• Steel and Composite Structures
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• v.45 no.4
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• pp.579-590
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• 2022

One of the biggest problems in structural steel calculation is the design of structures using the lowest possible material weight, making this a slow and costly process. To achieve this objective, several optimization methods have been developed and tested. Nevertheless, a method that performs very efficiently when applied to different problems is not yet available. Based on this assumption, this work proposes a hybrid metaheuristic algorithm for geometric and dimensional optimization of space trusses, called Simulated Squirrel Search Algorithm, which consists of an association of the well-established neighborhood shifting algorithm (Simulated Annealing) with a recently developed promising population algorithm (Squirrel Search Algorithm, or SSA). In this study, two models are tried, being respectively, a classical model from the literature (25-bar space truss) and a roof system composed of space trusses. The structures are subjected to resistance and displacement constraints. A penalty function using Fuzzy Logic (FL) is investigated. Comparative analyses are performed between the Squirrel Search Algorithm (SSSA) and other optimization methods present in the literature. The results obtained indicate that the proposed method can be competitive with other heuristics.

• Journal of Surface Science and Engineering
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• v.57 no.2
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• pp.105-114
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• 2024

Tempering behavior and mechanical properties in AISI H13 steel, quenched and tempered from 300 ℃ to 700 ℃ for different tempering time (1, 2, 5, 10, 20 hr) were quantitatively investigated by scanning electron microscopy (SEM), x-ray diffractometer (XRD), impact test machine, rockwell apparatus, ball-on-disk tester. Under the condition that the tempering time is 2 hours, the hardness increases slightly as the tempering temperature increases, but decreases rapidly when the tempering temperature exceeds 500 ℃, while the impact energy increases in proportion to the tempering temperature. Friction tests were conducted in dry condition with a load of 30 N, and the friction coefficient and wear rate according to tempering conditions were measured to prove the correlation with hardness and microstructure. In addition, primary tempering from 300 ℃ to 700 ℃ was performed at various times to establish a kinetic model to predict hardness under specific tempering conditions.

• Journal of the Korea institute for structural maintenance and inspection
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• v.10 no.5
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• pp.115-121
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• 2006

This paper deals with the influence of behavior of a variety of cable elements on the limit strength of steel cable-stayed bridges. The softening plastic-hinge model, which is represented in this study for the limit strength evaluation of the example bridge, considers both geometric and material nonlinearites. Geometric nonlinearity of beam-column members are accounted by using stability function, and material nonlinearity - by using CRC tangent modulus and parabolic function. Cable sag effect is considered for cable members. The result of this study shows that the limit strength of the example bridge using the equivalent of elasticity for truss straight elements is smaller than those using the cable or the catenary elements.

• Computers and Concrete
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• v.34 no.4
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• pp.427-446
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• 2024

The I-shaped steel reinforced recycled aggregate concrete (SRRC) composite structure has the advantages of high bearing capacity and environmental protection, and the interfacial bond strength is an important theory. To this end, the I-shaped SRRC bond strength and its calculation based on artificial neural network (ANN) will be studied. Firstly, 39 push out tests of I-shaped SRRC were conducted, the load-slip curve has obvious regularity, which is divided into 4 segments by 3 regular points. Three bond strengths were defined based on these three rule points, and the approximate ranges of their values and the laws of influence of each factor on them were found. Secondly, the Elman ANN model used for the prediction of bond strength was established, and the parameters of Elman ANN predicting I-shaped SRRC bond strength were studied, and the effects of detailed parameters on the prediction results were revealed. Finally, the bond strength of SRRC was predicted using Elman and BP (back propagation) neural network models, both of which showed good prediction results. This study is a theoretical basis for the design and fine simulation of I-shaped SRRC composite structures.

• Computers and Concrete
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• v.34 no.3
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• pp.367-378
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• 2024

This study evaluates the direct tensile strength of ultra-high-performance concrete (UHPC) using tests. A total of 45 dogbone-shaped specimens are tested, with the test variables being the fiber volume fraction and notch length. The test results showed that the material properties of UHPC were largely dependent on the fiber volume fraction and compressive strength. When steel fibers with more than 1% fiber volume fraction are mixed in the manufacturing of UHPC, the tensile strength can be more than twice that of plain UHPC. In addition, the incorporation of steel fibers enabled the significant improvement of the initial cracking strength. However, the effect of the notch length on the tensile behavior was insignificant. An assessment of the direct tensile strength is conducted using machine-learning algorithms (ML). For evaluation of the direct tensile strength of UHPC using ML, a total of 98 test data, including 53 data from other research works and 45 data from this experimental program, were collected. In total, 67 data with a 70% confidence interval on a normal distribution curve were selected, with 47 data among 67 used for ML training and 20 data used for ML testing. As a result, the machine-learning algorithm with a steel fiber volume fraction predicted that the tensile strength has an average of 0.98 and the lowest values of regression evaluation metrics among analytical and ML-based models. It is considered that an ML-based model can help to predict a more accurate tensile strength of UHPC.

• Nuclear Engineering and Technology
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• v.56 no.8
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• pp.3030-3042
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• 2024

Steel containment vessels for nuclear power plants can experience gas leakage due to minute defects such as cracks, corrosion, and aging, leading to gas leakage. A gas leakage model for microchannels is established to elucidate the mechanism underlying gas leakage within microchannels caused by these defects, specifically addressing the issue of unidirectional gas flow. Computational Fluid Dynamics (CFD) and the UK R6 method are employed to calculate the gas leakage rate within microchannels. Furthermore, the characteristics of gas flow within microchannels are explored, including the factors affecting the gas leakage rate. Validation of the calculation results is verified experimentally. The results indicate that the gas mass flow rate exhibits a linear decrease with decreasing internal pressure and a non-linear decline as temperature increases. Additionally, the gas mass flow rate demonstrates a negative correlation with the microchannel length but a positive association to its hydraulic diameter. The primary influencing factors on gas leakage rates are hierarchically ranked as follows: pressure difference, microchannel cross-sectional area, temperature, microchannel length, and microchannel hydraulic diameter.

• Structural Engineering and Mechanics
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• v.92 no.2
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• pp.133-147
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• 2024

Composite beams of steel and concrete strengthened with fiber-reinforced polymers (FRP) may exhibit considerably enhanced flexural behaviour, but the combination of three materials with different characteristics and the various possible failure mechanisms that may govern performance make their analysis quite demanding. Previous studies provided significant insights into this problem and several methods were proposed for calculating flexural stiffness and strength, but these studies are restricted to the single member level of a simply supported composite beam section. However, the problem considerably changes when the beam is part of a frame system due to the degree of continuity provided by the surrounding structure, which represents the most common situation in practice. This paper explores the behaviour of semi-continuous FRP-strengthened composite beams, by considering the response characteristics of their end connections and their effects on overall performance. A novel analytical model is derived, which enables a step-by-step representation of the nonlinear relationship between an incremental mid-span design bending moment and corresponding connection rotations. After verification against finite element analyses, a parametric study is conducted which shows that the substantially increased bending moment resistance of FRP-strengthened composite beams can hardly be fully utilized due to a deficiency of corresponding large deformation capacity available in the connections. The extent to which the presence FRP strengthening can be exploited to enhance the beam flexural response depends on the interplay between various structural parameters, including the connection rotation capacity, the beam span, and the FRP modulus of elasticity and ultimate strength.

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.439-446
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• 2003

In this paper the model tests have been conducted and the results are compared with those by the theoretical methods to study the behaviors of the piled raft. The size of model box is 2.2m${\times}$2m${\times}$2m. The raft is made of rigid steel plate and piles made of steel pipes. Generally the bearing capacity of group piles is designed with only the pile capacities, and the bearing capacity of raft is ignored. But the uncertainty of pile-raft-soil interaction leads to conservative design ignoring the bearing effects of raft. In the case of considering the bearing capacity of raft, the simple sum of bearing capacity of raft and that of each pile cannot be the bearing capacity of piled raft. Because the pile-raft-soil interaction affects the behavior of piled raft. Thus the effects of pile-raft-soil interaction are very important in the optimal design. In this paper, the behaviors of piled raft are studied through model tests of 2${\times}$2, 2${\times}$3, and 3${\times}$3 pile groups. The spacing between piles is changed in the model tests. And the behaviors of free standing and piled raft are also studied.

• Journal of the Korea Concrete Institute
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• v.16 no.6 s.84
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• pp.813-822
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• 2004

For the prediction of the shear strength of reinforced concrete members subjected to axial force, this paper presents a truss model, Transformation Angle Truss Model (TATM), that can predict the shear behavior of reinforced concrete members subjected to combined actions of shear, axial force, and bending moment. In TATM, as axial compressive stress increases, crack angle decreases and concrete contribution due to the shear resistance of concrete along the crack direction increases in order to consider the effect of the axial force. To verify if the prediction results of TATM have an accuracy and reliability for the shear strength of reinforced concrete members subjected to axial forces, the shear test results of a total of 67 RC members subjected to axial force reported in the technical literatures were collected and compared with TATM and existing analytical models(MCFT RA-STM and FA-STM). As a result of comparing with experimental and theoretical results, the test results was better predicted by TATM with 0.94 in average value of $\tau_{test}/\tau_{ana}$. and $11.2\%$ in coefficient of variation than other truss models. And theoretical results obtained from TATM were not effect by steel capacity ratio, axial force, shear span-to-depth ratio, and compressive steel ratio.

• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.573-580
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• 2010

In this study, an assessment method that considers the effects of directional wind speeds on buildings or structures that are sensitive to wind is proposed. Also, the basic characteristics of directional wind speeds were assessed by means of local annual maximum wind speeds. From the method of assessment of the characteristics of directional wind speeds, their goodness-of-fit was verified by applying extreme value distribution to the data on annual maximum wind speeds from the Korea Meteorological Administration. To consider the characteristics of directional winds, an assessment method is suggested that divides the directional wind pattern of each directional wind speed into four groups. From the study results, all the data on directional wind speeds based on the Gumbel distribution were examined using data on annual maximum wind speeds from Seoul, Tongyung, and Incheon. Since the Gumbel model of all directional wind speeds has independent probability characteristics that govern the 4 directional wind pattern groups, the application ratio proposed was based on the assessment of these four groups. According to the goodness-of-fit of the data on the annual maximum wind speeds based on the Gumbel distribution, new application ratios were proposed that consider the directional wind speeds in Seoul, Tongyung, and Incheon.