• Advances in concrete construction
• /
• v.10 no.1
• /
• pp.49-59
• /
• 2020

Precast concrete elements in accelerated bridge construction (ABC) extends from superstructure to substructure, precast pile foundation has proven a benefit for regions with fragile ecological environment and adverse geological condition. There is still a lack of knowledge of the seismic behavior and performance of the precast pile foundation. In this study, a 1/8 scaled model of precast pile foundation with elevated cap is fabricated for quasi-static test. The failure mechanism and responses of the precast pile-soil interaction system are analyzed. It is shown that damage occurs primarily in precast pile-soil interaction system and the bridge pier keeps elastic state because of its relatively large cross-section designed for railways. The vulnerable part of the precast pile with elevated cap is located at the embedded section, but no plastic hinge forms along the pile depth under cyclic loading. Hysteretic curves show no significant strength degradation but obvious stiffness degradation throughout the loading process. The energy dissipation capacity of the precast pile-soil interaction system is discussed by using index of the equivalent viscous damping ratio. It can be found that the energy dissipation capacity decreases with the increase of loading displacement due to the unyielding pile reinforcements and potential pile uplift. It is expected to promote the use of precast pile foundation in accelerated bridge construction (ABC) of railways designed in seismic regions.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.6 no.3
• /
• pp.223-230
• /
• 2005

Lately, massive concrete structures are increasingly built. Mass concrete structures are cast in many stages with construction joints. Individually constructed segment exhibit different heat source properpies and time dependent properties. As such construction stages must be incorporated in a heat of hydration analysis model to truly reflect a real construction process. Thermal stress analysis is conducted to find the way of controlling the thermal crack of pier footing mat in this paper. The footing mat model fur the analysis is $12m\times14m$ area and 3m height. This study show the process of construction stage and analyzes the results for a foundation structure constructed in 2 stage pours.

• Proceedings of the Korean Geotechical Society Conference
• /
• 2006.03a
• /
• pp.1245-1250
• /
• 2006

The rapid growth of the economy recently gas led to increasing social needs for large scaled structures, such as high-rise buildings and long span bridges. In building these large-scaled structures the trend has been to construct foundations beating on or in rock masses in order to ensure stability and serviceability of the structure under several significant loads. However. when designing the drilled shaft foundation socketed in rock masses in Korea, the bearing capacity for the pier used to be determined by using the empirical expression, which depends on the compressive strength of the rock, or presumable bearing capacity recommended on foreign references or manuals. In this study, numerical analyses are used to trace rock-socketed pile behavior and are made alike with pile load test result in field. The result of this numerical analyses study have shown that following factors have a significant influence on the load capacity and settlement of the pier. Significant influence first factor of the geometry of the socket as defined by the length to diameter ratio. Second factor of the modulus of the rock both around the socket and below the base. third factor of the condition of the end of the pier with respect to the removal of drill cuttings and other loose material from the bottom of the socket.

• Journal of the Korean Geotechnical Society
• /
• v.37 no.11
• /
• pp.61-69
• /
• 2021

In this study, scale down model bridge piers were fabricated and non-destructive experiments conducted with an impact load to determine scours in the ground adjacent to the bridge piers using the natural frequency of the bridge piers. Three scale-model bridge piers with different heights were fabricated, and they penetrated the ground at a depth of 0.35 m. The scours around the bridge piers were simulated as a side scour and foundation scour. The experiments were conducted in 13 steps, in which scouring around the model bridge piers was performed in 0.05 m excavation units. To derive the natural frequency, the impact load was measured with three accelerometers attached to the model bridge piers. The impact load was applied with an impact hammer, and the top of the model bridge pier was struck perpendicularly to the bridge axis. The natural frequency according to the scour progress was calculated with a fast Fourier transform. The results demonstrated that the natural frequency of each bridge pier tended to decrease with scour progress. The natural frequency also decreased with increasing pier height. With scour progress, a side scour occurred at 70% or higher of the initial natural frequency, and a foundation scour occurred at less than 70%.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.38 no.1
• /
• pp.116-127
• /
• 1996

This paper dealt with FEM analysis of foundation improved with pack drain. The theory on pack drain was scrutinized and observed values in the field were compared with numerical results. Work site of Kwangyang container pier was selected as a ease study in which measurement of settlement and pore water pressure was accurately carried out. Biot's consolidation equation was selected as governing One, coupled with modified Camclay model as constitutive one. Christian and Boehmer's numerical technique was adopted. Behavior of foundation with pack drain is not simple but very complicated. Discontinuity resulted from rigidity difference between adjacent materials, smear effect and complicated boundary conditions should be considered in the behavior analysis of foundation behavior. The results of numerical analysis were influenced by smear zone. In relevant to this effect, finite element analysis was carried out using the reduced horizontal coefficient of permeability in the smear zone; The numerical results were compared with observed values in surface settlement. including pore water pressure. However only lateral di5plaoement by numerical ana1Ysis was shown since its measurement was not performed in the field. The predication of settlement to be developed later can be effectively employed for the obtimization of construction. The predication of residual settlement using the data measured in the field was made by Hoshino, Asaoka and hyperbolic method. Among them, the hyperbolic method proved best one. Settlements accorded well between numsrical and observed values while pore pressure showed a slight difference. Lateral displacement showed largest values at constant distance from ground surface. The validation of foundation analysis improved with pack drain by computer program employed in this study selecting modified Cam-clay model was satisfactorily secured.

• Journal of Periodontal and Implant Science
• /
• v.46 no.4
• /
• pp.266-276
• /
• 2016

Purpose: The aim of the present study was to retrospectively investigate the influence of potential risk indicators on the development of peri-implant disease. Methods: Overall, 103 patients referred for implant treatment from 2000 to 2012 were randomly enrolled. The study sample consisted of 421 conventional-length (>6 mm) non-turned titanium implants that were evaluated clinically and radiographically according to preestablished clinical and patient-related parameters by a single investigator. A non-parametric Mann-Whitney U test or Kruskal-Wallis rank test and a logistic regression model were used for the statistical analysis of the recorded data at the implant level. Results: The diagnosis of peri-implant mucositis and peri-implantitis was made for 173 (41.1%) and 19 (4.5%) implants, respectively. Age (${\geq}65$ years), patient adherence (professional hygiene recalls <2/year) and the presence of plaque were associated with higher peri-implant probing-depth values and bleeding-on-probing scores. The logistic regression analysis indicated that age (P=0.001), patient adherence (P=0.03), the absence of keratinized tissue (P=0.03), implants placed in pristine bone (P=0.04), and the presence of peri-implant soft-tissue recession (P=0.000) were strongly associated with the event of peri-implantitis. Conclusions: Within the limitations of this study, patients aged ${\geq}65$ years and non-adherent subjects were more prone to develop peri-implant disease. Therefore, early diagnosis and a systematic maintenance-care program are essential for maintaining peri-implant tissue health, especially in older patients.

• Journal of the Korean Geotechnical Society
• /
• v.35 no.6
• /
• pp.17-26
• /
• 2019

In this study, the statistical characteristics of the resistance bias factors were analyzed using a high-quality field load test database, and the total resistance bias factors were estimated considering the soil uncertainty and construction errors for the application of the limit state design of aggregate pier foundation. The MLR model by Bong and Kim (2017), which has a higher prediction performance than the previous models was used for estimating the resistance bias factors, and its suitability was evaluated. The chi-square goodness of fit test was performed to estimate the probability distribution of the resistance bias factors, and the normal distribution was found to be most suitable. The total variability in the nominal resistance was estimated including the uncertainty of undrained shear strength and construction errors that can occur during the aggregate pier construction. Finally, the probability distribution of the total resistance bias factors is shown to follow a log-normal distribution. The parameters of the probability distribution according to the coefficient of variation of total resistance bias factors were estimated by Monte Carlo simulation, and their regression equations were proposed for simple application.

• Journal of the Korean GEO-environmental Society
• /
• v.23 no.2
• /
• pp.13-23
• /
• 2022

The ground-structure interaction of the bridge foundation has been pointed out as a major factor influencing the behavior of the bridge during earthquakes. In this study, the effect of characteristics of ground and bridge foundation on the earthquake vulnerability is investigated. From the pseudo-static analysis, it is confirmed that non-linearity becomes lesser and horizontal load becomes greater when surcharge is considered. It is also found that as the ground worsens and the size of foundation decreases, horizontal load reduces. To derive reasonable structural model for bridge foundation, fragility curve is obtained considering four conditions (fixed condition, equivalent linear condition, non-linear without surchage condition, non-linear with surcharge condition) and compared. Seismic analysis is performed on single pier with Opensees. From the earthquake vulnerability analysis, it is found that shallow foundation can be assumed as fixed condition. In conservative approach, stiffness of spring can be obtained based on Korean highway bridge design code for pile foundation which can consider the ground condition.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.349-352
• /
• 1999

Concrete cracks due to hydration heat are a serious problem, particularly in mass concrete structures such as box rahmen, dam or footing of pier, etc.. As a result of the temperature rise and restriction condition of foundation, the thermal stress which may induce the cracks can occur. In this, study, ABAQUS program package was used to calculate the temperature distributions generated by hydration heat and the thermal stress in box rahmen structure which have thickness of 1.7~2.2m, and applied for various equations of adiabatic temperature rise such as korean code, japanese code, convection coefficient and low heat cement code.

• Proceedings of the Computational Structural Engineering Institute Conference
• /
• 1999.04a
• /
• pp.177-186
• /
• 1999

Dynamic Characteristics of the bridge motions under seismic excitations are analyzed by adopting multi degree - of - freedom system to estimate the effect of restrainers. The applied restrainer is assumed to be a dead - band - system, which has the force clearance and the linear elastic force. The inelastic behaviors of pier and foundation motions are also considered in the study. It is found that the major effect of restrainer is to remarkably decrease the relative displacement between adjacent girders. It is found that restrainers placed on the parts of the bridge system rather than the whole system may increase the unseating failure.