• Structural Engineering and Mechanics
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• 제64권4호
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• pp.461-472
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• 2017

The dynamic tests of recycled aggregate concrete (RAC) are carried out, the rate-dependent mechanical models of RAC are proposed. The dynamic mechanical behaviors of RAC frame structure are investigated by adopting the numerical simulation method of the finite element. It is indicated that the lateral stiffness and the hysteresis loops of RAC frame structure obtained from the numerical simulation agree well with the test results, more so for the numerical simulation which is considered the strain rate effect than for the numerical simulation with strain rate excluded. The natural vibration frequency and the lateral stiffness increase with the increase of the strain rate. The dynamic model of the lateral stiffness is proposed, which is reasonably applied to describe the effect of the strain rate on the lateral stiffness of RAC frame structure. The effect of the strain rate on the structural deformation and capacity of RAC is analyzed. The analyses show that the inter-story drift decreases with the increase of the strain rate. However, with the increasing strain rate, the structural capacity increases. The dynamic models of the base shear coefficient and the overturning moment of RAC frame structure are developed. The dynamic models are important and can be used to evaluate the strength deterioration of RAC structure under dynamic loading.

• 한국산학기술학회논문지
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• 제18권11호
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• pp.762-769
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• 2017

준등방성 라미네이트내의 확장강성 계수는 방사방향으로균일하지만, 굽힘강성 계수는 플라이 적층순서에 의해 방사방향으로 변화한다. 이 논문에서는 복합재 광학에서 사용되는 단방향섬유 복합재료와 무작위로 분포된 단섬유 복합재료로 이루어진 세 가지 유형의 준 등방성 라미네이트 반사경내의 굽힘강성 계수의 방사방향의 변화량을 비교하였다. 단섬유 복합재료 반사경 방사방향의 확장강성 계수와 굽힘강성 계수는 균일하게 나타나는 반면, 단방향섬유 복합재료 반사경의 경우에는 굽힘강성 계수의 방사방향으로의변화량이 11%에서 많게는 26%까지 변화하는 것으로 나타났다. 또한 강성계수의 차이로 인한 굽힘-비틀림-커플링 효과 등 강성 민감도 또한 큰 것으로 나타났다. 이러한 요소는 정밀성이 요구되는 광학분야에 복합재 반사경의 적용을 어렵게 할 커다란 문제점으로 인식되며, 이러한 복합재료의 이방성 성질로 인한 필연적인방사형 방향으로의 강성계수의 변화 및 그 영향성을 줄이기 위해서는 단섬유나 무작위로 공간에 흩어져있는 섬유 복합재료를 사용하는 것이 복합재 반사경내에 존재하는 굽힘강성 계수의 변화를 제거하는 하나의 방법이다.

• Journal of Korean Neurosurgical Society
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• 제52권5호
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• pp.435-440
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• 2012

Objective : The purpose of this study is to find the optimal stiffness and volume of bone cement and their biomechanical effects on the adjacent vertebrae to determine a better strategy for conducting vertebroplasty. Methods : A three-dimensional finite-element model of a functional spinal unit was developed using computed tomography scans of a normal motion segment, comprising the T11, T12 and L1 vertebrae. Volumes of bone cement, with appropriate mechanical properties, were inserted into the trabecular core of the T12 vertebra. Parametric studies were done by varying the volume and stiffness of the bone cement. Results : When the bone cement filling volume reached 30% of the volume of a vertebral body, the level of stiffness was restored to that of normal bone, and when higher bone cement exceeded 30% of the volume, the result was stiffness in excess of that of normal bone. When the bone cement volume was varied, local stress in the bony structures (cortical shell, trabecular bone and endplate) of each vertebra monotonically increased. Low-modulus bone cement has the effect of reducing strain in the augmented body, but only in cases of relatively high volumes of bone cement (>50%). Furthermore, varying the stiffness of bone cement has a negligible effect on the stress distribution of vertebral bodies. Conclusion : The volume of cement was considered to be the most important determinant in endplate fracture. Changing the stiffness of bone cement has a negligible effect on the stress distribution of vertebral bodies.

• Structural Engineering and Mechanics
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• 제59권2호
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• pp.327-341
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• 2016

This study addresses the effect of pre-stressed cables on a pre-stressed mega-braced steel frame through employing static analysis and pushover analysis. The performances of a pre-stressed mega-braced steel frame and a pure steel frame without mega-braces are compared in terms of base shear, ductility, and failure mode. The influence of the cable parameters is also analyzed. Numerical results show that cable braces can effectively improve the lateral stiffness of a pure frame. However, it reduces structural ductility and degenerates structural pre-failure lateral stiffness greatly. Furthermore, it is found that 20% fluctuation in the cable pretension has little effect on structural ultimate bearing capacity and lateral stiffness. As comparison, 20% fluctuation in the cable diameter has much greater impact.

• International Journal of Aeronautical and Space Sciences
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• 제18권3호
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• pp.467-473
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• 2017

This paper focuses on the investigation of three-dimensional (3D) warping effect on the stiffness constants of composite beams with closed section profiles. A finite element (FE) cross-sectional analysis is developed based on the Reissner's multifield variational principle. The 3D in-plane and out-of-plane warping displacements, and sectional stresses are approximated as linear functions of generalized sectional stress resultants at the global level and as FE shape functions at the local sectional level. The classical elastic couplings are taken into account which include transverse shear and Poisson deformation effects. A generalized Timoshenko level $6{\times}6$ stiffness matrix is computed for closed section composite beams with and without warping. The effect of neglecting the 3D warping on stiffness constants is shown to be significant indicating large errors as high as 93.3%.

• 센서학회지
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• 제30권5호
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• pp.273-278
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• 2021

Here, we studied the change in the mechanical stiffness of a diaphragm according to the corrugation pattern. The diaphragm consists of a silicon oxide and nitride double layer; a corrugation pattern was formed by dry etching, and the diaphragm was released by wet etching. The fabrication of the thin film was verified using focused ion beam and scanning electron microscopy images. The mechanical stiffness of the diaphragm was obtained by measuring the surface vibration using a laser Doppler vibrometer while applying external sound pressure. Flat squares, diaphragms with square corrugations, and circular corrugation patterns were measured and compared. The stiffness of the diaphragm with a corrugation structure was found to be smaller than that without a corrugation structure; in particular, circular corrugation showed a better effect because of the high symmetry. Furthermore, the effect of corrugation was theoretically predicted. The proposed corrugated diaphragm showed comparable flexibility with the state-of-the-art MEMS microphone diaphragm.

• 대한가정학회지
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• 제31권2호
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• pp.189-203
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• 1993

The objective of this study was to investigate the changes of the fabric absorbency, stiffness and antistatic property by using a fabric softner at laundering. The samples selected in this study were cotton and polyester fabrics. The cotton fabric was treated with 1/2 times(0.035%), 1 time(0.07%), 3 times(0.21%) and 10 times(0.7%) of the commercially suggested concentration (0.07%) of the fabric softner. And polyester fabric was done at 1 time(0.07%) of that. In order to examine the effect of the fabric by using a fabric softner, the abstraction of a surface active agent and quantitative analysis was performed by using a UV/VIS Spectroscopy and the correlations among the absorbency, stiffness and antistatic property was analyzed. The results obtained from this study were as follows; 1. In the cotton fabric, fabric softner gave the degradation of absorbency, and stiffness improvement was not shown by repeated fabric softner on the cotton fabric. 2. In the polyester fabric, the absorbency increased and the stiffness in creased very slightly. Specially, it is desirable to use fabric softner on the polyester due to improvement of antistatic property.

• 한국지진공학회논문집
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• 제20권5호
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• pp.319-329
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• 2016

The Eradi Quake System (EQS) is a seismic isolation bearing system designed to minimize forces and displacements experienced by structures subjected to ground motion. The EQS dissipates seismic energy through friction of Poly Tetra Fluoro Ethylene (PTFE) disk pad. In general, a force-displacement relationship of EQS has post yield stiffness hardening during large inelastic displacement. In this study, seismic responses of seismically isolated nuclear power plant (NPP) subjected to design basis earthquake (DBE) and beyond design basis earthquakes (150% DBE and 167% DBE) are compared considering the post yield stiffness hardening effect of EQS. From the results, it can be observed that if the post-yield stiffness hardening effect of EQS is increased, the displacement response of EQS is reduced, and the acceleration and shear responses of containment structures of NPP is increased.

• Structural Engineering and Mechanics
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• 제39권5호
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• pp.661-667
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• 2011

In the famous equivalent elasticity modulus method proposed by Ernst for the geometrical nonlinear analysis of stay cables, the cable shape was assumed as a parabolic curve, and only a part of the gravity load normal to the chord was taken into account with the other part of gravity load parallel to the chord being ignored. Using the actual catenary curve and considering the entire gravity load of stay cables, the present study has derived the equivalent stiffness method to analyze the sag effect of stay cables in cable-stayed bridges. The derived equivalent stiffness can be degenerated into Ernst's equivalent elasticity modulus method with some approximations. Therefore, the Ernst's method is a special and approximate formulation of the present method. The derived equivalent stiffness provides a theoretical explanation for the famous Ernst's formula.

• Journal of Advanced Marine Engineering and Technology
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• 제29권2호
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• pp.194-201
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• 2005

For engineers in the industry, this study considers a reliable and practical finite element modeling technique to estimate the behavior of closed thin-walled members with spot weldings. Dynamic and static experiments confirm that the technique - modeling the spot weldings with solid elements which have the adjusted rotational freedoms and fill the welding space - Yields satisfactory results. Numerical studies on the double hat-shaped members. adopting this modeling technique. show the effect of the spot welding Pitch and the spot welding location in the flange on the stiffness of the members Using the principal stiffness and newly proposed GSPI(global stiffness performance index), we also carefully examine how the spot welding curvature, and sectional shape, etc.. synthetically influence the stiffness of a real excavator pillar in the field.