Tensile load tests were conducted on High-Shear Ring Anchors (HRAs) after shear load had been applied to the HRAs, which had been developed to reduce the number of the anchors. Test variables include the embedment length of the rod and the width of the specimens and a total of 12 specimens were tested. Test results show that the HRAs pulled out due to bond failure or steel failure occurred in case that the HRAs were installed to the members with 300mm or greater width and the embedment length of 160mm (the actual embedment of rod is 140mm) or deeper. Except 4 HRAs showing steel failure of rod, the minimum and average of test-to-prediction by ACI 318-14 ratios are 1.18 and 1.79, respectively. The tensile strength of HRAs, after shear load was applied to the HRAs, can be safely evaluated by the minimum among the concrete breakout strength and bond strength with the actual embedment length of the rod.

PURPOSES : Previously, airport concrete pavement was designed using only aircraft gear loading without consideration of environmental loading. In this study, a multiple-regression model was developed to predict maximum tensile stress of airport concrete pavement based on finite element analysis using both environmental and B777 aircraft gear loadings. METHODS: A finite element model of airport concrete pavement and B777 aircraft main gears were fabricated to perform finite element analysis. The geometric shape of the pavement, material properties of the layers, and the loading conditions were used as input parameters for the finite element model. The sensitivity of maximum tensile stress of a concrete slab according to the variation in each input parameter was investigated by setting the ranges of the input parameters and performing finite element analysis. Based on the sensitivity analysis results, influential factors affecting the maximum tensile stress were found to be used as independent variables of the multi regression model. The maximum tensile stresses predicted by both the multiple regression model and finite element model were compared to verify the validity of the model developed in this study. RESULTS: As a result of the finite element analysis, it was determined that the maximum tensile stress developed at the bottom of the slab edge where gear loading was applied in the case that environmental loading was small. In contrast, the maximum tensile stress developed at the top of the slab center situated between the main gears in the case that the environmental loading got larger. As a result of the sensitivity analysis and multiple regression analysis, a maximum tensile stress prediction model was developed. The independent variables used included the joint spacing, slab thickness, the equivalent linear temperature difference between the top and bottom of the slab, the maximum take-off weight of a B777 aircraft, and the composite modulus of the subgrade reaction. The model was validated by comparing the predicted maximum tensile stress to the result of the finite element analysis. CONCLUSIONS : The research shown in this paper can be utilized as a precedent study for airport concrete pavement design using environmental and aircraft gear loadings simultaneously.

폴리머 폼은 다공성을 가장 큰 특징으로 하는 재료이기 때문에, 본 연구에서 비가역 열역학 관점을 기반으로 폴리머 폼의 기공 성장 및 합체를 고려한 손상 탄성 구성방정식을 개발하였으며, 개발된 구성방정식은 unilateral 손상의 효과를 고려하였다. 유한요소해석의 적용을 위해 상용 유한요소해석 프로그램인 ABAQUS의 사용자 서브루틴 UMAT을 이용하여 제안된 구성방정식을 수치적으로 구현하였다. 비선형 유한요소해석 결과와 폴리머 폼의 인장 시험 결과와 비교를 통해 제안된 손상 모델의 유효성을 검증하였으며, 제안된 구성방정식의 재료모델상수가 손상에 미치는 영향에 대해 분석하였다.

This study deals with the microstructure and tensile properties of 700 MPa-grade high-strength and seismic reinforced steel bars. The high-strength reinforced steel bars (600 D13, 600 D16 and 700 D13 specimens) are fabricated by a TempCore process, while the seismic reinforced steel bar (600S D16 specimen) is fabricated by air cooling after hot rolling. For specimens fabricated by the TempCore process, the 600 D13 and 600 D16 specimens have a microstructure of tempered martensite in the surface region and ferrite-pearlite in the center region, while the 700 D13 specimen has a microstructure of tempered martensite in the surface region and bainite in the center region. Therefore, their hardness is the highest in the surface region and shows a tendency to decrease from the surface region to the center region because tempered martensite has a higher hardness than ferrite-pearlite or bainite. However, the hardness of the 600S D16 specimen, which is composed of fully ferritepearlite, increases from the surface region to the center region because the pearlite volume fraction increases from the surface region to the center region. On the other hand, the tensile test results indicate that only the 700 D13 specimen with a higher carbon content exhibits continuous yielding behavior due to the formation of bainite in the center region. The 600S D16 specimen has the highest tensile-to-yield ratio because the presence of ferrite-pearlite and precipitates caused by vanadium addition largely enhances work hardening.

In this study, tensile stresses of partially delaminated CFRP sheets were analytically evaluated. The analytical model is a 15-m long concrete beam with a rectangular cross-section of 2×3 m and uses 480 2D-plate elements and 5760 3D-solid elements for mesh construction. The elastic modulus of concrete and CFRP sheet used in the analysis are 27,536 MPa and 200,000 MPa, respectively, and the compressive strength of concrete and tensile strength of CFRP sheet are 30.0 MPa and 4,000 MPa, respectively. In order to evaluate the change of the tensile stress due to the delamination of the CFRP sheet, the whole attached model and the partially delaminated model according to the position of delamination were considered. As a result of the finite element analysis, the tensile stress of the entire attached CFRP sheet showed a constant tensile stress on the whole cross section, and the tensile stress of the partially delaminated CFRP sheet showed the maximum tensile stress on the position of delamination. Based on the results of this study, future research will be carried out to optimize the layout and shape of CFRP sheets embedded with optical fiber sensors.

As buildings are becoming larger, demand for large-scale composite columns for heavy load is increasing. Welded built-up CFT column (ACT Column I) previously developed by authors of this study is structurally stable and economical. Characteristic of welded built-up CFT column is that there is a limitation of cross-sectional size and application of external diaphragm connection to ensure continuity of rib. Then, composite mega column (ACT Column II) was developed to improve limit of cross-sectional size. Composite mega column has a closed cross section like welded built-up CFT column, but thick plate is inserted between cold-formed steel to expand cross section size. However, when external diaphragm connection is applied to composite mega column, amount of steel is increased greatly and interference with finishing material occurs. In this study, internal diaphragm connection is applied through characteristic of composite mega column to which beam flange or stiffener can be attached to plate. In order to analyze this, simple tensile experiment of composite mega column connection with T-shaped stiffener was performed.

In this paper, uniaxial tensile tests of ETFE films with three kinds of thicknesses(100, 200, 250μm) and two kinds of directions(machine direction & transverse direction) are performed and the tensile strength, the tensile strain at break and the Young’s modulus of ETFE films are compared for two kinds of specimen types(2 & 5). It could be figured out that there are no significant difference between tensile strengths of two specimen types but the tensile strain at break and the Young’s modulus of ETFE films are affected by the specimen types. And it is concluded that the uniaxial tensile test of specimen type 2 are more reliable than that of specimen type 5.

This paper presents experimental and analytical results for predicting tensile behavior of FRP Hybrid Bar(HYB). In order to confirm the tensile behavior of HYB wrapped with glass fiber reinforced polymer(GFRP) on deformed rebar, direct tensile tests were performed on 8 specimens. The diameter of the HYB was considered as a test variable and the tensile load, displacement, and tensile strain of each specimen were measured by tensile test. In order to predict the tensile behavior of HYB, numerical analysis based on tensile model of each material was performed. The tensile models of reinforcing bar, glass fiber, and resin, which are the constituent materials of HYB, are assumed to be simple shapes according to their material properties. The results of the numerical analysis through the strain compliance condition of each material were compared with the experimental results and both results showed consistent trends. The experimental and analytical ratios for yield and ultimate loads were 1.02 and 1.00, respectively, and the coefficient of variation were 3.61 and 2.54, respectively. However, a maximum of about 9 mm error occurred due to the slip generated by the direct tensile test in the comparison between the experimental results and the analytical results for the tensile displacement.

Four types of high Mn TWIP(Twinning Induced Plasticity) steels were fabricated by varying the Mn and Al content, and the tensile properties were measured at various strain rates and temperatures. An examination of the tensile properties at room temperature revealed an increase in strength with increasing strain rate because mobile dislocations interacted rapidly with the dislocations in localized regions, whereas elongation and the number of serrations decreased. The strength decreased with increasing temperature, whereas the elongation increased. A martensitic transformation occurred in the 18Mn, 22Mn and 18Mn1.6Al steels tested at −196 oC due to a decrease in the stacking fault energies with decreasing temperature. An examination of the tensile properties at −196 oC showed that the strength of the non-Al added high Mn TWIP steels was high, whereas the elongation was low because of the martensitic transformation and brittle fracture mode. Although a martensitic transformation did not occur in the 18Mn1.9Al steel, the strength increased with decreasing temperature because many twins formed in the early stages of the tensile test and interacted rapidly with the dislocations.

The effect of strain aging on the tensile properties of API X70 linepipe steel was investigated in this study. The API X70 linepipe steel was fabricated by controlled rolling and accelerated cooling processes, and the microstructure was analyzed using optical and scanning electron microscopes and electron backscatter diffraction. Strain aging tests consisting of 1% pre-strain and thermal aging at 200 oC and 250 oC were conducted to simulate U-forming, O-forming, Expansion(UOE) pipe forming and anti-corrosion coating processes. The API X70 linepipe steel was composed of polygonal ferrite, acicular ferrite, granular bainite, and bainitic ferrite whose volume fraction was dependent on the chemical composition and process conditions. As the thermal aging temperature increased, the steel specimens showed more clearly discontinuous type yielding behavior in the tensile stress-strain curve due to the formation of a Cottrell atmosphere. After pre-strain and thermal aging, the yield and tensile strengths increased and the yield-to-tensile strength ratio decreased because yielding and aging behaviors significantly affected work hardening. On the other hand, uniform and total elongations decreased after pre-strain and thermal aging since dislocation gliding was restricted by increased dislocation density after a 1% pre-strain.

시멘트 콘크리트 도로포장의 노후화와 함께 지속적으로 사용되어진 제설재의 영향으로 고속도로의 파손 및 관련된 유지보수 비용은 매년 급증하는 추세이다. 이러한 문제점의 극복을 위해 최근 유럽 및 선진국에서 기존 콘크리트 포장 상부에 아스팔트 포장을 시공하는 덧씌우기 포장을 적용하고 있으나, 거듭된 연구에도 불구하고 콘크리트 층의 조인트 부위에서 발생하는 반사균열에 대해 효과적으로 억제할 수 있는 방안은 미흡한 실정이다. 반사균열에 의한 문제점을 해결하기 위한 방안으로 개발된 것이 응력흡수층(SAMI, Stress Absorbing Membrane Interlayer) 포장공법으로 기존 포장층과 신설 포장층 사이에 별도의 응력흡수층을 설치하여 하부층의 균열을 상부층으로 전달되는 것을 방지하는 것을 목적으로 한다. 본 연구에서는 응력흡수층의 성능평가를 위해 시멘트 콘크리트 포장위에 아스팔트 콘크리트 덧씌우기를 모사한 4종류의 혼합물을 제작하였다. 그림 1.은 응력흡수층의 적용여부를 구분하여 제작한 혼합물을 나타낸다. 여기서, SAMI층의 경우 유리섬유를 포설한 섬유 그리드층과 유리섬유를 포설하지 않은 섬유 그리드층으로 구분하였다. 아스팔트 콘크리트 층은 덧씌우기에 효과가 우수하다고 판단되는 PSMA(Polymer mdified Stone Mastic Asphalt)로 제작하였으며 SMA 포장과 같은 13mm 골재를 사용하여 골재의 맞물림 효과를 충분히 발휘시키기 위한 목적으로 PG 76-22 등급의 바인더를 사용하였다. SAMI의 경우 하부 포장층과 접착이 불안정한 경우 소성변형 및 균열을 유발할 수 있기 때문에 부착강도는 중요 요소로 작용될 수 있으며, 덧씌우기층과 응력흡수층 사이의 밀림현상에 충분히 저항할 수 있어야 하므로 응력흡수층의 부착 및 전단 성능을 평가하기 위해 직접전단 및 인장시험을 실시하였다.

This present study deals with the microstructure and tensile properties of 600 MPa-grade high strength and seismic resistant reinforcing steels. The high strength reinforcing steel (SD 600) was fabricated by Tempcore processing, while the seismic resistant reinforcing steel (SD 600S) was air-cooled after hot-rolling treatment. The microstructure analysis results showed that the SD 600 steel specimen consisted of a tempered martensite and ferrite-pearlite structure after Tempcore processing, while the SD 600S steel specimen had a fully ferrite-pearlite structure. The room-temperature tensile test results indicate that, because of the enhanced solid solution and precipitation strengthening caused by relatively higher contents of C, Mn, Si and V in the SD 600S steel specimen, this specimen, with fully ferrite-pearlite structure, had yield and tensile strengths higher than those of the SD 600 specimen. On the other hand, the hardness of the SD 600 and SD 600S steel specimens changed in different ways according to location, dependent on the microstructure, ferrite grain size, and volume fraction.

Three-dimensional motion analysis systems and force plates are used for gait phase detection and ground reaction force(GRF) or ground reaction moment(GRM) data collection. But force plates as measurement systems are restricted to laboratory environments and have limitations for abnormal walking with foot dragging. Therefore the methods were proposed to compute the GRM from the kinematic data of three-dimensional motion analysis systems. Gait phase detection with kinematic data using foot velocity algorithm(FVA) was performed. The validity of gait phase detection was obtained comparing with the results of force plates. A gait model with 7 segments was composed to compute GRM. The results of gait model with kinematic data were compared with those of force plates. The result of the vertical direction is similar. But anterior-posterior direction and lateral direction show similar tendency with some gaps.

In this study, two Fe-30Mn-0.2C-(1.5Al) high-manganese steels with different surface conditions were hydrogencharged under high temperature and pressure; then, tensile testing was performed at room temperature in air. The yield strength of the 30Mn-0.2C specimen increased with decreasing surface roughness(achieved via polishing), but that of the 30Mn-0.2C- 1.5Al specimen was hardly affected by the surface conditions. On the other hand, the tendency of hydrogen embrittlement of the two high-manganese steels was not sensitive to hydrogen charging or surface conditions from the standpoints of elongation and fracture behavior. Based on the EBSD analysis results, the small decrease in elongation of the charged specimens for the Fe-30Mn-0.2C-(1.5Al) high-manganese steels was attributed to the enhanced dislocation pile-up around grain boundaries, caused by hydrogen