مجله پژوهش های زیرساخت های عمرانی
سال هشتم شماره 2 (پیاپی 15، پاییز و زمستان 1401)

In recent years, extensive studies have been conducted on the effect of different nanomaterials on the performance of asphalt mixtures. Also, in the present study, Nano graphene oxide (GO) in the amounts of 0.2, 0.5, and 0.8% by weight of bitumen was used to improve the fracture resistance of HMA asphalt mixture against cracking at negative temperatures. Nano graphene oxide (GO) has been introduced as the material of the century due to its very unique and excellent properties. For this purpose, to investigate the effect of this nanomaterial on the fracture resistance of the asphalt mixtures, the semi-circular bending (SCB) fracture test at temperatures of -5 and -15°C and four different loading modes have been used. In addition, conventional bitumen tests were performed to investigate the effect of Nano GO on pure bitumen in this study. The conventional bitumen tests showed that the addition of Nano GO to pure bitumen increased the softening point, viscosity, and specific gravity and reduced the penetration and ductility in pure bitumen. Also, the semi-circular bending (SCB) fracture test results indicate that using Nano graphene oxide increases the fracture energy of asphalt mixtures and improves the resistance of asphalt specimens to cracking. So that mixtures containing 0.5% of this additive have the best performance. The results show that the use of this amount of additive in the asphalt mixture at -5°C and pure loading mode I increases by 105% and at -15°C and pure loading mode II increases by 60% in the fracture energy.

The method for retaining the excavated pit could have a significant effect on the soil pressure acting on the retaining walls; For this purpose, since the Top-Down construction method is widely used, In this study, a series of numerical analyses has been conducted to investigate the effect of the excavation method and the distribution of the structural elements on the soil pressure distribution. Generally, for engineering purposes, active and at-rest soil pressure distribution and the Peck apparent pressure distribution (in the case of retained walls) are used for soil pressure determination. The results of the study suggest that in contrast to the at-rest and active soil pressure distribution, the pressure distribution on retaining walls has no similarity with the triangular distribution and the Peck's APD provides an acceptable estimation of soil pressure and its distribution. The results also show that with the increase of deformation due to the construction of the wall, as an example in one case, a 60% increase in ground settlement reduced the soil pressure acting on the walls by up to 15%. It's also noteworthy that this study focuses only on a special type of soil, So the result might be inapplicable to other circum-stances.

The durability of asphalt mixtures depends to a large extent on the asphalt film thickness. Stripping is the separation of the asphalt binder film from the aggregate surface due to the action and penetration of water. In this study, a gradation was prepared from basalt crushed aggregates. Then, by applying upper and lower allowable deviation tolerances to the fine aggregates of it, two gradations were produced. Nano-Organosilane Zycotherm was used as a liquid antistripping additive.  The guidelines of the MS-2 Journal of the Asphalt Institute, NCHRP 567 report, Austroads and VicRoads reports were used to calculate the asphalt film thickness. Scanning Electronic Microscopy (SEM) was also used to show the asphalt film thickness of the three asphalt mixtures. The Marshall Stability Ratio and Indirect Tensile Strength Ratio tests according to AASHTO T283 were used to evaluate the moisture durability of asphalt mixtures. The results showed that the gradation changes in the fine aggregates caused a 12.9% decrease in asphalt film thickness in asphalt mixtures with upper allowable deviation tolerances and a 17.7% increase in asphalt film thickness in asphalt mixtures with lower allowable deviation tolerances, and these changes necessitate durability tests.  Also, in the evaluation of moisture durability, all three asphalt mixtures were able to strip according to MSR and TSR indexes. Although Zycotherm had a positive effect on the MSR index of all three asphalt mixtures, according to the TSR index, the asphalt mixture with the lower allowable deviation tolerances was still able to stripe. Therefore, the moisture damage due to the gradation changes in this asphalt mixture is not improved by the Zycotherm additive.

In this study, the ogee spillway flow pattern under the influence of the spillway curve shape and upstream slope changes was evaluated using Flow-3D numerical simulator software. Thus, two ogee spillways with elliptical crest and USBR pattern were simulated in two vertical and oblique upstream modes with a slope of 3H:3V and three different heads, and the results of changes in effective parameters such as flow, velocity and pressure in the length of each spillway was examined. Validation of the results of the numerical model with the results of the Maynord experimental model showed that the Flow-3D numerical model has a high ability to simulate the flow field on the ogee spillway. Comparison of flow rate from numerical model with experimental data showed that the average computational error was less than 3% of the numerical model. Examination of the pressure field showed that at the height of the head equal to the design head, the pressures are close to atmospheric pressure and no negative pressure is created on the spillway crest, but at the head higher than the design head, negative pressure will be created on the spillway. The amount of negative pressure created at the beginning of the USBR spillway crest is higher than the negative pressure value of the elliptical spillway crest due to the lack of continuity in the crest and further separation of the flow lines from it.  The results also showed that the ogee spillway with oval crest has a relatively better performance in the flow over the spillway and in these spillways it is possible to pass more discharge with higher safety and sloping the upstream side of the spillway causes a change in the discharge coefficient and finally the flow rate of the spillways.

Soil pollution due to various factors is one of the world's problems in different countries, especially industrialized countries, which has attracted much attention in the form of various researches. To solve this problem, in this study, metakaolin was used to stabilize low-plasticity (CL) clay contaminated with lead and zinc nitrate. The present study consists of two main stages. The first stage examines the soil to identify the most critical concentrations of contaminated soils and soils contaminated with lead nitrate and zinc nitrate in a ratio of 1: 1 and with concentrations of 1000, 5000 and 10000 ppm with a curing time of 7 days. The results obtained in the first stage showed that increasing the concentration of pollutants has a negative effect on soil geotechnical parameters, which can be reduced to the maximum uniaxial compressive strength and reduced soil CBR resistance. This step aimed to identify the most critical concentration of contaminated soil, which was 100 ppm. The second stage examines the resistance tests of contaminated soil with a concentration of 10000 ppm and its stabilization with metakaolin at a rate of 5% by weight and with a curing time of 7, 14 and 28 days. The purpose of curing time is to investigate the effect of time on soil geotechnical parameters during the presence of metakaolin in the soil. In general, according to the results of these experiments, the maximum uniaxial compressive strength and soil CBR strength increased with increasing curing time. As the curing time increases, the soil adhesion increases and consequently the compressive strength of the soil increases.

The mix design of asphalt mixtures is one of the most important factors that affect their performance. Given the importance of the performance assessment of asphalt mixtures and volumetric parameters, a new method called balanced mix design (BMD) had been created. This method considers volumetric parameters as the initial criterion. The ultimate criterion to determine an appropriate range for the optimum bitumen percentage is the proper rutting and cracking performance of the asphalt mixture. In this study, five different asphalt mixture designs were first investigated using the Superpave method, using low (25%) and high (50%) percentages of RAPs and vegetable oil as a recycling agent. Then the mixtures were designed using the BMD method considering three different bitumen contents for each mixture. The Hamburg Wheel Tracking and I-FIT tests were performed to assess the rutting and cracking resistance, respectively. The results of this study show that the optimum binder content (OBC) obtained by BMD method is different from the Superpave method. The highest discrepancies are observed when 25% and 50% of the RAP materials are used without rejuvenator. In these mixtures, the results show that the OBC obtained by the BMD method compared to the Superpave method for mixtures containing 25 and 50% RAP without rejuvenator increased by 9.56 and 22.18%, respectively. In terms of performance, the percentage of OBC by the Superpave method is not suitable for mixtures containing RAP and rejuvenator.

In the present study, tests were performed on the chute with five different geometric shapes of baffles and at four different distances of baffles rows under different hydraulic conditions. The results showed that the baffles on the chute creates the flow resistance and with increasing turbulence causes the transfer of the inception point to the upstream of the chute and increases the rate of energy dissipation compare to the chute without baffles. Baffle chutes increased the aeration length by 5.8 times and increases the energy dissipation rate by 21 to 61 percent compared to the chute without baffles. In all models, the rate of energy dissipation in low discharges is higher and with increasing discharge, the energy dissipation decreases. By increasing the spaces between the baffles on the chute, the energy dissipation rate decreased in all models. In the M2 model as the superior model, increasing the spaces between the baffle reduces by 3.1% and 4.57% in the energy dissipation rate, respectively. The effect of longitudinal spaces between the baffles on the aeration and the energy dissipation rate is greater than its transverse spaces.

In this study, the effect of adding different percentages of recycled concrete aggregates to aggregate base layer materials on the fatigue and rutting life of pavement has been investigated. In the performed analyzes, nonlinear analysis by NonPAS software has been used. To this end six four-layered pavement sections with different layers thickness were analyzed for three types of very soft, soft and medium clay subgrade soil. The behavior of asphalt layer materials was considered as linear elastic and the behavior of base, subbase and subgrade materials was considered as nonlinear elastic. In all sections of pavement, the use of 0 to 100% of recycled concrete aggregates for all subgrades, at least 61.6% and maximum 198.5% increases the fatigue life and at least -22.6% and maximum 88.4% increases rutting life. In very soft clay subgarde, in thicknesses above 20 cm for the base layer and thicknesses above 30 cm for the subbase layer, it is possible to use recycled concrete materials. In medium clay subgrades, in thicknesses above 15 cm for the base layer, thicknesses above 20 cm for the subbase layer and also thicknesses above 15 cm for the asphalt layer, it is possible to use recycled concrete materials. In hard subgardes, there is no special considerations in terms of the thickness of pavement layers for the use of recycled concrete materials.

The non-uniform stress distribution that occurs in a tension member adjacent to a connection, in which all elements of the cross section are not directly connected, is commonly referred to as the shear lag effect. This effect reduces the design strength of the member because the entire cross section is not fully effective at the critical section location. This phenomenon has long been taken into account in various structural codes, however the rules of the codes used are somewhat conservative and it seems that they need to be reviewed. In this research, a series of steel box section connected through two wings and plate sections were studied through finite element method using ABAQUS software, and the ultimate member capacity was obtained. It can be seen that in this regard the relationship between the rules is somewhat conservative and optimized relationships have been proposed to address this issue. Parameters used include connection length, axial force eccentricity, and weld size. The results show that the length of the connection, the gusset plate thickness and also the eccentricity have a significant influence on the shear latency coefficient.

In this research, the effect of P-Delta column (leaning column) on the response of gravitational frames with lateral-load resistance system of base-rocking wall has been investigated. The studied structures have 4-, 8-, 12-, 16-, and 20-stories. Nonlinear dynamic behavior is performed under 22 far-field seismic records and 28 near-field seismic records, half of which are pulse-like, via OpenSees software. The ground motions are scaled at both DBE and MCE levels and applied to the structure. The modeling is done in two dimensions. As a results, it has been shown that 1) the higher modes effect increases with increasing earthquake intensity, 2) the higher modes effect are more visible in the records of far-field and near-field-non pulse-like, 3) residual displacements in The both earthquake levels studied are insignificant and negligible, 4) P-Delta column has been more effective in structures under near-field-pulse-like records, 5) The maximum effect of P-Delta column in increasing the moment of wall under near-field-pulse-like earthquake that the value is 12%, and 6) In general, the effect of the P-Delta column on the base-rocking wall structures in especially the stepping-wall can be ignored.

The Welded Unreinforced Flange-Welded Web (WUF-W) Moment Connection is one of the most common types of rigid connections in steel moment frames. However, due to continuity plates installing challenges in the box columns, developing the design equation of continuity plates and finding creative alternative solutions instead of installing inner continuity plates in box columns are the matter of interest to the researchers. Considering the new continuity plate design approach in the AISC 341-16 and the part 10 of the Iranian National Building Code and the ambiguities that have arisen, in this research 42 WUF-W connections have been modeled and numerically studied under monotonic and cyclic loading. The results show that the approach has been taken by the 5th editions of part 10 of the Iranian National Building Code based on mandatory installing the continuity plate in box columns is strict. It seems that the equation for design the minimum thickness of the continuity plates in 4th edition of part 10 of the Iranian National Building Code can be satisfy the seismic provisions of AISC 341-16 by the correction factor equal to 1.7.

Numerous researchers focus on monitoring the health of structures to ensure safety and reduce maintenance costs. Beams and columns are the primary elements of structures in civil engineering, and designers expect beams and columns to be the last elements to experience damage. This paper identifies steel beam damage based on dynamic modal data. After a modal analysis was performed on the modeled beam using the ABAQUS finite element software, modal information was extracted, including the frequencies and shapes of healthy and damaged modes. Due to the presence of damage, differences in the frequency values of primary and secondary conditions were observed. In addition, modal assurance criteria (MAC) values below one were obtained, confirming the presence of damage. Using an analytical method based on wavelet analysis, MATLAB.R2021a processed healthy and damaged mode shape signals. In all modes, a comparison of the output signal diagrams of healthy and damaged modes revealed the difference in the damaged area, allowing the damage locations to be identified with an error of less than 2 percent using a simple examination.