• 한국운동역학회지
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• 제25권3호
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• pp.335-342
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• 2015

Objective : The purposes of this study was to analyze the effects of the stirrup length fitted to the rider's lower limb length and it's impact on less skilled riders during trot in equestrian events. Methods : Participants selected as subjects consisted of less skilled riders(n=5, mean age: $40.02{\pm}10.75yrs$, mean heights: $169.77{\pm}2.08cm$, mean body weights: $67.65{\pm}7.76kg$, lower limb lengths: $97.26{\pm}2.35cm$, mean horse heights: $164.00{\pm}5.74cm$ with 2 type of stirrups lengths(lower limb ratio 74.04%, and 79.18%) during trot. The variables analyzed consisted of the displacement for Y axis and Z axis(head, and center of mass[COM]) with asymmetric index, trunk front-rear angle(consistency index), lower limb joint(Right hip, knee, and ankle), and average vertical forces of horse rider during 1 stride in trot. The 4 camcorder(HDR-HC7/HDV 1080i, Spony Corp, Japan) was used to capture horse riding motion at a rate of 60 frames/sec. Raw data was collected from Kwon3D XP motion analysis package ver 4.0 program(Visol, Korea) during trot. Results : The movements and asymmetric index didn't show significant difference at head and COM, Also, 74.04% stirrups lengths in trunk tilting angle showed significant difference with higher consistency than that of 79.18% stirrups lengths. Hip and knee joint angle showed significant difference with more extended posture than that of 74.04% stirrups lengths during trot. Ankle angle of 79.18% stirrups length showed more plantarflexion than that of 74.04% stirrups lengths. Average vertical force of rider showed significant difference with higher force at 79.18% stirrups lengths than that of 74.04% stirrups lengths during stance phase. Conclusion : When considering the above, 74.04% stirrups length could be effective in impulse reduction with consistent posture in rather less skilled horse riders.

• 한국운동역학회지
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• 제25권1호
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• pp.131-140
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• 2015

Purpose : The purpose of this study was to analyze the coordination of the trunk tilting angle and bilateral lower limbs according to the stirrups length during trot in equestrian. Methods : Participants selected as subject were consisted of adult male(n=7, mean age: $45.00{\pm}3.78yrs$, mean height: $172.50{\pm}2.44cm$, mean body mass: $76.95{\pm}4.40kg$, mean, mean leg length: $97.30{\pm}2.60cm$). They were divided into 3-types of stirrups lengths(67 cm, 72 cm, 77 cm) during trot. The variables analyzed were consisted of the trunk front-rear angle, lower limb joint(Right Left hip, knee, ankle), overall movement index(OMI) of the lower limbs(thigh, shank, foot) and asymmetry index(AI%) during trot. Results : The average angle in hip and knee joint showed more extended posture according to the increase of stirrups lengths and ankle angle showed more plantarflexion posture according to increase of stirrups length during 1 stride in trot. Also, average angle showed more extended posture in right hip and ankle joint than that of left. The angle of knee joint didn't show significant difference statistically between right and left. Also asymmetric index in average angle of hip, knee and ankle joint didn't show significant difference statistically in between lower limbs, but hip joint showed higher asymmetric index in stirrup length of 77 cm and ankle joint showed higher asymmetric index in stirrup length of 67 cm than that of the others respectively. The FR angle in trunk of horse-rider showed relative backward leaning motions at stirrup length of 67 cm and 77 cm than that of stirrup length of 72 cm during stance and swing phase. OMI in thigh, shank, and foot limbs didn't show significant difference statistically according to the stirrups length of right and left lower limbs, but left lower limbs showed higher index than that of right lower limb. Stirrup length of 72 cm in shank and foot limbs showed higher index than that of stirrup length of 67 cm and 77 cm. But stirrup length of 72 cm showed higher asymmetric index than that of stirrups length of 67 cm and 77 cm. Conclusions : When considering the above, 72 cm(ratio of lower limb 74.04%) stirrup lengths could be useful in posture correction and stabilization than 67cm(ratio of lower limb 68.69%) and 77 cm(ratio of lower limb 79.18%) stirrup lengths during trot in horse back riding.

• 한국운동역학회지
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• 제24권4호
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• pp.329-338
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• 2014

The purpose of this study was to analyze of the rider postural alignments according to the fitting of stirrups lengths during walk of high level riders. Participants selected as subject were consisted of horse riders of high level (age: $47.66{\pm}3.51yrs$, height: $168.40{\pm}4.84cm$, body weight: $73.36{\pm}15.58kg$, low extremity length: $94.76{\pm}3.98cm$, career: $23.33{\pm}5.77yrs$) and walk with 3 types of stirrup lengths(ratio of low extremity 68.04%, 73.25%, 78.48%). The variables analyzed were consisted of the displacement of Y axis (center of mass, head, thigh, shank and foot), FR angle, LR angle, dynamic postural stability index (DPSI), coefficient of variation (CV%), and distance (X axis) of low extremity limb between right and left. The displacement of Y axis in COM, thigh, shank, foot limbs were not statistically significant, but movements of head showed greater distance of B type and C type than that of A type during 1 stride of walk. The FR and LR angle in trunk of horse rider, dynamic postural stability index and, coefficient of variation didn't show significant difference statistically according to the fitting of stirrup lengths. Also the distance (X axis) of low extremity in thigh and shank didn't show significant difference statistically in between right and left, but right and left foot showed greater distance in C type than that of B and A types during walk in horse back riding. The hip and ankle joint angle not statistically significant according to stirrups lengths, But knee joint angle showed more extended according to the increase of stirrups lengths during stance and swing phase in walk.

• Advances in concrete construction
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• 제13권 2호
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• pp.183-190
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• 2022

A wide range of experimental bases and improved performance with different forms of Fiber Reinforced Polymer (FRP) have attracted researchers to produce eco-friendly and sustainable structures. The reinforced concrete (RC) beam's shear capacity has remained a complex phenomenon because of various parameters affecting. Design recommendations for the shear capacity of RC elements having FRP reinforcement need a more experimental database to improve design recommendations because almost all the recommendations replace different parameters with FRP's. Steel and FRP are fundamentally different materials. One is ductile and isotropic, whereas the other is brittle and orthotropic. This paper presents experimental results of the investigation on the beams with glass fiber reinforced polymer (GFRP) reinforcement as longitudinal bars and stirrups. Total twelve beams with GFRP reinforcement were prepared and tested. The cross-section of the beams was rectangular of size 230 × 300 mm, and the total length was 2000 mm with a span of 1800 mm. The beams are designed for simply-supported conditions with the two-point load as per specified load positions for different beams. Flexural reinforcement provided is for the balanced conditions as the beams were supposed to test for shear. Two main variables, such as shear span and spacing of stirrups, were incorporated. The beams were designed as per American Concrete Institute (ACI) ACI 440.1R-15. Relation of VExp./VPred. is derived with axial stiffness, span to depth ratio, and stirrups spacing, from which it is observed that current design provisions provide overestimation, particularly at lower stirrups spacing.

• 한국구조물진단유지관리공학회 논문집
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• 제19권1호
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• pp.62-71
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• 2015

KCI 2012와 ACI318-11에서 확대머리 이형철근에 대한 정착길이 산정식을 제시하고 있지만 확대머리 이형철근을 이용한 겹침이음상세에 대한 규정은 없다. 또한, 정착길이 산정에 있어서 횡보강근 효과는 고려하지 않고 있다. 본연구에서는 400MPa과 500MPa 설계기준항복강도를 가지는 확대머리 이형철근에 대하여 겹침이음구간에 대한 구속상세를 평가하기 위하여 겹침이음실험을 실시하였다. 겹침이음 구간내 적용되는 구속상세는 스터럽과 Tie-down 철근이다. 실험결과, 스터럽만으로 보강된 실험체들에서 겹침이음강도 증가에 큰 영향이 없어 취성적인 파괴를 나타낸 반면에, 스터럽과 Tie-down 철근으로 보강된 실험체들은 공칭휨강도 이상의 실험휨강도와 휨거동을 나타내었다. 따라서 스터럽과 Tie-down 철근 상세는 400MPa과 500MPa의 확대머리 이형철근에 대한 겹침이음 성능향상에 기여할 수 있는 것으로 사료된다.

• Steel and Composite Structures
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• 제32권1호
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• pp.111-126
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• 2019

This paper deals with experimental investigation and modeling of the static behavior of a novel RCS beam-column exterior joint. The studied joint detail is a through-column type in which an H steel profile totally embedded inside RC column is directly welded to the steel beam. The H steel profile was covered by two supplementary plates in the joint area in order to avoid the stirrups resisting shear in the joint area. Two full-scale through-column-type RCS joints were tested under static loading. The objectives of the tests were to examine the connection performance and to highlight the contribution of two supplementary plates on the shear resistance of the joint. A reliable nonlinear 3D finite element model was developed using ABAQUS software to predict the response and behavior of the studied RCS joint. An extensive parametric study was performed to investigate the influences of the stirrups, the encased profile length and supplementary plate length on the behavior of the studied RCS joint.

• Computers and Concrete
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• 제10권1호
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• pp.59-78
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• 2012

Although the effect of corrosion of reinforcing bar on the shear behavior of the reinforced concrete (RC) beam had been simulated by tests of the beam with unbonded, half-exposed or whole-exposed tensile steel reinforcements as well as defective stirrup anchorages, theoretical methods to accurately predict remaining capacity of this kind of RC beams, especially shear capacity, are still lacking. Considering the possible position of the critical inclined crack, the actual pattern of strains in the concrete body within the partial length and the proposed compatibility condition of deformations of the RC beam, shear strength of the RC beam with unbonded or exposed tensile steel reinforcements and/or defective stirrup anchorages is predicted. Comparison between the model's predictions with the experimental results published in the literature shows the practicability of the proposed model. Influence of the length of unbonded or exposed tensile steel reinforcements and the percentage of stirrups lacked end anchorages on the shear strength of the RC beam is discussed. It is concluded that, the shear strength of the RC beam with unbonded or exposed tensile steel reinforcements and/or defective stirrup anchorages is greatly influenced by the length of unbonded or exposed tensile steel reinforcements and the percentage of stirrups lacked end anchorages, this influence can be adverse, insignificant or even favourable, dependent on the given parameters of the corresponding normal bonded RC beam.

• 콘크리트학회논문집
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• 제25권2호
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• pp.217-224
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• 2013

ACI 318-08에 신설된 확대머리 철근의 정착길이 설계식은 콘크리트 강도, 철근 항복강도, 철근 지름만을 변수로 횡보강철근의 영향을 고려하지 않고 있다. 또한 제한적인 데이터에 근거한 설계식으로 순간격과 재료강도에 엄격한 제한을 두고 있다. 이 연구에서는 철근 항복강도 600 MPa의 고강도 철근을 사용하여, $2d_b$의 좁은 순간격을 갖고 횡보강철근을 배근한 겹침 이음 실험을 실시하였다. 실험 결과 횡보강철근을 배근하지 않은 실험체의 경우, 프라잉 거동으로 인해 하부 피복콘크리트가 일찍 탈락되었다. 전체 정착강도 중 확대머리 지압의 기여도는 평균 15%로 지압이 제대로 발현되기 전에 파괴되었다. 이음길이 전체에 스터럽을 배근한 횡보강 실험체는 프라잉 거동이 억제되고 횡보강에 의한 부착강도 증진으로 무보강에 비해 지압과 부착이 모두 증가하였다. 이음 단부에만 횡보강철근을 배근한 단부보강 실험체의 경우, 프라잉 거동은 억제되었지만 이음구간의 부착이 크게 증가되지 않아 지압이 충분히 발현되기 전에 부착에 의해 파괴되었다. 실험결과를 회귀 분석하여 확대머리 철근의 정착강도 평가식을 제안하였다. 평가식은 부착과 지압의 영향을 분리하여 구성하였으며, 콘크리트강도, 횡방향 철근 지수, 정착길이를 설계 변수로 포함하였다. 실험 결과와 비교한 결과 평균 1.0, 변동계수 6%로 변수에 따른 편향 없이 정착강도를 예측하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제20권4호
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• pp.144-152
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• 2016

본 논문은 단차가 있는 철근콘크리트 보에서 인장을 받는 하부 철근의 겹침이음 상세에 고강도 갈고리 철근 및 확대머리 철근을 사용하기 위하여 겹침이음 성능평가를 위한 실험적 연구결과를 다룬다. 겹침이음길이와 겹침이음구간내 스터럽 보강유무를 주요 변수로 한 실험을 통하여, 파괴유형, 초기강성, 최대내력, 변형성능 등을 분석하였고, KCI2012 정착설계식을 모델로 한 이론내력과 비교하였다. 그 결과, 모든 실험체들에서 확대머리 철근이 위치한 배근 방향으로 발생한 균열에 의하여 최종파괴가 나타났고, 초기 강성 및 휨균열 이후의 강성이 유사하게 나타났다. 스터럽 보강되지 않은 실험체에 대하여 HS 계열 실험체들은 겹침이음길이가 25% 증가할 때, 최대 실험내력은 11.8~18.1% 증가한 반면에, HH 계열 실험체들은 확대머리 철근의 프라이아웃거동에 의한 파괴로 내력 증가의 효과가 없었다. 현행 KCI2012에 의한 정착길이 설계식을 바탕으로 B급 겹침이음과 스터럽보강에 따른 감소계수 0.8을 고려하여 이론 겹침이음내력을 산정한 결과, HS 계열실험체는 이론 내력이 실험내력을 안전측으로 평가하고 있다. 반면에 스터럽이 보강되지 않은 HH 계열 실험체들은 이론내력이 실험내력을 불안전측으로 평가하고 있어 겹침이음 구간 내 스터럽 보강을 하여야 할 것으로 사료된다.

• Computers and Concrete
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• 제23권5호
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• pp.335-349
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• 2019

A low-cycle loading experiment of 16 transfer column specimens was conducted to study the influence of parameters, likes the extension length of shape steel, the ratio of shape steel, the axial compression ratio and the volumetric ratio of stirrups, on the shear distribution between steel and concrete, the concrete damage state and the degradation of lateral stiffness. Shear force of shape steel reacted at the core area of concrete section and led to tension effect which accelerated the damage of concrete. At the same time, the damage of concrete diminished its shear capacity and resulted in the shear enlargement of shape steel. The interplay between concrete damage and shear force of shape steel ultimately made for the failures of transfer columns. With the increase of extension length, the lateral stiffness first increases and then decreases, but the stiffness degradation gets faster; With the increase of steel ratio, the lateral stiffness remains the same, but the degradation gets faster; With the increase of the axial compression ratio, the lateral stiffness increases, and the degradation is more significant. Using more stirrups can effectively restrain the development of cracks and increase the lateral stiffness at the yielding point. Also, a formula for calculating the yielding lateral stiffness is obtained by a regression analysis of the test data.