• Land and Housing Review
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• v.2 no.4
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• pp.553-558
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• 2011

Existing method protruding strands that are embedded in PHC pile to connect pile head and foundation slab shows poor constructibility. As this causes crack and damage in pile head and casualties often occurs in construction site during the work, alternative method called one-cutting method, in which pile above the ground surface and strands embedded in pile are completely cut and pile head is reinforced with rebar for connection with foundation slab, is currently adopted. However, the capacity of details for these methods are not mechanically proved. In this study, in order to suggest proper details of reinforcement for one-cutting method, failures due to lack of shear resistance between infilled concrete and PHC pile are analyzed through experiments and embedded depth with infilled concrete inside PHC pile is suggested. Assuming that slip failure strength is 0.4MPa, which is obtained from experiment conservatively, to have rebar yielded before slip failure, minimum depth of infilled concrete for PHC 450 and PHC 500, need to be 600mm above, and for PHC 600, 1,000mm above.

• Steel and Composite Structures
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• v.50 no.1
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• pp.63-75
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• 2024

In this paper, the modified couple stress theory (MCST) and first order shear deformation theory (FSDT) are employed to investigate the free vibration and bending analyses of a three-layered micro-shell sandwiched by piezoelectric layers subjected to an applied voltage and reinforced graphene nanoplatelets (GPLs) under external and internal pressure. The micro-shell is resting on an elastic foundation modeled as Pasternak model. The mixture's rule and Halpin-Tsai model are utilized to compute the effective mechanical properties. By applying Hamilton's principle, the motion equations and associated boundary conditions are derived. Static/ dynamic results are obtained using Navier's method. The results are validated with the previously published works. The numerical results are presented to study and discuss the influences of various parameters on the natural frequencies and deflection of the micro-shell, such as applied voltage, thickness of the piezoelectric layer to radius, length to radius ratio, volume fraction and various distribution pattern of the GPLs, thickness-to-length scale parameter, and foundation coefficients for the both external and internal pressure. The main novelty of this work is simultaneous effect of graphene nanoplatelets as reinforcement and piezoelectric layers on the bending and vibration characteristics of the sandwich micro shell.

• Proceedings of the Korean Geotechical Society Conference
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• 2007.09a
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• pp.665-678
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• 2007

It was applied the grouting method to fill densely the space between the bottom of the caisson and the ground with the grout mixture mixed with anti-washout admixture after locating accurately the precast caisson on three concrete landing pads but it is far different from a costly conventional method, which place concrete to build the foundation of reinforcement concrete on the spot after excavating inside of the temporary coffering wall for the bridge foundation in the sea. To verify the grouting method in advance, the full-scale trial test was performed twice on the land. After confirming the fluidity of material for the injection and some possible problems during construction and then enhancing the original design, the main process is ongoing and it has been finished 12 spots until now. The purpose of this study is to introduces for the first time in Korea the grouting method including the automatic and the manual monitoring process applied to, based on the main process of the caisson foundation finished already in the site. In a similar construction it is sincerely expected to be referred to in the future.

• Journal of the Korean GEO-environmental Society
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• v.10 no.2
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• pp.45-50
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• 2009

The differential settlement may be generated by the variation of stresses caused by the soft ground or ground water. The cracks are usually created when the structures are leaned or deformed due to the differential settlement. A grouting method has been mainly used till now to improve the bearing capacity of the ground when the foundation of the structure is deformed by differential settlements. However, when this method is used, it takes too long time to obtain the required strength and the period of the reinforcement effect is not long enough. The advantage of GPCON injection method is to have good mechanical properties and durability, and easy construction. In addition, the GPCON method rapidly fills up the void in soils by injecting some materials into underground and also obtain the increase of bearing and shearing forces due to the expansion. In this paper the restoration capability of the foundation settlement of railway and subway subjected to cyclic loading is analytically and experimentally evaluated using the high density rapidly expansion GPCON in order to investigate the types of deformations and vibrational characteristics.

• Journal of KIISE:Software and Applications
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• v.35 no.3
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• pp.179-188
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• 2008

An important issue in multiagent reinforcement learning is how an agent should team its optimal policy through trial-and-error interactions in a dynamic environment where there exist other agents able to influence its own performance. Most previous works for multiagent reinforcement teaming tend to apply single-agent reinforcement learning techniques without any extensions or are based upon some unrealistic assumptions even though they build and use explicit models of other agents. In this paper, basic concepts that constitute the common foundation of multiagent reinforcement learning techniques are first formulated, and then, based on these concepts, previous works are compared in terms of characteristics and limitations. After that, a policy model of the opponent agent and a new multiagent reinforcement learning method using this model are introduced. Unlike previous works, the proposed multiagent reinforcement learning method utilize a policy model instead of the Q function model of the opponent agent. Moreover, this learning method can improve learning efficiency by using a simpler one than other richer but time-consuming policy models such as Finite State Machines(FSM) and Markov chains. In this paper. the Cat and Mouse game is introduced as an adversarial multiagent environment. And effectiveness of the proposed multiagent reinforcement learning method is analyzed through experiments using this game as testbed.

• Computers and Concrete
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• v.27 no.2
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• pp.85-97
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• 2021

In this study, the effect of steel fiber utilization, boundary conditions, different beam cross-section, and length parameter are investigated on the free vibration behavior of fiber reinforced self-compacting concrete beam on elastic foundation. In the analysis of the beam model recommended by Euler-Bernoulli, a method utilizing Stokes transformations and Fourier Sine series were used. For this purpose, in addition to the control beam containing no fiber, three SCC beam elements were prepared by utilization of steel fiber as 0.6% by volume. The time-dependent fresh properties and some mechanical properties of self-compacting concrete mixtures were investigated. In the modelled beam, four different beam specimens produced with 0.6% by volume of steel fiber reinforced and pure (containing no fiber) SCC were analyzed depending on different boundary conditions, different beam cross-sections, and lengths. For this aim, the effect of elasticity of the foundation, cross-sectional dimensions, beam length, boundary conditions, and steel fiber on natural frequency and frequency parameters were investigated. As a result, it was observed that there is a noticeable effect of fiber reinforcement on the dynamic behavior of the modelled beam.

• Journal of the Korean Geosynthetics Society
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• v.13 no.4
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• pp.161-167
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• 2014

This paper describes reinforcement method of reinforced earth wall near the abutment. The excessive displacement of a case affected by reduction of bearing capacity due to macro-environment condition like a coast. That is, the front displacement of reinforced earth wall has been happening continuously due to strength reduction of foundation ground. The micro pile is applied to reinforcement method, in order to secure a bearing capacity and global slope stability of reinforced earth wall. The results of numerical analysis confirmed that reinforcement method based on micro pile can secure a stability of structure, while the reconstruction of reinforced earth wall is impossible by construction and macro-environment condition.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.653-657
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• 2005

This study applied the NDS method to the creek levee and the foundation of a building, for the purpose of ground improvement and cut-off. The conclusions are shown in the following. (1) The results of the field tests in the creek levee are as follows; the N value of the standard penetration test is $2{\sim}3$ before NDS grout and $9{\sim}21$ after NDS grout; in the alluvial layer, $7{\sim}11$ before NDS grout and $14{\sim}23$ after NDS grout. This confirms increasing ground strength with consistency ranging from stiff to very stiff. (2) The result of the permeability test in the creek levee shows that the ground had a great hydraulic conductivity with complete leakage before ground improvement but that the hydraulic conductivity has significantly increased to $3.17{\times}10^{-5}{\sim}4.65{\times}10^{-5}cm/sec$ after ground improvement by the NDS method. (3) The result from the field test of the foundation of the building confirms great reinforcing effects, showing that the allowable bearing capacity has increased from Pa = 5.0 $t/m^2$ before reinforcement to Pa = 25.0 $t/m^2$ after reinforcement.

• Journal of the Korean GEO-environmental Society
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• v.11 no.10
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• pp.5-13
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• 2010

Low slump mortar grouting is widely used in reinforcement of structural foundation and ground improvement in soft ground, and has advantage which construction is possible in insufficient space. However it has been not yet studied sufficiently to estimate the effect of ground improvement in design step and to prove the estimating method. So the method must be developed in order to use the low slump mortar grouting method in various cases. In this study, the field tests were performed in the reclaimed soils to measure the effect of ground improvement. Then it was compared with what was calculated by the existing formula that was formerly suggested. The results show that the value from the formula was similar with the value from the field tests. Also it was proved that the formula was available to estimate the effect of ground improvement in the loose granular soils.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.4
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• pp.933-939
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• 1994

This paper has primarily been directed to evaluate the beneficial effects of geogrid reinforcement in a medium sand on the ultimate bearing capacity (UBC) of a surface foundation. Also, this study was conducted to investigate the permanent settlement of a shallow square foundation in improving the cyclic load-settlement characteristics of reinforced sand deposits by conducting a series of laboratory model tests. Use of geogrids provides an economical and time efficient method for improving load-settlement and strength characteristics of weak soils. Especially the geogrid reinforced soil will be necessary in the case of foundation supporting machines, embankments for railroads, and foundations of structures in earthquake-prone areas. Finally, the test results indicate that the use of geogrid reinforcement in sand subgrades improves their performance under dynamic loads which shows promise for future work.