• Journal of the Korea Concrete Institute
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• v.20 no.6
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• pp.697-704
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• 2008

This paper presents an analytical prediction of Nonlinear characteristics of prestressed concrete bridges by strengthened of externally tendon considering construction sequence, using unbonded tendon element and beam-column element based on flexibility method. Unbonded tendon model can represent unbounded tendon behavior in concrete of PSC structures and it can deal with the prestressing transfer of posttensioned structures and calculate prestressed concrete structures more efficiently. This tendon model made up the several nodes and segment, therefore a real tendon of same geometry in the prestressed concrete structure can be simulated the one element. The beam-column element was developed with reinforced concrete material nonlinearities which are based on the smeared crack concept. The fiber hysteresis rule of beam-column element is derived from the uniaxial constitutive relations of concrete and reinforcing steel fibers. The formulation of beam-column element is based on flexibility. Beam-column element and unbonded tendon element were be involved in A computer program, named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), that were used the analysis of RC and PSC structures. The proposed numerical method for prestressed concrete structures by strengthened of externally tendon is verified by comparison with reliable experimental results.

• Journal of Korea Water Resources Association
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• v.51 no.11
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• pp.989-998
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• 2018

Connectivity between water source and demand node can be served as a critical system performance indicator of the degree of water distribution network (WDN)' failure severity under abnormal conditions. Graph theory-based approaches have been widely applied to quantify the connectivity due to WDN's graph-like topological feature. However, most previous studies used undirected-unweighted graph theory which is not proper to WDN. In this study, the directed-weighted graph theory was applied for WDN connectivity analyses. We also proposed novel connectivity indicators, Source-to-Node Shortest Pathway (SNSP) and SNSP-Degree (SNSP-D) which is an inverse of the SNSP value, that does not require complicate hydraulic simulation of a WDN of interest. The proposed SNSP-D index was demonstrated in total 42 networks in J City, South Korea in which Pearson Correlation Coefficient (PCC) between the proposed SNSP-D and four other system performance indicators was computed: three resilience indexes and an energy efficiency metric. It was confirmed that a system representative value of the SNSP-D has strong correlation with all resilience and energy efficiency indexes (PCC = 0.87 on average). Especially, PCC was higher than 0.93 with modified resilience index (MRI) and energy efficiency indicator. In addition, a multiple linear regression analysis was performed to identify the system hydraulic characteristic factors that affect the correlation between SNSP-D and other system performance indicators. The proposed SNSP is expected to be served as a useful surrogate measure of resilience and/or energy efficiency indexes in practice.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.713-719
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• 2001

The aim of this study is to check the application criteria of the conventional techniques and clarify the effects of breaker depth, seabed conditions on the stability in relation to the effects of uncertainty of storm duration and directional irregular waves. The typical damage modes were divided by the direct wave force on the armor unit and by the local scouring around the toe of a breakwater head by the model experiments. The destruction modes are defined, and some criteria on the damage modes and scouring/deposition at the toe of a breakwater head in relating the wave-bottom-structural conditions can be checked using the multi-directonal irregular wave generator system. According to the results, it is emphasized that the 3-D effects on the stability should be analyzed in the design of multi-purpose/function coastal structures in consideration of the evaluation of spatial variation of damage modes and hydraulic characteristics as well as the wave distribution along the structures.

• Journal of the Korean Society of Marine Environment & Safety
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• v.20 no.4
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• pp.451-460
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• 2014

In this paper, we examined the problem of the structural stability according to the patch load of a rectangular plate that reflects the material properties of A6082-T6 is used primarily for marine plant structure. it applied to the four patch loading shapes, the effect of aspect ratio, a boundary condition and calculated the critical elastic buckling load. Calculating the critical elastic buckling load, During the eigenvalue buckling analysis it is applied to the shell181 as 4 node shell element. when the plate subjected to patch loading compare to the plate under a uniform axial compression load, it is possible observed to occur the different elastic buckling behaviour and it could be confirmed that it is affected significantly on a variable position and type of loadings, such as the effect of the aspect ratio. Also, Critical elastic buckling load according to th patch loading type in simply supported rectangular plate a/b=1.0, ${\gamma}b$=200mm are calculated 67%(Loading type I), 119 %(Loading type II), 76 %(Loading type III), 160 %(Loading type IV), respectively. Loading type I and III could be determined with the strong elastic buckling behavior much more than Loading type II and IV.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.6A
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• pp.495-502
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• 2010

A study for the nonlinear analysis method of flexural behavior of concrete girders strengthened with unbonded prestressed CFRP plates is presented. The concrete girders strengthened with unbonded prestressed CFRP plates exhibit more complex nonlinear behavior due to the slip between the concrete girder and the CFRP plates than the case of bonded CFRP plates. The unbonded CFRP plate is modeled as an assemblage of the curved elements both ends of which are rigidly linked to the nodes of fibered frame elements. The slip effect of the unbonded CFRP plate is taken into account using the force equilibrium relationship at each node. To evaluate the validity and the capability of the proposed analysis method, the ultimate analysis results of the concrete beams strengthened with unbonded prestressed CFRP plate are compared with the experimental results obtained from other investigators. The proposed analysis method is found to predict ultimate behaviors of these beams fairly well. Additionally the time-dependent deformations of the concrete beam seems to have little influence on the ultimate behaviors of concrete beams strengthened with unbonded prestressed CFRP plate, and the cracks of the concrete beam which occurred before strengthening it with CFRP plate are found to have almost no influence on the ultimate capacity of the beam.

• Geophysics and Geophysical Exploration
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• v.26 no.4
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• pp.268-274
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• 2023

Finite source inversion is performed with a Green's function matrix and geodetic coseismic displacement. Conventionally, the Green's function matrix is constructed using the Okada model (Okada, 1985). However, for more realistic earthquake simulations, recent research has widely adopted the physics-based model, which can consider various material properties such as elasticity, viscoelasticity, and elastoplasticity. We used the physics-based software PyLith, which is suitable for earthquake modeling. However, the PyLith does not provide a mesh generator, which makes it difficult to perform finite source inversions that require numerous subfaults and observation points within the model. Therefore, in this study, we developed CPInterface (COMSOL-PyLith Interface) to improve the convenience of finite source inversion by combining the processes of creating a numerical model including sub-faults and observation points, simulating earthquake modeling, and constructing a Green's function matrix. CPInterface combines the grid generator of COMSOL with PyLith to generate the Green's function matrix automatically. CPInterface controls model and fault information with simple parameters. In addition, elastic subsurface anomalies and GPS observations can be placed flexibly in the model. CPInterface is expected to enhance the accessibility of physics-based finite source inversions by automatically generating the Green's function matrix.

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.2
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• pp.387-393
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• 2021

In this study, finite element analysis was performed to evaluate a method of increasing the fatigue life of the pipe connection structure commonly used in the topside structure of offshore platforms. MSC Patran/Nastran, a commercial analysis program, was used, and the critical structural model was selected from the global analysis. To realize the stress concentration phenomenon according to the load, modeling using 8-node solid elements was implemented. The main loads were considered to be two lateral loads and a tensile load on a diagonal pipe. To check the hotspot stress at the main location, a 0.01 mm dummy shell element was applied. After calculating the main stress at the 0.5-t and 1.5-t locations, the stress generated in the weld was estimated through extrapolation. In some sections, this stress was observed to be below the fatigue life that should be satisfied, and reinforcement was required. For reinforcement, a bracket was added to reduce the stress concentration factor where the fatigue life was insufficient without changing the thickness or diameter of the previously designed pipe. Regarding the tensile load, the stress in the bracket toe increased by 23 %, whereas the stress inside and outside of the pipe, which was a problem, decreased by approximately 8 %. Regarding the flexural load, the stress at the bracket toe increased by 3 %, whereas the stress inside and outside of the pipe, which was also a problem, decreased by approximately 48 %. Owing to the new bracket reinforcement, the stress in the bracket toe increased, but the S-N curve itself was better than that of the pipe joint, so it was not a significant problem. The improvement method of fatigue life is expected to be useful; it can efficiently increase the fatigue life while minimizing changes to the initial design.

• The Journal of Korean Academy of Prosthodontics
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• v.48 no.3
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• pp.224-231
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• 2010

Purpose: This study was to investigate how the crestal module design could affect the level of marginal bone stress around dental implant. Materials and methods: A submerged implant of 4.1 mm in diameter and 10 mm in length was selected as baseline model (Dentis Co., Daegu,Korea).A total of 5 experimental implants of different crestal modules were designed (Type I model : with microthread at the cervical 3 mm, Type II model : the same thread pattern as Type I but with a trans-gingival module, Type III model: the same thread pattern as the control model but with a trans-gingival module, Type IV model: one piece system with concave transgingival part, Type V model: equipped with beveled platform). Stress analysis was conducted with the use of axisy mmetric finite element modeling scheme. A force of 100 N was applied at 30 degrees from the implant axis. Results: Stress analysis has shown no stress concentration around the marginal bone for the control model. As compared to the control model, the stress levels of 0.2 mm areas away from the recorded implant were slightly lower in Type I and Type IV models, but higher in Type II, Type III and Type V models. As compared to 15.09 MPa around for the control model, the stress levels were 14.78 MPa, 18.39 MPa, 21.11 MPa, 14.63 MPa, 17.88 MPa in the cases of Type I, II, III, IV and V models. Conclusion: From these results, the conclusion was drawn that the microthread and the concavity with either crestal or trans-gingival modules maybe used in standard size dental implants to reduce marginal bone stress.