연직진동말뚝의 동적 하중전이 특성

이승현(Lee Seung-Hyun),김응석(Kim, Eung-Sung),윤기용(Yoon Ki-Yong) 한국산학기술학회 2014 한국산학기술학회논문지 Vol.15 No.6

본 연구에서는 진동해머에 의해 시공되는 강널말뚝에 대한 계측시험결과를 바탕으로 진동해머에 의해 시공되는 말뚝 의 해석에 필요한 이론적인 동적 하중전이함수를 구하고자 하였다. 동적 하중전이함수를 결정하기에 앞서 정적 하중전이함 수를 Ramberg-Osgood 모델을 이용하여 모델링하였는데 Ramberg-Osgood 모델의 매개변수와 N값 사이의 평균 상관계수 는 주면마찰의 경우 0.97이었고 선단저항의 경우 0.98로서 신뢰도가 높았다. 동적 하중전이함수는 수정 Ramberg-Osgood 모델을 이용하여 표현하고자 하였는데 결정된 매개변수를 적용하여 해석한 결과를 계측시험결과와 비교해 볼 때 유사한 하 중전이특성을 보임을 알 수 있었다. In this study, the dynamic load transfer function, which is necessary for analyzing a pile installed by a vibro hammer, was determined by comparing the results of the analyses and instrumented tests. The static load transfer function was modeled by the Ramberg-Osgood model through an analytical method before determining the dynamic load transfer curve. The parameters of the Ramberg-Osgood model were correlated with the N value of the standard penetration test and average values of the correlation coefficient were 0.97 for the shaft load transfer and 0.98 for the base load transfer. The dynamic load transfer function was simulated using the modified Ramberg-Osgood model. The results showed that there were little differences in the characteristics of dynamic load transfer between the results of the measurement and prediction.

양방향 재하시험을 이용한 말뚝의 하중-변위곡선 추정방법

권오성,권오균,김명모,최용규 한국지반공학회 2006 한국지반공학회논문집 Vol.22 No.4

For the last decade, the bi-directional testing method has been advantageous over the conventional pile load testing method in many aspects. However, because the bi-directional test uses a loading mechanism entirely different from that of the conventional pile load testing method, many investigators and practicing engineers have been concerned that the bi-directional test would give inaccurate results, especially about the pile head settlement behavior. Therefore, a bi-directional load test and the conventional top-down load test were executed on 1.5 m diameter cast-in-situ concrete piles at the same time and site. Strain gauges were placed on the piles. The two tests gave similar load transfer curves at various depth of piles. However, the top-down equivalent curve constructed from the bi-directional load test results predicted the pile head settlement under the pile design load to be about one half of that predicted by the conventional top-down load test. To improve the prediction accuracy of the top-down equivalent curve, a simple method that accounts for the pile compression is proposed. It was also shown that the strain gauge measurement data from the bi-directional load test could reproduce almost the same top-down curve.

Monitoring of tension force and load transfer of groundanchor by using optical FBG sensors embedded tendon

Young-Sang Kim,김재민,Hyun-Jong sung,Hyun-Woo Kim 국제구조공학회 2011 Smart Structures and Systems, An International Jou Vol.7 No.4

A specially designed tendon, which is proposed by embedding an FBG sensor into the center king cable of a 7-wire strand tendon, was applied to monitor the prestress force and load transfer of ground anchor. A series of tensile tests and a model pullout test were performed to verify the feasibility of the proposed smart tendon as a measuring sensor of tension force and load transfer along the tendon. The smart tendon has proven to be very effective for monitoring prestress force and load transfer by measuring the strain change of the tendon at the free part and the fixed part of ground anchor, respectively. Two 11.5 m long proto-type ground anchors were made simply by replacing a tendon with the proposed smart tendon and prestress forces of each anchor were monitored during the loading-unloading step using both FBG sensor embedded in the smart tendon and the conventional load cell. By comparing the prestress forces measured by the smart tendon and load cell, it was found that the prestress force monitored from the FBG sensor located at the free part is comparable to that measured from the conventional load cell. Furthermore, the load transfer of prestressing force at the tendon-grout interface was clearly measured from the FBGs distributed along the fixed part. From these pullout tests, the proposed smart tendon is not only expected to be an alternative monitoring tool for measuring prestress force from the introducing stage to the long-term period for health monitoring of the ground anchor but also can be used to improve design practice through determining the economic fixed length by practically measuring the load transfer depth.

Monitoring of tension force and load transfer of ground anchor by using optical FBG sensors embedded tendon

Kim, Young-Sang,Sung, Hyun-Jong,Kim, Hyun-Woo,Kim, Jae-Min Techno-Press 2011 Smart Structures and Systems, An International Jou Vol.7 No.4

A specially designed tendon, which is proposed by embedding an FBG sensor into the center king cable of a 7-wire strand tendon, was applied to monitor the prestress force and load transfer of ground anchor. A series of tensile tests and a model pullout test were performed to verify the feasibility of the proposed smart tendon as a measuring sensor of tension force and load transfer along the tendon. The smart tendon has proven to be very effective for monitoring prestress force and load transfer by measuring the strain change of the tendon at the free part and the fixed part of ground anchor, respectively. Two 11.5 m long proto-type ground anchors were made simply by replacing a tendon with the proposed smart tendon and prestress forces of each anchor were monitored during the loading-unloading step using both FBG sensor embedded in the smart tendon and the conventional load cell. By comparing the prestress forces measured by the smart tendon and load cell, it was found that the prestress force monitored from the FBG sensor located at the free part is comparable to that measured from the conventional load cell. Furthermore, the load transfer of prestressing force at the tendon-grout interface was clearly measured from the FBGs distributed along the fixed part. From these pullout tests, the proposed smart tendon is not only expected to be an alternative monitoring tool for measuring prestress force from the introducing stage to the long-term period for health monitoring of the ground anchor but also can be used to improve design practice through determining the economic fixed length by practically measuring the load transfer depth.

양방향 말뚝선단재하시험에 의한 암반근입 현장타설말뚝의 하중-침하거동 분석

설훈일,정상섬,김재영,한근택 한국지반공학회 2008 한국지반공학회논문집 Vol.24 No.11

Load settlement behaviors and load transfer characteristics of rock-socketed pile subjected bi-directional load at pile tip were investigated using bi-directional pile load tests (BD PLT) performed on ten large-diameter drilled shafts at four sites. Based on test results, additional pile-toe displacement (wbs) by coupled soil resistance was analyzed, and thus equivalent top loaded load-settlement curve of pile subjected bi-directional load was proposed by taking into account the coupled soil resistance. Through comparisons with field case studies, it is found that for test piles there exists effect of coupled soil resistance, which is represented by wbs, and thus an equivalent curve obtained by existing uncoupled methods can overestimate bearing capacity of piles by BD PLT. On the other hand, the analysis by the proposed method with soil coupling effect has a considerably larger settlement when compared with the results by uncoupled load transfer method and estimates reasonable load-settlement behaviors of test piles. In case of pile socketed in high strength rocks, however, effects of coupled soil resistance can be neglected.

이승 보조 돌봄 작업의 수동 돌봄(Manual Care)과 로봇 돌봄(Robot-aided Care)의 작업부하 비교를 위한 작업부담 평가체계 개발

공용구(Yong-Ku Kong),최경희(Kyeong-Hee Choi),심현호(Hyun-Ho Shim),조민욱(Min-Uk Cho),김민정(Min-Jung Kim),박상수(Sang-Soo Park),심진우(Jin-Woo Shim),김승연(Seoung-Yeon Kim) 대한인간공학회 2021 大韓人間工學會誌 Vol.40 No.5

Objective: The aim of this study was to develop an assessment system for quantitatively comparing the workloads of manual care (MC) and robot-aid care (RC) of the care jobs. Background: Due to the rapid aging of Korea, the demand for human resources for elderly care tasks has been rapidly increased. Caregivers taking care of the elderly have been under high physical and mental stress due to various types of care work. Recently, many care robots using the technology of the 4th Industrial Revolution have been proposed as a solution to reduce caregiver’s load. However, there is still insufficient research to evaluate the physical and mental load relief effects of caregivers through comprehensive assessment. Method: The upper index (physical and mental loads) and the lower indexes of each upper index were determined through the literature survey and 42 ergonomic experts’ opinions. Ergonomics experts and caregivers also conducted the Analytic Hierarchy Process (AHP) to determine weights of the upper and lower indexes. Two task types (Bed to Chair and Chair to Bed) and two care types (Manual care and Robot-aid care) were performed to estimate the final work load scores based on the task types and care types in this study. Results: The results of the AHP analysis showed that the physical load was higher than the mental load for elderly caring tasks. Muscle load was the highest work stress in the physical load, followed by subjective body and posture loads. Safety stress was the most in the mental load, followed by task-difficulty stress and emotional stress, respectively. Robot-aided care showed a lower final workload score, including physical and mental load scores, than manual care in both types of tasks (Bed to Chair, Chair to Bed). Conclusion: A workload assessment system was developed by selecting assessment indexes of physical and mental loads that reflect the characteristics of transfer assistive care. It was noted that the physical and mental loads might be reduced in robot-aided care compared to manual care based on this study. Application: The workload assessment system can be used to quantitatively evaluate the reduction of workloads for applying different types of manual care and robot-aided care systems in elderly care work.

말뚝-지반 상호작용을 고려한 수정된 하중전이함수법 제안

설훈일(Seol Hoon-Il),정상섬(Jeong Sang-Seom),김영호(Kim Young-Ho) 대한토목학회 2008 대한토목학회논문집 C Vol.28 No.6

말뚝의 하중전이거동 및 변형특성 해석을 위해 하중전이함수법이 널리 사용된다. 본 연구에서는 말뚝-지반의 상효작용 즉, 지반의 연속성을 고려한 하중전이해석에 고찰하였으며, Mindlin 해를 이용하여 이를 고려함으로써 말뚝의 실제 거동에 보다 부합되도록 수정된 하중전이 해석방법을 제안하였다. 이를 통해 말뚝지반 상호작용의 영향인자인 말뚝직경-지반계수의 비(D/Es)과 주면마찰력-재하하중의 비(Rs/Q)를 고려할 수 있었다. 제안된 하중전이함수법의 타당성을 검증하기 위하여 현장재하시험 사례와의 비교분석 결과, 제안된 해석방법은 암반 근입 현장타설말뚝의 하중침하 거동 및 하중전이특성을 적절히 예측함을 알 수 있었다. The load distribution and deformation of pile subjected to axial loads are evaluated by a load-transfer method. The emphasis is on quantifying the effect of coupled soil resistance that is closely related to the ratio of pile diameter to soil modulus (D/Es) and the ratio of total shaft resistance against total applied load (Rs/Q), in rock-socketed drilled shafts using the coupled load-transfer method. The proposed analytical method that takes into account the soil coupling effect was developed using a modified Mindlin's point load solution. Through comparisons with field case studies, it was found that the proposed method in the present study estimated reasonable load transfer behavior of pile and coupling effects due to the transfer of shaft shear loading, and thus represents a significant improvement in the prediction of load deflections of drilled shafts.

유한요소해석을 통한 암반에 근입된 현장타설말뚝의하중전이거동 분석

설훈일,김영호,정상섬 한국지반공학회 2008 한국지반공학회논문집 Vol.24 No.12

The load distribution and deformation of rock-socketed drilled shafts subjected to axial loads are evaluated by a load-transfer method. The emphasis is on quantifying the effect of coupled soil resistance in rock-socketed drilled shafts using the 2D elasto-plastic finite element analysis. Slippage and shear load transfer behavior at the pile-soil interface are investigated by using a user-subroutine interface model (FRIC). It is shown that the coupled soil resistance provides the influence of pile toe settlement as the shaft resistance is increased to an ultimate limit state. The results show that the coupling effect is closely related to the value of pile diameter over rock mass modulus (D/Emass) and the ratio of total shaft resistance against total applied load (Rs/Q). Through comparisons with field case studies, the 2D numerical analysis reseanably presented load transfer of pile and coupling effect due to the transfer of shaft shear loading, and thus represents a significant improvement in the prediction of load deflections of drilled shafts.

강관 매입말뚝의 주면 하중전이 곡선(t-z) 제안

김도현,박종전,장용채,정상섬 한국지반공학회 2018 한국지반공학회논문집 Vol.34 No.12

In this study, the load-transfer behavior along the shaft of the prebored and precast piles was investigated by pile loading tests. Special attention was given to quantifying the skin frictions developed between the pile-soil interfaces of the 14 instrumented test piles. Based on this detailed field tests, the load - settlement curves and axial load distributions of piles were obtained and the load-transfer curves (t-z curves) for the test piles were proposed. As such, it is found that the test results show two different load transfer behaviors; ductile and brittle behavior curves. The corresponding t-z curves are proposed based on the hyperbolic- and sawtooth-shape, respectively. By validating the accuracy of the proposed curves, it is also found that the prediction results based on the proposed load-transfer curve are in good agreement with the general trends observed by the field loading tests.

수질오염총량관리 합류식지역의 우기시 관거이송 변화유형

박준대 ( Jun Dae Park ),오승영 ( Seung Young Oh ),김지태 ( Ji Tae Kim ) 한국물환경학회 2010 한국물환경학회지 Vol.26 No.6

Discharged pollution load is varied as rainfall changes in the area with combined sewer system. Changes in discharged pollution load are directly related with those of sewer transfer flow. Therefore, it is important to identify the pattern of sewer transfer flow for the analysis of changes in discharged pollution load. This study reviewed the type of distribution of sewer transfer flow for 17 sewage treatment plants and developed simple formular to estimate sewer transfer flow as rainfall changes. 11 facilities showed to have some relation with rainfall in the change of sewer transfer flow but 6 facilities to have no relation. Relationships between rainfall amount and sewer transfer flow showed that 6 facilities out of 11 had relatively strong relationships above R2=0.5, which were considered to be affected directly by rainfall changes. The formular which explain the relationship between rainfall and sewer transfer flow can be applied in the analysis of rainfall effects on discharged pollution load, therefore, the more appropriate evaluation will be done.