• 소성∙가공
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• 제16권2호
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• pp.101-106
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• 2007

Uniaxial displacement controlled tests were performed on annealed Type 304 stainless steel at room temperature. A servo-controlled testing machine and strain measurement on the gage length were employed to measure the response to a given input. The test results exhibit that the flow stress increases nonlinearly with the strain rate and the relaxed stress at the end of the relaxation periods depends strongly on the strain rate preceding the relaxation test. The rate-dependent inelastic deformation behavior is simulated using a new unified viscoplasticity model that has the rate-dependent format of nonlinear kinematic hardening rule, which plays a key role in modeling the rate dependence of relaxation behavior. The model does not employ yield or loading/unloading criteria and consists of a flow law and the evolution laws of two tensor and one scalar-valued state variables.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2005년도 학술발표회 논문집
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• pp.145-152
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• 2005

This paper presents a deformable strut-and-tie model of determining the shear strengths and ultimate deformations of the shear-dominant reinforced concrete members. The proposed model originates from the strut-and-tie model concept and satisfies equilibrium, compatibility, constitutive laws, and the geometric conditions of shear deformation. This study attempts to apply deformation patterns to strut-and-tie models. The yielding of flexural reinforcements determines yielding states and the ultimate states of reinforced concrete coupling beam are defined as the ultimate compressive strain of struts and the degradation of compressive strength due to principal tensile strain of struts. The validity and accuracy of the proposed model is then tested against available experimental data. The parameters reviewed include the ratios of truss action and arch action, the reinforcement ratios, and the shear span-depth ratio. It is expected that this model can be applied to displacement-based design methods.

• 콘크리트학회논문집
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• 제12권5호
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• pp.81-92
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• 2000

A fixed angle softened truss model has been developed in order to predict both shear strength and deformation of reinforced concrete members. The model takes into account the contribution of concrete by accuming the angle of cracks in the postcracking concrete that coincides with the reinforced concrete principal compressive angle determined by the applied stresses. Therefore, this model is capable of predicting the contribution of concrete from the govering equilibrium and compatibility equations including the shear stress and strain developed along concrete diagonal crack. However, the model has a limiting range to be applicable for reinforced concrete members. This research proposes a new algorthm of fixed angle softened truss model capable of removing the limitation of applicability. The proposed algorithm adopts a new conception of constitutive laws. The average normal stresses of concrete in the x- y- directions can be calculated by transforming the principal stresses of concrete. The proposed algorthm is verified by comparing to the test results.

• 한국구조물진단유지관리공학회 논문집
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• 제6권2호
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• pp.157-165
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• 2002

Nonlinear analysis of the reinforced concrete beam subjected to torsion is presented. Seventeen equations involving seventeen variables are derived from the equilibrium equation, compatibility equation, and the material constitutive laws to solve the torsion problem. Newton method was used to solve the nonlinear simultaneous equations and efficient algorithms are proposed. Present model covers the behavior of reinforced concrete beam under pure torsion from service load range to ultimate stage. Tensile resistance of concrete after cracking is appropriately considered. The softened concrete truss model and the average stress-strain relations of concrete and steel are used. To verify the validity of present model, the nominal torsional moment strengths according to ACI-99 code and the ultimate torsional moment by present model are compared to experimental torsional strengths of 55 test specimens found in literature. The ultimate torsional moment strengths by the present model show good results.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 봄학술 발표회 논문집(I)
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• pp.139-142
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• 2005

This paper presents a deformable strut-and-tie model of determining the shear strengths and ultimate deformations of the shear-dominant reinforced concrete members. The proposed model originates from the strut-and-tie model concept and satisfies equilibrium, compatibility, constitutive laws, and the geometric conditions of shear deformation. This study attempts to apply deformation patterns to strut-and-tie models. The yielding of flexural reinforcements determines yielding states and the ultimate states of reinforced concrete coupling beam are defined as the ultimate compressive strain of struts and the degradation of compressive strength due to principal tensile strain of struts. The validity and accuracy of the proposed model is then tested against available experimental data. The parameters reviewed include the ratios of truss action and arch action, the reinforcement ratios, and the shear span-depth ratio. It is expected that this model can be applied to displacement-based design methods.

• Structural Engineering and Mechanics
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• 제12권4호
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• pp.429-448
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• 2001

An analytical model incorporating bending and shear behavior is presented to predict the lateral loading characteristic for rectangular hollow columns. The moment-curvature relationship for the rectangular hollow sections of a column is firstly determined. Then the nonlinear lateral load-displacement relationship for the hollow column can be obtained accordingly. In this model, thirteen constitutive laws for confined concrete and five approaches to estimate the shear capacity are used. A series of tests on 12 model hollow columns aimed at the seismic shear behavior are reported, and the test data are compared to the analytical results. It is found that the analytical model reflects the experimental results rather closely.

• Structural Engineering and Mechanics
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• 제4권6호
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• pp.601-612
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• 1996

To simulate the large-scale failure evolution with current computational facilities, a simple approach, that catches the essential feature of failure mechanisms, must be available so that the routine use of failure analysis is feasible. Based on the previous research results, a simple analysis procedure is described in this paper for failure simulation. In this procedure, the evolution of localization is represented by a moving surface of discontinuity, and the transition between continuous and discontinuous failure modes are described via the moving jump forms of conservation laws. As a result, local plasticity and damage models, that are formulated based on thermodynamic restrictions, are still valid without invoking higher order terms, and simple integration schemes can be designed for the rate forms of constitutive models. To resolve localized large deformations and subsequent cracking, an efficient structural solution scheme is given for Static and dynamic problems.

• Structural Engineering and Mechanics
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• 제5권6호
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• pp.785-801
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• 1997

Reinforced Concrete beams with tension and compression softening material constitutive laws are studied. Energy-based and non-local regularisation techniques are presented and applied to a R.C. element. The element characteristics (sectional tangent stiffness matrix, element tangent stiffness matrix restoring forces) are directly derived from their symbolic expressions through numerical integration. In this way the same spatial grid allows us to obtain a non-local strain estimate and also to sample the contributions to the element stiffness matrix. Three examples show the spurious behaviors due to the strain localization and the stabilization effects given by the regularisation techniques, both in the case of tension and compression softening. The possibility to overestimate the ultimate load level when the non-local strain measure is applied to a non softening material is shown.

• Steel and Composite Structures
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• 제6권3호
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• pp.183-202
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• 2006

The behavior of steel-concrete composite beams is strongly influenced by the type of shear connection between the steel beam and the concrete slab. For accurate analytical predictions, the structural model must account for the interlayer slip between these two components. This paper focuses on a procedure for response sensitivity analysis using state-of-the-art finite elements for composite beams with deformable shear connection. Monotonic and cyclic loading cases are considered. Realistic cyclic uniaxial constitutive laws are adopted for the steel and concrete materials as well as for the shear connection. The finite element response sensitivity analysis is performed according to the Direct Differentiation Method (DDM); its analytical derivation and computer implementation are validated through Forward Finite Difference (FFD) analysis. Sensitivity analysis results are used to gain insight into the effect and relative importance of the various material parameters in regards to the nonlinear monotonic and cyclic response of continuous composite beams, which are commonly used in bridge construction.

• Structural Engineering and Mechanics
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• 제17권6호
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• pp.829-862
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• 2004

This paper presents a method for the nonlinear analysis of beam elements subjected to the cyclical combined actions of torsion, biaxial flexure and axial forces based on an extension of the disturbed compression field (DSFM). The theoretical model is based on a hybrid formulation between the full rotation of the cracks model and the fixed direction of the cracking model. The described formulation, which treats cracked concrete as an orthotropic material, includes a new approach for the evaluation of the re-orientation of both the compression field and the deformation field by removing the restriction of their coincidence. A new equation of congruence permits evaluating the deformation of the middle line. The problem consists in the solution of coupled nonlinear simultaneous equations expressing equilibrium, congruence and the constitutive laws. The proposed method makes it possible to determine the deformations of the beam element according to the external stresses applied.