Concurrent flexural strength and deformability design of high-performance concrete beams

J.C.M. Ho,K.J.H. Zhou 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.40 No.4

In the design of earthquake resistant reinforced concrete (RC) structures, both flexural strength and deformability need to be considered. However, in almost all existing RC design codes, the design of flexural strength and deformability of RC beams are separated and independent on each other. Therefore, the pros and cons of using high-performance materials on the flexural performance of RC beams are not revealed. From the theoretical results obtained in a previous study on flexural deformability of RC beams, it is seen that the critical design factors such as degree of reinforcement, concrete/steel yield strength and confining pressure would simultaneously affect the flexural strength and deformability. To study the effects of these factors, the previous theoretical results are presented in various charts plotting flexural strength against deformability. Using these charts, a "concurrent flexural strength and deformability design" that would allow structural engineers to consider simultaneously both strength and deformability requirements is developed. For application in real construction practice where concrete strength is usually prescribed, a simpler method of determining the maximum and minimum limits of degree of reinforcement for a particular pair of strength and deformability demand is proposed. Numerical examples are presented to illustrate the application of both design methods.

Concurrent flexural strength and deformability design of high-performance concrete beams

Ho, J.C.M.,Zhou, K.J.H. Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.40 No.4

In the design of earthquake resistant reinforced concrete (RC) structures, both flexural strength and deformability need to be considered. However, in almost all existing RC design codes, the design of flexural strength and deformability of RC beams are separated and independent on each other. Therefore, the pros and cons of using high-performance materials on the flexural performance of RC beams are not revealed. From the theoretical results obtained in a previous study on flexural deformability of RC beams, it is seen that the critical design factors such as degree of reinforcement, concrete/steel yield strength and confining pressure would simultaneously affect the flexural strength and deformability. To study the effects of these factors, the previous theoretical results are presented in various charts plotting flexural strength against deformability. Using these charts, a "concurrent flexural strength and deformability design" that would allow structural engineers to consider simultaneously both strength and deformability requirements is developed. For application in real construction practice where concrete strength is usually prescribed, a simpler method of determining the maximum and minimum limits of degree of reinforcement for a particular pair of strength and deformability demand is proposed. Numerical examples are presented to illustrate the application of both design methods.

자동차 시트 쿠션 프레임 및 백 프레임의 구조 강도 해석

김성수(Kim Seong-Soo),김기선(Kim Key-Sun),최두석(Choi, Doo-Seuk),박상흡(Park, Sang-Heup),김세환(Kim Sei-hwan),조재웅(Cho Jae-Ung) 한국산학기술학회 2012 한국산학기술학회논문지 Vol.13 No.11

자동차의 다양한 부품 중 자동차 시트는 인간과의 직접 접촉 부위로서 승차감을 평가 할 수 있는 가장 기 본적인 항목이다. 따라서 자동차 시트는 승차감과 동시에 충분한 강성과 강도를 가져야 할 것이다. 본 연구에서는 자동차 시트에서의 시트 쿠션 프레임과 백 프레임을 3D 모델링하였고, 쿠션 프레임의 비틀림 강도, 수직하중강도 시 험, 백 프레임의 강도 시험 3가지 실험에 대해서 시뮬레이션으로 구조해석을 하였다. 해석결과, 쿠션 프레임 비틀림 강도 시험에서는 초기 전변형량의 최대값은 5.8421mm가 나왔고, 영구 전변형량의 최대값은 0.02539mm가 나왔다. 쿠션 프레임 수직하중강도 시험에서는 쿠션 프레임 앞쪽 끝단의 전변형량은 2.1159mm이고, 뒤쪽 끝단은 0.0606mm 이다. 하중을 더 증가한 경우는 전변형량의 최대값은 3.1739mm가 나왔다. 3 가지의 백 프레임 강도 시험에서는 최 대의 전변형량은 0.18634mm로 나타났다. 본 연구결과는 자동차 시트 쿠션 프레임 및 백프레임의 과도한 변형 및 파 괴가 없음으로서 승객의 안전을 보장하는 충분한 강성과 강도를 검증할 수 있었다. Among the various parts of automobile, automotive seat is the most fundamental item that ride comfort can be evaluated as the direct contact part with human body. Automotive seat must have the sufficient rigidity and strength at the same time with ride comfort. In this study, cushion frame and back frame at car seat are modelled with 3D. There are structural simulation analyses about 3 kinds of tests on torsion strength, vertical load strength and back frame strength. In the analysis result, the initial total deformation and the permanent total deformation has the maximum values of 5.4821 mm and 0.02539mm respectively at the torsion strength test of cushion frame. Total deformations at front and rear end parts of cushion frame become the values of 2.1159mm and 0.0606mm respectively at the test of vertical load strength of cushion frame. In case of more than this load, the maximum value of total deformation also becomes 3.1739mm. The maximum value of total deformation becomes 0.18634mm at 3 kinds of the strength tests on back frame. By the study result of no excessive deformation and no fracture cushion frame and back frame at automotive seat, the sufficient rigidity and strength to guarantee the safety of passenger can be verified.

대학생의 배근력 차이에 따른 척추변형 정도

이은욱 ( Lee Eunwook ),김규완 ( Kim Kewwan ),전경규 ( Jeon Kyoungkyu ) 인천대학교 스포츠과학연구소 2018 스포츠科學硏究誌 Vol.31 No.0

이 연구는 대학생의 배근력의 차이가 어느 정도 척추변형의 차이를 가져오는지 탐색하고자 하였다. 연구의 목적을 달성하기 위하여 인천광역시 소재 I대학교의 재학생 142명을 임의 표집 하여 이들을 배근력이 높은 집단과 낮은 집단으로 구분하였고, 이들을 대상으로 척추구조분석 및 배근력을 측정하였다. 이 연구에서 척추변형 정도를 알아보기 위해 분석한 변인은 체간의 길이, 정중면상 체간의 길이와 각도, 전후면상 체간의 길이와 각도, 골반 각도, 척추 만곡 각도이다. 변인의 측정을 위하여 Formetric 4D(척추구조분석기)와 배근력 측정기를 사용하였다. 수집한 자료의 처리는 Window용 SPSS 23.0을 이용하였으며 배근력의 크기에 따른 척추변형의 차이를 알아보기 위하여 독립표본 t-test를 사용하였다. 이 연구의 결과 체간길이는 배근력이 높은 남자 집단에서 유의하게 작게 나타났고 골반의 각도는 배근력이 높은 남자 집단에서 유의하게 크게 나타났다. 척추측만각도는 배근력이 높은 여자 집단에서 측만각도가 유의하게 낮은 것으로 나타났다. 이와는 반대로 전만각도는 배근력이 낮은 여자 집단에서 유의하게 낮은 것으로 나타났다. 따라서 배근력의 차이에 따라 척추의 변형정도 차이가 나타난 것을 알 수 있었다. The purpose of this study was to investigate the effect of back muscle strength on spinal deformity in college students. We recruited 142 university students, and divided into four groups based on the level of back muscle strength: (a) male with higher back muscle strength, (b) male with lower back muscle strength, (c) female with higher back muscle strength, and (d) female with lower back muscle strength. Using Formetric 4D, we measured trunk length, sagittal imbalance, coronal imbalance, pelvic angle, and curvature of the spine angle. Independent t-tests were used for statistical analysis using SPSS 23.0. The findings revealed that trunk length was significantly smaller in the male with higher back muscle strength than with the male with lower back muscle strength. Pelvic angle was significantly greater in the male students with higher back muscle strength than the male with lower back muscle strength. Scoliosis angle was significantly smaller in the female with higher back muscle strength than the female with lower back muscle strength. However, lordotic angle was significantly smaller in the female with lower back muscle strength than the female with higher back muscle strength. These findings indicated that back muscle strength may influence the deformation of the spine, however these patterns were inconsistent across male and female groups.

Experimental Study on the Physical-Mechanical Properties of Frozen Silt

Martin Christ,김영진 대한토목학회 2009 KSCE JOURNAL OF CIVIL ENGINEERING Vol.13 No.5

The objective of this study was to investigate the physical-mechanical characteristics of frozen Siberian silt. Unfrozen water content, uniaxial compressive strength and direct-tensile strength of frozen silt samples at different moisture contents were determined in the laboratory. Experimental results revealed that the amount of unfrozen water in the silt decreased with descending temperature and stabilized at temperatures below -10˚C. Even at very low temperatures a considerable amount of unfrozen water remained. Mechanical strength test results showed a strong dependence of the stress-strain behavior of the frozen silt on the moisture content and temperature. The strength for compression and tension increased with decreasing temperature and increasing moisture content. At any given temperature and moisture content compressive strength was significantly greater than tensile strength. Based on the compressive and tensile stress-strain relationship at a given temperature and moisture content, approximate values of strength ratio, failure strain ratio and deformation modulus ratio were established. The objective of this study was to investigate the physical-mechanical characteristics of frozen Siberian silt. Unfrozen water content, uniaxial compressive strength and direct-tensile strength of frozen silt samples at different moisture contents were determined in the laboratory. Experimental results revealed that the amount of unfrozen water in the silt decreased with descending temperature and stabilized at temperatures below -10˚C. Even at very low temperatures a considerable amount of unfrozen water remained. Mechanical strength test results showed a strong dependence of the stress-strain behavior of the frozen silt on the moisture content and temperature. The strength for compression and tension increased with decreasing temperature and increasing moisture content. At any given temperature and moisture content compressive strength was significantly greater than tensile strength. Based on the compressive and tensile stress-strain relationship at a given temperature and moisture content, approximate values of strength ratio, failure strain ratio and deformation modulus ratio were established.

Strength and Deformation Characteristics of Silty Sand Improved by Gravel

Ai-jun Chen,Jia-sheng Zhang 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.2

Silty sand is a poor filler of highway and railway subgrade, and various physical and chemical improving methods have been applied to increase the strength and stability of silty sand. Adding gravel to silty sand is a routine physical improving method. In this paper, large-scale triaxial tests were carried out on silty sand and improved soil which is obtained by adding 4 different proportions of gravel into the silty sand in order to analyze the strength and deformation characteristics of the improved soil. The stress-strain relations obtained from tiaxial tests were analyzed and the effect of coarse particles and fine particles on the strength and deformation of the specimen were also analyzed. The test results show that with more coarse particles and under a higher confining pressure, a greater deviator stress is required to produce the same axial strain. The increase of coarse particles helps to enlarge the angle of internal friction and cohesion, while the increase of fine particles decreases the angle of internal friction and cohesion. Under low confining pressure, the soil specimens with more coarse particles exhibit evident shear dilation. Under high confining pressure, the soil specimens produce a greater volume strain. Adding appropriate amount of gravel into the silt soil can increase its strength and restrain its deformation, but excessive amount of gravel may produce too much volume deformation.

저온 분사 공정으로 제조된 초고강도 Cu 벌크 소재의 인장 및 압축 변형 거동

김영균,이기안 대한금속·재료학회 2020 대한금속·재료학회지 Vol.58 No.11

In this study, high-strength pure Cu bulk material was manufactured using a cold spray additive manufacturing process, and its microstructure, tensile and compressive deformation behaviors were investigated and compared. The cold spray additive manufactured Cu bulk material showed a heterogeneous grain structure consisting of fine-grains and coarse-grains, and only α – Cu single phase was identified. The cold spray Cu exhibited yield strengths of ~415 MPa in tensile- and compression tests, indicating that it had similar mechanical properties in different deformation modes. The yield strength values were similar to that of Cu manufactured by equal channel angular pressing (ECAP), a severe plastic deformation (SPD) method which enables ultra-high strength. Concerning tensile characteristics, the cold sprayed Cu exhibited partial plastic deformation that has not been reported to date. In addition, some nano-sized dimples, suggesting metallurgical bonding, were also found in the fracture surface. Regarding compression characteristics, the strain softening phenomenon, which is not a general tendency in room temperature deformation, appeared. This unique softening behavior was attributed to dynamic recovery and dynamic recrystallization during compression testing. Based on the above results, we discuss the tensile/compressive deformation behavior of the cold spray Cu bulk material, and predict compressive deformation behavior considering the constitutive equation.

Evaluation of Installation Damage According to Simulated Installation Test Conditions and Creep Deformation of Geosynthetic Reinforcements

최부열,한상민,이승호,김승현,전한용,Choi, Bu Yeol,Han, Sang Min,Lee, Seung Ho,Kim, Seung Hyun,Jeon, Han-Yong The Korean Fiber Society 2021 한국섬유공학회지 Vol.58 No.4

In this study, a total of six geosynthetic reinforcements, including five geogrid types (design strengths of 4, 6, 8, 10, and 15 ton/m) and a woven geotextile (design strength of 4 ton/m) were used to simulate the degree of damage according to the installation damage test conditions, and property evaluation by creep deformation was performed. The degree of installation damage during the construction period of the geosynthetic samples was tested in accordance with ISO 10722:2019, and soil structure compaction was performed with fill thicknesses of 20, 30, 40, 60, 80, and 100 cm. After the installation damage test, geosynthetic samples were removed, and the tensile strength before and after the installation damage test was compared by applying a wide tensile strength test (ASTM D 4595). Jumunjin standard sand was used as the filling material and after a soil compaction installation damage test, the tensile strength of the reinforcing geosynthetic sample decreased by 2-30% overall, and the reduction factor owing to installation damage was calculated by comparing the tensile strength before and after installation damage testing. The GRI GS-10 test method was used to evaluate the creep deformation at 10 000 h, and the GRI GG-4 method was used to determine the reduction coefficient owing to creep deformation. From the creep test, it was found that the creep strain of the damaged geosynthetic sample by filling depth under the same load conditions was approximately 1-2% higher than that of the undamaged sample.

Deformation-based Strut-and-Tie Model for flexural members subject to transverse loading

홍성걸,이수곤,홍성원,강현구 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.18 No.6

This paper describes a deformation-based strut-and-tie model for the flexural members at post-yield state. Boundary deformation conditions by flexural post-yield response are chosen in terms of the flexural bar strains as the main factor influenced on the shear strength. The main purpose of the proposed model is to predict the shear capacities of the flexural members associated with the given flexural deformation conditions. To verify the proposed strut-and-tie model, the estimated shear strengths depending on the flexural deformation are compared with the experimental results. The experimental data are in good agreement with the values obtained by the proposed model.

Strength and Deformation Characteristics of Calcareous Sands Improved by PFA

Qing-Sheng Chen,Wan Peng,Gao-LiangTao,Sanjay Nimbalkar 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.1

Calcareous sand is widely distributed in the islands of the South China Sea, which could be promisingly used as the construction materials. However, particle breakage commonly occurs in calcareous sands, which may significantly influence their mechanical characteristics. To address these issues, an eco-friendly agent, i.e., polyurethane foam adhesive (PFA) is proposed to improve the engineering properties of calcareous sands, compared to the commonly used alkaline stabilizing agents (e.g., lime, cement). The objective of this work is to examine the effectiveness of using PFA in improving the strength-deformation properties of calcareous sand. A series of laboratory tests including direct shear tests, unconfined compression tests, and oedometer tests were performed on the calcareous sands improved by PFA. In addition, A scanning electron microscope (SEM) was conducted to reveal microstructural analysis of using PFA for calcareous sand. The experimental results provided insights into the shear strength, deformation modulus, as well as the micro-structural characteristics of improved calcareous sands with various PFA contents and particle size distributions.