• Steel and Composite Structures
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• v.9 no.2
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• pp.131-158
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• 2009

This paper presents a modelling technique for the nonlinear analysis of composite steel-concrete beams with partial shear interaction. It extends the applicability of two stiffness elements previously derived by the authors using the direct stiffness method, i.e. the 6DOF and the 8DOF elements, to account for material nonlinearities. The freedoms are the vertical displacement, the rotation and the slip at both ends for the 6DOF stiffness element, as well as the axial displacement at the level of the reference axis for the 8DOF stiffness element. The solution iterative scheme is based on the secant method, with the convergence criteria relying on the ratios of the Euclidean norms of both forces and displacements. The advantage of the approach is that the displacement and force fields of the stiffness elements are extremely rich as they correspond to those required by the analytical solution of the elastic partial interaction problem, thereby producing a robust numerical technique. Experimental results available in the literature are used to validate the finite element proposed in the paper. For this purpose, those reported by Chapman and Balakrishnan (1964), Fabbrocino et al. (1998, 1999) and Ansourian (1981) are utilised; these consist of six simply supported beams with a point load applied at mid-span inducing positive bending moment in the beams, three simply supported beams with a point load applied at mid-span inducing negative bending moment in the beams, and six two-span continuous composite beams respectively. Based on these comparisons, a preferred degree of discretisation suitable for the proposed modelling technique expressed as a function of the ratio between the element length and depth is proposed, as is the number of Gauss stations needed. This allows for accurate prediction of the nonlinear response of composite beams.

• Structural Monitoring and Maintenance
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• v.6 no.4
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• pp.317-346
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• 2019

Performance assessment of pavements proves useful, in terms of handling the ride quality, controlling the travel time of vehicles and adequate maintenance of pavements. Roughness profiles provide a good measure of the deteriorating condition of the pavement. For the accurate estimates of pavement roughness from dynamic vehicle responses, vehicle parameters should be known accurately. Information on vehicle parameters is uncertain, due to the wear and tear over time. Hence, condition monitoring of pavement requires the identification of pavement roughness along with vehicle parameters. The present study proposes a scheme which estimates the roughness profile of the pavement with the use of accurate estimates of vehicle parameters computed in parallel. Pavement model used in this study is a two-layer Euler-Bernoulli beam resting on a nonlinear Pasternak foundation. The asphalt topping of the pavement in the top layer is modeled as viscoelastic, and the base course bottom layer is modeled as elastic. The viscoelastic response of the top layer is modeled with the help of the Burgers model. The vehicle model considered in this study is a half car model, fitted with accelerometers at specified points. The identification of the coupled system of vehicle-pavement interaction employs a coupled scheme of an unbiased minimum variance estimator and an optimization scheme. The partitioning of observed noisy quantities to be used in the two schemes is investigated in detail before the analysis. The unbiased minimum variance estimator (MVE) make use of a linear state-space formulation including roughness, to overcome the linearization difficulties as in conventional nonlinear filters. MVE gives estimates for the unknown input and fed into the optimization scheme to yield estimates of vehicle parameters. The issue of ill-posedness of the problem is dealt with by introducing a regularization equivalent term in the objective function, specifically where a large number of parameters are to be estimated. Effect of different objective functions is also studied. The outcome of this research is an overall measure of pavement condition.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.6
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• pp.762-771
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• 2003

Statement of problem. In dentistry, the minimally prepared inlay resin-bonded fixed partial denture (FPD) made of new ceromer / fiber-reinforced composite (FRC) was recently introduced. However, the appropriate dimensions for the long-term success and subsequent failure strength are still unknown. Purpose. The aim of this study was to investigate the most fracture-resistible thickness combination of the ceromer / FRC using a universal testing machine and an AE analyzer. Material and Methods. A metal jig considering the dimensions of premolars and molars was milled and 56-epoxy resin dies, which had a similar elastic modulus to that of dentin, were duplicated. According to manufacturer's instructions, the FRC beams with various thicknesses (2 to 4 mm) were constructed and veneered with the 1 or 2 mm-thick ceromers. The fabricated FPDs were luted with resin cement on the resin dies and stored at room temperature for 72 hours. AE (acoustic emission) sensors were attached to both ends, the specimens were subjected to a compressive load until fracture at a crosshead speed of 0.5 mm/min. The AE and failure loads were recorded and analyzed statistically. Results. The results showed that the failure strength of the ceromer/FRC inlay FPDs was affected by the total thickness of the connectors rather than the ceromer to FRC ratio or the depth of the pulpal wall. Fracture was initiated from the interface and propagated into the ceromer layer regardless of the change in the ceromer / FRC ratio. Conclusion. Within the limitations of this study, the failure loads showed significant differences only in the case of different connector thicknesses, and no significant differences were found between the same connector thickness groups. The application of AE analysis method in a fiber-reinforced inlay FPD can be used to evaluate the fracture behavior and to analyze the precise fracture point.

• Journal of Korean Society for Atmospheric Environment
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• v.24 no.1
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• pp.30-42
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• 2008

In this study, the chemical compositions of $PM_{2.5}$ samples collected at the Redwood National Park IMPROVE site in California from March 1988 to May 2004 were analyzed to provide source identification and apportionment. A total of 1,640 samples were collected and 33 chemical species were analyzed by particle induced X-ray emission, proton elastic scattering analysis, photon induced X-ray fluorescence, ion chromatography, and thermal optical reflectance methods. Positive matrix factorization (PMF) was used to develop source profiles and to estimate their mass contributions. The PMF modeling identified five sources and the average mass was apportioned to motor vehicle (35.8%, $1.58\;{\mu}g/m^3$), aged sea salt (23.2%, $1.02\;{\mu}g/m^3$), fresh sea salt (21.4%, $0.94\;{\mu}g/m^3$), wood/field burning (16.1%, $0.71\;{\mu}g/m^3$), and airborne soil (3.5%, $0.15\;{\mu}g/m^3$), respectively. To analyze local source impacts from various wind directions, the CPF and NPR analyses were performed using source contribution results with the wind direction values measured at the site. These results suggested that sources of $PM_{2.5}$ are also sources of visibility degradation and then source apportionment studies derived for $PM_{2.5}$ are also used for understanding visibility problem.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.53-58
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• 2006

Today, harbor oscillation problems are the most significant factor to consider when designing harbors serving very large ships. In coastal harbors, large vessels moored in the elastic hawsers are often displaced due to the resonance between long period waves and mooring systems. As a result, cargo handling may be interrupted and the hawsers may be broken, especially when the amplification becomes extreme. The most significant harbor confronted with harbor oscillation problem in Korea is Pohang New port. Many cases of problems are being reported by the pilot association and the local office of MOMAF (Ministry of Maritime Affairs and Fisheries). However, it is difficult to prevent the arrival of long waves causing oscillation within this harbor. Moreover, the Korean government has already started a new port plan at the mouth of Yeongil Bay without addressing the problems that have occurred in Pohang New port. This study deals with the variation of harbor oscillation due to the construction of a 4.1 km breakwater at the bay mouth including the arrangement of the new berths. Numerical methods used are in fairly standard form from the extended mile slope equation. The obtained numerical results were compared with field measurement from the previous and this will bring a certain level of discussion and consideration of variation to the future port development.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.9
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• pp.983-989
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• 2011

A numerical algorithm for predicting fretting wear was developed using the boundary element method (BEM). A contact analysis was performed numerically using the relation between the elastic displacement and uniformly distributed loading of a rectangular patch on a semi-infinite solid. Geometrical updating based on nodal wear depths was performed. The wear depths were computed using the Archard's equation for sliding wear. In order to investigate the efficiency of BEM for predicting fretting wear, a problem involving a two-dimensional cylinder on a flat contact was analyzed, comparing it with the simulation model proposed by McColl et al. that was based on the finite element method. The developed method was then applied to the analysis of a spherical contact and it was shown that the developed simulation technique could efficiently predict fretting wear. Moreover, the effect of a step cycle on the solution obtained by the developed method was investigated.

• Journal of the Society of Naval Architects of Korea
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• v.31 no.4
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• pp.130-138
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• 1994

Bottom plates of empty hold are subjected to not only water pressure but also bi-axial inplane loads, specially in the alternate full loading full loading condition of bulk carrier. This kind of plate behaviours is very difficult to be explained and to be estimated using common buckling design guide in the initial design stage of hull structure, therefore, some more concrete studies for this plate structure was performed based on the currently developed buckling estimation formula. In this buckling formula, torsional stiffness effects of edge stiffener are included additionally and effects of elastic buckling strength of plate panel are treated as characteristic value problem. Also considering boundary stiffener effects and inplane and lateral loading, evaluation of bottom plate scantling using this formula, calculated results using various classification regulation of buckling strength and results of first report approach are compared each other and useful guides using developed formula for bottom plate scantling design are discussed.

• Journal of the Society of Naval Architects of Korea
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• v.57 no.1
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• pp.23-34
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• 2020

This paper covers the development of prediction techniques for ice load on ice-breakers operating in continuous ice-breaking under level ice conditions using particle-based continuum mechanics. Ice is assumed to be a linear elastic material until the fracture occurs. The maximum normal stress theory is used for the criterion of fracture. The location of the crack can be expressed using a local scalar function consisting of the gradient of the first principal stress and the corresponding eigen-vector. This expression is used to determine the relative position of particle pair to the new crack. The Hertz contact model is introduced to consider the collisions between ice fragments and the collisions between hull and ice fragments. In order to verify the developed technique, the simulation results for the three-point bending problems of ice-specimen and the continuous ice-breaking problem around a wedge-type model ship with bow angle of 20° are compared with the experimental results carrying out at Korea Research Institute of Ships and Ocean Engineering (KRISO).

• Nuclear Engineering and Technology
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• v.47 no.7
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• pp.791-803
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• 2015

The effective cross sections (XSs) in the direct whole core calculation code nTRACER are evaluated by the equivalence theory-based resonance-integral-table method using the WIMS-based library as an alternative to the subgroup method. The background XSs, as well as the Dancoff correction factors, were evaluated by the enhanced neutron-current method. A method, with pointwise microscopic XSs on a union-lethargy grid, was used for the generation of resonance-interference factors (RIFs) for mixed resonant absorbers. This method was modified by the intermediate-resonance approximation by replacing the potential XSs for the non-absorbing moderator nuclides with the background XSs and neglecting the resonance-elastic scattering. The resonance-escape probability was implemented to incorporate the energy self-shielding effect in the spectrum. The XSs were improved using the proposed method as compared to the narrow resonance infinite massbased method. The RIFs were improved by 1% in $^{235}U$, 7% in $^{239}Pu$, and >2% in $^{240}Pu$. To account for thermal feedback, a new feature was incorporated with the interpolation of pre-generated RIFs at the multigroup level and the results compared with the conventional resonance-interference model. This method provided adequate results in terms of XSs and k-eff. The results were verified first by the comparison of RIFs with the exact RIFs, and then comparing the XSs with the McCARD calculations for the homogeneous configurations, with burned fuel containing a mixture of resonant nuclides at different burnups and temperatures. The RIFs and XSs for the mixture showed good agreement, which verified the accuracy of the RIF evaluation using the proposed method. The method was then verified by comparing the XSs for the virtual environment for reactor applicationbenchmark pin-cell problem, as well as the heterogeneous pin cell containing burned fuel with McCARD. The method works well for homogeneous, as well as heterogeneous configurations.

• Steel and Composite Structures
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• v.30 no.4
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• pp.365-382
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• 2019

In steel frame-tube structures (SFTSs) the application of flexural beam is not suitable for the beam with span-to-depth ratio lower than five because the plastic hinges at beam-ends can not be developed properly. This can lead to lower ductility and energy dissipation capacity of the SFTS. To address this problem, a replaceable shear link, acting as a ductile fuse at the mid length of deep beams, is proposed. SFTS with replaceable shear links (SFTS-RSLs) dissipate seismic energy through shear deformation of the link. In order to evaluate this proposal, buildings were designed to compare the seismic performance of SFTS-RSLs and SFTSs. Several sub-structures were selected from the design buildings and finite element models (FEMs) were established to study their hysteretic behavior. Static pushover and dynamic analyses were undertaken in comparing seismic performance of the FEMs for each building. The results indicated that the SFTS-RSL and SFTS had similar initial lateral stiffness. Compared with SFTS, SFTS-RSL had lower yield strength and maximum strength, but higher ductility and energy dissipation capacity. During earthquakes, SFTS-RSL had lower interstory drift, maximum base shear force and story shear force compared with the SFTS. Placing a shear link at the beam mid-span did not increase shear lag effects for the structure. The SFTS-RSL concentrates plasticity on the shear link. Other structural components remain elastic during seismic loading. It is expected that the SFTS-RSL will be a reliable dual resistant system. It offers the benefit of being able to repair the structure by replacing damaged shear links after earthquakes.