• Proceedings of the Korean Geotechical Society Conference
• /
• 2008.03a
• /
• pp.587-598
• /
• 2008

In the trackbed design using elastic multi-layer model, the stress-dependent resilient modulus is an important input parameter, which reflects substructure performance under repeated traffic loading. The resilient moduli of crushed stone and weathered granite soil were developed using nonlinear dynamic stiffness, which can be measured by in-situ and laboratory seismic tests. The prediction models of resilient modulus varying with the deviatoric or bulk stress were proposed (Park et al., 2008). To investigate the performance of the prediction models proposed herein, the elastic response of the test trackbed near PyeongTaek, Korea was evaluated using a 3-D nonlinear elastic computer program (GEOTRACK) and compared with measured elastic vertical displacement during the passages of freight and passenger trains. The material types of the test sub-ballasts are crushed stone and weathered granite soil, respectively. The calculated vertical displacements within the sub-ballasts are within the order of 1mm, and agree well with measured values with the reasonable margin. The prediction models are thus concluded to work properly in the preliminary investigation. The prediction models proposed for resilient modulus were verified by the comparison of the calculated vertical displacements with measured ones during train passages.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.11 no.1
• /
• pp.9-16
• /
• 2016

Since most of devices in the IEEE 802.15.4 LR-WPAN are expected to operate on batteries, they must be designed to consume energy in a very conservative way. Two energy conservation algorithms are proposed for the LR-WPAN: DDC (Dynamic Duty Cycle) and DBT (Dynamic Beacon Tracking). The DDC algorithm adjusts duty cycle dynamically depending on channel conditions. The DBT algorithm switches beacon tracking mode on and off adaptively depending on traffic conditions. Combining the two algorithms reduces energy consumption more efficiently for a wide range of input loads, while maintaining frame delivery ratio and average delay at satisfactory levels.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.157-160
• /
• 2008

Bridge decks are directly exposed to traffic loads and environmental conditions like rainfall water and de-icing chemicals. In this reason, there are often observed the deteriorations of asphalt overlay and concrete deck. In this study, 32 concrete decks were evaluated by the road inspection vehicle and the GPR mounted on the vehicle. The GPR could detect the deteriorations of concrete decks under asphalt overlay, even though the asphalt overlay looks like soundness. Therefore, for the efficient maintenance of concrete bridge decks, GPR examination should be performed with visual inspection.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.425-428
• /
• 2008

Concrete bridge decks, as well as asphalt pavement, are directly exposed to traffic loads and environmental conditions like rain water and deiceing chemicals. In this reason, there are often observed the deteriorations of asphalt overlay and of concrete deck under pavement. In this reason, it is important to identify the clear cause of concrete quality from a practical point of view. Therefore, in this paper it was initiated to ultimately suggest a protocol offering guidance as to assurance the quality control of concrete bridge deck on the part of void characteristics of concrete. Examinations such as visual inspection, deteriorated depth, and various void characteristic performed from cored specimens of 19 concrete bridge decks of various local conditions on the expressway. This paper discuss that the bridge deck condition analyses from the testing results were compared to a foreign guide line.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.28 no.9B
• /
• pp.813-822
• /
• 2003

Conventional TCPs are designed to work efficiently on wired network where any transmission errors rarely take place. However, the probability of transmission error in a wireless network is much higher than in a wired network, due to pass loss, multipath fading, and many kinds of interference. There were many researches on preventing the degradation of TCP performance in these wireless networks with bad channel condition. One of these researches is the SNOOP protocol which is link-layer solution for achieving high throughput of TCP. However, this SNOOP protocol is apt to retransmit some TCP segments unnecessarily, which could cause some increased traffic loads in a wireless network. In this paper, we propose a new algorithm to prevent the unnecessary retransmission of TCP segments and to achieve increased performance of TCP.

• Steel and Composite Structures
• /
• v.7 no.1
• /
• pp.1-18
• /
• 2007

Additional cutouts in the floorbeam webs of orthotropic plated bridge decks relieve the highly stressed lower flange of the ribs passing through these floorbeam webs from possible fatigue damage. Conversely, the floorbeam webs themselves suffer from high stress concentrations, especially along the free edges of the additional cutouts. These stresses result from a combination of direct introduction of vertical traffic loads in the weakened web and from the truss action of the floorbeam. The latter differs from a simple beam action due to the presence of the openings and corresponds more to the behaviour of a Vierendeel truss. Close assessment of the appearing stresses, highly relevant for fatigue resistance, requires the use of elaborate finite element modelling. However, a full finite element analysis merely provides the results of total stresses, leaving the researcher or designer the difficult task of finding the origin of these stress components. This paper presents a calculation method for cutout stresses based on a combination of a framework analysis and a two dimensional finite element analysis of much smaller parts of the floorbeam. This method provides more insight in the origin of the stress components, as well as it simplifies any comparison of different additional cutout geometries, independent of the floorbeam topology.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.14 no.3
• /
• pp.13-19
• /
• 2014

Improvement of performances of potable communication devices such as laptops, tablets, and smart-phones enables people to do group meetings in any place. However, even though group members in a meeting locate close, data or information to be shared in the group are exchanged through the cellular networks. This increases unnecessary traffic loads in the wireless/backbone networks and as consequence it increase delays in communications. To resolve the problem, an android-based application is developed in this paper. The application utilizes Wi-Fi Direct so that all members in the meeting can direct exchange materials for the meeting without using cellular networks.

• The Journal of the Acoustical Society of Korea
• /
• v.17 no.4E
• /
• pp.28-34
• /
• 1998

In most switching system, the processing unit is designed to work efficiently even at relatively high loads, but when the offered traffic exceeds a particular level, the rate of completed calls can fall drastically. A single call handled by the switching system consists of a sequence of events or messages that has to be processed by the control unit. The control unit is not only incapable of handling all of the offered calls, but also its call handling capability can drop as the offered load increases. The real time available for call processing is a critical resource that requires careful management. Therefore, the overloading of this resource must be detected by a subscriber in the from of a dial tone delay or an uncompleted call which is either blocked or mishandled. The subscriber may respond by either dialing prematurely or by re-attempting a call. This action can further escalate the processors load, which is spent for uncompleted calls. Unless a proper control is used, the switching system can finally break down. In this paper, we paper, we propose a fuzzy overload detection and control method for switching systems, which can by generating fuzzy rules via fuzzy aggregation networks. Simulation results involving a switching system is given.

• International Journal of Highway Engineering
• /
• v.20 no.1
• /
• pp.97-105
• /
• 2018

PURPOSES : Asphalt concrete pavement is damaged by various causes such as traffic and environmental loads. The distressed pavement should be maintained by various methods to provide a comfortable and safe pavement for the driver. This study evaluates the effect of adding a mixing procedure to enhance the mixture quality in the hot in-placement recycled asphalt pavement method, which is an asphalt-pavement maintenance method. METHODS : Various test methods such as Marshall stability and dynamic stability, were employed to estimate the recycled asphalt mixture with and without an additional mixing, using the hot in-placement recycled asphalt pavement method. RESULTS : The mixture samples used in this study were taken before and after the addition of the mixer in the hot in-placement recycled asphalt pavement method (HIR) at field construction sites in GongJu and JinJu in South Korea. The test results of both mixtures satisfied the asphalt-mixture standard specifications. CONCLUSIONS : This study confirmed that adding a mixer in the HIR method results in a well-mixed new asphalt mixture, rejuvenator, and reclaimed asphalt mixture.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.49 no.4
• /
• pp.43-49
• /
• 2007

The reinforced concrete slab is one of main structure members in the construction industry sector. However, most of researches regarding to RC slabs have been focused on two-dimensional Mindlin-type plate element on the basis of laminated plate theory since three-dimensional solid element has a lot of difficulties in finite element formulation and costs in CPU time. In reality, the RC slabs are subjected to dynamic loads like a heavy traffic vehicle load, and thus should insure the safety from the static load as well as dynamic load. Once we can estimate the dynamic behaviour of RC slabs exactly, it will be very helpful for design of it. In this study, the 20-node solid element has been used to analyze the dynamic characteristics of RC slabs with clamped edges. The elasto-visco plastic model for material non-linearity and the smeared crack model have been adopted in the finite element formulation. The applicability of the proposed finite element has been tested for dynamic behaviour of RC slabs with respect to characteristics of concrete materials in terms of cracking stress, crushing strain, fracture energy and Poisson's ratio. The effect on dynamic behaviour is dependent on not crushing strain but cracking stress, fracture energy and Poisson's ratio. In addition to this, it is shown the damping phenomenon of RC slabs has been identified from the numerical results by using Rayleigh damping.