNPX, MATLAB software, and the ART algorithm. In the ART method, it is assumed that the cross-section contains unknown pixels. A row matrix (1 × n) and a column matrix (n × 1), which are the sum of the row pixels and column pixels of the image are defined as input for ART algorithm. The output is a matrix (n × n) that matrix arrays (n × n) are cross-section image pixels. Therefore, using these arrays, the cross-sectional image is reconstructed. The reconstructed image showed the correct location of the air holes. According to the obtained results, the proposed gamma radiation tomography technique is an appropriate and non-invasive technique in order to cross-sectional analysis of concrete structures.

Unlike previous studies in Non-Newtonian fluids that use complex two-dimensional models to calculate the velocity gradient in this research one-dimensional models have been used to calculate non-residual losses that can be implemented faster And have higher execution speeds. The main objective of this research is to investigate the phenomenon of water hammer in Non-Newtonian fluids of power type (Power Law) using Brunon and Zeilke models. In order to calculate the shear stress in relation to the momentum of the Zeilke and Brunon model, and to solve the equations, the line characteristics of the nonlinear fluid solution have been used. The Brunon model is based on the assumption that the shear stress of the wall changes due to the acceleration of the acceleration, proportional to the acceleration of the fluid. Zilck's method for calculating unsteady friction coefficient presents a model based on the analytic integral of convolution. The velocity gradient in steady state is used to obtain the velocity gradient in the Zeilke model. Finally, numerical results are compared with the results of other papers to ensure the accuracy of the solution algorithm. The results of non-Newtonian fluid modeling show significant changes in pressure values. The proposed formulas, similar to the two-dimensional models, can simulate these changes. As expected in the same continuous flow conditions, the maximum pressure decreases with decreasing viscosity of the fluid. In other words, by decreasing the viscosity of the fluid, the amount of drop across the pipe path will be reduced.

Due to the composition, the production of self-consolidating concrete (SCC) requires more mixing energy to uniform and homogenize the concrete components. This limits the rate of concrete production in comparison with the convectional concrete and therefore is an important financial factor. So mixing energy (mixing time and power) is one of the main factors in concrete production and before large production, the appropriate mixing time and speed should be determined for each mixture. In this study, according to objectives and considering that mixing time and speed are two main factors in content of mixing energy and according to guidelines and regulations, two SCC mix designs (powder type and VMA type) were mixed in three mixing times (3, 8 and 11 minutes) and each of them in two mixing speeds (20 and 40 RPM) and their effect on rheological properties was evaluated. The results showed that in each series of mixtures by increasing the mixing time up to a certain level that is called stabilization time (the shortest mixing time) and in this study is 8 minutes, the workability of concrete increases and after that by mixing up to 11 minutes it decreases 6 percent. Static yield stress in the 8 minutes mixing has minimum amount too and by mixing up to 11 minutes it increases 42 percent. This increment reaches to 62 percent for Dynamic yield stress, so the rheology tests also confirm these results.

Today, it is possible to detect damage in the early stages with the aid of structural health monitoring (SHM) techniques to avoid financial losses and loss of lives. However, large expenses of SHM systems has caused low popularity of such systems in our country. The aim of this study is to provide a low-cost damage detection technique for bridges based on signal processing and machine learning. To reduce expenses, the number of sensors to monitor vibration of the structure is decreased to only one sensor. Since reduction of number of sensors can lead to drop in damage detection accuracy, most up to date signal processing methods are used. In the first step of the paper, several time-frequency signal processing techniques are compared and EWT is selected as the best signal processing method. In the next step, after decomposition of signals by time-frequency techniques, a new damage index is introduced base on cross wavelet transform (CWT) and then calculated damaged indices are classified using support vector machine (SVM) to be able to distinguish healthy and damage states. Results show that the proposed method can detect damage with high accuracy.

Cadmium is a very toxic metal that have adverse effects on human health and aquatic environments even at low concentrations. It can cause some diseases in human lungs and kidney. Therefore, efforts should be made to eliminate this metal from aquatic ecosystems. This study was carried out in order to remove cadmium ions from aqueous solutions by thiolated graphene oxide in batch system. In this study, effect of experimental parameters such as pH, adsorbent dosage and initial cadmium concentration were investigated. To characterize the adsorbent properties, SEM and FT-IR analyses were utilized. The results showed that, with increasing initial concentration of cadmium, the amount of adsorption decreased and increasing the dose of adsorbent and pH increased the percentage of cadmium removal. Comparison of isotherm and kinetic adsorption models showed that Langmuir and Pseudo-second order models, with R2 values of 0.97 and 0.99 respectively, had a better fitness and describe the adsorption data better than other models. Thus, as a general conclusion it can be said that the synthesized adsorbent had high capability to remove cadmium from aqueous solutions.

In this paper, the effect of various modeling parameters such as beam – column connections, soil and shallow foundation types are studied to assess the seismic response of steel moment frames. For this purpose, five-story special steel moment frames with two different soil types (II and IV) have been considered. The footing and strip shallow foundations have been designed for these buildings, with safety factor of three. Prequalified bolted flang plate connections are used in these buildings. The finite element models are developed using OpenSees software considering soil – foundation – structure interaction. The seismic performance of SMFs are evaluated using nonlinear time history analyses, through seven far–fault ground motions. Nonlinear behavior of soil is modeled by nonlinear Winkler springs. The numerical results show that in the models that considered beam-column connections, SFSI and soil type IV, the maximum inter-story drift is more, compare to models without connections and with fixed based conditions. The maximum base shear of structures in the mentioned models is reduced. In models, that structures rested on soil type II, maximum values of these two parameters are diminished. The effect of foundation type in models resting on the soil type IV is more than models with soil type II. Generally, connections, foundation type and soil-foundation-structure interactions have a great influence on the nonlinear responses of steel moment frames.