• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2017.11a
• /
• pp.157-158
• /
• 2017

This tests examined bond stress-slip relationship of V-ties embedded into concrete as a supplementary lateral reinforcement proposed for ductility of concrete flexural members. The different leg shapes of V-ties were prepared as a test parameter. The V-tie with pressed end-legs exhibited 28% higher bond strength than the conventional V-ties, whereas bond stress-slip curves were insignificantly affected by the embedment length of V-ties.

• Nuclear Engineering and Technology
• /
• v.45 no.2
• /
• pp.223-236
• /
• 2013

In the present study the behavior of fire and the residual strength of fire-ignited RC slabs are investigated by experimental tests and numerical simulations. The fire tests of RC slabs were carried out in a furnace using the ISO 834 standard fire. The load capacity of the cooled RC slabs that were not loaded during the fire tests was evaluated by additional 3 point bending tests. The influence of the proportion of PP (polypropylene) fibers in the RC slabs on the structural behavior of the RC slabs after the fire loading was investigated. The results of the fire tests showed that the maximum temperature of concrete with PP fiber was lower than that of concrete without PP fiber. As the concrete was heated, the ultimate compressive strength decreased and the ultimate strain increased. The load-deflection relations of RC slabs after fire loading were compared by using existing stress-strain-temperature models. The comparison between the numerical analysis and the experimental tests showed that some numerical analyses were reliable and therefore, can be applied to evaluate the ultimate load of RC slabs after fire loading. The ultimate load capacity after cooling down the RC slabs without PP fiber showed a considerable reduction from that of the RC slabs with PP fiber.

• Journal of the Korean Geosynthetics Society
• /
• v.11 no.2
• /
• pp.1-9
• /
• 2012

In order to review the utility of Lade's single hardening constitutive model, a series of isotropic compression-expansion tests and consolidated drained triaxial tests including as CTC, TC, RTC, and OSP were performed by Baekma river sand with various of stress path. Parameters required in model were determined using these tests. The accuracy of analysis was reviewed by back analysis of test results used to determine the 11 parameters of soil property through the test of each stress path. Also. for verifying the accuracy of prediction for the stress-strain behavior using failure criterion related 9 parameters with correlational equation and constant and yield criterion related parameters h, ${\alpha}$ and ${\eta}_1$, when stress path is different with each other, it has been obtained in the review result of stress path dependent characteristics of the constitutional model through the analyzing results of CTC, TC, RTC, OSP, and fine silica sand tests.

• The Journal of Engineering Geology
• /
• v.17 no.2 s.52
• /
• pp.299-307
• /
• 2007

We collected data of hydraulic fracturing tests and overcoring tests conducted in 84 boreholes in the south-east Korea in order to analyze the contemporary state of stress in this region. The average direction of the maximum horizontal stress was determined to be $N66^{\circ}{\pm}31^{\circ}E$. The relative magnitudes of the three principal stresses was ${\sigma}_v$ (vertical stress) < ${\sigma}_h$ (minimum horizontal stress) < ${\sigma}_H$ (maximum horizontal stress), indicating thrust fault stress regime. The stress ratio K (horizontal stress/vertical stress) was relatively high (2.2

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.32 no.4C
• /
• pp.169-175
• /
• 2012

Soil water retention characteristics are influenced by factors of the confining stress and hysteresis in the variably saturated soil. In the description of effective stress based on hydraulic characteristics, the contribution of a matric suction to effective stress then varies with depth or is different between the processes of infiltration and evaporation. Unsaturated effective stress can be described based on suction stress characteristic curve, in which a representative soil water retention curve is required to evaluate. Pressure palate extractor tests under various confining stresses were performed and the hysteresis of drying and wetting process was also acquired. In the process of drying or wetting, a unique relationship has been estimated on the effective volumetric water content and the matric suction, which defines suction stress characteristic curve. In the unsaturated shear strength from triaxial tests, the suction stress and the effective stress were evaluated by matric suctions. The failure envelop by effective stress based on soil water retention characteristics was unique and the same as the saturated one. The measured suction stress from triaxial tests was similar to that from the soil water retention curve. Therefore it is verified that a representative soil water retention curve can be defined which is independent of the confining effect under wetting or drying process of the hysteresis.

• Geotechnical Engineering
• /
• v.12 no.2
• /
• pp.9-18
• /
• 1996

The results of a series of triaxial compression tests on remolded normally consolidated clay are compared with the predictions .by the isotropic single -hardening constitutive model, which incorporates eleven parameters. The parameters can be determined from undrained triaxial compression tests on isotropically consolidated specimens of remolded clay. The model with the determined parameters is applied to predict the stress-strain and pore pressure behaviors for untrained triaxial compresion tests on anisotropically consolidated specimens. Also the model is utilized to predict the stress strain and voltmetric strain behavior for drained triaxial compression tests on both isotropic and anisotropic specimens. The predicted response agrees well with the measured behavior for undrained triaxial compression tests on not only isotropically but also anisotroically but also anisotropically consolidated specimens. The initial volumetric strain is, however, predicted to be less than the measured value from drained triaxial compression tests, while the predicted volumetric strain close to failure is greater than the measured value. Nevertheless, it may be stated generally that overall acceptable predictions are produced. Therefore, the results of this study indicate that the applicability of the model on prediction of the behavior of normally consolidated clay is achieved sufficiently.

• Journal of the Korean Geotechnical Society
• /
• v.20 no.6
• /
• pp.137-150
• /
• 2004

Aging effect of sands showed insignificant result in comparison with that of clay, so that it has not been studied so far. But, as penetration resistance increase has been observed with the lapse of time after deposition and disturbance, aging effect of sands has been actively investigated by field tests, and recently many researchers are performing not oかy field tests but also laboratory tests on sands, so aging effects of sands have been also examined by laboratory tests. In this study, to observe the aging effect of undrained static shear behavior for Nak-Dong River sand, undrained static triaxial tests were performed with changing relative density$(D_r)$, consolidation stress ratio$(K_c)$, and consolidation time. These tests showed that modulus within elastic section increased as consolidation time increased, and in addition, phase transformation point strength$(S_{PT})$ and critical stress ratio point strength $(S_{CSR})$ also increased. But pore water pressure ratio$(u/{p_c}')$ decreased as consolidation time increased, so with this various result, aging effect of static shear for sands can be observed as well.

• Journal of Ocean Engineering and Technology
• /
• v.9 no.2
• /
• pp.141-148
• /
• 1995

Fatigue tests were carried out by a rotary bending testing machine of cantilever type. M.E.F.(ferrite encapsulated islands of martensite) materials were made by a series of heat treatment from a low carbon steel(SM 20 C). The fatigue tests were conducted at stress levels of 302 MPa and with frequencies of 25Hz, 2.5 Hz and 0.5 Hz in 3% NaCl solution. The fatigue strength increased with frequency got higher. The microcracks and corrosion pits were generated at the boundary between the matrix and the 2nd phase. The cracks generated by the corrosion pits were coalesced with the pits around the notch and became the initial crack. The $N_i/N_f$ ratio increased as the frequency and stress level decreased. The interference phenomenon increased with stress level and frequency gots higher. The crack propagation rate was delayed as the stress level lowers and the frequency gets higher, however, the range of the stress intensity factor depended only on a stress level.

• Geomechanics and Engineering
• /
• v.11 no.3
• /
• pp.325-343
• /
• 2016

A total stress-based bounding surface model is developed to predict the undrained behaviour of saturated soft clays under cyclic loads based on the anisotropic hardening modulus field and bounding-surface theories. A new hardening rule is developed based on a new interpolation function of the hardening modulus that has simple mathematic expression and fewer model parameters. The evolution of hardening modulus field is described in the deviatoric stress space. It is assumed that the stress reverse points are the mapping centre points and the mapping centre moves with the variation of loading and unloading paths to describe the cyclic stress-strain hysteresis curve. In addition, by introducing a model parameter that reflects the accumulation rate and level of shear strain to the interpolation function, the cyclic shakedown and failure behaviour of soil elements with different combinations of initial and cyclic stresses can be captured. The methods to determine the model parameters using cyclic triaxial compression tests are also studied. Finally, the cyclic triaxial extension and torsional shear tests are performed. By comparing the predictions with the test results, the model can be used to describe undrained cyclic stress-strain responses of elements with different stress states for the tested clays.

• Journal of Industrial Technology
• /
• v.23 no.A
• /
• pp.139-147
• /
• 2003

The purpose of this study was to investigate and analyze the fatigue test data of pavement concrete. The static strength tests were carried out to check the compressive strength, flexural strength, and split tension strength at 56 days in order to minimize strength variation effect during test. The specimens were fabricated at twelves sections at a construction site of highway. The stress level and stress ratio of fatigue test were determined from static test results. The results are as follow: The flexural strength at 28 days mostly satisfied the criterion for design, but the compressive strength at 28 days were slightly below the criterion even though it satisfied at 56 days. The fatigue limit was 2 million cycles if the specimen was not failed to that cycles. The S-N curves were developed from the fatigue test results at each stress levels and each stress ratio. Then, the fatigue life of pavement concrete at a given stress level and fatigue strength of pavement concrete could be derived from these curves. Analysis using method No.2 was more acceptable because resulting of comparison and analysis using method No.2 was presented 2 sections were presented $R^2$ < 0.7, and other 2 sections were presented 0.7 < $R^2$ < 0.8, and the others 8 sections were $R^2{\geq}0.8$.