• Structural Engineering and Mechanics
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• v.90 no.5
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• pp.435-446
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• 2024

The use of cold-formed steel members is increasing day by day, especially in regions where earthquake effects are intensively experienced. Among cold-formed steel members (CFS), "channel" members are used more than other crosssectional members, especially in buildings or industrial structures. In recent years, several studies have been carried out on the axial load and flexural performance of these members under monotonic loading. In this study, CFS beam-column members were cyclically and monotonically loaded under combined axial load and biaxial bending moments, and their buckling behavior, load bearing capacity, stiffness, ductility, and energy absorption capacity were determined. For this purpose, monotonic and cyclic loading experiments were carried out on 30 CFS channel members at 15 different eccentricities. Then, material properties were determined by axial monotonic tensile and very low cycle fatigue tests for use in numerical studies. From the experimental results, the buckling modes, bearing capacities, ductility, stiffness, and energy absorption capacities of the members were obtained. The characteristics of the members were compared according to the stress state of the lips. According to the data obtained from the displacement transducer placed on the lips and on the back of the web, information about the buckling mode and curvature of the members was obtained. Finally, monotonic, and cyclic loading results were compared to determine the differences in the buckling behavior of the members.

• Geomechanics and Engineering
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• v.7 no.5
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• pp.569-587
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• 2014

Triaxial compression creep tests were performed on salt rock samples using cyclic confining pressure with a static axial pressure. The test results show that, up to a certain time, changes in the confining pressure have little influence on creep properties of salt rock, and the axial creep curve is smooth. After this point, the axial creep curve clearly fluctuates with the confining pressure, and is approximately a straight line both when the confining pressure decreases and when it increases within one cycle period. The slope of these lines differs: it is greater when the confining pressure decreases than when it increases. In accordance with rheology model theory, axial creep equations were deduced for Maxwell and Kelvin models under cyclic loading. These were combined to establish an axial creep equation for the Burgers model. We supposed that damage evolution follows an exponential law during creep process and replaced the apparent stress in creep equation for the Burgers model with the effective stress, the axial creep damage equation for the Burgers model was obtained. The model suitability was verified using creep test results for salt rock. The fitting curves are in excellent agreement with the test curves, so the proposed model can well reflect the creep behavior of salt rock under low-frequency cyclic loading. In particular, it reflects the fluctuations in creep deformation and creep rate as the confining pressure increasing and decreasing under different cycle periods.

• Nuclear Engineering and Technology
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• v.49 no.1
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• pp.245-253
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• 2017

The relative displacement of a piping system installed between isolated and nonisolated structures in a severe earthquake might be larger when without a seismic isolation system. As a result of the relative displacement, the seismic risks of some components in the building could increase. The possibility of an increase in seismic risks is especially high in the crossover piping system in the buildings. Previous studies found that an elbow which could be ruptured by low-cycle ratcheting fatigue is one of the weakest elements. Fatigue curves for elbows were suggested based on component tests. However, it is hard to find a quantitative evaluation of the ultimate state of piping elbows. Generally, the energy dissipation of a solid structure can be calculated from the relation between displacement and force. Therefore, in this study, the ultimate state of the pipe elbow, normally considered as failure of the pipe elbow, is defined as leakage under in-plane cyclic loading tests, and a failure estimation method is proposed using a damage index based on energy dissipation.

• Journal of the Korean Wood Science and Technology
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• v.41 no.2
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• pp.123-133
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• 2013

This paper presents experimental and numerical tests on a recently developed timber column concealed base joint. This joint was designed to replace the wood-wood connection found in the post-and-beam structure of Hanok, the traditional Korean timber house. The use of metallic connectors provides an increased ductility and energy dissipation for a better performance under reversed loading, especially seismic. In this study, we investigate the performance of the joint under pseudo-static reversed cyclic moment loading through the study of its ductility and energy dissipation. We first perform experimental tests. Results show that the failure occurs in the metallic connector itself because of stress concentrations, while no brittle fracture of wood occur. Subsequent numerical simulations using a refined finite element model confirm these conclusions. Then, using a practical modification of the joint configuration with limited visual impact, we improve the ductility and energy dissipation of the joint while retaining a same level of rotational strength as the originally designed configuration. We conclude that the joint has a satisfying behavior under reversed moment loading for use in earthquake resistant timber structure in low to moderate seismicity areas like Korea.

• Steel and Composite Structures
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• v.42 no.5
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• pp.657-669
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• 2022

Structural materials can experience large plastic deformation under extreme cyclic loading that is caused by events like earthquakes. To evaluate the seismic safety of a structure, accurate numerical material models should be used. For a steel structure, the cyclic strain hardening behavior of structural steel should be correctly modeled. In this study, a combined hardening model, consisting of one isotropic hardening model and three nonlinear kinematic hardening models, was used. To determine the values of the combined hardening model parameters efficiently and accurately, the improved opposition-based particle swarm optimization (iOPSO) model was adopted. Low-cycle fatigue tests were conducted for three steel grades commonly used in Korea and their modeling parameters were determined using iOPSO, which was first developed in Korea. To avoid expensive and complex low cycle fatigue (LCF) tests for determining the combined hardening model parameter values for structural steel, empirical equations were proposed for each of the combined hardening model parameters based on the LCF test data of 21 steel grades collected from this study. In these equations, only the properties obtained from the monotonic tensile tests are required as input variables.

• Transactions of the Korean Society of Pressure Vessels and Piping
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• v.14 no.2
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• pp.24-31
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• 2018

In this paper, specimen tests with simulated large seismic conditions have been carried out to investigate damage characteristics such as structural deformation and crack initiation under seismic loading. The mechanical behavior of the specimens is predicted by numerical simulations and the strain-based damage evaluations are performed. Finite element analyses of the specimens under the simulated seismic loading at room and operating temperatures were carried out for low alloy steel and stainless steel materials. Peak strain amplitude, cumulative fatigue damage and cumulative strain limit damage are calculated considering the nature of cyclic loading. In all cases, the allowable damage criteria are exceeded at the time of observing cracks visually in the tests. Therefore, it is confirmed that the material behavior due to the large seismic loads can be predicted by the numerical method and the structural damage of the materials can be evaluated conservatively based on the strain criteria.

• Structural Engineering and Mechanics
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• v.3 no.4
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• pp.341-358
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• 1995

The results of a series of ten W-shaped test specimens subjected to monotonic, quasi-static cyclic loading and fatigue type of loading in the form of constant amplitude tests are presented. The objectives were to assess and compare the rotation capacity and energy absorption of monotonically and cyclically loaded beams, and for the latter specimens to document the deterioration in the form of low cycle fatigue due to local buckling. In addition, strength and energy dissipation deterioration and damage models have been developed for the steel beam section under consideration. Finally, a generalized model which uses plate slenderness values and lateral slenderness is proposed for predicting rate in strength deterioration per reversal and cumulated damage after a given number of reversals.

• Structural Engineering and Mechanics
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• v.33 no.2
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• pp.137-158
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• 2009

This paper investigates the behavior of reinforced concrete (RC) circular columns under combined loading including torsion. The main variables considered in this study are the ratio of torsional moment to bending moment (T/M) and the level of detailing for moderate and high seismicity (low and high transverse reinforcement/spiral ratio). This paper presents the results of tests on seven columns subjected to cyclic bending and shear, cyclic torsion, and various levels of combined cyclic bending, shear, and torsion. Columns under combined loading were tested at T/M ratios of 0.2 and 0.4. These columns were reinforced with two spiral reinforcement ratios of 0.73% and 1.32%. Similarly, the columns subjected to pure torsion were tested with two spiral reinforcement ratios of 0.73% and 1.32%. This study examined the significance of proper detailing, and spiral reinforcement ratio and its effect on the torsional resistance under combined loading. The test results demonstrate that both the flexural and torsional capacities are decreased due to the effect of combined loading. Furthermore, they show a significant change in the failure mode and deformation characteristics depending on the spiral reinforcement ratio. The increase in spiral reinforcement ratio also led to significant improvement in strength and ductility.

• Journal of Welding and Joining
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• v.9 no.1
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• pp.40-47
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• 1991

The most fatigue tests carried out under the either stress or strain control, but machines and structures had taken variable stress. This variable stress was treated as statistics based on p-type distributions. In this paper, the cumulative fatigue damage of SM45C round bar specimens having a center hole resulting from block loading with p-distributions in rotating bending conditions, is presented. The value of p was changed in the range from 0.25 to 1; 0.25, 0.5, 0.75, 1. The following conclusions were obtained through the constant stress amplitude experiments and the block loading experiments. (1) In constant loading test, fatigue life was affected by cyclic rate. From experimental data, N$_{f}$ (100cpm)/N$_{f}$(3000cpm)equal to 0.56. (2) In case of the cyclic rate 100cpm and 3000cpm, at the high stress amplitude level the crack propagation life N$_{*}$f is longer than the low stress amplitude level. (3) Miner's hypothesis may be valid for p=0.75 and prediction of fatigue life by Haibach's method agree with experimental data well for the case p=0.5, while the modified Miner's method agree with experimental data well for the case p=0.25.5.

• Journal of the Korean Society of Hazard Mitigation
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• v.6 no.1 s.20
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• pp.39-48
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• 2006

A laboratory investigation was performed to estimate the moduli values of asphalt concrete mixture due to various sinusoidal loadings in compression and tension. Total five modes of loading were used under five testing temperatures of 32, 50, 68, 86, and $104^{\circ}F$ (0, 10, 20, 30, and $40^{\circ}C$); repeated compressive haversine loading with rest period, repeated tensile haversine loading with rest period, cyclic compressive loading, cyclic tensile loading, and alternate tensile-compressive loadings. The test results showed that, due to the repeated haversine loading with rest period, asphalt concrete demonstrated similar moduli in tension and compression at low temperatures,(0 and $10^{\circ}C$) while those moduli were different at high temperatures (20, 30, and $40^{\circ}C$). At high temperatures the compressive moduli were always higher than the tensile moduli. The uniaxial tensile moduli were higher than indirect tensile moduli at low temperatures. However, those moduli were similar at high temperatures. In uniaxial cyclic tension, compression, and alternate tension-compression tests, compressive moduli were higher than tensile and alternate tensile-compressive moduli throughout the temperatures. Generally, the moduli from the repeated haversine loading with rest period were always lower than those from the cyclic sinusoidal loading. The difference in moduli from the repeated haversine loading with rest period and cyclic sinusoidal loading becomes more significant as the temperature decreases.