• Steel and Composite Structures
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• v.43 no.6
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• pp.809-819
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• 2022

This paper proposes a method to predict the deflection of prestressed concrete (PC) beams with corrugated steel web (CSW) under constant load concerning time-dependent variation in concrete material. Over time, the top and bottom concrete slabs subjected to asymmetric compression experience shrinkage and creep deformations. Here, the classical Euler-Bernoulli beam theory assumption that the plane sections remain plane is not valid due to shear deformation of CSW. Therefore, this study presents a method based on the first-order shear deformation to find the long-term deflection of the composite beams under bending by considering time effects. Two experimental prestressed beams of this type were monitored under their self-weight over time, and the theoretical results were compared with those data. Additionally, 3D analytical models of the experimental beams were used according to material properties, and the results were compared with two previous cases. There was good consistency between the analytical and numerical results with low error, which increased by wave radius. It is concluded that the proposed method could reliably be used for design purposes.

• Journal of the Korean Geotechnical Society
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• v.24 no.8
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• pp.125-135
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• 2008

Rigid-soft particle mixtures, which consist of sand and rubber, are investigated for the understanding of the stress-deformation and elastic moduli. Specimens are prepared with various size ratio sr between sand and rubber particles, and different volumetric sand fraction sf. Small strain shear waves are measured under $K_o$-loading condition incorporated with the stress-deformation test by using oedometer cell with bender elements. The stress-deformation and small strain shear wave characteristics of rigid-soft particle mixtures show the transition from a rigid particle behavior regime to a soft particle behavior regime under fixed size ratio. A sudden rise of $\Lambda$ factor and the maximum value of the $\zeta$ exponent in $G_{max}=\;{\Lambda}({\sigma}'_{o}/kPa)^{\zeta}$ are observed at $sf\;{\approx}\;0.4{\sim}0.6$ regardless of the size ratio sf. Transition mixture shows high sensitivity to confining stress. The volume fraction for the minimum porosity may depend on the applied stress level in the rigid-soft particle mixtures because the soft rubber particles easily distort under load. In this experimental study, the size ratio and volumetric sand fraction are the important factors which determine the behavior of rigid and soft particle mixtures.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.29 no.3
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• pp.154-161
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• 2017

The purpose of this study was to investigate the change of length, opening width, and number of openings effecting on topography change around artificial reefs under erosive wave condition. Hydraulic model test was conducted to see sediment transport around the structures and the relation among the installation condition of the artificial reefs, generated velocity, wave deformation, and topographic change was reviewed. Experimental results show that the sediment transport rate was reduced; however, the scour around the structures was increased under the condition of having a single opening compared to the structures having a plurality of openings which shows inversely proportional to the size of Lr/W.

• Explosives and Blasting
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• v.35 no.2
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• pp.9-17
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• 2017

The Wheatstone bridge is an important electrical circuit that is widely used to measure extremely small resistance changes in strain gages. The strain gages are attached to the structure or specimen whose deformation is to be detected. The Wheatstone bridge finds one of its major applications in the areas of static and dynamic strength tests for various engineering materials. In the split Hopkinson pressure bar (SHPB) system, for example, the bridge circuit is required to measure the dynamic strains of the incident and transmitted bars along which the stress wave propagates. In this article, the principles of the Wheatstone bridge circuit are in detail explained for easy reference during laboratory experiments associated with rock dynamics. Especially, the circuit arrangements of the quater, half, and full bridges are presented with their basic uses.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.3
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• pp.99-109
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• 2000

Elastic dynamic responses analysis program for ship hulls considering slamming impact loads due to the voyage in large amplitude waves is developed. Ship hull structures are modeled by a thin-walled beam model in order to consider effects of shear deformation. The momentum slamming theory is used to derive nonlinear hydrodynamic forces considering intersection between wave particles and ship section. For the validation of the developed computer program, motions of a V-shaped simple section model and S-175 standard container model are calculated and analyzed. In each numerical example, time histories of relative displacement, velocity and vertical bending moment of a ship section are derived, considering the effect of slamming impacts in various wave conditions.ures near the free surface as well as the wake of the hydrofoil.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.2 s.173
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• pp.496-505
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• 2000

A semi-infinite parallel crack propagated with constant velocity in two bonded anisotropic strip under anti-plane clamped displacement is analyzed. Using Fourier integral transform a Wiener-Hopf equation is derived. By solving this equation the asymptotic stress and displacement fields near the crack tip are determined, where the results give the more general expression applicable to the extent of the anisotropic material having one plane of elastic symmetry for the parallel crack. The dynamic stress intensity factor and energy release rate are also obtained as a closed form, which are the results applicable to the problem both of dynamic and static crack under the same geometry as this study. The stress intensity factor approaches zero at the critical crack velocity which is less than the shear wave velocity, but in typical case of isotropic or orthotropic material agrees with the velocity of shear wave. Also a circular shear stress around crack tip is considered, from which the stress is shown to be approximately symmetric about the horizontal axis. Referring to the maximum stress criteria, it could be shown that a brenched crack is formed by crack growth as crack velocity increases.

• Magazine of the Korea Concrete Institute
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• v.10 no.6
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• pp.203-211
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• 1998

It is well recognized recently that acoustic emission, which is an elastic wave generated from rapid release of elastic energy in steressed solids, is very useful tool for on-line monitoring of microscopic behavior of deformation of material. In this study, three point bend test was performed to evaluate the microscopic damage progress during the loading and failure mechanism of mortar beam by monitoring the characteristic of AE signal. The relationship between AE characteristic and microscopic failure mechanism is discussed. In addition 2 dimensional AE source location based on triangular method was also done to monitor the intiation and propagation of micro crack around notch tip of mortar beam. It was shown that AE source location was very effective to predict the growth behavior of micro crack in mortar beam specimen.

• Journal of Korean Society of Water and Wastewater
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• v.27 no.4
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• pp.479-487
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• 2013

This study was to investigate characteristics for the pressure wave propagation and the maximum pressure near a rapid closure valve which was installed the end of multi piping network. The multi piping network consists of one inlet and three outlet with straight pipes. The diameter of the pipes including the valve was 100 mm, 80 mm, 80 mm respectively. The valve was rapidly closed with the instantaneous time which was 0.023s in the level for the water hammer. For the simulation, the influence of the pipe thickness and deformation due to pressure-wave-propagation was not considered. CFD was conducted under the following condition : the initial pressure was 1bar in the inlet and the mass flow rate was 7.83 kg/s in the outlet(the velocity in the pipe with 100 mm diameter was 1 m/s). As the valve have conditions that were status with and without fluid flow in the pipe after valve closing, the maximum pressure change and the frequency analysis were examined. As the results, the case that was status with fluid flow appeared the higher maximum pressure than another's, the maximum frequency band was about 10 ~ 11 Hz.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.2
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• pp.132-142
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• 2017

As the International Maritime Organization (IMO) recently introduced the Energy Efficiency Design Index (EEDI) for new ships building and the Energy Efficiency Operational Indicator (EEOI) for ship operation, thus an accurate estimation of added resistance of ships advancing in waves has become necessary. In the present study, OpenFOAM, computational fluid dynamics libraries of which source codes are opened to the public, was used to calculate the added resistance and motions of the KCS. Unstructured grid using a hanging-node and cut-cell method was used to generate dense grid around a wave and KCS. A dynamic deformation mesh method was used to consider the motions of the KCS. Five wavelengths from a short wavelength (${\lambda}/LPP=0.65$) to a long wavelength (${\lambda}/LPP=1.95$) were considered. The added resistance and the heave & pitch motions calculated for various waves were compared with the results of model experiments.

• Computers and Concrete
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• v.20 no.6
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• pp.711-718
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• 2017

Nanotechnology is a new filed in concrete structures which can improve the mechanical properties of them in confronting to impact and blast. However, in this paper, a mathematical model is introduced for the concrete models subjected to impact load for wave propagation analysis. The structure is simulated by the sinusoidal shear deformation theory (SSDT) and the governing equations of the concrete model are derived by energy method and Hamilton's principle. The silicon dioxide ($SiO_2$) nanoparticles are used as reinforcement for the concrete model where the characteristics of the equivalent composite are determined using Mori-Tanaka approach. An exact solution is applied for obtaining the maximum velocity of the model. In order to validate the theoretical results, three square models with different impact point and Geophone situations are tested experimentally. The effect of different parameters such as $SiO_2$ nanoparticles volume percent, situation of the impact, length, width and thickness of the model as well as velocity, diameter and height of impactor are shown on the maximum velocity of the model. Results indicate that the theoretical and experimental dates are in a close agreement with each other. In addition, using from $SiO_2$ nanoparticles leads to increase in the stiffness and consequently maximum velocity of the model.