• Steel and Composite Structures
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• v.46 no.4
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• pp.471-483
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• 2023

This paper presents an analytical hyperbolic theory based on the refined shear deformation theory for mechanical stability analysis of the simply supported advanced composites plates (exponentially, sigmoidal and power-law graded) under triangular, trapezoidal and uniform uniaxial and biaxial loading. The developed model ensures the boundary condition of the zero transverse stresses at the top and bottom surfaces without using the correction factor as first order shear deformation theory. The mathematical formulation of displacement contains only four unknowns in which the transverse deflection is divided to shear and bending components. The current study includes the effect of the geometric imperfection of the material. The modeling of the micro-void presence in the structure is based on the both true and apparent density formulas in which the porosity will be dense in the mid-plane and zero in the upper and lower surfaces (free surface) according to a logarithmic function. The analytical solutions of the uniaxial and biaxial critical buckling load are determined by solving the differential equilibrium equations of the system with the help of the Navier's method. The correctness and the effectiveness of the proposed HyRPT is confirmed by comparing the results with those found in the open literature which shows the high performance of this model to predict the stability characteristics of the FG structures employed in various fields. Several parametric analyses are performed to extract the most influenced parameters on the mechanical stability of this type of advanced composites plates.

• Tribology and Lubricants
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• v.39 no.1
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• pp.1-7
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• 2023

Fluid pumps in chemical processes are typically driven by electric motors. Even if the motor is separated from the pump with seals, wear resulting from friction and misalignment can lead to leakage of chemical fluid, causing corrosion in the bearing supporting the motor, and, eventually, failure of the motor. It is thus a standard procedure to replace bearings at regular intervals. In this article, we propose 3D-printed plastic ball bearings for use as an alternative to commercial stainless-steel ball bearings. The plastic bearings are easy to manufacture, require less time to replace, and are chemically resistant. To validate the applicability of the plastic bearings, we first conducted chemical resistance tests. Bearings were immersed in 30 caustic acid and 30 nitric acid for 30 min and 24 h, respectively. The test results showed no corrosive damage to the bearings. A test rig was set up to compare the performance of the plastic bearings with that of the commercially equivalent deep-groove ball bearings. Loading test results showed that the plastic bearings performed as well as the commercial bearing in terms of vibration level and load-handling capability. Finally, a plastic bearing was subjected to a clean-in-place process for three months. It actually outperformed the commercial bearing in terms of chemical resistance. Thus, 3D-printed plastic bearings are a viable alternative to stainless-steel ball bearings.

• Earthquakes and Structures
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• v.23 no.5
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• pp.473-491
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• 2022

The research investigates experimentally the effect of confinement on structural behavior at the ends of beam-column in reinforced concrete (RC) frames. In the experimental study, five specimens consisting of 1/3-scaled RC frames having single-bay, representing the traditional deficiencies of existing buildings constructed without receiving proper engineering service is investigated. The RC frame specimens were produced to represent most of the existing buildings in Turkey that have damage potential. To decrease the probable damage to the existing buildings exposed to earthquakes, the carbon Textile Reinforced Mortar (TRM) strengthening technique (fully wrapping) was used on the ends of the RC frame elements to increase the energy dissipation and deformation capacity. The specimens were tested under reversed cyclic lateral loading with constant axial loads. They were constructed satisfying the weak column-strong beam condition and consisting of low-strength concrete, such as compressive strength of 15 MPa. The test results were compared and evaluated considering stiffness, strength, energy dissipation capacity, structural damping, ductility, and damage propagation in detail. Comprehensive investigations of these experimental results reveal that the strengthening of a brittle frame with fully-TRM wrapping with non-anchored was effective in increasing the stiffness, ductility, and energy dissipation capacities of RC bare frames. It was also observed that the frame-only-retrofitting with an infill wall is not enough to increase the ductility capacity. In this case, both the frame and infill wall must be retrofitted with TRM composite to increase the stiffness, lateral load carrying, ductility and energy dissipation capacities of RC frames. The presented strengthening method can be an alternative strengthening technique to enhance the seismic performance of existing or moderately damaged RC buildings.

• Structural Engineering and Mechanics
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• v.86 no.3
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• pp.385-397
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• 2023

This study presents an experiment and analysis to compare the seismic behavior of full-scale reinforced concrete beam-column joint strengthened by prestressed steel strips, externally bonded steel plate, and CFRP sheets. For experimental investigation, five specimens, including one joint without any retrofitting, one joint retrofitted by externally bonded steel plate, one joint retrofitted by CFRP sheets, and two joints retrofitted by prestressed steel strips, were tested under cyclic-reserve loading. The failure mode, strain response, shear deformation, hysteresis behavior, energy dissipation capacity, stiffness degradation and damage indexes of all specimens were analyzed according to experimental study. It was found that prestressed steel strips, steel plate and CFRP sheets improved shear resistance, energy dissipation capacity, stiffness degradation behavior and reduced the shear deformation of the joint core area, as well as changed the failure pattern of the specimen, which led to the failure mode changed from the combination of flexural failure of beams and shear failure of joints core to the flexural failure of beams. In addition, the beam-column joint retrofitted by steel plate exhibited a high bearing capacity, energy consumption capacity and low damage index compared with the joint strengthened by prestressed steel strip, and the prestressed steel strips reinforced joint showed a high strength, energy dissipation capacity and low shear deformation, stirrups strains and damage index compared to the CFRP reinforced joint, which indicated that the frame joints strengthened with steel plate exhibited the most excellent seismic behavior, followed by the prestressed steel strips.

• Journal of the Korea institute for structural maintenance and inspection
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• v.27 no.4
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• pp.11-22
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• 2023

In this study, a structural concrete square beam was developed using the centrifugal molding technique. In order to secure the bending stiffness of the cross section, the hollow rate of the cross section was set to 10% or less. Instead of using the current poor mixture of concrete, a special formwork for producing a centrifugal square beam was manufactured, and a concrete mixing ratio with a high slump (150-200) and a design strength of 100 MPa or more was developed and applied. The produced centrifugally formed rectangular beams were subjected to performance tests according to the standard bending and shear test standards for centrifugally formed members. The static load test results for the four specimens exceeded both the nominal bending strength and nominal shear strength, which are design values through structural design, proving the structural reliability of the ultra-high-strength centrifugally formed square beam.

• Steel and Composite Structures
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• v.48 no.4
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• pp.385-403
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• 2023

To avoid premature damage to the connection joints of a conventional precast concrete shear wall, a new precast concrete shear wall system (NPSW) based on a plastic damage relocation design concept was proposed. Five specimens, including one monolithic cast-in-place concrete shear wall (MSW) as a reference and four NPSWs with different connection details (TNPSW, INPSW, HNPSW, and TNPSW-N), were designed and tested by lateral low-cyclic loading. To accurately assess the damage relocation effect and quantify the damage and deformation, digital image correlation (DIC) and conventional data acquisition methods were used in the experimental program. The concrete cracking development, crack area ratio, maximum residual crack width, curvature of the wall panel, lateral displacement, and deformed shapes of the specimens were investigated. The results showed that the plastic damage relocation design concept was effective; the initial cracking occurred at the bottom of the precast shear wall panel (middle section) of the proposed NPSWs. The test results indicated that the crack area ratio and the maximum residual crack width of the NPSWs were less than those of the MSW. The NPSWs were deformed continuously; significant distortions did not occur in their connection regions, demonstrating the merits of the proposed NPSWs. The curvatures of the middle sections of the NPSWs were lower than that of the MSW after a drift ratio of 0.5%. Among the NPSWs, HNPSW demonstrated the best performance, as its crack area ratio, concrete damage, and maximum residual crack width were the lowest.

• Journal of the Korean Society of Industry Convergence
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• v.26 no.2_2
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• pp.333-340
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• 2023

Environmental regulations are being strengthened worldwide to solve global warming. For this reason, interest in eco-friendly gas fuels such as LNG and hydrogen is continuously increasing. However, when adopting eco-friendly gas fuel, liquefying at a cryogenic temperature is essential to ensure economic feasibility in storage and transportation. Although austenitic stainless steel is typically applied to store cryogenic liquefied gas, structural steel can experience sudden heat shrinkage in the case of leakage in the loading and unloading process of LNG. In severe cases, the phase of the steel may change, so care is required. This study conducted Charpy impact tests on steel material in nine different temperature ranges, from room to cryogenic temperatures, to analyze the effects of cryogenic liquefied gas leaks. As a result of the study, it was not easy to find variations in ductile to brittle transition temperature (DBTT) due to the leakage of cryogenic liquefied gas. Still, the overall impact toughness tended to decrease, and these results were verified through fracture surface analysis. In summary, brittle fracture of the steel plate may occur when a secondary load is applied to steel for hull structural use exposed to a cryogenic environment of -40 ℃ or lower. Therefore, it needs to be considered in the ship design and operating conditions.

• Computers and Concrete
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• v.31 no.3
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• pp.253-265
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• 2023

In this research, the gene expression programming (GEP) technique was employed to provide a new model for predicting the maximum loading capacity of concrete-encased steel (CES) columns. This model was developed based on 96 CES column specimens available in the literature. The six main parameters used in the model were the compressive strength of concrete (f_c), yield stress of structural steel (f_ys), yield stress of steel rebar (f_yr), and cross-sectional areas of concrete, structural steel, and steel rebar (A_c, A_s and A_r respectively). The performance of the prediction model for the ultimate load-carrying capacity was investigated using different statistical indicators such as root mean square error (RMSE), correlation coefficient (R), mean absolute error (MAE), and relative square error (RSE), the corresponding values of which for the proposed model were 620.28, 0.99, 411.8, and 0.01, respectively. Here, the predictions of the model and those of available codes including ACI ITG, AS 3600, CSA-A23, EN 1994, JGJ 138, and NZS 3101 were compared for further model assessment. The obtained results showed that the proposed model had the highest correlation with the experimental data and the lowest error. In addition, to see if the developed model matched engineering realities and corresponded to the previously developed models, a parametric study and sensitivity analysis were carried out. The sensitivity analysis results indicated that the concrete cross-sectional area (A_c) has the greatest effect on the model, while parameter (f_yr) has a negligible effect.

• Composites Research
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• v.20 no.4
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• pp.1-8
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• 2007

In this study, carbon fiber reinforced polymeric (CFRP) composites with different resin composition were manufactured and resin formulation in composite materials were presented through tensile tests for cryogenic use. Thermo-mechanical cyclic loading (up to 6 cycles) was applied to CFRP unidirectional laminate specimens from room temperature to $-150^{\circ}C$. Tensile tests were then performed at $-150^{\circ}C$ using an environmental test chamber. In addition, matrix-dominant properties such as the transverse and in-plane shear characteristics of each composite model were measured at $-150^{\circ}C$ to examine the effects of resin formulation on their interfacial properties. The tensile tests showed that the composite models with large amounts of bisphenol-A epoxy and CTBN modified rubber in their resin composition had good mechanical performance at cryogenic temperature (CT).

• Composites Research
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• v.22 no.6
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• pp.1-6
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• 2009

This paper presents an experimental study on the piezoresistive behavior of nanocomposite strain sensors subjected to various loading modes and their capability to detect structural deformations and damages. The electrically conductive nanocomposites were fabricated in the form of a film using various types of thermoplastic polymers and multi-walled carbon nanotubes (MWNTs) at various loadings. In this study, the nanocomposite strain sensors were bonded to a substrate and subjected to tension, flexure, or compression. In tension and flexure, the resistivity change showed dependence on measurement direction, indicating that the sensors can be used for multi-directional strain sensing. In addition, the sensors exhibited a decreasing behavior in resistivity as the compressive load was applied, suggesting that they can be used for pressure sensing. This study demonstrates that the nanocomposite strain sensors can provide a pathway to affordable, effective, and versatile structural health monitoring.