• Title, Summary, Keyword: Uplift load

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Comparative field tests on uplift behavior of straight-sided and belled shafts in loess under an arid environment

  • Qian, Zeng-zhen;Lu, Xian-long;Yang, Wen-zhi;Cui, Qiang
    • Geomechanics and Engineering
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    • v.11 no.1
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    • pp.141-160
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    • 2016
  • This study elucidates the uplift behaviors of the straight-sided and belled shafts. The field uplift load tests were carried out on 18 straight-sided and 15 belled shafts at the three collapsible loess sites under an arid environment on the Loess Plateau in Northwest China. Both the site conditions and the load tests were documented comprehensively. In general, the uplift load-displacement curves of the straight-sided and belled shafts approximately exhibited an initial linear, a curvilinear transition, and a final linear region, but did not provide a well defined peak or asymptotic value of the load, and therefore their uplift resistances should be interpreted from the load test results using an appropriate criterion. Nine representative uplift resistance interpretation criteria were used to define the "interpreted failure load" for each of the load tests, and all of these interpreted uplift resistances were normalized by the failure threshold, $T_{L2}$, obtained using the $L_1-L_2$ method. These load test data were compared statistically and graphically. For the straight-sided and belled shafts, the normalized uplift load-displacement curves were respectively established by the plots that related the mean interpreted uplift resistance ratio against the mean displacement at the corresponding interpreted criteria, and the comparisons of the normalized load-displacement curves were made. Specific recommendations for the designs of uplift belled and straight-sided shafts in the loess were given, in terms of both capacity and displacement.

Characterization and uncertainty of uplift load-displacement behaviour of belled piers

  • Lu, Xian-long;Qian, Zeng-zhen;Zheng, Wei-feng;Yang, Wen-zhi
    • Geomechanics and Engineering
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    • v.11 no.2
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    • pp.211-234
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    • 2016
  • A total of 99 full-scale field load tests at 22 sites were compiled for this study to elucidate several issues related to the load-displacement behaviour of belled piers under axial uplift loading, including (1) interpretation criteria to define various elastic, inelastic, and "failure" states for each load test from the load-displacement curve; (2) generalized correlations among these states and determinations to the predicted ultimate uplift resistances; (3) uncertainty in the resistance model factor statistics required for reliability-based ultimate limit state (ULS) design; (4) uncertainty associated with the normalized load-displacement curves and the resulting model factor statistics required for reliability-based serviceability limit state (SLS) design; and (5) variations of the combined ULS and SLS model factor statistics for reliability-based limit state designs. The approaches discussed in this study are practical and grounded realistically on the load tests of belled piers with minimal assumptions. The results on the characterization and uncertainty of uplift load-displacement behaviour of belled piers could be served as to extend the early contributions for reliability-based ULS and SLS designs.

Uplift Capacity and Creep Behavior of Concrete Pile Driven in Clay (점토지반에 타입된 콘크리트 말뚝의 인발저항 및 크리프 거동)

  • 신은철;김종인;박정준;이학주
    • Proceedings of the Korean Geotechical Society Conference
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    • pp.371-378
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    • 2001
  • The working load at pile is sometimes subjected to not only compression load but also lateral load and uplift forces. Pile foundation is essential and uplift load can be applied because of buoyancy, a typhoon, wind or seismic forces. This study was carried out to determine the uplift capacity of concrete pile foundation driven in clay. Pile was driven in clay, between pile and clay adhesion factor was estimated, and it is the mean value between the cast-in-situ-pile and steel pipe pile. When pile foundation is loaded for long time, creep behavior occurs. The behavior of creep is originated from the clay creep contacted with pile. The creep behavior of pile foundation embedded in clay is heavily depended on the thickness of clay around the pile shaft, pore water pressure in clay, and creep behavior of clay.

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Generalized load cycles for dynamic wind uplift evaluation of rigid membrane roofing systems

  • Baskaran, A.;Murty, B.;Tanaka, H.
    • Wind and Structures
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    • v.14 no.5
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    • pp.383-411
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    • 2011
  • Roof is an integral part of building envelope. It protects occupants from environmental forces such as wind, rain, snow and others. Among those environmental forces, wind is a major factor that can cause structural roof damages. Roof due to wind actions can exhibit either flexible or rigid system responses. At present, a dynamic test procedure available is CSA A123.21-04 for the wind uplift resistance evaluation of flexible membrane-roofing systems and there is no dynamic test procedure available in North America for wind uplift resistance evaluation of rigid membrane-roofing system. In order to incorporate rigid membrane-roofing systems into the CSA A123.21-04 testing procedure, this paper presents the development of a load cycle. For this process, the present study compared the wind performance of rigid systems with the flexible systems. Analysis of the pressure time histories data using probability distribution function and power spectral density verified that these two roofs types exhibit different system responses under wind forces. Rain flow counting method was applied on the wind tunnel time histories data. Calculated wind load cycles were compared with the existing load cycle of CSA A123.21-04. With the input from the roof manufacturers and roofing associations, the developed load cycles had been generalized and extended to evaluate the ultimate wind uplift resistance capacity of rigid roofs. This new knowledge is integrated into the new edition of CSA A123.21-10 so that the standard can be used to evaluate wind uplift resistance capacity of membrane roofing systems.

Evaluation Method for Uplift Load-carrying Capacity of Inclined Group Micropiles in Dense Sand (조밀한 사질토지반에서 경사로 설치된 그룹 마이크로파일의 인발지지력 평가방법)

  • Kyung, Doohyun;Kim, Garam;Kim, Incheol;Lee, Junhwan
    • Journal of the Korean Geotechnical Society
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    • v.33 no.1
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    • pp.67-77
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    • 2017
  • In the present study, uplift load carrying behavior of micropiles with installation angle and pile spacing was investigated based on uplift load tests using single and group micropiles. In addition, evaluation methods of uplift load carrying capacity of group micropiles were proposed based on FHWA (2005) and Madhav (1987) and they were compared with test results to confirm the validity of proposed methods. From the test results, uplift load carrying capacities of single and group micropiles increased with the increase of the installation angle up to $30^{\circ}$, whose values also increased slightly with increasing pile spacing. For the proposed method based on FHWA (2005), the estimated values were similar to measured values up to $15^{\circ}$ of installation angle and 5D of pile spacing. For the proposed method based on Madhav (1987), on the other hand, it was observed that the estimated values were in good agreement with measured values in all installation conditions.

Effect of Embedment Ratio and Loading Rate on Uplift Adhesion Factor of Concrete Driven Pile (근입비와 인발속도가 콘크리트 항타말뚝의 인발부착계수에 미치는 영향)

  • Kim Jong-In;Park Jeong-Jun;Shin Eun-Chul
    • Journal of the Korean Society for Railway
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    • v.8 no.4
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    • pp.367-371
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    • 2005
  • Pile foundations are utilized when soil is so weak that shallow foundations are not suitable or point load is concentrated in small area. Such soil can be formed by the land reclamation works which have extensively been executed along the coastal line of southern and western parts of the Korean Peninsula. The working load at pile is sometimes subjected to not only compression load but also lateral load sad uplift forces. But in most of the practice design, uplift capacity of pile foundation is not considered and estimation of uplift capacity is presumed on the compression skin friction. This study was carried out to determine that the effect of embedment ratio and loading rate on uplift adhesion factor of concrete pile driven in clay. Based on the test results, the critical embedment ratio is about 9. Adhesion factor is constant under the critical embedment ratio, and decreasing over the critical embedment ratio. Also, adhesion factor is increased with the loading rate is increased.

Ultimate Uplift Capacity of Permanent Anchor Embedded in Weathered Rock (풍화암에 근입된 영구 앵커의 극한인발력)

  • Yoo, Nam-Jae;Park, Byung-Soo;Jeong, Gil-Soo;Kim, Jin-Hwang
    • Journal of Industrial Technology
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    • v.21 no.B
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    • pp.195-203
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    • 2001
  • The purpose of this study is to estimate ultimate uplift capacity of permanent anchor which was cast into weathered rock. The ultimate uplift capacity was estimated from the load-displacement curve of four different anchors which have different bond length. The creep test was performed for 15minutes under the maximum load of each step in order to understand the load-transfer property of permanent anchor and to decide which anchor to choose. The destruction range of soil due to the changes in load was estimated by installing dial gauge on the ground which was cast into the weathered rock. Ultimately, the study on the behavior of the anchor case into the weathered rock was performed by comparing and analyzing the estimated result of the UUC obtained by the full scale pull out test in the field with the exsting theoretical and practical results of soil and rock anchor.

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Characteristics of Field Uplift Tests of Continuous Greenhouse using the Load Control Method (하중 제어법을 이용한 파이프 줄기초의 현장 인발저항 특성)

  • Lim, Seong-Yoon;Kim, Myeong-Hwan;Kim, Yu-Yong;Yu, Seok-Chul;Kim, Seok-Jin;Lim, Jae-Sam
    • Journal of The Korean Society of Agricultural Engineers
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    • v.60 no.4
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    • pp.105-111
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    • 2018
  • Institutional inertia anti-disaster standard was presented mainly on the upper surface, it is necessary to improve to the soil type standard and uplift the resistance standard greenhouse that are vulnerable to strong winds. In this study, we carried out a field test using the load control method in order to evaluate the uplift resistance of continuous foundation of greenhouse with different depths of the rafters. Institutional inertia anti-disaster standard of greenhouse foundation did not protect the greenhouse structure from the damages caused by strong winds and heavy snow. Therefore, field tests for behavior characteristics of continuous greenhouse foundation were carried out to ensure stable facility cultivation. The field test condition was evaluated using different embedded depth as follows: 30cm, 40cm, 50cm and spacing 50cm, 60cm, 70 cm. As a result of the uplift resistance field tests using the load control method, the minimum uplift resistance was found to be over 90kg and uplift resistance displacement was 9.4mm. Uplift resistance of the continuous greenhouse foundation was in the range of 90-180 kg according to embedded depth and spacing. Using the test condition, there was no constant trend in the uplift resistance.

Study on Pullout Behavior and Determination of Ultimate Uplift Capacity of Pile Driven in Small Pressured Chamber (소형 압력 토조내에 타입된 말뚝의 인발 거동과 극한 인발 지지력 결정에 관한 연구)

  • 최용규
    • Geotechnical Engineering
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    • v.11 no.2
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    • pp.19-28
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    • 1995
  • Based on the various test data acquired in the field, the large pressure chamber and the small pressure chamber, uplift behaviors and method of determining the ultimate uplift capacity of pile driven in small pressure chamber were studied. After uplift pile experienced 2 or 3 sudden slip due to increase of uplift load, complete pullout failure was occurred. Thus, it appears that the ultimate uplift capacity could be identified as the load at displacement where first slip occurs. The ultimate uplift capacity might be determined in every test and the disturbance after first uplift test could be recovered by adding one blow of the drop hammer, which had to depend on the model pile capacity.

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Uplift Behavior of Group Micropile according to Embedded Pile Condition in Sand (사질토지반에서 그룹 마이크로파일의 설치조건에 따른 인발거동특성)

  • Kyung, Doo-Hyun;Kim, Ga-Ram;Park, Dae-Sung;Kim, Dae-Hong;Lee, Jun-Hwan
    • Journal of the Korean Geotechnical Society
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    • v.31 no.2
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    • pp.27-37
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    • 2015
  • The micropile is small diameter pile foundation of which diameter is below 300 mm. This system has been applied to reinforce the foundation structure. In the present study, the effects of embedded conditions of group micropiles were investigated from a series of uplift load tests. For the study, uplift load tests were performed using group micropiles in various pile spacing and installation angle. The increase of uplift resistance and the reduction of uplift displacement were investigated in the tests. As the result, the resistances were principally changed by embedded pile angle, the resistance increase were 33%, 59% and 5% for $15^{\circ}$, $30^{\circ}$ and $45^{\circ}$ of embedded pile angle. The uplift displacement reduction increases with lower pile spacing condition and the reduction ratios of uplift displacements in the same spacing condition were 50%, 53%, -45% for $15^{\circ}$, $30^{\circ}$ and $45^{\circ}$ of embedded pile angle.