experimental

In general, mode I loading (pure tension) on the road surface occurs when the crack is placed between the front and rear wheels of the pavement. The results of this research indicate that the amount of fracture toughness depends on factors such as the test temperature, the thickness of the piece, the percentage of free space, and also the parameters of the geometry of the piece. Most of the researches conducted on one or two loading modes are based on the environmental characteristics of asphalt mixtures, and the geometrical conditions of asphalt mixture samples, including their cut thickness and the effect of different percentages of filler on the samples, have not been paid attention to. Therefore, in this research, the issue of how the geometrical characteristics of the part can affect the failure toughness of the bending half-disk samples under Mode I loading has been investigated. According to the obtained results, it was observed that as the cutting thickness of the piece increases, more force is required to break the sample.

Dimensional analysis methods have shortcomings in predicting the behavior of full-scale samples using small-scale results due to non-linearity of behavior, loading, or changes in material type, the inability to simultaneously predict two parameters with the same unit, and a limited number of independent degrees of freedom are independent. Recently, a new theory called Finite Similitude has been proposed to solve these problems, and in this article, using this theory to analyze the prediction of the dynamic behavior of concrete beams using the results of concrete beams on a smaller scale and beams with similar behavior to concrete (plaster-stone) under dynamic impact loading has been discussed. The predicted results such as force, displacement, energy, and time show that the dimensional analysis of the results with different materials is not accurate enough and in some cases, the difference in the results is more than 50%. However, with the finite similitude method, the behavior of full-scale concrete beams can be predicted by using small-scale plaster-stone samples with less cost, reduced construction time, and high accuracy, so that the error percentage in dynamic analysis in all samples is almost less than 10% was achieved.

Shear failure of structural elements such as beams and columns is considered as a brittle failure. Accordingly, the design standards provide conservative equations for determining shear strength to ensure to delay of this abrupt failure. In this regard, the AISC 360 Standard provides equations to determine the shear strength of encased composite members considering the steel contribution, the reinforced concrete contribution, and the strength of the steel section in combination with the transverse reinforcement. The AISC 360 conservatively ignores the combination of the shear strength of steel section and reinforced concrete to determine the shear strength of encased composite members due to insufficient research.
This study investigates the shear behavior of encased composite (EC) columns experimentally and numerically. Short EC columns in which their behavior is governed by shear are tested considering several design variables, including the concrete compressive strength, the steel ratio, the shape of the steel core, the ratio of longitudinal reinforcement, the transverse reinforcement spacing, and the level of the composite action. Failure mode, the crack pattern, the load-displacement response, the nominal shear strength of EC columns, the yield condition of steel core, and the effects of key variables on the shear strength of EC columns are presented and discussed. The results of this study show that the exclusion of steel section or reinforced concrete contribution leads to a significant underestimation of the shear strength of encased composite members. Out of the considered design variables, the transverse reinforcement ratio, concrete compressive strength, and steel core ratio are the most influential variables affecting the shear behavior of EC columns.

The stone columns, as a method of soil improvement, significantly reduce soil settlement due to incoming loads and increase soil load-bearing capacity. Adding geotextile as a stone column encasement has a considerable impact on this relationship. In this study, the amount of loose sandy soil settlement was investigated by numerical modelling of stone columns with the Plaxis 3D Foundation software, and the results were validated by using laboratory modelling,. For this purpose, a single stone column was modelled in two modes of rainfall density and compacted states and continuously the group mode in the soil was investigated. Also, the effect of adding geotextile encasement to the inner part of stone column investigated as a central core. So, a 6 centimetre diameter of central core that surrounded with geotextile encasement has considered inside of a 10 centimetre diameter of stone column in both rainfall density and compacted state. The results of experimental and numerical modelling were well-matched with each other. Also, it was clear that the increasing of stone column number and compaction can enhance soil bearing capacity, considerably. The adding of central core has had considerable effect on soil bearing capacity, too. This is due to the increase of all-round stress in the interior of the stone columns. The results showed that the stone column with a diameter of 10 cm increased the bearing capacity compared to unreinforced soil by 36%, while in the stone column with central core in rainfall density and compacted states, this amount is 43% and 54%, respectively. Also by evaluation of appearance deformations in stone columns after loading showed that increasing the density and adding geotextile encasement to the central core has a considerable effect on the created deformations and prevention of local ruptures and the process of deformation becomes more favorable.

One way to reduce seismic force is to use knee bracing systems. In this method, the diagonal limbs of the brace are connected to the knee joint. The duty of the brace is to create stiffness and the duty of knee member is to create ductility like a yielding damper. In this method, some novel results are achieved by combining Y type bracing with the knee members. In this regard, three samples of the proposed frame were tested in the laboratory of structure based on the ATC24 loading protocol. The results show that this seismic system has a good performance in energy absorption and stability. At lower frame displacements, the knee element begins the absorb energy process faster. The use of a knee bracing system can be a good alternative to the brace system due to its ease of replacement. The behavior of the hysteresis (force-displacement) curves obtained from the experimental tests show good results in force balancing. Moreover, due to relatively lower initial stiffness and strength, the proposed frame will perform well in low-intensity earthquakes. It was observed that the failure mechanism of the structure has an acceptable ductility in the plastic part of the system. In addition, it was shown that by moving the middle node towards the corner of the frame and increasing the eccentricity of this point, the stiffness of the frame decreases and as a result, the natural vibration period and system displacement increases under constant load.

The pipeline in service may be subjected to complicated loads (including lateral, axial, vertical loads and hydrostatic pressure in addition to internal pressure) when crossing complex geohazard regions. In this study, two kind of loads that cloud be more fundamental are numerically investigated using finite element method. The loads imposed on pipelines depend on the pipe content and the environment that the pipeline is passing through. Axial compression can arise within pipelines from thermal loads arising from hot hydrocarbon passage from offshore oil wells to an onshore station or can arise from anchor forces acting on pipelines and External pressure can arise within pipelines from hydrostatic pressure, sudden valve closures, and pump failures. It is very important to select suitable geometric imperfection form to exact investigation behavior of pipelines and mechanism of failures. In order to verification response of numerical analyses, one of the experimental results is compared with numerical result and concluded that there is a good agreement between results. Meanwhile, the effect of the eccentric axial compression, pipe diameter to wall thickness ratio (D/t) on the buckling external pressure are studied. The interaction between the axial load and external pressure was graphically demonstrated and compared for different geometrical ratios through numerical analysis. During analysis, the eccentric axial compression load in the pipe was primarily induced and maintained constant less than its capacity. Subsequently, the uniform peripheral pressure was gradually increased until failure, and, besides, the response of some specimens was separately investigated under pure external pressure and axial compression load. It was found that the D/t ratio is the decisive parameter to specify the buckling behavior of steel pipelines and type of created failure mode subjected to axial compression. Some significant conclusions were drawn based on extensive parametric studies. The buckling external pressure reduces with the increase of pre-axial compression and diameter to thickness ratio.

In this paper, a new kind of ring damper composed of three rings is introduced and investigated numerically and experimentally. The proposed damper combined three steel ring damper in order to dissipate energy of two different level of predefined excitation such as moderate and severe one. first fuse (outer pipe) and second fuse (inner pipes) can absorb energy in moderate and severe earthquakes respectively. To evaluate the introduced damper, numerical finite element models are developed to clarify the effect of thickness and diameter variation of main fuse. Results of force- displacement curves obtained from cyclic loading confirmed the two level performance of models. Stiffness and fore increase have been observed after gap displacement and improved the energy dissipation capacity after the predefined displacement gap. Also, damping ratio are calculated for all samples and results showed that equivalent damping ratio have been improved when main fuse was engaged. Two experimental samples have been constructed based on numerical models details and examined under cyclic loading with constant displacement amplitudes. Defined force-displacement results of experiments showed that samples could tolerate more than 20 cycles of 10 times of yield displacement amplitude. Good agreement between numerical model and experimental samples results have been achieved.

Weirs are widely used in many different shapes to control a water level, facilitate flow diversion, and to regulate the flow of water. Given that the overflow zone is often laterally restricted, the overflow depths can become excessive. As a result, non-linear weirs e.g., Labyrinth with different forms have been developed to increase weir length and discharge capacity within a fixed overflow width. Accurate estimation of the maximum possible depth of scour at weirs is important in decision-making for the safe depth of burial of footings. The design of labyrinth weirs foundations based on equilibrium clear water scour depths may yield considerably greater values than if the flow is of short duration. For a known time-to-peak value of the design flood hydrograph, smaller scour depths may be obtained, which reduces the total cost of construction. Therefore, investigation of temporal variation of clear water scour at labyrinth weirs is important to estimate the possible extension of the scour hole. This would provide useful information for the safe design of footing and the selection of scouring counter-measure to be implemented. In the present study, temporal variation of scour and at labyrinth weirs was studied. In experiments, labyrinth weirs were used and seven head to weir height ratios ( H/p =0.1-0.7) for cycles with 6 different sidewall angles (150, 300,450, 67.50, Linear). In this study, the effect of Alfa and sidewall angles on temporal variation of scour depth and scour depth location were investigated. The results indicated that the mechanism and the value of scouring at weir varied for the different value head and sidewall angles. When head to height weir increased, the value of instantaneous scour depth significantly increased. The results also showed that in all experiments, the scour rate is more severe in the early stages and 80% of the development of scour depth occurs in the early 10% of equilibrium time. Furthermore, When H/P increased 5 times, the equilibrium time of scour depth increased to 6, while whit increasing the sidewall angles to 6 times, equilibrium time decreased 45%.

In a knee steel braced frame the main diagonal braces are connected to short knee elements. The knee elements act sacrificially and reducing the demands on the main structure during an earthquake, and can be replaced after the earthquake. However, careful design of the knee elements is required to ensure that they are able to absorb energy through repeated large plastic deformation without suffering collapse or instability. A program of laboratory testing has been undertaken in order to optimize the design and useful results from experimental tests are presented in this paper. For testing, the knee elements were mounted horizontally in a reaction frame and loaded vertically by a hydraulic actuator. In this research one kind of new weakening symmetrical perforated knee element are studied. Extensive experimental program of experimental testing by applied cyclic loading behavior on perforated knee element fuse and compare that’s result with a solid element fuse has been undertaken. ANSYS software was used for simulation and the numerical analyses in order to verified experimental tests for specimens. Results show that applied cyclic loading on both knee specimens produce sustain stable hysteresis loops and it is shown that excellent performance to absorb energy can be achieved using perforated knee elements.

In the present study, the effect of geogrid layers and soil density were investigated in the sand slope model reinforced with geogrid layers. The soil slope did not have stability in normal condition and was unusable for embankment operations. But it reached to the appropriate bearing capacity for embankment operation with improvement made by reinforcing and compacting the desired soil. The main purpose was to compare the footing bearing capacity and soil swelling of the reinforced with the non-reinforced states and also to evaluate the impact of the two soil compacted states with various thicknesses. 19 different states were investigated. The main parameters studied were soil density, the number of geogrid layers, and the distance from the slope edge. The results indicated that the soil slope, which had no stability in the non-compacted -unreinforced state, achieved high bearing capacity using geogrid layers and soil compaction. So that the maximum bearing capacity in compacted reinforced state and when footing was located 30 cm from the slope edge was 433 percent higher than the only reinforced state and 325 percent higher than only compacted state. Also, swelling of first layer of slope was significantly lower relative to the tolerance amount of bearing capacity and more uniformity was observed in all slope locations.The results also indicated that, in the compacted-unreinforced state, an increase in the number of compaction layers did not affect the bearing capacity of footing in the vicinity of the slope. But by moving the footing from the slope edge to 30 cm, the increasing the number of compaction layers from 5 to 7 layers caused increasing the bearing capacity by 34%.s.

One of the weakness of concentric braces is lower ductility and early buckling under compressive loading. One method to improve the ductility is to use energy-dissipater members situated at the intersection of the braces. Regarding this, the usage of steel rings made of steel pipes as an energy dissipater has been considered for solving weakness of ductility. Following this, the main objective of this study is to assess evaluate experimentally the dynamic behavior of steel ring filled with compressive plastic (S.R.P.) situated at the intersection of the braces. In addition, this connection was modeled by means of finite element (FE) method employing ABAQUS software. The accuracy of the FE models is confirmed using outputs of experimental studies where the nonlinear behavior of this connection was investigated both experimentally and numerically. Results indicate that the S.R.P. constructed from steel plates and plastic has a suitable performance relative to the pipe ring and exhibits good ductility and energy dissipation. In addition, this connection can enhance ductility of concentric braces in seismic loads. Concerning this matter, the brace with the S.R.P. ring shows a steady and wide hysteresis curve where tensile ductility factor of 2.77 was achieved. Another matter is that the maximum stress of this connection was obtained numerically in failure zone as indicated in experimental results. Furthermore, the maximum tensile load and corresponding vertical displacement were 99.48 kN, 16.01 mm, respectively, and also the maximum compressive load and corresponding vertical displacement were 101.55 kN and 11.5 mm, respectively.

Predicting the shear capacity of reinforced concrete beams with a suitable accuracy is an essential issue for engineering applications, especially for the rehabilitation and design of such structures. It was found that there is a significant difference between experimental and existing code recommendations for shear capacity predictions. Shear capacity assessment of slender reinforced concrete beams in reason of several assumptions to equation developing is one of the most important issues. An artificial neural network has been developed as a reliable method to simulate and determine the shear capacity of slender concrete beams. For this purpose, the effects of several parameters on the shear strength of concrete beams were evaluated. Finally, an empirical formula with suitable accuracy was obtained to determine the shear strength of slender concrete beams. Experimental, code recommendations and model suggested by artificial neural networks for shear strength of concrete beams show that the model suggested by artificial neural networks gives more exact predictions.

Some uncertainties in the field parameters such as dispersion and hydraulic conductivity, unknown boundary conditions and the noise of the measured data are among the main limiting factors in the groundwater flow and contaminant transport modeling. Thus, simulation of contaminant transport can be an important task in hydro-environmental researchs and consequently, it is necessary to develop the robust models which can determine the temporal and spatial forecast of contaminant. For temporal modeling contaminant concentration, several numerical methods, such as finite volume method, finite difference method, boundary element method and finite element method have been used for computional solution of governing advection-dispersion partial differential equation. In this study, a new hybrid model based on adaptive neuro-fuzzy inference system (ANFIS) as an black-box model and radial basis function (RBF) as a meshless method was developed. In fact, the proposed method employed the advantageous of both arthificial intelligence and meshless techniqus for modeling contaminant transport in porous media. In this research, an experimental was done for examining the efficiency of the proposed method. In this way, an acrylic sand tank was made with ten piezometers, one inlet with three adjustors. In order to supply contaminant a submersible pump was used. Also, constant water level was maintained using adjustor valves at both end of the tank. The thickness of acrylic sand tank 10 mm and dimensions 2.00×1.30×0.20 m3 were chosen. The sand sample porosity was measured 0.3. The grid size and time interval were considered 0.1×0.1 m×m and 3-minute, respectively. The constant-head test was employed to meaure the hydraulic conductivity of soil as a standard laboratory test. An UV Spectrophotometer (DR5000, HACH Company, USA) was used for measurement of the AO7 concentration. The maximum wavelength was measured 485 nm for AO7 concentration. Also, an electrical conductivity meter (EC600, A FLIR Company, USA) was used for measurement of the resistivity and electrical conductivity of AO7. In this study, time series of AO7 concentration observed at different piezometers of sand tank were firstly de-noised by the wavelet-based data de-noising approach. Then, the effect of noisy and de-noised data on the performance of ANFIS model was compared. For this end, time series of AO7 concentration observed in 10 different piezometers were trained and verified via ANFIS model to predict the AO7 concentration at one month ahead. Then, considering the predicted AO7 concentration of piezometers as interior conditions, the multiquadric radial basis function as a meshless method which solves partial differential equation of contaminant transport modeling in porous media, was employed to estimate AO7 concentration values at any point within the study area (in the experiment, sand tank) where there is not any piezometer. In this stage, optimal values of dispersion coefficient in advection-dispersion partial differential equation and shape coefficient of MQ-RBF were determined using cross validation approche. The cross validation method was finally applied to verify the performance of the proposed ANFIS-RBF model for two piezometers which were not considered in the calibration stage.In temporal contaminanat transport modeling, de-noised data enhanced the performance of ANFIS methods up to 5 percent in the experimental study. Results showed that the efficiency of ANFIS-RBF model is a reliable thechnique for contaminant transport modeling in porous media.

Estimation of maximum possible scour depth around spur dike is an important step in the design of spur dike foundations To determine the maximum scour depth in the design of spur dike foundations, the equilibrium scour depth, which is commonly estimated using peak-flow conditions for engineering design of spur dike foundations, are used.. In fluvial rivers, significant transport of bed materials often takes place during peak-flow discharge in a flood event. For large rivers, the duration of a flood event may last for a few months, but for others the unsteadiness of a flood can be pronounced. The general practice of employing peak-flow discharge to evaluate the maximum scour depth for design may be questioned because the maximum scour depth occurring under a flood hydrograph can be much smaller than the calculated value using peak-flow discharge. In other words, using the peak-flow discharge for design can greatly overestimate the maximum scour depth in comparison to the actual conditions under the flood hydrograph. Therefore, when the flow unsteadiness is pronounced, investigation of temporal variation of clear water scour at spur dike is important to estimate the possible extension of the scour hole. This would provide useful information for safe design of footing and the selection of scour counter-measure to be implemented. The degree of severity of the problem is dictated by the magnitude of this scour hole. In this experimental study, the scour around the single spur dike was investigated under unsteady flow. These tests have been done in terms of clear water and non cohesive sediments. In order to investigating the scour around the spur dike, experiments have been done by changing the properties of normal hydrograph such as peak discharge and durability time. In order to producing the hydrograph, we used a device for adjusting the speed of pump motor and generating the variable discharge according to actual discharge time series. In the inlet pipe of pump, a magnetic flow meter is located that Measures the discharge in per one tenth of a second. Thus, the system verifies of requested discharge at any time. The results show that one of the influential parameters that affect the scour around the spur dike is the durability time of hydrograph. We concluded that when the durability time increases 6-times, scour depth will increase 40 percent, because with increasing durability time, the time that spur dike exposes tensions increases. Also, the depth of scour has increased 35 percent, by increasing 25 percent of peak discharge of hydrograph that is caused by increasing stresses imposed on the bed. Finally, the resulted scour under unsteady flow was compared with the resulted scour under steady flow (With flood peak discharge), with a significant difference between the scour under steady and unsteady flow. Then, an imperial equation was proposed for calculating the scour depth under hydrograph. This equation was obtained by adding the unsteady coefficient of flow in the equation of equilibrium scour depth under steady flow. This unsteady coefficient of flow includes effective parameters of hydrograph such as peak flow of hydrograph, peak time, durability time of hydrograph and equilibrium time of scour.

By the research on the behavior of fracture toughness in asphalt mixtures, it has been suggested that several components have been proposed to test the mode III (KIIIc) fracture toughness of asphalt mixtures. But until now, a standard piece not been provided for testing fracture toughness (KIIIc) of asphalt. Such specimen should have appropriate geometric and loading conditions. In addition, it could be compatibility with the most common features in the inherent of tested materials and provide repeatable, reliable and integrity data of fracture resistance in asphalt mixture. ENDB is one of the specimens that could provide these items for calculating KIIIC of asphalt materials. It seems to be a good choice in comparing with other samples due to advantages such as ease of construction, cracks creation and simulation facilities of mode I loading for investigating of asphalt fracture behavior. The aim of this study was to investigate the effect of geometry and characteristics of asphalt mixtures on the behavior of ENDB fracture toughness. Using the finite element software (ABAQUS), geometry and meshing of the desired part have been performed. The result of this research can help in selecting and introducing the appropriate standard specimen and appropriate specifications of asphalt mixtures to determine the amount of KIIIC of asphalt mixtures to researchers. The important results of this research can be mentioned as the effect of thickness on the degree of fracture toughness in loading mode III. So the fracture toughness in the specimen with a higher thickness increases, and with the decrease in the percentage of air void and the test temperature, the degree of toughness of the fracture also increases.

Few studies are made about the effect of environmental conditions on the leakage flow rate. Some of these researches show that environmental conditions play an important role in leakage flow rate. On the contrary, there are other researches opposing this idea. The purpose of this research is to investigate evidence of the effect of environmental conditions on leakage flow rate. Based on this idea, some tests were carried out in the college of engineering at the university of Tehran, using a circular experimental set up at high pressure discharging to the atmosphere. Various ranges of pressure up to 50 m of water were imposed on a 110 mm diameter aged steel pipe with some holes on the pipe surface. In the next step, by using the experimental results, an analytical model in ANSYS software was developed and outputs were compared with experimental data. Later a proper mathematical turbulent model was derived. Furthermore, the effect of submerged conditions was investigated by this appropriate numerical model. The results of this research showed that static pressure fluctuations in submerged jet had significant effect on discharge and the rate of leakage was reduced in comparison with atmospheric discharge. According to the results, pressure reduction in 5 m head pressure could affect the leakage discharge under submerged condition up to 55 percent when compared with the case of discharging to the atmosphere. With pressures above 20 m, smaller changes were observed. These changes were limited to less than 10 percent. The aforementioned reduction depended on the imposed head of water at leakage point and pressure value inside the pipe. Finally, a relationship between leakage outflow and internal pressure of pipe was proposed.