• Architectural research
• /
• v.15 no.1
• /
• pp.53-58
• /
• 2013

High strength concrete is being used increasingly in mass structure projects. The purpose of this study is to investigate the influence of temperature during mixing, placing and curing on the strength development, hydration products and pore structures of high strength concrete in mass structures. The experiments were conducted with two different model walls, viz.: 1.5 m and 0.3 m under typical summer and winter weather conditions. The final part of this study deal with the clarification of the relationship between the long-term strength loss and the microstructure of the high strength concrete at high temperatures. Test results indicated that high elevated temperatures in mass concrete structures significantly accelerate the strength development of concrete at the early ages, while the long-term strength development is decreased. The long-term strength loss is caused by the decomposition of ettringite and increased the total porosity and amount of small pores.

• Proceedings of the Earthquake Engineering Society of Korea Conference
• /
• 2002.03a
• /
• pp.93-100
• /
• 2002

In this paper, new simple model is developed to evaluate the variation of the magnitude and the phase contrast of force components with the development of excess pore pressure in backfill soil. Also, Newmark sliding block analysis is performed inputting the calculated total force from new model. The applicability of new simple model and Newmark sliding block model is verified from the analyses of 1g shaking table test results.

• Journal of the Korean Geotechnical Society
• /
• v.22 no.5
• /
• pp.59-67
• /
• 2006

The centrifuge and 1-g shaking table tests were performed simultaneously to compare the dynamic behaviors of loose sands of the same geotechnical properties. The prototype soils were 10 m thick liquefiable loose sands. The geometric scaling factors were 20 for 1-g and 40 for centrifuge tests. The excess pore pressure, surface settlement, and acceleration in the soil were measured at the same locations in the 1-g and centrifuge tests. The total excess pore pressure from development to dissipation was measured. In the centrifuge test, viscous fluid was used as the pore water to eliminate the time scaling difference between dynamic time and dissipation time. In the 1-g tests, the steady state concept was applied to determine the unit weight of the model soil, and two different time scaling factors were applied for the dynamic time and the dissipation time. It is concluded that the 1-g tests can simulate the excess pore pressure of the prototype soil if the permeability of the model soil is small enough to prevent dissipation of excess pore pressure during shaking and the dissipation time scaling factor is properly determined.

• Journal of the Korean Geotechnical Society
• /
• v.20 no.9
• /
• pp.91-103
• /
• 2004

A series of shaking table model tests were performed to verify the validity of similitude law, which is suggested by lai (1989) to simulate the dynamic behavior of soil-fluid-structure system for is shaking table tests. In the tests, the similitude law suggested by lai was applied to determine the length and the time scaling factors. Also, the steady state concept was used in determining the density of model backfill soil, which is a key factor in simulating the development of excess pore pressure during shaking. The similitude law was verified by checking whether three different sizes of quay walls show the identical behavior or not. The similar responses of acceleration, excess pore pressure and horizontal displacement of walls were obtained far the small and large models. However, the medium model showed larger responses than those of the small and large models because of the resonance between the frequency of input acceleration and the natural frequency of the wall system. In addition, the vertical displacement and rotational angle of the walls became larger with the increase of model size.

• Advances in concrete construction
• /
• v.13 no.6
• /
• pp.423-431
• /
• 2022

Although the influence of moisture content on the mechanical properties of concrete has been studied for a long time, research related to its influence on the damping and energy dissipation property of concrete structure is still very limited. In this paper, the relationship between damping property and moisture content of concrete using cyclic uniaxial compression is firstly presented, and the mechanism of the influence of moisture content on concrete damping and energy dissipation capacity is analyzed. Based on the experimental research, moisture-related damping and energy dissipation model is proposed. Results show that the dissipated energy of concrete and loss factor increase as the moisture content increasing. The energy dissipation coefficient reflecting the influence of stress level of concrete under cyclic load, decreases first and then increases as the moisture content increasing. The mechanism of moisture-related energy dissipation behavior can be divided into the reactive force of water, the development of the internal micro cracks and the pore water pressure. Finally, the proposed moisture-related damping and energy dissipation model are verified.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.03a
• /
• pp.435-441
• /
• 2008

More time is required for consolidating soft clay when its hydraulic conductivity around the vertical drains is reduced by soil disturbance. One of the methods to be proposed to solve such problem is the electro-osmotic flow application. This study presents the experimental results of model tests using a modified oedometer and a large-scale cylinder with a sand drain. Results show that the development of negative excessive pore water pressure due to the DC electrical field in saturated clay can be transformed to additional loads causing more consolidation settlement.

• Geotechnical Engineering
• /
• v.3 no.3
• /
• pp.63-74
• /
• 1987

A practical constitutive equation with sufficient generality is proposed for porous materials to deal with plastic pore compaction and pore related strain-hardening. With an application of this proposed model, finite element calculations are executed for the compaction of a porous material. Results show powerful potential of finite element method in a quantitative investigation of the process of the compaction. Special attention is given to the process of unloading during which the development of tensile principal stress may lead to phenomena such as lamination and end-capping.

• Current Applied Physics
• /
• v.18 no.11
• /
• pp.1388-1392
• /
• 2018

Metal thin films are used widely to solve the vibration problem. However, damping mechanism is still not clear, which limits the further improvement of the damping properties for film and the development of multi-functional damping coating. In this paper, Damping microscopic mechanism of porous metal films was investigated at both macroscopically and microscopically mixed levels. Molecular dynamics simulation method was used to model and simulate the loading-unloading numerical experiment on the micro-pore and vacancy model to get the stress-strain curve and the microstructure diagram of different defects. And damping factor was calculated by the stress-strain curve. The results show that dislocations and new vacancies appear in the micro-pores when metal film is stretched. The energetic consumption from the motion of dislocation is the main reason for the damping properties of materials. Micro-mechanism of damping properties is discussed with the results of in-situ experiment.

• Geomechanics and Engineering
• /
• v.1 no.3
• /
• pp.193-204
• /
• 2009

A 10.4-m high highway embankment retained behind mechanically stabilized earth (MSE) walls is under construction in the northeastern part of the Indian state of Bihar. The structure is constructed with compacted, micaceous, grey, silty sand, reinforced with polyester (PET) geogrids, and faced with reinforced cement concrete fascia panels. The connections between the fascia panels and the geogrids failed on several occasions during the monsoon seasons of 2007 and 2008 following episodes of heavy rainfall, when the embankment was still under construction. However, during these incidents the MSE embankment itself remained by and large stable and the collateral damages were minimal. The observational data during these incidents presented an opportunity to develop and calibrate a simple procedure for estimating rainfall induced pore water pressure development within MSE embankments constructed with backfill materials that do not allow unimpeded seepage. A simple analytical finite element model was developed for the purpose. The modeling results were found to agree with the observational and meteorological records from the site. These results also indicated that the threshold rainwater infiltration flux needed for the development of pore water pressure within an MSE embankment is a monotonically increasing function of the hydraulic conductivity of backfill. Specifically for the MSE embankment upon which this study is based, the analytical results indicated that the instabilities could have been avoided by having in place a chimney drain immediately behind the fascia panels.

• Proceedings of the Korean Ceranic Society Conference
• /
• 2007.07a
• /
• pp.129-137
• /
• 2007

This paper presents a numerical model which can predict degree of hydration of cement mineral component, such as $C_{3}S$, $C_{2}S$, $C_{3}A$, $C_{4}AF$ and microstructure of hydrating cement as a function of water to cement ratio, cement particle size distribution, cement mineral components and temperature. In this model cement particles are parked randomly in cell space and hydration process is described using a multi-component integrated kinetic model. The simulation result of degree of hydration of cement mineral component agrees well with experiment result. The content of cement hydration product, such as CSH and CH can be obtained as an accompanied result during hydration process. By introducing of equal-area projection method, water withdrawl mechanism and contact area among cement particles can be considered in detail. By using proposed method, pore size distribution of hydrating cement is predicted.