• Steel and Composite Structures
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• v.22 no.2
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• pp.399-409
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• 2016

The fracture propagation mechanism and fractured rock mass failure mechanism were important research in geotechnical engineering field. Many failures and instability in geotechnical engineering were related on fractures propagation, coalescence and interaction in rock mass under the external force. Most of the current research were limited to two-dimensional for the brittleness and transparency of three-dimensional fracture materials couldn't meet the requirements of the experiment. New materials with good transparent and brittleness were developed by authors. The making method of multi fracture specimens were established and made molds that could be reused. The tension-compression ratio of the material reached above 1/6 in normal temperature. Uniaxial and biaxial loading tests of single and double fracture specimens were carried out. Four new fractures were not found in the experiment of two-dimensional fractures such as the fin shaped crack, wrapping wing crack and petal crack and anti-wing crack. The relationship between stress and strain of the specimens were studied. The specimens with the load had experienced four stages of deformation and the process of the fracture propagation was clearly seen in each stage. The expansion characteristics of the fractured specimens were more obvious than the previous research.

• Computers and Concrete
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• v.8 no.1
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• pp.1-22
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• 2011

A numerical model that can simulate the nonlinear behavior of ultra high strength fiber-reinforced concrete (UHSFRC) structures subject to monotonic loadings is introduced. Since engineering material properties of UHSFRC are remarkably different from those of normal strength concrete and engineered cementitious composite, classification of the mechanical characteristics related to the biaxial behavior of UHSFRC, from the designation of the basic material properties such as the uniaxial stress-strain relationship of UHSFRC to consideration of the bond stress-slip between the reinforcement and surrounding concrete with fiber, is conducted in this paper in order to make possible accurate simulation of the cracking behavior in UHSFRC structures. Based on the concept of the equivalent uniaxial strain, constitutive relationships of UHSFRC are presented in the axes of orthotropy which coincide with the principal axes of the total strain and rotate according to the loading history. This paper introduces a criterion to simulate the tension-stiffening effect on the basis of the force equilibriums, compatibility conditions, and bond stress-slip relationship in an idealized axial member and its efficiency is validated by comparison with available experimental data. Finally, the applicability of the proposed numerical model is established through correlation studies between analytical and experimental results for idealized UHSFRC beams.

• Composites Research
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• v.13 no.6
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• pp.9-22
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• 2000

The Rayleigh-Ritz procedure based on energy method is used to present analytically the natural frequencies and the critical buckling loads for four types of loading conditions: (1) uniaxial, (2) biaxial, (3) positive shear and (4) negative shear, of the rectangular, composite plates unidirectionally stiffened with box beam type stiffeners. In analysis the discrete stiffener theory is adopted to present the effect of stiffeners in the plate structure. The convergence study is presented to demonstrate the accuracy of the results. Contour plots of the vibrated and buckled mode shapes are shown for some examples. The effect of various parameters such as numbers, position, aspect ratio of stiffener and layer angle, aspect ratio of plate are focused.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.292-297
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• 2000

In this research, the dynamic photoelastic experimental hybrid method for bimaterial is introduced. Dynamic biaxial loading device is developed, its strain rate is 31.637 s-1 and its maximum impact load is 20 ton. Manufactured methods for model of the dynamic photoelastic experiment for bimaterial are suggested. They are bonding method(bonding material: AW106, PC-1) and molding method. In the bonding method, residual stress is not occurred in the manufactured bimaterial. Crack is propagated along the interface or sometimes deviated from the interface. While in the molding method, residual stress is occurred in the manufactured bimaterial. Crack is always deviated from the interface and propagated in the epoxy region(softer materila). In order to propagate with constant velocity along the interface of bimaterial with arbitrary stiffer material, edge crack should be located along the interface of the acute angle side of the softer material in the bimaterial.

• Journal of the Korea institute for structural maintenance and inspection
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• v.5 no.1
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• pp.195-205
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• 2001

An analytical finite element approach to nonlinear behavior of reinforced concrete shear walls with opening under monotonic loading was presented in this paper. In order to achieve the objectives of present paper, the orthogonal anisotropic models for cracked reinforced concrete element based on smeared crack concept were used as the nonlinear material models of biaxial state of stress. The stiffness of cracked concrete was evaluated through the combined use of tension and compression stiffness models in and parallel directions of crack, respectively and shear transfer effect due to the aggregate interlocking at crack surface. The stress and strain of reinforcement in concrete was evaluated using the average stress and average strain relation with bond effect. based on smeared crack concept. The diagonal reinforcing bar was modeled using truss element with bond effect. A special significance of diagonal reinforcement near opening was given to the shear wall with opening and an effective distribution of diagonal reinforcement was presented in order to give an ultimate strength increment as well as a crack control.

• Structural Engineering and Mechanics
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• v.55 no.1
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• pp.47-64
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• 2015

This paper presents the effect of hybridization material on variation of critical buckling load with different cross-ply laminates plate resting on elastic foundations of Winkler and Pasternak types subjected to combine uniaxial and biaxial loading by using two variable refined plate theories. Governing equations are derived from the principle of virtual displacement; the formulation is based on a new trigonometric shape function of displacement taking into account transverse shear deformation effects vary parabolically across the thickness satisfying shear stress free surface conditions. These equations are solved analytically using the Navier solution of a simply supported. The influence of the various parameters geometric and material, the thickness ratio, and the number of layers symmetric and antisymmetric hybrid laminates material has been investigated to find the critical buckling loads. The numerical results obtained through the present study with several examples are presented to verify and compared with other models with the ones available in the literature.

• Structural Engineering and Mechanics
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• v.69 no.3
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• pp.335-345
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• 2019

In present study, a novel refined hyperbolic shear deformation theory is proposed for the buckling analysis of thick isotropic plates. The new displacement field is constructed with only two unknowns, as against three or more in other higher order shear deformation theories. However, the hyperbolic sine function is assigned according to the shearing stress distribution across the plate thickness, and satisfies the zero traction boundary conditions on the top and bottom surfaces of the plate without using any shear correction factors. The equations of motion associated with the present theory are obtained using the principle of virtual work. The analytical solution of the buckling of simply supported plates subjected to uniaxial and biaxial loading conditions was obtained using the Navier method. The critical buckling load results for thick isotropic square plates are compared with various available results in the literature given by other theories. From the present analysis, it can be concluded that the proposed theory is accurate and efficient in predicting the buckling response of isotropic plates.

• Structural Engineering and Mechanics
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• v.70 no.1
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• pp.113-123
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• 2019

In the classical stability investigation of rectangular plates the classical thin plate theory (CPT) is often employed, so omitting the transverse shear deformation effect. It seems quite clear that this procedure is not totally appropriate for the investigation of moderately thick plates, so that in the following the first shear deformation theory proposed by Meksi et al. (2015), that permits to consider the transverse shear deformation influences, is used for the stability investigation of simply supported isotropic rectangular plates subjected to uni-axial and bi-axial compression loading. The obtained results are compared with those of CPT and, for rectangular plates under uniaxial compression, a novel direct formula, similar to the conventional Bryan's expression, is found for the Euler stability stress. The accuracy of the present model is also ascertained by comparing it, with model proposed by Piscopo (2010).

• Structural Engineering and Mechanics
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• v.85 no.6
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• pp.765-780
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• 2023

In this work, a novel combined logarithmic, secant and tangential 2D and quasi-3D refined higher order shear deformation theory is proposed to examine the buckling analysis of simply supported uniform functionally graded plates under uniaxial and biaxial loading. The proposed formulations contain a reduced number of variables compared to others similar solutions. The combined function employed in this study ensures automatically the zero-transverse shear stresses at the free surfaces of the structure. Various models of the material distributions are considered (linear, quadratic, cubic inverse quadratic and power-law). The differentials stability equations are derived via virtual work principle with including the stretching effect. The Navier's approach is applied to solve the governing equations which satisfying the boundary conditions. Several comparative and parametric studies are performed to illustrates the validity and efficacity of the proposed model and the various factors influencing the critical buckling load of thick FG plate.

• Journal of Chest Surgery
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• v.42 no.5
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• pp.566-575
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• 2009

Background: The function of a bioprosthetic heart valve is determined largely by the material properties of the valve cusps. The uniaxial tensile test has been studied extensively. This type of testing, however, does not replicate the natural biaxial loading condition. The objective of the present study was to investigate the regional variability of the biaxial strain versus pressure relationship based on the types of fixation liquid models. Material and Method: Porcine aortic valves and pulmonary valves were assigned to three groups: the untreated fresh group, the fixed with glutaraldehyde (GA) group, and the glutaraldehyde with solvent (e.g., ethanol) group. For each group we measured the radial and circumferential stretch characteristics of the valve as a function of pressure change. Result: Radial direction elasticity of porcine aortic and pulmonary valves were better than circumferential direction elasticity in fresh, GA fixed and GA+solvent fixed groups (p=0.00). Radial and circumferential direction elasticity of pulmonary valves were better than aortic valves in GA fixed, and GA+solvent fixed groups (p=0.00). Radial and circumferential direction elasticity of aortic valves were decreased after GA and GA+solvent fixation(p=0.00), except for circumferential elasticity of GA+solvent fixed valves (p=0.785). The radial (p=0.137) and circumferential (p=0.785) direction of elasticity of aortic valves were not significantly different between GA fixed. and GA+solvent fixed groups. Radial (p=0.910) and circumferential (p=0.718) direction of elasticity of pulmonary valve also showed no significant difference between GA fixed and GA+solvent fixed groups. Conclusion: When fixing porcine valves with GA, adding a solvent does not cause a loss of mechanical properties, but, does not improve elasticity either. Radial direction elasticity of porcine aortic and pulmonary valves was better than circumferential direction elasticity.