نشریه مهندسی عمران
سال پنجاه و پنجم شماره 3 (خرداد 1402)

In this study biocompatible carbon quantum dots (CQDs) were prepared in a single step by hydrothermal method from walnut skin as a carbon source. Particle size, surface chemistry and crystal structure of carbon quantum dots were investigated using FTIR, DLS and XRD analyzes and optical properties of the material were investigated using absorption and fluorescence analyzes. The results showed that the quantum dots of synthesized carbon had a good particle size distribution and the average particle size was 5.7 ± 2.5. Also, the effect of temperature on initial carbonization was investigated, which with increasing the temperature of pyrolysis furnace, the percentage of carbon also increased, which was 46% by weight at 150 ° C and 83% by weight at 450 ° C. . Due to the fact t the difference in weight of carbon produced between temperatures of 350 and 450 degrees is very small, and considering the increase of 100 degrees, the temperature of 350 degrees was considered as a suitable temperature for the initial carbonization of walnut shell. The results of the absorption spectrum and fluorescence show that at the 238 wavelength an absorption peak of the sample is observed and the sample shows a good fluorescence scattering at the wavelength of 402 nm.According to the results of the studied FT-IR spectrum, the quantum surface of carbon dots is covered by hydrophilic functional groups such as hydroxyl, carbonyl and amine groups, and based on this, the synthesized nanoparticles are expected to show high dispersion in water.

Intake towers form the entrance to the reservoir spillway or diversion system and thus play a key role in the seismic resistance of the whole system. safety and proper functioning of the intake towers in the event of a major earthquake is very important, since the release controlled by the reservoir can help to prevent the failure of the dam after an earthquake by reducing the water pressure. In addition, the current seismic assessment based on linear elastic constitutive model cannot adequately describe the seismic capacity of intake towers. Thus, to investigate the proper functioning of intake towers in the event a earthquake, it is necessary to introduce IDA that takes into fully assess the seismic performance of intake towers based on nonlinear dynamic analysis. In this paper by modeling the intake tower of the Briones dam, intake tower in three conditions of the intake tower, the intake tower-reservoir (outside water) and the tower-reservoir-inside water, under the influence of 12 earthquake records, each of which has a magnitude of seven in the earthquake intensity scale, has been investigated. The displacement at the top of the intake tower, damage of the intake tower body and the maximum tensile stress of the rebar in the intake tower were studied in all the three condition are considered as damage measure (DM), and the results were reported in the form of IDA curves. Then based on the results, the function and different limit-states (key points) of the intake tower structure are determined.

Considering the successful usage of alkali activated mortars in several countries and limited research on the durability of these materials, in this paper, permeability and durability of alkali activated slag and pumice mortar in chloride environments have been studied. In order to investigate the mechanical properties and permeability of alkali activated slag and pumice mortars tests such as workability, compressive strength, capillary water absorption, water absorption, chloride ion penetration in the Persian Gulf environment and mercury intrusion porosimetry have been conducted.The results show that the compressive strength of alkali activated slag mortar containing potassium hydroxide was slightly higher than the compressive strength of samples containing sodium hydroxide. In addition, the use of 10% pumice instead of slag has increased the compressive strength of alkali activated slag mortar. Also, the 91-day compressive strength of alkali activated mortars cured in the water was 48.4% higher than those cured in the air. In general, the diffusion coefficient of chloride ions in alkali activated slag mortars was lower than the diffusion coefficient of chloride ions in Portland cement mortar, which was due to less porosity in alkali activated slag mortars and the denser structure. Also, alkali activated mortars containing 90% of slag and 10% of pumice had the lowest diffusion coefficient of chloride ions and Portland cement mortar showed the highest one, which was well matched with the result of capillary water absorption coefficient.

The in situ evaluation of the masonry mechanical properties is a very complicated task. A viable alternative is based on the use of brick cores including a central mortar layer lying on a symmetry plane. The obtained core is then subjected to a splitting test with a set up providing a different inclination of the mortar layer with respect to the loading plane. In here the test is used for masonry with sand and cement mortar. this test can be a good alternative to other semi-destructive tests, especially the shove test. The latter test has defect, that’s due to the lack of effect of dilatancy in the shear behavior of mortar in the shove test, the values obtained in terms of cohesion and friction angle will be greater than the actual value. In the following, a 3D continuous micromodel is presented in order to predict unreinforced masonry behavior. Due to the difference in the modulus of elasticity, the Poisson ratio and the thickness of the brick and mortar, several efforts have been made to simulate the compressive behavior of the masonry using different models with different goals and results. in one hand, two-dimensional models are not able to consider 3d confined effect. On the other hand, the three-dimensional models are not able easily to control the effect of 3d confined and dilatation explicitly. The proposed model is based on the concept of micro-plane and is developed to model failure in masonry structures.

Despite substantial environmental and economic benefits, cold recycling of asphalt pavements is not common due to some poor field performance reports. This study investigates the effect of fiber reinforcement on the performance of cold recycled mixtures. For this purpose, cold recycled mixtures were reinforced using polypropylene fibers at two different lengths and three different contents. Indirect tensile strength, IDEAL-CT, and semicircular bending tests were carried out to find the optimum length and content of the fiber. The effect of cement on performance of fiber reinforced mixtures was also evaluated. The results show that although the use of polypropylene fibers reduces the wet strength by up to 54%, it can increase the dry strength by up to 39%. The results also indicate a significant improvement in fracture indices obtained from IDEAL-CT and SCB tests in the presence of fiber. Crack tolerance index was 3.5 times and flexibility index was 2.8 times higher at the optimum fiber content and length compared with the control mixture. It was also concluded that the addition of cement to fiber reinforced mixture can eliminate the adverse effect of fiber on moisture sensitivity, while maintaining the fracture properties similar to the control mixture. The study results show that the combined use of fibers and cement can lead to an economical cold recycled mixture with reduced emulsified asphalt content and improved mechanical properties.

The Iran civil code is based mainly on the Egyptian Civil Law (ECL), which is itself derived from two principal sources like French civil law and Islamic law. On the other hand the general conditions of contracts published by the Fédération Internationale des Ingénieurs-Conseils or International Federation of Consulting Engineers (FIDIC), which based on common law principles and this standard form of contract, have been applied in large construction projects in Iran. Due to the Iran legal system is rooted in civil law, FIDIC forms of contract may face serious challenges. This research, through a comparative method, has analyzed the Egypt Civil Code (ECC) and Iran (as two members of the Islamic legal system) for better decisions in FIDIC-based contracts. Our study offers some strategies for modification of the FIDIC 1999 Red Book [FIDIC (CONS)] and also Iran Civil Code for construction contracts, which are associated with the termination for convenience clause. Therefore, with a better understanding of the termination for convenience by the employer clause, which has referred to in many contractual claims in arbitration centers and courts, can be prevented disputes. Moreover, this study is useful for other Middle East countries because most of them follow the civil law jurisdictions.

Liquefaction is one of the most devastating Geotechnical phenomena that severely damages vital structures and lifelines. accurate understanding of the dynamic response of the site prone to liquefaction and improved with different modern methods and comparing it with the unimproved site improves the ability of engineers to choose the appropriate improvement method. Before construction, it is necessary to solve the geotechnical problem. Among the methods of land improvement to deal with liquefaction, gravel columns and deep mixing columns can be mentioned. In this study, the results of 1g shaking table tests by flexible box on the foundation located on the liquefiable ground surface and reinforced with aforementioned techniques have been investigated. The dynamic responses of the reinforced ground in different thicknesses of the liquefiable layer and the different frequency of the input movement have been investigated based on stress-strain behavior, secant shear modulus of the soil and excess pore water pressure versus shear strain. The results of the tests show that the thickness of the liquefiable layer has a considerable effect on the dynamic responses of the soil, including the shear behavior and the shear modulus of the soil. By increasing the thickness of the liquefiable layer, the values of secant shear modulus and shear strain of the improved mass decrease and increase respectively. Also, the dynamic performance of deep mixing columns in thicker layers is more suitable compared to gravel columns, and at lower thicknesses, the dynamic behavior of gravel columns approaches that of deep mixing columns.

Low-cement roller compacted concrete is one of the special types of concrete that has a low amount of cement in its mixture proportion in order to reduce the heat caused by the hydration reaction. This increases the permeability of roller compacted concrete compared to conventional concrete. The increase in permeability also leads to the entry of destructive ions into concrete of mass structures and ultimately the instability of these structures. Cement supplementary materials such as zeolite can reduce permeability, so in this research, the effect of replacing a part of cement with zeolite on durability and mechanical properties of roller compacted concrete has been investigated. First, chemical analysis and pozzolanic activity of zeolite were investigated. Then, in order to evaluate the effect of zeolite on the properties of concrete, samples of roller compacted concrete were made in four mixture proportions with replacement percentages of 0%, 15%, 30% and 40% of cement with zeolite and subjected to compressive strength, water penetration depth, water absorption, Rapid Chloride Permeability Test (RCPT), electrical resistivity, Ultrasonic Pulse Velocity (UPV). The workability of the roller compacted concrete mixtures was also determined by the V.B. table test. The results showed that according to RCPT, water penetration depth and electrical resistivity tests, replacing 15% of cement weight with zeolite reduces permeability and significantly improves durability properties of roller compacted concrete. Also, increasing the percentage of zeolite reduces the compressive strength of the specimens.

In this paper, an innovative finite element updating method is presented based on the sensitivity of wavelet transform coefficients of correlations function structural parameters is proposed to identify the damage. The Quasi-linear sensitivity of the wavelet coefficients of the WTCF concerning the structural parameters is evaluated based on incomplete measured structural responses. This WTCF sensitivity is more sensitive to local structural changes than the wavelet transform function response sensitivity. The model is updated by the wavelet transform coefficients achieved in the frequency range in the vicinity of the resonances, in which damping and incomplete measurements have no significant effect on the results of the parameter estimation. The proposed algorithm is used to estimate the structural parameters of the frame model. By the solution of the sensitivity equation through Least-squares method, the finite element model of the structure is updated for estimation of the location and severity of structural damages, simultaneously. The proposed method was successfully applied to a 2D frame model using simulated data contaminated by measurement and modeling errors. The robustness of the method against modeling and mass measurement errors is investigated by adding random errors to the mass parameters of the frame model.

RC beam-column joints play a crucial role in transferring gravity and lateral loads from beam to column. By examining damaged buildings in recent earthquakes, RC beam-column joints are among the most vulnerable members of RC moment frames. The main type of failure of RC joints is shear failure due to the lack of transverse reinforcement and confinement in this area. The laboratory program of the current study suggests external post-tensioned bolts to retrofit RC joints. External post-tensioned bolts increase the confinement and enlargement of the joint panel zone and subsequently eliminate the deficient shear joints. Regarding that the forces applied to the joint panel zone are implemented diagonally, the external post-tensioned bolts were used in two horizontal-vertical (HV) and diagonal (Di) patterns around the joint. The test program includes four RC beam-column joint specimens with half-scale. One specimen was constructed as a standard criterion with all seismic requirements, and three specimens were made at the joint without implementing transverse reinforcement. One deficient specimen was used as a control specimen, and two specimens were subjected to cyclic loading after retrofitting by the proposed patterns. In order to investigate the effect of the proposed method, parameters such as; the force-displacement hysteresis response, energy absorption and damping value of the specimens were considered. The test results confirm the significant effect of the retrofit system against seismic loading so that in retrofitted specimens. The final capacity of the retrofitted specimens increased by about 50% and their energy absorption by about 200%.

Concrete-filled steel tubular (CFST) gusset plate connection is a commonly used method in which the plates are welded directly to the columns. Due to the importance of stress distribution and energy absorption capacity on the behavior of the mentioned connections, in the present study, numerical analysis of the behavior of these connections under different loadings has been investigated. The studied variables include the thickness of the gusset plate, the compressive strength of the concrete, the D/t (diameter to thickness) ratio of CFST, and the type of loading. The results show that although filling hollow tubular sections with concrete prevents the local buckling of the steel wall, the use of concrete with higher compressive strength does not always lead to increased load capacity and energy absorption, so that in many of the studied models, the energy absorption capacity decreases by 18% to 30%. On the other hand, the results showed that the diameter-to-thickness ratio has a significant effect on the energy absorption capacity of the simulated connections, so that with increasing this ratio, the energy absorption capacity has decreased in the range of 76% to 91%. Also, the loading condition is effective in the load-bearing capacity and the energy absorption of the structure. So that in the case of eccentric tension and in-plane bending, the energy absorption capacity is reduced by 53% and 86%, respectively, compared to axial tension loading.

In this paper, the fracture parameters of lightweight geopolymer concrete based on the C - class fly ash (LWFCGC) are presented. The experiments include three-point bending tests on 36 beams with different activator to binder ratios. Compressive and tensile strength tests were also performed on hardened concrete after 24 hours of curing at 80 ° C. In this research, three mix designs with activator to binder ratios of 0.4, 0.5 and 0.6 were considered. The samples showed relatively decent compressive strengths. In each mixture, the fracture parameters were analyzed using size effect method. The results showed that by increasing the activator to binder ratio fracture toughness and fracture energy decreased. Moreover, the ductility, measured by means of the effective length of fracture process zone, increased.The samples showed relatively decent compressive strengths. In each mixture, the fracture parameters were analyzed using size effect method. The results showed that by increasing the activator to binder ratio fracture toughness and fracture energy decreased. Moreover, the ductility, measured by means of the effective length of fracture process zone, increased.