• Structural Engineering and Mechanics
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• v.14 no.4
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• pp.435-454
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• 2002

The paper proposes analytical forms able to represent with very good approximation the constitutive law experimentally deducible by means of uniaxial cyclic compressive tests on material having softening post-peak behaviour in compression and negligible tensile strength. The envelope, unloading and reloading curves characterizing the proposed model adequately approach structural responses corresponding to different levels of nonlinearity and ductility, requiring a not very high number of parameters to be calibrated experimentally. The reliability of the model is shown by comparing the results that it is able to provide with the ones analytically deduced from two reference models (one for concrete, another for masonry) available in the literature, and with experimental results obtained by the authors in the framework of a research in progress.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.453-458
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• 2001

This paper presents the procedure to find the hysteresis loop of RC member using a modified strut-and-tie model. The forces and displacements at critical points, that are initial yielding point, target displacement point, unloading elastic limit, and reloading point after pinching, are investigated with the strut-and-tie models. Using bond-slip relationship, the elastic behavior of tie element is determined. The plastic flow behavior after flexural yielding is expressed by changing the location of longitudinal strut. Determination of pinching effect completes the initial hysteresis loop, assuming that the behavior of the opposite direction is symmetrical form.

• Structural Engineering and Mechanics
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• v.64 no.1
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• pp.11-21
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• 2017

It has been observed in the past that, the reinforced concrete (RC) bridge columns are very often subjected to torsional moment in addition to flexure and shear during seismic vibration. Ignoring torsion in the design can trigger unexpected shear failure of the columns (Farhey et al. 1993). Performance based seismic design is a popular design philosophy which calls for accurate prediction of the hysteresis behavior of structural elements to ensure safe and economical design under earthquake loading. However, very few investigations in the past focused on the development of analytical models to accurately predict the response of RC members under cyclic torsion. Previously developed hysteresis models are not readily applicable for torsional loading owing to significant pinching and stiffness degradation associated with torsion (Wang et al. 2014). The present study proposes an improved polygonal hysteresis model which can accurately predict the hysteretic behavior of RC circular and square columns under torsion. The primary curve is obtained from mechanics based softened truss model for torsion. The proposed model is validated with test data of two circular and two square columns. A good correlation is observed between the predicted and measured torque-twist behavior and dissipated energy.

• Journal of the Korean Ceramic Society
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• v.34 no.3
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• pp.296-302
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• 1997

The effect of cold cyclic compaction on densification of SiC whisker/Al2O3 composite was investigated. Re-lative density of the compact increased as the number of cycle and the compaction pressure increased and the bias pressure decreased. The rate of loading and unloading and the frequency of cold cyclic compaction did not affect much on sliding and rearrangement of the particles. Fracture of SiC whisker was hardly ob-served during cold cyclic compaction and the direction of whisker was randomly oriented throughout the compact regardless of the direction of compaction. Thus, cold cyclic compaction may be an efficient method to densify SiC whisker/Al2O3 composite.

• Journal of the Korea Institute of Military Science and Technology
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• v.17 no.6
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• pp.844-852
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• 2014

PBX simulant is known to exhibit highly nonlinear behaviors of deformation such as the stress softening, hysteresis under cyclic loading, residual strain after unloading, and aging. This paper proposes a new pseudo-elastic model for PBX simulant considering stress softening and residual strain. Uniaxial loading and unloading tests at quasi-static states were carried out in order to obtain the mechanical properties of the PBX simulants. And then the Dorfmann-Ogden model is modified to make it consistent with the test result of PBX simulants. Prediction with the new model shows a good correspondence to the experimental data demonstrating that the model properly describes stress softening and residual strain of PBX simulants.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.4
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• pp.7-13
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• 2002

The behaviors of the reinforced concrete membrane elements are expected by Navier's three principles of the mechanics of materials. The adopted cyclic stress-strain curves of concrete consist of seven different unloading and loading stages in the compressive zone and six other stages in the tensile zone. The curves took into account the softening of concrete that was influenced by the tensile strain in the perpendicular direction of cracks. The stress-strain relationships for steel bar embedded in concrete subjected to reversed cyclic forces considered the tension stiffening effect and Baushinger effect. The predicted results of the analysis based on Navier's principles were in good agreement with the observed shear stress-strain relationships as well as transverse and longitudinal strains.

• Journal of the Korea Concrete Institute
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• v.25 no.1
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• pp.19-28
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• 2013

The longitudinal axial strain in the plastic hinge region of reinforced concrete (RC) columns influences on the structural behavior of RC structures subjected to reversed cyclic loading. This strain decreases the effective compressive strength of concrete and increases the lateral displacements between stories by causing the elongation of member length. This paper investigated the effects of the axial force on the elongation of a RC member by using a sectional analysis of RC members. The analytical and experimental results indicated that the axial force decreased the axial strain in the plastic hinge region of RC columns. In this study, a model was proposed to predict the axial strain of RC columns. The proposed model considering the effects of axial force ratio consisted of three path types ; Path 1-loading region, Path 2-unloading region, and Path 3-reversing cyclic loading region. The axal strains predicted by the proposed model were compared with the test results of RC columns with various axial force ratios, and agreed reasonably with the observed longitudinal strains.

• Journal of the Korean Ceramic Society
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• v.28 no.9
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• pp.712-720
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• 1991

The effect of cyclic compressive stress on fracture responses of Al2O3 was investigated under uniaxial stress cycling. Experimental data were obtained for Al2O3 tension specimens under uniaxial tension-unloading and tension-compression cyclic loading conditions. To investigate the effect of compressive stress on the crack growth, theoretical results from the crack growth rate were compared with measured stress vs. failure relations. At low stress level in tension-compression cycling, residual tensile strains were also observed about failure time.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.10a
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• pp.475-482
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• 2002

A moment-curvature relationship to simulate the behavior of reinforced concrete (RC) columns under cyclic loading is introduced. Unlike previous moment4curvature models and the layered section approach, the proposed model takes into account the bond-slip effect by using a monotonic moment-curvature relationship constructed on the basis of the bond-slip relation and corresponding equilibrium equation at each nodal point. In addition, the use of curved unloading and reloading branches inferred from the stress-strain relation of steel gives more exact numerical result. The pinching effect caused by axial force is considered with an assumption that the absorbing energy corresponding to any deformation level maintains constant regardless of the magnitude of applied axial lone. The advantages of the proposed model, comparing to layered section approach, may be on the reduction in calculation time and memory space in case of its application to large structures. Finally, correlation studies between analytical result and experimental studies are conducted to establish the validity of the proposed model.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.700-705
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• 2007

In this study, we observe the application of shape memory alloy(SMA) into smart structures for repeatable actuation, because SMA changes its material properties and characteristics progressively under cyclic loading conditions and finally reaches stable path(state) after a certain number of stress/temperature loading-unloading cycles, so called 'training'. In this paper, SMA wires that have been in a stable state through the training are used. Stress-strain curve of the SMA wire at different temperature levels are measured. In addition, we observe other important effects such as the rate effect according to strain rates for rapid actuation response. The current work presents the experimental test using SMA wire after training completion by mechanical cycling. Through these tests, we measure the characteristics of SMA. With the estimated SMA properties and effects, we compare the experimental results with the simulation results based on the SMA constitutive equations.