• 대한토목학회논문집
• /
• 제31권3C호
• /
• pp.103-108
• /
• 2011

본 연구에서는 대변형율 시험을 위한 공진주/비틂전단 시험기의 한계점과 해결방안을 기술하였다. 대변형율 시험의 세가지 한계점은 첫째, 시험기의 제한된 회전거리이며 둘째, 시험기의 제한된 비틂력과 셋째, 변형측정 시스템의 한계 등이 있다. 대변형율 시험의 제한요소 중에서 시험기의 제한된 회전거리를 해결하기 위하여 시료 받침대를 개량하였으며 비틂력을 향상 시키기 위하여 가진기 팔의 개수를 증가시키고 가진기 코일의 연결방법을 변경하여 보다 강한 비틂력을 얻을 수 있었다.

• Earthquakes and Structures
• /
• 제9권1호
• /
• pp.145-171
• /
• 2015

Due to earthquakes, many structures suffered extensive damages that were attributed to the torsional effect caused by mass, stiffness or strength eccentricity. Due to this type of asymmetry torsional moments are generated that are imposed by means of additional shear forces developed at the vertical resisting structural elements of the buildings. Although the torsional effect on the response of reinforced concrete buildings was the subject of extensive research over the last decades, a quantitative index measuring the amplification of the shear forces developed at the vertical resisting elements due to lateral-torsional coupling valid for both elastic and elastoplastic response states is still missing. In this study a reliable index capable of assessing the torsional effect is proposed. The performance of the proposed index is evaluated and its correlation with structural response quantities like displacements, interstorey drift, base torque, shear forces and upper diaphragm's rotation is presented. Torsionally stiff, mass eccentric single-story and multistory structures, subjected to bidirectional excitation, are considered and nonlinear dynamic analyses are performed using natural records selected for three hazard levels. It was found that the proposed index provides reliable prediction of the magnitude of torsional effect for all test examples considered.

• Computers and Concrete
• /
• 제29권 5호
• /
• pp.285-301
• /
• 2022

This study aims at developing a torsional strength model based on a nonlinear analysis method presented in the previous studies. To this end, flexural neutral axis depth of a reinforced concrete section and effective thickness of an idealized thin-walled tube were formulated based on reasonable approximations. In addition, various sectional force components, such as shear, flexure, axial compression, and torsional moment, were considered in estimating torsional strength by addressing a simple and linear strain profile. Existing test results were collected from literature for verifications by comparing with those estimated from the proposed model. On this basis, it can be confirmed that the proposed model can evaluate the torsional strength of RC members subjected to combined loads with a good level of accuracy, and it also well captured inter-related mechanisms between shear, bending moment, axial compression, and torsion.

• 대한기계학회논문집A
• /
• 제41권6호
• /
• pp.567-573
• /
• 2017

자동차 부품 중 드라이브 샤프트는 엔진에서 발생하는 토크를 바퀴에 전달하는 동력 전달장치의 핵심 부품이다. 엔진에서 입력되는 비틀림 하중과 주행 중 발생하는 실동하중에 의한 부품의 파손을 방지하기 위해, 고주파 열처리로 강도 및 피로수명이 개선되고 있다. 본 연구에서는 고주파 열처리에 따른 드라이브 샤프트의 피로수명을 정량적으로 평가할 수 있는 피로수명 평가기법을 구축하였다. 드라이브 샤프트의 소재인 SAE10B38M2 강재로 모재 및 경화깊이가 서로 다른 고주파 열처리 시편 두 종을 제작하여 비틀림 하중 하에서의 전단 변형률 제어 피로시험을 진행하였고, 변형률-수명 피로수명 평가에 필요한 피로 물성값을 구하였다. 얻어진 피로 물성값을 이용하여 드라이브 샤프트의 변형률 기반 피로해석을 진행하였으며, 얻어진 피로수명 결과를 시제품 피로시험 결과와 비교하여 해석기법의 타당성을 검증하였다.

• 대한금속재료학회지
• /
• 제46권9호
• /
• pp.545-553
• /
• 2008

Dynamic deformation behavior of ultra-fine-grained pure coppers fabricated by equal channel angular pressing (ECAP) was investigated in this study. Dynamic torsional tests were conducted on four copper specimens using a torsional Kolsky bar, and then the test data were analyzed by their microstructures and tensile properties. The 1-pass ECAP'ed specimen consisted of fine dislocation cell structures elongated along the ECAP direction, which were changed to very fine, equiaxed subgrains of 300~400 nm in size as the pass number increased. The dynamic torsional test results indicated that maximum shear stress increased with increasing ECAP pass number. Adiabatic shear bands were not found at the gage center of the dynamically deformed torsional specimen of the 1- or 4-pass ECAP'ed specimen, while some weak bands were observed in the 8-pass ECAP'ed specimen. These findings suggested that the grain refinement according to the ECAP was very effective in strengthening of pure coppers, and that ECAP'ed coppers could be used without serious reduction in fracture resistance under dynamic torsional loading as adiabatic shear bands were hardly formed.

• Earthquakes and Structures
• /
• 제19권1호
• /
• pp.59-77
• /
• 2020

The code static eccentricity model for elastic torsional design of structures has two critical shortcomings: (1) the negation of the inertial torsional moment at the center of mass (CM), particularly for torsionally-unbalanced (TU) building structures, and (2) the confusion caused by the discrepancy in the definition of the design eccentricity in codes and the resistance eccentricity commonly used by engineers such as in FEMA454. To overcome these shortcomings, using the resistance eccentricity model that can accommodate the inertial torsional moment at the CM, interactive relations between shear and torsion are proposed as follows: (1) elastic responses of structures at instants of peak edge-frame drifts are given as functions of resistance eccentricity, and (2) elastic hysteretic relationships between shear and torsion in forces and deformations are bounded by ellipsoids constructed using two adjacent dominant modes. Comparison of demands estimated using these two interactive relations with those from shake-table tests of two TU building structures (a 1:5-scale five-story reinforced concrete (RC) building model and a 1:12-scale 17-story RC building model) under the service level earthquake (SLE) show that these relations match experimental results of models reasonably well. Concepts proposed in this study enable engineers to not only visualize the overall picture of torsional behavior including the relationship between shear and torsion with the range of forces and deformations, but also pinpoint easily the information about critical responses of structures such as the maximum edge-frame drifts and the corresponding shear force and torsion moment with the eccentricity.

• 토지주택연구
• /
• 제2권4호
• /
• pp.387-395
• /
• 2011

국내 건축구조물의 내진설계기준에 의하면 현장탄성파시험으로 전단파속도를 측정하여 지반을 5종으로 분류하고 이에 의해 건축물에 작용하는 지진하중을 산정하고 있으나 공정상 성토지반에 대해서는 현장탄성파시험을 할 수 없다. 이에 실내에서 간편하게 현장의 상황을 고려하여 전단파속도를 추정할 수 있는 방법을 찾고자 공진주/비틂전단시험과 각종 현장 탄성파 시험결과를 비교 분석하였다. 분석결과 성토체의 구속압을 적절히 고려할 경우 현장탄성파 시험결과와 매우 유사한 결과를 얻을 수 있었다. 또한, 공진주/비틂전단시험에 의해 최대 전단탄성계수와 구속압의 영향평가를 실시한 결과 n값이 0.434~0.561의 일반적 범위의 값을 나타내어 공진주/비틂전단시험으로도 현장지반 전단탄성계수를 유용하게 추정할 수 있는 것으로 나타났다.

• 한국해양공학회지
• /
• 제27권6호
• /
• pp.73-80
• /
• 2013

The dynamic characteristics of west coast sand were investigated in order to evaluate the design properties of the offshore wind turbine foundations to be constructed in the West Sea. Torsional shear tests were performed at different confining pressures and densities on specimens constituted by the dry fluviation method. The strain-dependent shear modulus and damping curves were obtained, together with modulus degradation curves. The results show that the confining pressure is more influential on the dynamic characteristics of the sand than the density. It was also found that the dynamic curves from this study were similar to those proposed by others. The modulus degradation ratio $G/G_{1st}$ varies slightly at a small strain level, but increases significantly once beyond the intermediate strain level.

• Structural Engineering and Mechanics
• /
• 제33권2호
• /
• pp.137-158
• /
• 2009

This paper investigates the behavior of reinforced concrete (RC) circular columns under combined loading including torsion. The main variables considered in this study are the ratio of torsional moment to bending moment (T/M) and the level of detailing for moderate and high seismicity (low and high transverse reinforcement/spiral ratio). This paper presents the results of tests on seven columns subjected to cyclic bending and shear, cyclic torsion, and various levels of combined cyclic bending, shear, and torsion. Columns under combined loading were tested at T/M ratios of 0.2 and 0.4. These columns were reinforced with two spiral reinforcement ratios of 0.73% and 1.32%. Similarly, the columns subjected to pure torsion were tested with two spiral reinforcement ratios of 0.73% and 1.32%. This study examined the significance of proper detailing, and spiral reinforcement ratio and its effect on the torsional resistance under combined loading. The test results demonstrate that both the flexural and torsional capacities are decreased due to the effect of combined loading. Furthermore, they show a significant change in the failure mode and deformation characteristics depending on the spiral reinforcement ratio. The increase in spiral reinforcement ratio also led to significant improvement in strength and ductility.

• Computers and Concrete
• /
• 제15권6호
• /
• pp.935-950
• /
• 2015

The aim of this study is to provide experimental data regarding the compressive, shear and torsional strength of self-compacting concrete (SCC) used in rectangular beams, and then comparing the results with the equations presented by the CSA A23.3-04 and ACI 318-11. In fact, the gathered information in this field is quite useful for calibrating the computer models of other researchers. The other goal of this study was to investigate the effects of silica fume and superplasticizer dosages on the mechanical properties of SCC. In this research, SCC is made based on 16 different type mixing layout. Also two normal concrete (NC) or vibrating concrete are constructed to compare the results of SCC and NC. This work concentrated on concrete mixes having water/binder ratios of 0.45 and 0.35, which contained constant total binder contents of $400kg/m^3$ and $500kg/m^3$, respectively. The percentages of silica fume that replaced cement were 0% and 10%. The superplasticizer dosages utilized in the mixtures were 0.4%, 0.8%, 1.2% and 1.6% of the weight of cement. Beam dimensions used in this test were $30{\times}30{\times}120cm^3$. The results of this research indicated that shear and torsional strength of SCC beams to be used in computer models can be calculated utilizing the equations presented in CSA A23.3-04 and ACI 318-11.