• Structural Engineering and Mechanics
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• v.9 no.4
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• pp.375-382
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• 2000

Experimental investigation into the cyclic behaviour of sand plast brick masonry was performed on forty two square panels. The panels were subjected to cyclic uniaxial compression for two cases of loading: normal to bed joint and parallel to bed joint. Experimental data were used to plot the unloading-reloading curves for the entire range of the stress-strain curve. Mathematical expressions to predict the reloading and unloading stress-strain curves at various values of residual strain are proposed. A simple parabola and an exponential type formula are found adequate to model the unloading and reloading curves respectively. The models account for the potential effects of residual strain on these curves. Comparison of test results with the proposed mathematical expression shows good correspondence.

• Journal of the Korean Geotechnical Society
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• v.28 no.8
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• pp.65-78
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• 2012

Elastic moduli and behavioral characteristics changes of very widely according to stress level resulting from uniaxial compressive test of sedimentary rock. This means that elastic moduli do not indicate constants but variables. More appropriate and reasonable outcome will be accepted through loading-reloading test in design and construction progress. An attention for behavioral characteristics of elastic moduli shown in low level of stress should be paid.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.09a
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• pp.1156-1167
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• 2010

The constant rate of strain (CRS) consolidation test has been widely used to evaluate consolidation characteristics of soils instead of the standard Incremental Loading Test. In practical problems, after the ground improvement, the condition of the soil is over-consolidated. Therefore, it is important to determine the recompression indices and the coefficient of consolidation(or the coefficient of swelling) of unloading-reloading cycle to predict the settlement behavior. However, since standard testing procedures or studies related with strain rate are insufficient especially in unloading-reloading cycle, it is difficult to predict the settlement field behavior accurately from the CRS consolidation test results in spite of its lots of strengths. The several CRS consolidation tests were performed changing the unloading strain rate from 0.2%/hr to 20%/hr with vertical drainage condition using the reconstituted kaolinite sample. For the reconstituted kaolinite sample in CRS consolidation test, the recompression indices are insensitive to the strain rate. It is revealed that the coefficient of consolidation of reloading is affected by the developed pore pressure during unloading. Additionally, the test should be conducted in the positive pore pressure ratio range (3~15%) to obtain the reasonable coefficient of consolidation in the whole range(loading, unloading and reloading).

• Structural Engineering and Mechanics
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• v.11 no.5
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• pp.565-574
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• 2001

Experimental investigation into the behaviour of half-scale brick masonry panels were conducted under cyclic loading normal to the bed joint and parallel to the bed joint. For each cycle, full reloading was performed with the cycle peaks coinciding approximately with the envelope curve. Unloading, however, was carried out fully to zero stress level and partially to two different stress levels of 25 percent and 50 percent of peak stress. Stability point limit exhibits a unique stress-strain curve for full unloading but it could not be established for partial unloading. Common point limit was established for all unloading-reloading patterns considered, but its location depends on the stress level at which unloading is carried to. Common point curves were found to follow an exponential formula, while residual strains versus envelope strains can be expressed by a polynomial function of a single term. The relation between residual strain and envelope strain can be used to determine the stress level at which deterioration due to cyclic loading began.

• Journal of the Korean Geotechnical Society
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• v.21 no.8
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• pp.85-93
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• 2005

Earth pressures acting on unmovable rigid walls vary according to loading-unloading conditions due to compaction experienced by backfill soil. Appropriate coefficients of earth pressure at rest with considering this influence need to be determined to estimate earth pressures more reasonably.0 this study, a single cycle hysteretic model simulating soil's loading-unloading-reloading behavior under $K_o-condition$ was reproduced by conducting a series of $K_o-triaxial$ test for compacted residual soils. Based on the results, coefficients of earth pressure at rest at each stage of stress paths such as, virgin loading, unloading and reloading were determined. Also, applicabilities of empirical equations to the estimation of the coefficients were evaluated by comparing the experimental results with those estimated by the equations. As a result, it was concluded that the empirical equations could be applied reasonably to the estimation of the coefficients for compacted residual soils in cases where some amount of error might be acceptable for the reloading stage of the hysteretic model.

• Elastomers and Composites
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• v.42 no.3
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• pp.168-176
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• 2007

When the rubber vulcanizates reinforced with carbon black or silica are subjected to cyclic loading from its virgin state, the stress required on reloading is less than that on the initial loading. This stress softening phenomenon is referred to as the Mullins effect. The strain energy function of rubber vulcanizates was investigated using theory of pseudo-elasticity incorporated damage parameter that Ogden and Roxburgh have proposed to describe the damage-induced stress softening effect in rubber-like solids. The quasi-static cyclic loading test was performed using the NR-SBR vulcanizates reinforced with carbon black, and then the effect of a damage parameter to stress-strain curve in reloading and subsequent reloading paths was studied. The strain energy function of the rubber vulcanizates with a different filler content was also evaluated.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.113-121
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• 2004

The present study is suggested to estimate the degree of secondary consolidation caused by various changes of stress such as loading, unloading and reloading in improving poor subsoil through pre-compression loading construction method and, for this purpose, examined the characteristics of the consolidation of Kunsan clay through incremental loading test (IL) using standard consolidation tester and constant loading rate test (CLR), which were adapted from the constant rate of strain test (CRS). In addition, after CRS test, this study determined the characteristics of secondary consolidation and relationships among void ratio, effective stress and time according to the ratio of effective over-consolidation on reloading at the point of time of random expansion. Kunsan clay had larger expansion and smaller secondary consolidation settlement when the ratio of effective over-consolidation was high. In addition, when loading was applied after the load was removed at once, the secondary consolidation coefficient $C'_{\alpha}$ was smaller than that when the load was removed gradually, and when the ratio of effective over-consolidation was over 1.4 a similar value was produced. Based on the entire settlement resulting from reloading, the secondary consolidation coefficient $C"_{\alpha}$ increased non-linearly with the lapse of time but the final value was similar to that in the case of rapid removal. The strain velocity of void ratio was in a regular linear relationship with the increase of loading time regardless of the ratio of effective over-consolidation in both tests and it grew smaller with the increase of the ratio of effective over-consolidation.tion.

• Journal of The Korean Society of Agricultural Engineers
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• v.51 no.6
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• pp.83-90
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• 2009

This study was carried out to evaluate the vertical stress properties in sandy soil according to changes of loading type in soil bin compacted three layers. The following conclusions and comparisons have been made based on careful analysis from theoretical and experimental methods. : When sandy soil subjected to cycle-loading, compression of foundation and diffusion of vertical stress increment(${\Delta}{\sigma}_2$) were influenced by magnitude of loading plate. When sandy soil subjected to reloading after removing of pre-loading, the distribution of ${\Delta}{\sigma}_2$ depth at one time of loading plate width was different from its distribution at more deep point cause of load hysteresis, so in case of design of structure, the effect of ${\Delta}{\sigma}_2$ as depth must be considered. The increment of vertical stress will be different as loading condition and foundation depth, the loading condition must be considered in case of structure design.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.14 no.4
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• pp.537-549
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• 2001

The effect of partially restrained(PR) connections and the uncertainties in them on the reliability of steel frames subjected to seismic loading is addressed. A stochastic finite element method(SFEM) is proposed combining the concepts of the response surface method(RSM), the finite element method(FEM), the first-order reliability method (FORM), and the iterative linear interpolation scheme. The behavior of PR connections is captured using moment-relative rotation curves, and is represented by the four-parameter Richard model. For seismic excitation, the loading, unloading, and reloading behavior at PR connections is modeled using moment-relative rotation curves and the Masing rule. The seismic loading is applied in the time domain for realistic representation. The reliability of steel frames in the presence of PR connections is calculated considering all major sources of nonlinearity. The algorithm is clarified with the help of an example.

• Journal of Ocean Engineering and Technology
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• v.15 no.4
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• pp.92-100
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• 2001

It is very important to determine the coefficient of earth pressure at rest accurately in order to estimate the behavior of soil structure. For estimation of K/sub 0/-value depending upon the stress history of dry sand, a new type of K/sub 0/-oedeometer apparatus is devised, and the horizontal earth pressure is accurately measured. For this study, 2 types of one-cyclic K/sub 0/-Loading/unloading models have been studied experimentally using four relative densities of the sand. The results obtained in this test are as follows : K/sub on'/ the coefficient of earth pressure at - rest for virgin loading is a function of the angle of internal friction Φ' of the sand and is determined as K/sub on/=1 - 0.914 sin Φ', K/sub ou'/ the coefficient of earth pressure at rest for virgin unloading is a function of K/sub on/ and over consolidation ratio(OCR), and is determined as K/sub ou/=K/sub on/(OCR)K/sup a/. The exponent α, increases as the relative density increases. K/sub or'/ the coefficient of earth pressure at rest for virgin reloading decreases in hyperbola type as the vertical stress, σ/sub v/’, increases. And, the stress path at virgin reloading leads to the maximum prestress point, independent upon the value of the minimum unloading stress. The gradient of this curve, m/sub r/ increases as OCR increases.