• 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.

• International Journal of Naval Architecture and Ocean Engineering
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• v.5 no.4
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• pp.569-579
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• 2013

A steel-type breakwater that uses a submerged dual horizontal porous plate was originally proposed by Kweon et al. (2005), and its hydrodynamic characteristics and design methodology were investigated in a series of subsequent researches. In particular, Kweon et al. (2011) proposed a method of estimating the vertical uplift force that acts on the horizontal plate, applicable to the design of the pile uplift drag force. However, the difference between the method proposed by Kweon et al. (2011), and the wave force measured at a different time without a phase difference, have not yet been clearly analyzed. In this study, such difference according to the method of estimating the wave force was analyzed, by measuring the wave pressure acting on a breakwater model. The hydraulic model test was conducted in a two-dimensional wave flume of 60.0 m length, 1.5 m height and 1.0 m width. The steepness range of the selected waves is 0.01~0.03, with regular and random signals. 20 pressure gauges were used for the measurement. The analysis results showed that the wave force estimate in the method of Kweon et al. (2011) was smaller than the wave force calculated from the maximum pressure at individual points, under a random wave action. Meanwhile, the method of Goda (1974) that was applied to the horizontal plate produced a smaller wave force, than the method of Kweon et al. (2011). The method of Kweon (2011) was already verified in the real sea test of Kweon et al. (2012), where the safety factor of the pile uplift force was found to be greater than 2.0. Based on these results, it was concluded that the method of estimating the wave force by Kweon et al. (2011) can be satisfactorily used for estimating the uplift force of a pile.

• International Journal of High-Rise Buildings
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• v.4 no.3
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• pp.219-226
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• 2015

By the end of 2014, the number of completed and under-construction supertall buildings above 250 meters in China reached 90 and 129, respectively. China has become one of the centers of supertall buildings in the world. Supertall buildings in China are getting taller, more slender, and more complex. The structural design of these buildings focuses on the efficiency of lateral resisting systems and the application of energy dissipation. Furthermore, the research, design, and construction of high-performance materials, pile foundations, and mega-members have made a lot of progress. Meanwhile, more and more challenges are presented, such as the improvement of structural system efficiency, the further understanding of failure models, the definition of design criteria, the application of high-performance materials, and construction monitoring. Thus, local structural engineers are playing a more important role in the design of supertall buildings.

• Journal of the Korean GEO-environmental Society
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• v.18 no.7
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• pp.37-47
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• 2017

In this study, a series of full-scale field tests on prebored and precast steel pipe piles and the corresponding numerical analysis have been conducted in order to study the characteristics of pile load-settlement relations and shear stress transfer at the pile-soil interface. Dynamic pile load tests (EOID and restrike) have been performed on the piles and the estimated design pile loads from EOID and restrike tests were analysed. Class-A type numerical analyses conducted prior to the pile loading tests were 56~105%, 65~121% and 38~142% respectively of those obtained from static load tests. In addition, design loads estimated from the restrike tests indicate increases of 12~60% compared to those estimated in the EOID tests. The EOID tests show large end bearing capacity while the restrike tests demonstrate increased skin friction. When impact energy is insufficient during the restrike tests, the end bearing capacity may be underestimated. It has been found that total pile capacity would be reasonably estimated if skin friction from the restrike tests and end bearing capacity from the EOID are combined. The load-settlement relation measured from the static pile load tests and estimated from the numerical modelling is in general agreement until yielding occurs, after which results from the numerical analyses substantially deviated away from those obtained from the static load tests. The measured pile behaviour from the static load tests shows somewhat similar behaviour of perfectly-elastic plastic materials after yielding with a small increase in the pile load, while the numerical analyses demonstrates a gradual increase in the pile load associated with strain hardening approaching ultimate pile load. It has been discussed that the load-settlement relation mainly depends upon the stiffness of the ground, whilst the shear transfer mechanism depends on shear strength parameters.

• Journal of the Korean Geotechnical Society
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• v.30 no.4
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• pp.93-99
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• 2014

Use of geothermal energy has been increased for its economical application and environmentally friendly utilization. Particularly, for energy piles, a spiral coil type ground heat exchanger (GHE) is more preferred than line type GHEs such as U and W shaped GHEs. A PHC energy pile with spiral coil type GHE was installed in an area of partially saturated dredged soil deposit, and a thermal response test (TRT) was conducted for 240 hours under a continuous operation condition. Besides, remolded soil samples from different layers were collected in the field, and soil specimens were reconstructed according to the field ground condition. Non-steady state probe methods were conducted in the lab, and ground thermal conductivity and thermal diffusivity were measured for the different soil layers. An equivalent ground thermal conductivity was calculated from the lab test results and it was compared with the field TRT result. The difference was less than 5%, which advocates the use of an equivalent ground thermal conductivity for the multi-layered ground. Furthermore, this paper also represents an equivalent ground thermal diffusivity evaluation method which is another very important design parameter.

• Journal of the Korean GEO-environmental Society
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• v.15 no.9
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• pp.47-58
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• 2014

This study explores methods for modeling the foundation-seabed interaction needed for the load analysis of an offshore wind energy system. It comprises the comparison study of foundation design load analyses for NREL 5 MW turbine according to various soil-foundation interaction models by conducting the load analysis with GH-Bladed, analysis software for offshore wind energy systems. Furthermore, the results of the aforementioned load analysis were applied to foundation analysis software called L-Pile to conduct a safety review of the foundation cross-section design. Differences in the cross-section of a monopile foundation were observed based on the results of the fixed model, winkler spring and coupled spring models, and the analysis of design load cases, including DLC 1.3, DLC 6.1a, and DLC 6.2a. Consequently, under all design load conditions, the diameter and thickness of the monopile foundation cross-section were found to be 7 m and 80 mm, respectively, using the fixed and coupled spring models; the results of the analysis conducted using the winkler spring model showed that the diameter and thickness of the monopile foundation cross-section were 5 m and 60 mm, respectively. The study found that the soil-foundation interaction modeling method had a significant impact on the load analysis results, which determined the cross-section of a foundation. Based on this study, it is anticipated that designing an offshore wind energy system foundation taking the above impact into account would reduce the possibility of a conservative or unconservative design of the foundation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.2
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• pp.155-163
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• 2012

The aim of this study is to evaluate the performance of the GHP system with 150 energy piles for a commercial building. In order to demonstrate the feasibility of a sustainable performance of the system, simulations were conducted over 1-year and 20-year periods, respectively. The 1-year simulation results showed that the maximum and minimum temperatures of brine returning from the energy piles were $23.80^{\circ}C$ and $7.90^{\circ}C$, which were in a range of design target temperatures. In addition, after 20 years' operation, these returning temperatures decreased slowly to $23.05^{\circ}C$ and $6.98^{\circ}C$, and finally reached to stable state. The results also showed that the energy piles injected heat of 65.6 MWh to the ground and extracted heat of 96.0 MWh from the ground, respectively. Also, it is expected this GHP system with energy piles can operate with average SPF of more than 4.15 for long term.

• Nuclear Engineering and Technology
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• v.52 no.9
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• pp.1974-1982
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• 2020

Numerical prediction of fission product plateout and circulating coolant activities under normal operating conditions is crucial in the design of a high temperature gas-cooled reactor (HTGR). The results are used for the maintenance and repair of the components as well as the safety analysis regarding early source terms under loss of coolant accident scenarios. In this work, a new computer code named POSCA (Plate-Out Surface and Circulating Activities) was developed based on a one-dimensional model to evaluate fission product plateout and circulating coolant activities within the primary circuit of a HTGR. The verification and validation of study for the POSCA code was done using available analytical results and two in-pile experiments (i.e., OGL-1 and VAMPYR-1). The results of the POSCA calculations show that POSCA is able to simulate plateout and circulating coolant activities in a HTGR with fast computation and reasonable accuracy.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.1
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• pp.28-36
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• 2013

The aim of this study is to evaluate the performance of the GHP system with 45 cast-in-place energy piles(CEP) for a commercial building. In order to demonstrate the feasibility of a sustainable performance of the system, transient simulations were conducted over 1-year and 20-year periods, respectively. The 1-year simulation results showed that the maximum and minimum temperatures of brine returning from the CEPs were $23.91^{\circ}C$ and $6.66^{\circ}C$, which were in a range of design target temperatures. In addition, after 20 years' operation, these returning temperatures decreased to $21.24^{\circ}C$ and $3.68^{\circ}C$, and finally reached to stable state. Annual average extraction heat of cast-in-place energy piles was 94.3 MWh and injection heat was 65.7 MWh from the 20 years of simulation results. Finally, it is expected this GHP system can operate with average heating SPF of more than 3.45 for long-term.

• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.305-309
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• 2007

FTL(Fuel Test Loop) is a facility that confirms performance of nuclear fuel at a similar irradiation condition with that of nuclear power plant. FTL construction work began on August, 2006 and ended on March, 2007. During Construction, ensuring the worker's safety was the top priority and installation of the FTL without hampering the integrity of the HANARO was the next one. The installation works were done successfully overcoming the difficulties such as on the limited space, on the radiation hazard inside the reactor pool, and finally on the shortening of the shut down period of the HANARO. The Commissioning of the FTL is to check the function and the performance of the equipment and the overall system as well. The FTL shall start operation with high burn up test fuels in early 2008 if the commissioning and licensing progress on schedule.