• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.655-658
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• 2004

This study was performed to verify the possibility of the integrity estimation of the bridge substructure focusing on the dynamic property change of concrete pier with penetration depths using experimental modal analysis. As a result of the impact vibration test, it is found that scour reduces the stiffness of the foundation, and measurement the accelerance residue and natural frequency can be used for the estimation of the integrity index.

• Journal of the Korean Geotechnical Society
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• v.36 no.8
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• pp.61-72
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• 2020

It is generally considered that differences of axial stiffness between exiting pile and reinforcing pile affect the load distribution ratio during vertical extension remodeling. But there are few cases to verify the effect of stiffness by field load test on load distribution ratio in Korea. In this paper, a series of load tests for micropiles were carried out to evaluate the effect of axial stiffness on the load distribution ratio. First, different types of micropiles were constructed so that conventional micropiles simulated existing piles and waveform micropiles simulated reinforcing piles. Secondly, load tests were performed to evaluate the stiffness of each piles. After then, the raft was installed to make a piled raft system and load tests were applied on foundation to verify the effect of axial stiffness on the load distribution ratio. The experimental results show that the stiffness of waveform micropiles were 2.5 times larger than that of conventional micropiles, and the load distribution ratio between existing and reinforcing piles was increased according to axial stiffness of piles.

• Steel and Composite Structures
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• v.49 no.1
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• pp.81-89
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• 2023

A simplified calculation method of natural vibration characteristics of high-speed railway multi-span bridge-longitudinal ballastless track system is proposed. The rail, track slab, base slab, main beam, bearing, pier, cap and pile foundation are taken into account, and the multi-span longitudinal ballastless track-beam-bearing-pier-cap-pile foundation integrated model (MBTIM) is established. The energy equation of each component of the MBTIM based on Timoshenko beam theory is constructed. Using the improved Fourier series, and the Rayleigh-Ritz method and Hamilton principle are combined to obtain the extremum of the total energy function. The simplified calculation formula of the natural vibration frequency of the MBTIM under the influence of vertical and longitudinal vibration is derived and verified by numerical methods. The influence law of the natural vibration frequency of the MBTIM is analyzed considering and not considering the participation of each component of the MBTIM, the damage of the track interlayer component and the stiffness change of each layer component. The results show that the error between the calculation results of the formula and the numerical method in this paper is less than 3%, which verifies the correctness of the method in this paper. The high-order frequency of the MBTIM is significantly affected considering the track, bridge pier, pile soil and pile cap, while considering the influence of pile cap on the low-order and high-order frequency of the MBTIM is large. The influence of component damage such as void beneath slab, mortar debonding and fastener failure on each order frequency of the MBTIM is basically the same, and the influence of component damage less than 10m on the first fourteen order frequency of the MBTIM is small. The bending stiffness of track slab and rail has no obvious influence on the natural frequency of the MBTIM, and the bending stiffness of main beam has influence on the natural frequency of the MBTIM. The bending stiffness of pier and base slab only has obvious influence on the high-order frequency of the MBTIM. The natural vibration characteristics of the MBTIM play an important guiding role in the safety analysis of high-speed train running, the damage detection of track-bridge structure and the seismic design of railway bridge.

• Journal of the Korean Geosynthetics Society
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• v.18 no.3
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• pp.33-44
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• 2019

Clinker layer is a stratum structure distributed in volcanic area such as Jeju Island. The clinker layers were formed in between the repetitive action of eruption and solidification of lava flows. Since the clinker layer contains a large amount of voids accompanied by the lava gas ejection process, there is a possibility of inducing overall stability of the ground due to the low stiffness and strength of the clinker layer. Therefore, in this study, site investigation was carried out at both ends of the 00 bridge where the clinker layers exist. And, based on the ground survey results, the behavior of shallow foundations was analyzed numerically. In addition, the improved shallow foundation behavior in grouting substitution using the chemical injection method of the clinker layer was compared with the shallow foundation behavior in the ground, and the grouting substitution efficiency of each layer was analyzed. As a result, the bearing capacity, the replacement efficiency and elastic settlement were different according to the presence or absence of the sediment layer. This is because the sediment layer has a lower stiffness and density than the clinker layer.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.2
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• pp.23-31
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• 2008

Dynamic earth pressure acting on geotechnical structures can be driving force or resisting force for the displacement of the structure according to the phase relation between the dynamic earth pressure and inertia force of structures. In this research, the evaluation procedure of the phase relation between the dynamic earth pressure and the inertia force was proposed. According to the procedure, numerical analyses on caisson foundation of bridges were performed and the phase relation was analyzed. The analysis results showed that the dynamic earth pressure becomes the driving force, which increases the displacement of the structure, if the displacement amplitude of ground is larger than that of structure due to the low stiffness of the ground, and the dynamic earth pressure becomes the resisting force against the displacement of the structure if the displacement amplitude of ground is smaller than that of structure due to the high stiffness of the ground.

• Structural Engineering and Mechanics
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• v.65 no.4
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• pp.491-504
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• 2018

Because of sandwich structures with low weight and high stiffness have much usage in various industries such as civil and aerospace engineering, in this article, buckling and free vibration analyses of coupled micro composite sandwich plates are investigated based on sinusoidal shear deformation (SSDT) and most general strain gradient theories (MGSGT). It is assumed that the sandwich structure rested on an orthotropic elastic foundation and make of four composite face sheets with temperature-dependent material properties that they reinforced by carbon and boron nitride nanotubes and two flexible transversely orthotropic cores. Mathematical formulation is presented using Hamilton's principle and governing equations of motions are derived based on energy approach and applying variation method for simply supported edges under electro-magneto-thermo-mechanical, axial buckling and pre-stresses loadings. In order to predict the effects of various parameters such as material length scale parameter, length to width ratio, length to thickness ratio, thickness of face sheets to core thickness ratio, nanotubes volume fraction, pre-stress load and orthotropic elastic medium on the natural frequencies and critical buckling load of double-bonded micro composite sandwich plates. It is found that orthotropic elastic medium has a special role on the system stability and increasing Winkler and Pasternak constants lead to enhance the natural frequency and critical buckling load of micro plates, while decrease natural frequency and critical buckling load with increasing temperature changes. Also, it is showed that pre-stresses due to help the axial buckling load causes that delay the buckling phenomenon. Moreover, it is concluded that the sandwich structures with orthotropic cores have high stiffness, but because they are not economical, thus it is necessary the sandwich plates reinforce by carbon or boron nitride nanotubes specially, because these nanotubes have important thermal and mechanical properties in comparison of the other reinforcement.

• Magazine of the Korean Society of Agricultural Engineers
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• v.38 no.3
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• pp.82-91
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• 1996

This is a basic study for the static and dynamic analysis on the elasto-plastic and elasto-viscoplastic of an axi-symmetric shell. The objective of this study was to investigate the mechanical characteristics of a nuclear reinforced concrete containment structure, which was selected as a model, by a numerical analysis using a finite element method. The structure was modeled with discrete ring elements of 8-noded isoparametric element rotating against the symmetrical axis, and the interaction between the foundation and the structure was modeled by Winkler's model. Also, the meridional tendon was modeled with 2-node truss elements, and the hoop tendon was done with point elements in two degrees of freedom. The effect of the tendon was considered without the increasement in total degree of freedom as the stiffness matrix of modeled tendon elements was assembled on the stiffness matrix of ring elements linked with the tendon. The results obtained from the analysis of an example were summarized as follows : 1. The stresses in the hoop direction on the interior and exterior surfaces of the structure were shown in changes of similar trend, and high stresses appeared on the structure wall 2. The stresses in the meridional direction on the interior and exterior surfaces were shown in change of different trend. Especially, the stresses at the junctions between the dome and the wall and between the wall and the bottom plate of the structure were very high, compared with those at other parts of the structure. 3. The stress changes in the direction of thickness on the crown of the dome were much linearly distributed. However, as the amount of tendon increased, the stresses in the upper and lower parts of the wall established with the tendon were shown stress concentration. 4. The stress changes in the direction of thickness on the center of the structure wall was linearly distributed in the all cases, and special stress due to the use of the tendon was not shown.

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

• Smart Structures and Systems
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• v.29 no.2
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• pp.267-278
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• 2022

Pre-stressed concrete circular spun piles are widely used in various infrastructure projects around the world and offer an economical deep foundation system with consistent and superior quality compared to cast in-situ and other concrete piles. Conventional methods for measuring the lateral response of piles have been limited to conventional instrumentation, such as electrical based gauges and pressure transducers. The problem with existing technology is that the sensors are not able to assist in recording the lateral stiffness changes of the pile which varies along the length depending on the distribution of the flexural moments and appearance of tensile cracks. This paper describes a full-scale bending test of a 1-m diameter spun pile of 30 m long and instrumented using advanced fibre optic distributed sensor, known as Brillouin Optical Time Domain Analysis (BOTDA). Optical fibre sensors were embedded inside the concrete during the manufacturing stage and attached on the concrete surface in order to measure the pile's full-length flexural behaviour under the prescribed serviceability and ultimate limit state. The relationship between moments-deflections and bending moments-curvatures are examined with respect to the lateral forces. Tensile cracks were measured and compared with the peak strains observed from BOTDA data which corroborated very well. By analysing the moment-curvature response of the pile, the structure can be represented by two bending stiffness parameters, namely the pre-yield (EI) and post-yield (EI_cr), where the cracks reduce the stiffness property by 89%. The pile deflection profile can be attained from optical fibre data through closed-form solutions, which generally matched with the displacements recorded by Linear Voltage Displacement Transducers (LVDTs).

• Journal of Korean Society of Steel Construction
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• v.26 no.6
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• pp.537-547
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• 2014

A steel modular unit structural system has been used increasingly for mid and high-rise buildings, since the building can be easily constructed by assembling the pre-made modular unit structures. For this structural system, each modular unit structures have to be properly connected to the foundation to transfer the axial force and the bending moment that are generated from external load to the ground. In this study, a new type of the embedded steel column-to-foundation connection was proposed, and its flexural behavior was evaluated through a series of experimental study. Five full scale specimens for the proposed connections were constructed and tested. The effect of the main parameters that affect the flexural behavior of the proposed connection, such as embedment length and shape of end plate, were studied. From the results, it was found that the flexural stiffness of the proposed connection was higher than that of the semi-rigid connection for all test specimens, and 200 mm of embedment length was proper for the given test specimens in this study.