• International Journal of Concrete Structures and Materials
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• v.5 no.1
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• pp.57-64
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• 2011

An extensive database has been constructed of reinforced concrete (RC) beam-column connection tests subjected to cyclic lateral loading. All cases within the database experienced joint shear failure, either in conjunction with or without yielding of longitudinal beam reinforcement. Using the experimental database, envelope curves of joint shear stress vs. joint shear strain behavior have been created by connecting key points such as cracking, yielding, and peak loading. Various prediction approaches for RC joint shear behavior are discussed using the constructed experimental database. RC joint shear strength and deformation models are first presented using the database in conjunction with a Bayesian parameter estimation method, and then a complete model applicable to the full range of RC joint shear behavior is suggested. An RC joint shear prediction model following a U.S. standard is next summarized and evaluated. Finally, a particular joint shear prediction model using basic joint shear resistance mechanisms is described and for the first time critically assessed.

• Computers and Concrete
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• v.15 no.4
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• pp.673-686
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• 2015

R-curve based on the size effect law previously developed for geometrically similar specimens (geometry type III) is extended to geometries with variable depth (geometry type I) as well as with variable notch (geometry type II), where the R-curve is defined as the envelope of the family of critical strain energy release rates from specimens of different sizes. The results show that the extended R-curve for type I tends to be the same for different specimen configurations, while it is greatly dependent on specimen geometry in terms of the initial crack length. Furthermore, the predicted load-deflection responses from the suggested R-curve are found to agree well with the testing results on concrete and rock materials. Besides, maximum loads for type II specimen are predicted well from the extended R-curve.

• Smart Structures and Systems
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• v.26 no.6
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• pp.703-720
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• 2020

This paper investigates the safety of the wind turbine blade against excessive deformation. For this purpose, the performance of the blade in the along-wind direction is improved by longitudinal stiffener made of shape memory alloy. The rationale behind the selection of this smart material is due to its ability to offer excellent thermo-mechanical behaviour at low strain. Here, Liang-Roger model is adopted for vibration control, and the super-elastic effects are utilised for blade stiffening. Turbulent wind fields are generated at the hub height using TurbSim and the corresponding loads are evaluated using blade element momentum theory. An efficient switching algorithm is developed along with performance curves that enable the designer to select an optimal mode of heating depending upon the operational scenario. Numerical results presented in this paper clearly demonstrate the performance envelope of the proposed stiffener and its influence on the reliability of the blade.

• Journal of the Earthquake Engineering Society of Korea
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• v.19 no.2
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• pp.63-74
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• 2015

This study investigated the influence of probabilistic variability in stiffness and nonlinearity of soil on response of nuclear power plant (NPP) structure subjected to seismic loads considering the soil-structure interaction (SSI). Both deterministic and probabilistic methods have been employed to evaluate the dynamic responses of the structure. For the deterministic method, $SRP_{min}$ method given in USNRC SRP 3.7.2(2013) (envelope of responses using three shear modulus profiles of lower bound($G_{LB}$), best estimate($G_{BE}$) and upper bound($G_{UB}$)) and $SRP_{max}$ method (envelope of responses by more than three ground profiles within range of $G_{LB}{\leq}G{\leq}G_{UB}$) have been considered. The probabilistic method uses the Latin Hypercube Sampling (LHS) that can capture probabilistic feature of soil stiffness defined by the median and the standard deviation. These analysis results indicated that 1) number of samples shall be larger than 60 to apply the probabilistic approach in SSI analysis and 2) in-structure response spectra using equivalent linear soil profiles considering the nonlinear behavior of soil medium can be larger than those based on low-strain soil profiles.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.32 no.6
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• pp.409-416
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• 2019

An improved numerical model for non-linear analysis of reinforced concrete (RC) slabs subjected to blast loading is proposed. This approach considers a strain rate dependent orthotropic constitutive model that directly determines the stress state using the stress-strain relation acquired from the data obtained using the biaxial strength envelope. Moreover, the bond-slip between concrete and reinforcing steel is gradually enlarged after the occurrence of cracks and is concentrated in the plastic hinge region. The bond-slip model is introduced to consider the crack direction of the concrete under a biaxial stress state. Correlation studies between the numerical analysis and the experimental results were performed to evaluate the analytical model. The results show that the proposed model can effectively be used in dynamic analyses of reinforced concrete slab members subjected to explosive loading. Moreover, it was determined that it is important to consider biaxial behavior in the material model and the bond-slip effect.

• Journal of Microbiology
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• v.42 no.1
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• pp.25-31
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• 2004

Sf9 cells have obvious advantages for the conventional production technology of vaccine. They are useful tools for high concentration and large-scale cultures. Sf9 cells were grown to maximal concentration, 8${\times}$l0$\^$6/ cells/$m\ell$ in a 500$m\ell$ spinner flask, with a doubling time at the exponentially growing phase of 24.5 hours, using serum-free media. To explore the ability of Sf9 cells to be infected by the Japanese encephalitis (JE) virus Beijing-l strain, Sf9 cells were infected with the virus. By 4-5 days post-infection, 10-15 % of the Sf9 cells showed cytopathic effect (CPE), from granularity to the formation of syncytia and multinucleated giant cells continuously observed over a period of 35 days. Positive fluorescent reactions were detected in 30-40% of cells infected with the JE virus Beijing-l strain, and the uninfected Sf9 cells were completely negative. Virus particles, propagated in Sf9 and Vero cells, were concentrated by sedimentation on 40% trehalose cushions by ultracentrifugation, and showed identical patterns of viral morphogenesis. Complete virus particles, 40 to 50 nm in diameter, were observed, and JE virus envelope (E) proteins, at 53 kDa, were found in the western blot analysis to the anti-JE virus E protein monoclonal antibody and reacted as a magenta band in the same position to the glycoprotein staining. To evaluate whether the infectious virus was produced in Sf9 cells inoculated with the JE virus Beijing-l stain, Sf9 cells were inoculated with the virus, and sample harvested every 5 days. The titers of the JE virus Beijing-l strain rose from 1.0${\times}$l0$\^$5/ to 1.5${\times}$l0$\^$6/ pfu/$m\ell$. The infected Sf9 cells could be subcultured in serum-free medium, with no change in the plaque sizes formed by the JE virus Beijing-l strain in the plaque assay. It is suggested that the ability of the JE virus Beijing-l strain to infect Sf9 cells in serum-free media will provide a useful insect cell system, where the JE virus replication, cytopathogenicity and vaccine immunogen can be studied.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.69-77
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• 2003

One directional and biaxial tension tests of 13 reinforced concrete panels were conducted to derive a constitutive law of concrete. Based on the test results, a model equation is derived for the stress-strain relationship of concrete in tension. Main test variables are reinforcement ratio and the load ratio applied in two directions. In addition a failure envelope of concrete in tension-tension region is suggested based on the initial crack occurrence. Test results show that the concrete carries substantial tensile stress even after cracking occurrence. However, the application of this proposed stress-strain relationship for concrete is limited to the case where the direction of reinforcement coincides with the direction of the applied principal stresses.

• Geomechanics and Engineering
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• v.34 no.6
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• pp.683-696
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• 2023

The destruction and fracture of rock masses are crucial components in engineering and there is an increasing demand for the study of the influence of rock mass heterogeneity on the safety of engineering projects. The numerical manifold method (NMM) has a unified solution format for continuous and discontinuous problems. In most NMM studies, material homogeneity has been assumed and despite this simplification, fracture mechanics remain complex and simulations are inefficient because of the complicated topology updating operations that are needed after crack propagation. These operations become computationally expensive especially in the cases of heterogeneous materials. In this study, a heterogeneous model algorithm based on stochastic theory was developed and introduced into the NMM. A new fracture algorithm was developed to simulate the rupture zone. The algorithm was validated for the examples of the four-point shear beam and semi-circular bend. Results show that the algorithm can efficiently simulate the rupture zone of heterogeneous rock masses. Heterogeneity has a powerful effect on the macroscopic failure characteristics and uniaxial compressive strength of rock masses. The peak strength of homogeneous material (with heterogeneity or standard deviation of 0) is 2.4 times that of heterogeneous material (with heterogeneity of 11.0). Moreover, the local distribution of parameter values can affect the configuration of rupture zones in rock masses. The local distribution also influences the peak value on the stress-strain curve and the residual strength. The post-peak stress-strain curve envelope from 60 random calculations can be used as an estimate of the strength of engineering rock masses.

• Geomechanics and Engineering
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• v.7 no.3
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• pp.317-333
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• 2014

The study of the mechanical behavior of rockfill materials under three-dimensional loading conditions is a current research focus area. This paper presents a microscale numerical study of rockfill deformation and strength characteristics using the Combined Finite-Discrete Element Method (FDEM). Two features unique to this study are the consideration of irregular particle shapes and particle crushability. A polydisperse assembly of irregular polyhedra was prepared to reproduce the mechanical behavior of rockfill materials subjected to axial compression at a constant mean stress for a range of intermediate principal stress ratios in the interval [0, 1]. The simulation results, including the stress-strain characteristics, relationship between principal strains, and principal deviator strains are discussed. The stress-dilatancy behavior is described using a linear dilatancy equation with its material constants varying with the intermediate principal stress ratio. The failure surface in the principal stress space and its traces in the deviatoric and meridian plane are also presented. The modified Lade-Duncan criterion most closely describes the stress points at failure.

• Structural Engineering and Mechanics
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• v.31 no.6
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• pp.697-716
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• 2009

This paper summarizes an experimental and analytical study on the seismic behavior of high strength reinforced concrete columns under cyclic loading. In total six cantilever columns with different sizes and concrete compressive strengths were tested. Three columns, small size, had a $325{\times}325$ mm cross section and the three other columns, medium size, were $520{\times}520$ mm. Concrete compressive strength was 80, 130 and 180 MPa. All specimens were designed in accordance with the Japanese design guidelines. The tests demonstrated that, for specimens made of 180 MPa concrete compressive strength, spalling of cover concrete was very brittle followed by a significant decrease in strength. Curvature was much important for the small size than for the medium size columns. Concrete compressive strength had no effect on the curvature distribution for a drift varying between -2% and +2%. However, it had an effect on the drift corresponding to the peak moment and on the equivalent viscous damping variation. Simple equations are proposed for 1) evaluating the concrete Young's modulus for high strength concrete and for 2) evaluating the moment-drift envelope curves for the medium size columns knowing that of the small size columns. Experimental moment-drift and axial strain-drift histories were well predicted using a fiber model developed by the authors.