PURPOSES : Concrete, which is a construction material, is the most widely used compression material; however, unlike steel, it exhibits nonlinear material characteristics. Therefore, to examine the behavior of structures under the nonlinear conditions of concrete materials, one must select an appropriate numerical-analysis technique and a reasonable material model. When performing the nonlinear numerical analysis of a structure using general-purpose structural analysis software, the stress–strain curve or the Mohr–Coulomb failure criterion is typically employed to consider the nonlinear material characteristics. In this study, an efficient nonlinear numerical analysis is conducted by defining the stress–strain curves and Mohr–Coulomb parameters applicable to Strand7 to examine and design the stability of reinforced concrete structures. METHODS : This study was conducted by improving existing data. Based on the tensile region of the concrete stress–strain curve presented in a simple shape and the results of the splitting test, the proposed Mohr–Coulomb parameter was improved based on regulations stipulated in the design standards of concrete structures. The characteristics and usability of the improved material models were examined using concrete splitting tensile and bending models. RESULTS : A yield area distribution similar to that of the reference data is obtained when the Mohr–Coulomb material model is used in the numerical analysis of the concrete splitting tension, thus confirming the validity of the model. In the Mohr–Coulomb material model, nonlinear resistance continues even after the maximum reaction force occurs. However, when the stress–strain curve material model is applied, at the moment the maximum reaction force occurs, the material yields and begins to be damaged. In addition, by applying the Mohr–Coulomb material model to the bending numerical-analysis model, the magnitude of stress in the tensile region from the initial stage exceeds the yield stress defined in the stress–strain curve. CONCLUSIONS : Based on a series of examples, the usability of the proposed concrete stress–strain curve and Mohr–Coulomb parameters is confirmed. However, to obtain numerical-analysis results that are consistent with the nonlinear behavior of actual structures, nonlinear testing of reinforced concrete structures shall be conducted and material models shall be improved.

In this study, a numerical approach based on mid-point integrated finite elements and a viscous boundary is proposed for time-domain wave-propagation analyses in infinite poroelastic media. The proposed approach is accurate, efficient, and easy to implement in time-domain analyses. In the approach, an infinite domain is truncated at some distance. The truncated domain is represented by mid-point integrated finite elements with real element-lengths and a viscous boundary is attached to the end of the domain. Given that the dynamic behaviors of the proposed model can be expressed in terms of mass, damping, and stiffness matrices only, it can be implemented easily in the displacement-based finite-element formulation. No convolutional operations are required for time-domain calculations because the coefficient matrices are constant. The proposed numerical approach is applied to typical wave-propagation and soil-structure interaction problems. The model is verified to produce accurate and stable results. It is demonstrated that the numerical approach can be applied successfully to nonlinear soil-structure interaction problems.

이 연구는 자유단에 경사 종동력을 받는 변단면 기하 비선형 캔틸레버 기둥의 수치해석에 관한 연구이다. 기둥의 단면은 휨 강성이 부재축을 따라 함수적으로 변화하는 변단면으로 선택하였다. 이러한 기둥의 정확탄성곡선을 지배하는 미분방정식을 대변형 이론을 이용하여 유도하였다. 이 미분방정식은 자유단 수직변위, 수평변위 및 회전각의 3개의 미지변수를 갖는다. 이 미분방정식을 반복법으로 수치해석하여 기둥의 미지변수와 정확탄성곡선을 산정하였다. 이 연구의 이론을 검증하기 위하여 실험실 규모의 실험을 실행하였다.

이 연구는 조합하중을 받는 변단면 변화곡선 보의 기하 비선형 수치해석 방법에 관한 연구이다. 보의 좌단은 회전지점이 고 우단은 마찰이 없는 활동(滑動)지점으로 지지되어 있어 하중이 작용하면 보의 축방향 길이가 증가하여 평형상태를 이룬 다. 조합하중은 회전지점에 작용하는 모멘트 하중과 집중하중을 고려하였다. 보의 단면은 휨 강성이 부재축을 따라 함수적 으로 변화하는 변단면으로 선택하였다. 이러한 보의 비선형 거동을 지배하는 연립 미분방정식을 Bernoulli-Euler 보 이론으 로 유도하였다. 이 미분방정식을 반복법으로 수치해석하여 보의 정확탄성곡선을 산정하였다. 이 연구의 이론을 검증하기 위하여 실험실 규모의 실험을 실행하였다.