نشریه مهندسی عمران
سال پنجاه و یکم شماره 6 (بهمن و اسفند 1398)

This paper conducted research on numerical studies of fracture mechanics related to crack propagation of functionally graded concrete resistant to projectile impact consisting of plain, fiber reinforced and tough aggregate concrete layers, which are presented by modeling a three point bending test in presence of initial notch. To consider fracture behavior in process zone, a bilinear softening model for plain and tough aggregate concrete and a trilinear softening model obtained from traction-separation relationship of cohesive zone model is used. extented finite element method is utilized for numerical analysis. result of numerical modeling of three point bending test have been investigated and compared using loading versus crack mouth opening displacement (P-CMOD) curves. Functionally graded model has been studied in comparison with homogeneous plain, fiber reinforced and tough aggregate concrete models, and the results showed that homogeneous fiber reinforced concrete model has a better fracture behavior than others models. The functionally graded model has not been subjected to sudden failure in comparison with plain and tough aggregate concrete models due to the fiber reinforced in end layer. Also, effect of each layer and their thickness change in the functionally graded model are evaluated and it was observed that fiber reinforced layer due to high fracture energy created by fiber bridging has a beneficial effect on the fracture behavior related to other layers. In this way, by considering proper position and thickness for this layer, in addition to providing appropriate performance in the fracture behavior, cost of materials also be significantly reduced.

In present study, the impact of filter which located in downstream of hydraulic structures in reduction uplift pressure and hydraulic gradient was investigated. Impact filter effectively parameters such as length and distance from downstream structures and also upstream head was evaluated. The results of this study showed by design of filter with equal 0.057, 60% of downstream uplift pressure and 10% of upstream uplift pressure will be reduced and the effect of filter in uplift reduction in downstream of floor are impressive. By increasing the filter length, exit gradient always decreasing and with increasing distance of downstream (x), the effect of filter in reduction exit gradient increases. Design of Filter with equal 0.057 have good impact on exit gradient reduction (65%), witch by increasing length, gradient reduction will be reduced. Finally was used from regression and artificial intelligence models such as RBF, MLP and SVM for prediction of uplift and exit gradient in structure with filter. With comparing of this models in base of RMSE, MAE and, was introduced regression model as suitable model and SVM as poor model in prediction of uplift and gradient.

The release of oil pollutants in the soil causes changes in the structure, texture and the relationship between the soil particles. This has destructive effects on the physical and mechanical properties of soils. In recent years, improvement of degraded engineering properties of these soils for their use in construction projects has been a challenge for researchers and engineers. In this paper, the effect of adding two types of clay nano-particles on the improvement of mechanical properties of Clayey Sand contaminated with gas-oil has been investigated. For this purpose, after determining the basic properties of natural soil, soil with 6% and 8% gas-oil, contaminated soil stabilized with nano-clay in values of (0.5, 1, 2 and 3%) and organo-clay in values of (0.3, 0.5, 0.7 and 1%), standard compaction and unconfined compressive strength tests during the two curing periods (7 and 28 days) were performed on them. Scanning electron microscopy (SEM) was also used to evaluate the microstructure of natural soil samples. Also, the microstructure of natural soil, contaminated soil and contaminated soil stabilized with nano-particles was studied with the help of scanning electron microscopy (SEM). The results of the tests showed that maximum dry density, optimum water content, and unconfined compressive strength have decreased in the soil with gas-oil.....

Setting time and thixotropy of self-consolidating concrete (SCC) mixtures are two important parameters that affect the early age properties. In order to determine these parameters, there are traditional methods that have advantages and disadvantages such as low accuracy or high cost of testing. The aim of this study is introducing an acceptable method (called plate test) of determining setting time and thixotropy of SCC mixtures. The proposed method is including a rough plate immersed in fresh mixture from one side and attached to the accurate scale from another side. In this study the thixotropy of different self-consolidating concrete mixtures (SCC) containing silica fume and slag were tested. Results of the thixotropy obtained from the plate test were compared with the results obtained from penetration resistance and rheometer respectively. Results showed that the mixture containing slag produced the less temperature comparing with the mixture containing silica fume. It was also shown that the amount of thixotropy obtained from the plate test had a difference of 4% up to 10% in comparison with the rheometer and the results of the setting time had also shown a maximum difference of 9% compared with the results of penetration resistance test. The results proved that the plate test has an acceptable accuracy and can be recommended.

The present research aims to investigate the feasibility of using ambient vibration tests for system identification of elevated water tank. To this end, the elevated water tank located in TMU campus is utilized. The tank is instrumented with a sensitive velocimeter sensor and the ambient velocity of the tank is recorded for 30 minutes in three perpendicular axes. The amplitude of the velocity signal reaches to about 30 mm/s. using the peak picking method, the fundamental frequency of the tank is determined about 1.9 Hz. Although, considering the non-perfect symmetry of the tank and the misaligned orientation of the sensor the obtained values in two lateral directions differ 5%. Then, the numerical model of the tank is prepared in software and calibrated. In the primary modeling, the values of natural frequencies of the tank are in good agreement with the results of the ambient vibration data. It shows the calibration of the numerical model which can be used in the assessment of the seismic behavior of the elevated water tank.

A number of regions around the world have suffered severe subsidence due to groundwater withdrawal. Mashhad as one of the largest municipalities in Iran has suffered subsidence due to deep groundwater overextraction. Land subsidence in this area can be destructive for urban infrastructures and can create serious environmental issues and structural damages. So, the aim of this research is to precisely determine the uninterrupted vertical subsidence in Mashhad by Permanent Scatterer InSAR technique and also to assess the previous reports on the study area. We complement previous works using more accurate data and procedure in an urban area. Furthermore, we considered geotechnical properties which was not focused in the previous studies. For this purpose, 69 descending and ascending C-band radar images, provided by relatively high-resolution Sentinel-1A satellite, were used to estimate the deformation-trend of the interest area. The method was applied to the images spanning October, 2014, and February, 2017 investigating land subsidence. The assessment procedure demonstrated a high-rate of subsidence in northwest of Mashhad with the significant deformation of 140 mm/year. The outputs were validated using in-situ measurements data and hydraulic head variations respecting piezometric data from groundwater wells. Subsequently, the geotechnical properties of the chosen area were considered to interpret the results. It was illustrated that the land subsidence in the case study is brutally continuous and there is no decrease on the deformation rate.

Based on the important effects of filler on performance-related properties of asphalt mixtures, this study investigates the influence of filler type on moisture susceptibility of asphalt mixtures under multiple freeze-thaw cycles. Furthermore, the effect of changing the type of mineral fillers, especially replacing fillers with recycled concrete materials on moisture resistance of asphalt mixture, with sustainable development approach, is evaluated. In this study, first, the indirect tensile strength and the resilient modulus tests are conducted following 1, 3, 6, and 10 cycles of freeze-thaw and then the fracture energy is calculated through the results of indirect tensile test. Next, the surface free energy components of mastics with different types of filler are calculated using the static contact angle measurement method. The results of performance-based moisture susceptibility tests show that replacing natural filler with Portland cement can result in the best performance compared to control mixture, limestone filler, and RCA filler. However, the evolution of mechanical properties of control filler, limestone filler, and RCA filler depends on the number of freeze/thaw cycles. At higher conditioning cycles, TSR values demonstrate a different behavior such that the TSR values of the asphalt mixture containing RCA filler increase up to 15% on average compared to the asphalt mixture containing limestone filler after the first cycle. Although the results of mechanical properties in initial freeze-thaw cycles are similar to surface free energy results. However, these results cannot predict the behavior of asphalt mixtures at higher freeze-thaw cycles.

Over the past three decades, many approaches and methods have been investigated based on the inverse problem solving to recover the temporal release rate of pollutant sources, especially in groundwater. But, number of studies is limited about the rivers; therefore, developing a method which can determine temporal release rate of pollutant sources in the river precisely and at the same time be able to consider the conditions of the flow and bed is promising. In the present study, the inverse solution of the advection-dispersion equation for recovering the temporal release rate of pollutant sources leads to the solution of a linear overdetermined system of equations type of ill-posed problem. Therefore, in this research a numerical model based on the inverse matrix approach based on the Tikhonov regularization method and the results of the superposition principle has been applied to the recovery of the temporal release rate of pollutant sources and the exact time of release of the pollutant from the source. The model has been designed to retrieve the complexity time of multiple pollutant sources in a complex state. Also, the model has been verified using real two-dimensional data of Ohio River located in the United States. Finally, a general and practical framework has been introduced to apply in real condition. Eventually, the computational results were showed that, the inverse model can recover the temporal release rate of pollutant sources using the lowest field and downstream data containing high error rate at each point of the river.

Wrapping reinforced concrete (RC) column with FRP sheets improve compressive strength of concrete. Since stress-strain curve of concrete confined with FRP is different from stress-strain curve of normal concrete, equations presented by codes to design and analysis of normal (unstrengthened) RC column and are based on stress-strain curve of normal concrete cannot be used for design and analysis of columns strengthen with FRP. In this research, first by using stress-strain curve of confined concrete presented by researchers and ACI code, an algorithm was designed to determine axial and flexural capacity of strengthened column and implemented in Visual C# environment. Verification of this work was investigated and confirmed by comparing it with experimental results. The programming was developed in a way that it could be used to optimize the design. Thus, by specifying required information including sectional dimensions, number and diameter of rebars, applied axial load and bending moment on column, and FRP sheet properties and price, the performed programming can determine which type of FRP, if used, while supplying the required flexural and axial capacity has also the minimum price.

One of the important applications of geosynthetics in the earth's slopes, such as landfills and waste disposal areas, is to use them as liner system. Proper assessment of the interaction of geosynthetics at slopes, such as landfill, is an important issue in preventing the slip and instability of the slopes. The inclined plane is a suitable method for assessing the interaction between the geosynthetics interacting in a sloping and tilted state under low normal stresses. The European Standard EN ISO 12957-2 provides a "standard displacement" for estimating the geocynthetic interface's friction angle. In this paper, inclined plane device, which for the first time in Iran was completely designed and constructed, describes the technical characteristics of the device and prepares the sample. This apparatus has the ability to perform experiments to investigate the interaction of soil-soil, soil-geosynthetics and geosynthetic-geosynthetic interfaces at low normal stress. Experiments are carried out on geomembrane and geotextile types to investigate the interaction of their surface. By changing the type of geosynthetics, it was observed that friction angle of geosynthetic interfaces is not constant and depends on the type of geomembrane and the woven or non-woven geotextile. The geomembrane-geotextile interface is the least amount of geomembrane with hard polyethylene, and the highest amount is used when polyvinyl chloride is used.

The implementation of an efficient pavement management system is dependent on the acquiring desired information from the pavement condition. The automatic data collection were welcomed by mechanized systems due to adequate precision and speed. But the various systems were developed that had high construction and operation costs. Therefore, the development of cost-effective devices that is independent from the vehicle vibrations and equipped with instrumentation is necessary. In this study, the Health Monitoring System (HMS) is developed as a system of longitudinal profile measurement and road roughness evaluation based on response-type vehicle with applying the mode combined of accelerometers, distance meter, GSM. Upon harvesting the vibration response of the HMS and the vehicle, data preparation and signal filtration are performed through the Digital Signal Processing (DSP) techniques. So the dynamic equations governing the behavior of the HMS are derived based on one degree of freedom. The dynamic parameters of system are extracted based on optimization approach using GA and PSO algorithms. Afterwards, the extracted longitudinal profile based on the vibration responses is become to the longitudinal profile with the specific speed by the algorithm of the relationship between speed and frequency of harvested data. Then, the International Roughness Index (IRI) is calculated from the longitudinal profile of the studied pathway by ProVal software. Finally, the accuracy of the HMS results is validated by manual method with measuring the AEP and the NRMSD between the outputs of the system and the Road Surface Profiler (RSP) with values of 19.72% and 9.68% respectively.

Nowadays, there is a spread use of steel plates in various structures because of their well performance and economic advantages. Hence, investigating their behavior is necessary. In this study, the buckling behavior of long steel plates under combination of bending, shear and axial loadings is studied using the finite element method. The effects of fixed and pinned boundary conditions along the longitudinal edge are considered. Also the influence of adding some holes with varying diameters but with the fixed spatial place is investigated. The buckling behavior of the plate under various combinations of the loads in both non-pierced and pierced plates are compared. The loadings are applied along the plate’s edges such that, first, two loads are applied with various magnitudes, and then the third load is applied and its critical buckling load is computed. The obtained results show that the long plate under axial compressive loading has less sensitivity to the holes in comparison with the shear and bending loads. The holes with diameters equal or less than 0.06 of the plate’s width can hardly affect the critical buckling load.