• Computers and Concrete
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• 제15권4호
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• pp.563-588
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• 2015

Piers are the most vulnerable part of a bridge structure during an earthquake event. During Kobe earthquake in 1995, several bridge piers of the Hanshin Expressway collapsed for more than 600m of the bridge length. In this paper, the most important results of an experimental and analytical investigation of ten reinforced concrete bridge piers specimens with the same cross section subjected to constant axial (or variable) load and reversed (or one direction) cycling loading are presented. The objective was to investigate the main parameters influencing the seismic performance of reinforced concrete bridge piers. It was found that loading history and axial load intensity had a great influence on the performance of piers, especially concerning strength and stiffness degradation as well as the energy dissipation. Controlling these parameters is one of the keys for an ideal seismic performance for a given structure during an eventual seismic event. Numerical models for the tested specimens were developed and analyzed using SeismoStruct software. The analytical results show reasonable agreement with the experimental ones. The analysis not only correctly predicted the stiffness, load, and deformation at the peak, but also captured the post-peak softening as well. The analytical results showed that, in all cases, the ratio, experimental peak strength to the analytical one, was greater than 0.95.

• Advances in nano research
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• 제13권5호
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• pp.465-474
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• 2022

Based on the nonlocal strain gradient (NSG) theory and considering the influence of moment of inertia, the governing equations of motion of porous functionally graded (FG) nanoplates with four edges clamped are established; The Galerkin method is applied to eliminate the spatial variables of the partial differential equation, and the partial differential governing equation is transformed into an ordinary differential equation with time variables. By satisfying the boundary conditions and solving the characteristic equation, the dispersion relations of the porous FG strain gradient nanoplates with four edges fixed are obtained. It is found that when the wave number is very small, the influences of nonlocal parameters and strain gradient parameters on the dispersion relation is very small. However, when the wave number is large, it has a great influence on the group velocity and phase velocity. The nonlocal parameter represents the effect of stiffness softening, and the strain gradient parameter represents the effect of stiffness strengthening. In addition, we also study the influence of power law index parameter and porosity on guided wave propagation.

• 로봇학회논문지
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• 제19권2호
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• pp.221-228
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• 2024

As the importance of cardiovascular health is highlighted, research on its correlation with blood pressure, the most important indicator, is being actively conducted. Therefore, extensive clinical data is essential, but the measurement of the central arterial blood pressure waveform must be performed invasively within the artery, so the quantity and quality are limited. This study suggested a mock circulatory robot and artificial aorta to reproduce the blood pressure waveform generated by the overlap of forward and reflected waves. The artificial aorta was fabricated with biomimetic silicone to mimic the physiological structure and vascular stiffness of the human. A pressurizing chamber was implemented to prevent distortion of the blood pressure waveform due to the strain-softening of biomimetic silicone. The reproduced central arterial blood pressure waveforms have similar magnitude, shape, and propagation characteristics to humans. In addition, changes in blood pressure waveform due to aging were also reproduced by replacing an artificial aorta with various stiffness. It can be expanded to construct a biosignal database and health sensor testing platform, a core technology for cardiovascular health-related research.

• 한국강구조학회 논문집
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• 제29권3호
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• pp.229-236
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• 2017

이 연구에서는 고무스프링의 동적 압축실험을 수행하여 고무스프링의 거동 및 특성을 규명하고 압축 강성도를 계산하여 실제 설계값에 대해 알아보고자 하였다. 고무스프링의 동적 압축실험을 수행하기 위하여, L80-D55, L90-D58, L100-D60의 고무스프링의 형상계수를 구하여 총 9개의 고무스프링을 주문 제작 하여 실험에 사용하였다. 실험은 고무스프링의 길이에 따라 기압축을 제어하여 수행하였으며, 기압축은 변형률의 5%, 10%, 15%, 20%, 25% 순서로 증가시켰다. 실험결과를 통해 힘-변형률 곡선을 얻을 수 있었고, 변형률의 증가함에 따라 강도감소 현상과 강도증가 현상이 발생함을 확인하였다. 또한 고무스프링의 크기와 지름에 따라 강성저하 및 강성증가 현상이 확연하게 나타남을 확인하였고, 힘-변형률 곡선에서 할선기울기를 이용하여 유효 압축강성도를 추정하였다. 유효압축강성도를 이용하여 실제 설계에 사용할 수 있는 설계값을 제시하였다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.479-482
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• 1999

The tension stiffening effect, which means the maintaining a part of stiffness after cracking of concrete in tensile, exists at a reinforced concrete member because of the concrete softening and bonding stress between cracks. It is required to consider it for precise analysis and evaluation o structural behavior, due to the possibility of discrepancy between the actual behavior and the analysis without considering the tension stiffening effect. Making and adopting a tension stiffening model is the most simple and effective way for considering it at nonlinear analysis which indicated the estimation from models and experimental results were similar each others. The comparisons on RC beam were, also performed in order to analyzed the influence of concrete strength and steel ratio into the structural behavior. They indicated that the results from analysis estimated quite closely to the test results at low steel ratio, however, overestimated at high steel ratio. The overestimation increase linearly as concrete strength or steel ratio increased.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 봄 학술발표회 논문집
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• pp.215-222
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• 2000

The reinforced roadbed should have the ability to spread out the load intensity lower than the bearing capacity of the subgrade of track structure as well as to prevent the softening of roadbed by providing appropriate stiffness in the roadbed, thus fully supports the track structures. Full scale reinforced roadbeds with several different types of monotoring sensors was also constructed to evaluate the performance of each reinforced roadbed through the continuous monitoring while the train operation. In this study, Field tests such as PLT, SASW were also carried out at each reinforced roadbed. The results of the field and lab tests, installation and calibration of sensors, as well as construction condition of the reinforced roadbed are presented.

• Structural Engineering and Mechanics
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• 제4권4호
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• pp.437-450
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• 1996

A study on the behaviour of fibre reinforced concrete deep beams with and without web openings is carried out using nonlinear finite element analysis. Eight node isoparametric plane stress elements are employed to model the fibre reinforced concrete materials. Steel bars are treated using a compatible three node truss elements. The constitutive equations for fibre reinforced concrete materials take into account the softening effect of co-existing shear strains. Element stiffness at each step is formulated based on the tangent modulus at the current level of principal strains. Transformation between principal directions and global coordinate system is imposed. Comparison of analytical results with experimental values indicates reasonably good agreement. The proposed numerical model can be used to study the behaviour of this composite structures of practically any geometries.

• Structural Engineering and Mechanics
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• 제75권1호
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• pp.87-100
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• 2020

The present paper investigates the combination resonance behavior of imperfect spiral stiffened functionally graded (SSFG) cylindrical shells with internal and external functionally graded stiffeners under two-term large amplitude excitations. The structure is embedded within a generalized nonlinear viscoelastic foundation, which is composed of a two-parameter Winkler-Pasternak foundation augmented by a Kelvin-Voigt viscoelastic model with a nonlinear cubic stiffness, to account for the vibration hardening/softening phenomena and damping considerations. With regard to classical plate theory of shells, von-Kármán equation and Hook law, the relations of stress-strain are derived for shell and stiffeners. The spiral stiffeners of the cylindrical shell are modeled according to the smeared stiffener technique. According to the Galerkin method, the discretized motion equation is obtained. The combination resonance is obtained by using the multiple scales method. Finally, the influences of the stiffeners angles, foundation type, the nonlinear elastic foundation coefficients, material distribution, and excitation amplitude on the system resonances are investigated comprehensively.

• Steel and Composite Structures
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• 제37권1호
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• pp.27-35
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• 2020

This study examines the wave propagation of the functionally graded polymer composite (FG-PC) nanoplates reinforced with graphene nanoplatelets (GNPs) resting on elastic foundations in the framework of the nonlocal strain gradient theory incorporating both stiffness hardening and softening mechanisms of nanostructures. To this end, the material properties are based on the Halpin-Tsai model, and the expressions for the classical and higher-order stresses and strains are consistently derived employing the second-order shear deformation theory. The equations of motion are then consistently derived using Hamilton's principle of variation. These governing equations are solved with the help of Trial function method. Extensive numerical discussions are conducted for wave propagation of the nanoplates and the influences of different parameters, such as the nonlocal parameter, strain gradient parameter, weight fraction of GNPs, uniform and non-uniform distributions of GNPs, elastic foundation parameters as well as wave number.

• Elastomers and Composites
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• 제28권4호
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• pp.274-282
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• 1993

Resorcinol-tannin-formaldehyde-latex(RTFL) adhesive was prepared to bond SBR to nylon in reinforced rubber composites. A key factor of adhesive contributes to the adhesion strength between SBR and nylon was the toughness of adhesive itself. Although the stiffness and strength of adhesive film decreased slightly with increasing level of tannin substitution for resorcinol in a standard RFL adhesive, the maximum toughness of adhesive film, which showed yield behavior and high dissipative capacity, was obtain by 60% tannin substitution. However, a marked softening and reduction in toughness occurred at sufficiently high substitution. Also, the adhesive film, which was heat-treated to simulate cure, showed higher strength than the unheated film. Thus, the properties of tannin containing adhesives could be optimized by using 40/60 weight ratio of the resorcinol/tannin in RTFL adhesive composition as well as heat treatment of adhesive film.