시험/상시주행열차를 이용한 철도교량 내하력 응답보정계수 산정

박용주,최은철,박용걸 한국철도학회 2020 한국철도학회논문집 Vol.23 No.7

In domestic circumstances, it is difficult to conduct standardized field load tests due to conflicts with scheduling and work time management as load testing can only be conducted after commercial train operation time. In this situation, difficulties of work safety, high costs, and workmanship in performing field measurement become hindering factors. In order to improve the problems of existing field load testing, a study was conducted to verify that reliable data on load carrying capacity of railway bridge structures can be secured by using load data obtained from commercial train operation. This paper discusses the difference between the response correction factor obtained from field load testing conducted on the Komo railway bridge under various span length and type conditions for commercial train and load test train. Comparative analysis results showed that there was minimal difference between the response correction factors obtained using different trains, where a minimum of 1.63% to a maximum of 4.22%, and an average of 3.11% difference was found. Results of the comparative analysis show that a standard field load test can be carried out using measurement data of a commercial train to evaluate the load carrying capacity of a railway bridge.

Load-carrying behavior of tranmission-tower connected foundations subjected to different load directions

Kyung, D.,Lee, J. Japanese Society of Soil Mechanics and Foundation 2015 Soils and foundations Vol.55 No.3

Connected foundations comprise an effective option for improving the mechanical performance of transmission tower foundations. In this study, the load-carrying behavior of connected foundations for transmission tower structures was investigated focusing on the effect of the load direction based on the field experimental testing program. Improved performances of connected foundations were observed for load directions of both θ=0<SUP>o</SUP> and 45<SUP>o</SUP> considered in this study. The downward settlements at the compressive side for θ=45<SUP>o</SUP> were larger than those for θ=0<SUP>o</SUP>, while the upward displacements were similar. For both vertical and lateral displacements, the use of connected foundations was more effective for θ=45<SUP>o</SUP>, and the effectiveness became more pronounced as the connection-beam stiffness increased. However, the lateral load-carrying capacities for θ=0<SUP>o</SUP> and 45<SUP>o</SUP> were not significantly different for all connection-beam conditions. From the prototype-scaled model load tests, it was confirmed that the use of connected foundations for transmission tower structures is similarly effective for different load directions. Based on the test results, it was suggested that a unified design methodology is applicable for the stability analysis of transmission tower structures subjected to different load directions.

Field distribution factors and dynamic load allowance for simply supported double-tee girder bridges

Brian Kidd,Sandip Rimal,Junwon Seo,Mostafa Tazarv,Nadim Wehbe 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.82 No.1

This paper discusses the field testing of two single-span double-tee girder (DTG) bridges in South Dakota to determine live load distribution factors (LLDFs) and the dynamic load allowance (IM). One bridge had seven girders and another had eight girders. The longitudinal girder-to-girder joints of both bridges were deteriorated in a way that water could penetrate and the joint steel members were corroded. A truck traveled across each of the two bridges at five transverse paths. The paths were tested twice with a crawl speed load test and twice with a dynamic load. The LLDFs and IM were determined using strain data measured during the field tests. These results were compared with those determined according to the AASHTO Standard and the AASHTO LRFD specifications. Nearly all the measured LLDFs were below the AASHTO LRFD design LLDFs, with the exception of two instances: 1) An exterior DTG on the seven-girder bridge and 2) An interior DTG on the eight-girder bridge. The LLDFs specified in the AASHTO Standard were conservative compared with the measured LLDFs. It was also found that both AASHTO LRFD and AASHTO Standard specifications were conservative when estimating IM, compared to the field test results for both bridges.

Field behaviour geotextile reinforced sand column

Tandel, Yogendra K.,Solanki, Chandresh H.,Desai, Atul K. Techno-Press 2014 Geomechanics & engineering Vol.6 No.2

Stone columns (or granular column) have been used to increase the load carrying capacity and accelerating consolidation of soft soil. Recently, the geosynthetic reinforced stone column technique has been developed to improve the load carrying capacity of the stone column. In addition, reinforcement prevents the lateral squeezing of stone in to surrounding soft soil, helps in easy formation of stone column, preserve frictional properties of aggregate and drainage function of the stone column. This paper investigates the improvement of load carrying capacity of isolated ordinary and geotextile reinforced sand column through field load tests. Tests were performed with different reinforcement stiffness, diameter of sand column and reinforcement length. The results of field load test indicated an improved load carrying capacity of geotextile reinforced sand column over ordinary sand column. The increase in load carrying capacity depends upon the sand column diameter, stiffness of reinforcement and reinforcement length. Also, the partial reinforcement length about two to four time's sand column diameter from the top of the column was found to significant effect on the performance of sand column.

연약지반의 쇄석다짐말뚝에 대한 거동 분석(I)

배경태,이종규 한국지반공학회 2007 한국지반공학회논문집 Vol.23 No.4

Numerical analysis was performed to investigate the behavior of rammed aggregate piers (RAP) in soft ground with various interface conditions, area replacement ratio, aspect ratio and surcharge loads of pile and soil. And field modulus load test was carried out to predict the input parameters. Field prototype (unit cell) tests are in progress to compare the result of numerical analysis. Also a modified load transfer equation of RAP on soft foundation was proposed. According to the results, the behavior of RAP depended on such as interface conditions, settlement characteristics (free strain) and stress concentration ratio. On the other hand, maximum stress concentration ratio increased as area replacement ratio and aspect ratio increased, and it was remarkably affected by surcharge loads.

풍화지반에 근입된 마이크로파일의 하중전이곡선 추정을 위한 경험식 개발

노강구,박성완,조국환 한국지반공학회 2007 한국지반공학회논문집 Vol.23 No.1

Micropiles have been used for underpinning or rehabilitation of existing foundations, and direct structural support system as well. However, relatively few studies have been done on the load-transfer mechanism of micropile systems in Korea. In addition to that, only the limited information is available for estimating the side friction values on micropiles installed in weathered soils. In this study, a full-scale test on an instrumented micropile is performed in order to establish the load-transfer curves based on a hyperbolic function. Then, an empirically derived equation that correlates the load-transfer curve of micropiles with the N values from field standard penetration tests is proposed. The results from all procedures are presented in this paper. Finally, back analysis using a finite difference method and the published field data are adopted for examination of a developed skin friction equation of micropile in weathered soils respectively.

Prediction of load transfer depth for cost-effective design of ground anchors using FBG sensors embedded tendon and numerical analysis

Do, Tan Manh,Kim, Young-Sang Techno-Press 2016 Geomechanics & engineering Vol.10 No.6

The load transfer depth of a ground anchor is the minimum length required to transfer the initial prestressing to the grout column through the bonded part. A thorough understanding of the mechanism of load transfer as well as accurate prediction of the load transfer depth are essential for designing an anchorage that has an adequate factor of safety and satisfies implicit economic criteria. In the current research, experimental and numerical studies were conducted to investigate the load transfer mechanism of ground anchors based on a series of laboratory and field load tests. Optical FBG sensors embedded in the central king cable of a seven-wire strand were successfully employed to monitor the changes in tensile force and its distribution along the tendons. Moreover, results from laboratory and in-situ pullout tests were compared with those from equivalent case studies simulated using the finite difference method in the FLAC 3D program. All the results obtained from the two proposed methods were remarkably consistent with respect to the load increments. They were similar not only in trend but also in magnitude and showed more consistency at higher pullout loading stages, especially the final loading stage. Furthermore, the estimated load transfer depth demonstrated a pronounced dependency on the surrounding ground condition, being shorter in hard ground conditions and longer in weaker ones. Finally, considering the safety factor and cost-effective design, the required bonded length of a ground anchor was formulated in terms of the load transfer depth.

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.

Mechanical Behavior of Hybrid Soil Nail-Anchor System

서형준,이인모,류영무,정지희 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.10

Prestressed soil-nail system has two reinforcing components: steel bar and PC strands. The steel bar with relatively less elongation yields earlier than PC strands. Thus, yield displacements of these two components should be matched to maximize the design load (capacity) of prestressed soil-nail. To achieve this, PC strands need to be prestressed before applying pullout load. In this study, load transfer mechanisms of soil-nail and prestressed soil-nail were determined based on skin friction theory and load transfer theory. The load transfer was derived analytically based on the assumption that skin friction at the interface was fully mobilized. It was then compared with results from field pullout tests performed to identify in-situ load transfer mechanism. Additionally, optimum prestress level required to maximize the pullout loading capacity was evaluated and compared with those obtained from field tests.

고속철도교량의 상시재하시험 타당성 분석에 관한 연구

배석복,박순응,정찬묵 한국철도학회 2020 한국철도학회논문집 Vol.23 No.6

For the safety assessment of a bridge, detailed guidelines for safety and maintenance of the facility are based on field load tests that calculate the response correction factor from the static and dynamic response ratios. The actual deflection of the static response ratio uses the measured value of the static or pseudo-static test; the actual impact factor applies the maximum impact factor value for each load case by speed of the dynamic load test. However, because highspeed railway bridges have a fixed size load compared to road bridges, it is deemed efficient to utilize the measurement of a regular train (safety inspection train) that operates at 170 km/h per day instead of the static load test when calculating the static response ratio. Therefore, to compare the measured values of static and 170 km/h regular operation trains and to ensure their reliability, structural analysis and field load tests were conducted on a PSC Box Girder Bridge, RPF Composite Bridge, and Steel Box Bridge, which are representative superstructure types of high-speed railway bridges.