• Advances in concrete construction
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• v.16 no.1
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• pp.69-78
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• 2023

This investigation delves into the adverse repercussions stemming from the impact of arsenic on steel pipes concealed within soil designated for rice cultivation. Simultaneously, the study aims to ascertain effective techniques for detecting arsenic in the soil and to provide strategies for mitigating the corrosion of steel pipes. The realm of nanotechnology presents promising avenues for addressing the intricate intersection of renewable energy, oil, and environmental pollution from a novel perspective. Nanostructured materials, characterized by distinct chemical and physical attributes, unveil novel pathways for pioneering materials that exert a substantial impact across diverse realms of food production, storage, packaging, and quality control. Within the scope of the food industry, the scope of nanotechnology encompasses processes, storage methodologies, packaging paradigms, and safeguards to ensure the safety of consumables. Of particular note, silver nanoparticles, in addition to their commendable antibacterial efficacy, boast anti-fungal and anti-inflammatory prowess, environmental compatibility, minimal irritability and allergenicity, resilience to microbial antagonism, thermal stability, and robustness. Confronting the pressing issue of arsenic contamination within both environmental settings and the food supply is of paramount importance to preserve public health and ecological equilibrium. In response, this study introduces detection kits predicated upon silver nanoparticles, providing an expeditious and economically feasible avenue for identifying arsenic concentrations ranging from 0.5 to 3 ppm within rice. Subsequent quantification employs Hydride Atomic Absorption Spectroscopy (HG-AAS), which features a detection threshold of 0.05 ㎍/l. A salient advantage inherent in the HG-AAS methodology lies in its capacity to segregate analytes from the sample matrix, thereby significantly reducing instances of spectral interference. Importantly, the presence of arsenic in the soil beneath rice cultivation establishes a causative link to steel pipe corrosion, with potential consequences extending to food contamination-an intricate facet embedded within the broader tapestry of renewable energy, oil, and environmental pollution.

• Computers and Concrete
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• v.33 no.5
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• pp.559-572
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• 2024

Problems of under-sized dams (small dams with large basin area) could get worse under the global warming condition. This study evaluates the possible change of these problems with the Namgang Dam, an under-sized dam in Korea. For this purpose, first, this study simulates the dam inflow data using a rainfall-runoff model, which are then used as input for the reservoir operation. As a result, daily dam storage, dam release, and dam water supply are derived and compared for both past observed period (1973~2022) and future simulated period (2006~2099) based on the global warming scenarios. Summarizing the results are as follows. First, the inflow rate in the future is expected to be increased significantly. The maximum inflow could be twice of that observed in the past. As a result, it is also expected that the frequency of the water level reaching the high level is increasing. Also, the amount and frequency of dam release are to be increased in the future period. More seriously, this increase is expected to be concentrated on rather extreme cases with large dam release volume. Simply, the condition for flood protection in the downstream of the Namgang Dam is becoming worse and worse. Ironically, the severity of water shortage problem is also expected to become much worse. As the most extreme case, the frequency of no water supply was zero in the observed period, but in the future period, it becomes once every five years. Both the maximum consecutive shortage days and the total shortage volume are expected to become more than twice in the future period. To prevent or mitigate this coming problem of an under-sized dam, the only countermeasure at this moment seems to be its redevelopment. Simply a bigger dam with larger dam reservoir can handle this adverse effect more easily.

• Computers and Concrete
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• v.33 no.5
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• pp.595-603
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• 2024

In the construction industry, there has been a surge in the implementation of high-tech equipment in recent years. Various technologies are being considered as potential solutions for future construction projects. Building information modeling (BIM), which utilizes advanced equipment, is a promising solution among these technologies. The need for safety inspection has also increased with the aging structures. Nevertheless, traditional safety inspection technology falls short of meeting this demand as it heavily relies on the subjective opinions of workers. This inadequacy highlights the need for advancements in existing maintenance technology. Research on building safety inspection using 3D laser scanners has notably increased. Laser scanners that use light detection and ranging (LiDAR) can quickly and accurately acquire producing information, which can be realized through reverse engineering by modeling point cloud data. This study introduces an innovative evaluation system for building safety using a 3D laser scanner. The system was used to assess the safety of an existing three-story building by implementing a reverse engineering technique. The 3D digital data are obtained from the scanner to detect defects and deflections in and outside the building and to create an as-built BIM. Subsequently, the as-built structural model of the building was generated using the reverse engineering approach and used for structural analysis. The acquired information, including deformations and dimensions, is compared with the expected values to evaluate the effectiveness of the proposed technique.

• Computers and Concrete
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• v.33 no.5
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• pp.621-630
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• 2024

This study presents novel electromagnetic wave-based methods for evaluating the integrity of cement-based structures using time domain reflectometry (TDR). Two cement-based plates with embedded rebars are prepared under sound and defective conditions. TDR tests are carried out using transmission lines with various numbers of artificial joints, and electromagnetic waves are measured to assess the integrity of the plates. The experimental results show that the travel time of electromagnetic waves is consistently longer in sound plates than in defective ones, and an increase in the reflection coefficients is observed in the defect zone of the defective plates. Electromagnetic wave velocities are higher in the defective plates, especially when connectors are present in the transmission line. A novel approach based on the area of the reflection coefficient provides larger areas in the defective plates, and the attenuation effect of the electromagnetic waves induces a difference in the areas of the reflection coefficient between the two defect conditions. An alternative method using the centroid of the defect zone slightly overestimates the location of the defect zone. The length of the defect zone is estimated using the defect ratio and wave velocities of cement, air, and plate. The length of the defect zone can also be calculated using the travel times within the plate, total measured length of the plate, and wave velocities in the cement and air. Therefore, the electromagnetic wave-based methods proposed in this study may be useful for estimating the location and length of defect zones by considering attenuation effects.

• Earthquakes and Structures
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• v.26 no.5
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• pp.401-416
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• 2024

Long-span structures, such as bridges, can experience different seismic excitations at the supports due to spatially variability of ground motion. Regarding current bridge designing codes, it is just EC 2008 that suggested some regulations to consider it and in the other codes almost ignored while based on some previous studies it is found that the effect of mentioned issue could not be neglected. The current study aimed to perform a comprehensive study about the effect of spatially varying ground motions on the dynamic response of a reinforced concrete bridge under asynchronous input motions considering soil-structure interactions. The correlated ground motions were generated by an introduced method that contains all spatially varying components, and imposed on the supports of the finite element model under different load scenarios. Then the obtained results from uniform and non-uniform excitations were compared to each other. In addition, the effect of soil-structure interactions involved and the corresponding results compared to the previous results. Also, to better understand the seismic response of the bridge, the responses caused by pseudo-static components decompose from the total response. Finally, an incremental dynamic analysis was performed to survey the non-linear behavior of the bridge under assumed load scenarios. The outcomes revealed that the local site condition plays an important role and strongly amplifies the responses. Furthermore, it was found that a combination of wave-passage and strong incoherency severely affected the responses of the structure. Moreover, it has been found that the pseudo-static component's contribution increase with increasing incoherent parameters. In addition, regarding the soil condition was considered for the studied bridge, it was found that a combination of spatially varying ground motions and soil-structure interactions effects could make a very destructive scenarios like, pounding and unseating.

• Computers and Concrete
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• v.33 no.1
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• pp.27-39
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• 2024

In this study, the authors investigate the free vibration behavior of three-phases functionally graded sandwich plates using a novel nth-order shear deformation theory. These plates are composed of a homogeneous core and two face-sheet layers made of different functionally graded materials. This is the novel type of the sandwich structures that can be applied in many fields of mechanical engineering and industrial. The proposed theory only requires four unknown displacement functions, and the transverse displacement does not need to be separated into bending and shear parts, simplifying the theory. One noteworthy feature of the proposed theory is its ability to capture the parabolic distribution of transverse shear strains and stresses throughout the plate's thickness while ensuring zero values on the two free surfaces. By eliminating the need for shear correction factors, the theory further enhances computational efficiency. Equations of motion are established using Hamilton's principle and solved via Navier's solution. The accuracy and efficiency of the proposed theory are verified by comparing results with available solutions. The authors then use the proposed theory to investigate the free vibration characteristics of three-phases functionally graded sandwich plates, considering the effects of parameters such as aspect ratio, side-to-thickness ratio, skin-core-skin thicknesses, and power-law indexes. Through careful analysis of the free vibration behavior of three-phases functionally graded sandwich plates, the work highlighted the significant roles played by individual material ingredients in influencing their frequencies.

• Earthquakes and Structures
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• v.26 no.1
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• pp.31-48
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• 2024

In order to get a better understanding of seismic performance of exterior beam-column joint, reciprocating loading tests with variable loading speeds or axial forces were carried out. The main findings indicate that only few cracks exist on the surface of the joint core area, while the plastic hinge region at the beam end is seriously damaged. The damage of the specimen is more serious with the increase of the upper limit of variable axial force. The deflection ductility coefficient of specimen decreases to various degrees after the upper limit of variable axial force increases. In addition, the higher the loading speed is, the lower the deflection ductility coefficient of the specimen is. The stiffness of the specimen decreases as the upper limit of variable axial force or the loading speed increase. Compared to the influence of variable axial force, the influence of the loading speed on the stiffness degradation of the specimen is more obvious. The cumulative energy dissipation and the equivalent viscous damping coefficient of specimen decrease with the increase of loading speed. The influence of variable axial force on the energy dissipation of specimen varies under different loading speeds. Based on the truss model, the biaxial stress criterion, the Rankine criterion, the Kent-Scott-Park model, the equivalent theorem of shearing stress, the softened strut-and-tie model, the controlled slip theory and the proposed equations, a calculation method for the shear capacity is proposed with satisfactory prediction results.

• Steel and Composite Structures
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• v.50 no.3
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• pp.347-362
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• 2024

Controlling vibrations and noise in steel box girders is important for reducing noise pollution and avoiding discomfort to residents of dwellings along bridges. The fundamental approach to solving this problem involves first identifying the main path of transmission of the vibration energy and then cutting it off by using targeted measures. However, this requires an investigation of the characteristics of flow of vibration energy in the steel box girder, whereas most studies in the area have focused on analyzing its single-point frequency response and overall vibrations. To solve this problem, this study examines the transmission of vibrations through the segments of a steel box girder when it is subjected to harmonic loads through structural intensity analysis based on standard finite element software and a post-processing code created by the authors. We identified several frequencies that dominated the vibrations of the steel box girder as well as the factors that influenced their emergence. We also assessed the contributions of a variety of vibrational waves to power flow, and the results showed that bending waves were dominant in the top plate and in-plane waves in the vertical plate of the girder. Finally, we analyzed the effects of commonly used stiffened structures and steel-concrete composite structures on the flow of vibration energy in the girder, and verified their positive impacts on energy regionalization. In addition to providing an efficient tool for the relevant analyses, the work here informs research on optimizing steel box girders to reduce vibrations and noise in them.

• Advances in concrete construction
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• v.16 no.3
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• pp.169-176
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• 2023

The aim of the study was to establish the influence of particle size, chemical and phase composition of fine microspherical high-calcium fly ash (HCFA), as well as superplasticizer content on the strength of cementless composite materials based on 100% HCFA and mixtures of HCFA with Portland cement (PC). For the initial HCFA fractions, the particle size distribution, chemical and quantitative phase composition were determined. The compressive strength of cured composite materials obtained at W/B 0.4 and 0.25 was determined at a curing time of 3-300 days. For cementless materials, it was found that a change in the particle size d90 from 30 ㎛ (fraction 3) to 10 ㎛ (fraction 4) leads to an increase in compressive strength by more than 2 times. Compressive strength increases by at least another 2.2 times with the addition of Melflux 5581F superplasticizer (0.12%) and at W/B 0.25. The HCFA-PC blends were investigated in the range of 60-90% HCFA and the maximum compressive strength was found at 80% HCFA. On the basis of 80% HCFA-20% PC blend, the samples of ultra-high strength (108 and 150 MPa at 28 and 100 days of hardening) were obtained with the addition of 0.3% Melflux 5581F and 5% silica fume. The quantitative phase composition was determined for composite materials with a curing age of 28 days. It has been established that in a sample with ultra-high strength, a more complete transformation of the initial phases of both HCFA and PC occurs as compared to their transformation separately.

• Advances in concrete construction
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• v.16 no.6
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• pp.291-302
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• 2023

As the first part of the body that strikes the ground during running, sports shoes are especially important for improving performance and reducing injuries. The use of new nanotechnology materials in the shoe's sole that can affect the movement angle of the foot and the ground reaction forces during running has not been reported yet. It is important to consider the material of the sole of the shoe since it determines the long-term performance of sports shoes, including their comfort while walking, running, and jumping. Running performance can be improved by polymer foam that provides good support with low energy dissipation (low energy dissipation). Running shoes have a midsole made of ethylene propylene copolymer (EPP) foam. The mechanical properties of EPP foam are, however, low. To improve the mechanical performance of EPP, conventional mineral fillers are commonly used, but these fillers sacrifice energy return. In this study, to improve the magnificence of physical education training with nanotechnology, carbon nanotubes (CNTs) derived from recycled plastics were prepared by catalytic chemical vapor deposition and used as nucleating and reinforcing agents. As a result of the results, the physical, mechanical, and dynamic response properties of EPP foam combined with CNT and zinc oxide nanoparticles were significantly improved. When CNT was added to the nanocomposites with a weight percentage of less than 0.5 wt%, the wear resistance, physical properties, dynamic stiffness, compressive strength, and rebound properties of EPP foams were significantly improved.