Transfer length in full-scale pretensioned concrete beams with 1.4 m and 2.4 m section depths

Yang, Jun-Mo,Kim, Jin-Kook,Yoo, Doo-Yeol Elsevier 2018 ENGINEERING STRUCTURES Vol.171 No.-

<P><B>Abstract</B></P> <P>This study aims to investigate the transfer length of full-scale prestressed concrete (PSC) beams with lengths of 30 m and 35 m and section depths of 1.4 m and 2.4 m for highway and railway bridge girders, respectively. To do this, newly developed high-strength (<I>f<SUB>pu</SUB> </I> of 2400 MPa) prestressing (PS) strands were used. The initial and effective prestressing forces applied were 94% of the yield strength and 70% of the ultimate tensile strength of the strands. The difference between the transfer lengths at the cut end and dead end was reduced by increasing the section depth. Greater strains were found at the cut end due to a lateral expansion of the strands by the Hoyer effect compared with those at the dead end, causing a greater stress concentration. The eight most widely used prediction models were adopted to predict the transfer lengths of high-strength PS strands in full-scale PSC beams, and it was found that all models significantly overestimated the transfer lengths. Accordingly, the conservative use of the ACI recommendation of 50<I>d<SUB>b</SUB> </I> is suggested based on this study.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Transfer length of newly developed PS strand in full-scale girders is examined. </LI> <LI> Shorter transfer length is obtained with an increase in section depth. </LI> <LI> Greater section depth mitigates the effect of detensioning method on transfer length. </LI> <LI> A conservative use of ACI recommendation (50<I>d<SUB>b</SUB> </I>) is suggested for transfer length prediction of full-scale girders. </LI> </UL> </P>

Transfer Lengths in Pretensioned Concrete Measured Using Various Sensing Technologies

Se-Jin Jeon,Ho Shin,Sang-Hyun Kim,Sung Yong Park,Jun-Mo Yang 한국콘크리트학회 2019 International Journal of Concrete Structures and M Vol.13 No.6

Although pretensioned concrete structures have increasingly been used worldwide, a number of design issues need to be addressed to further improve the structural performance. Transfer length of pretensioned members was investigated with several test variables in this study by adopting various sensing technologies including the Smart Strands with embedded fiber optic sensors. The effect of increased strength in 2360 MPa high-strength strand on the transfer length was also analyzed. Representative provisions widely used in design were compared with the test results for consistency and appropriate conservatism. The strain distribution required for the transfer length depended partly on the type and location of sensors, which suggests the challenges associated with reasonable determination of the transfer length. According to the results of the analysis, the predictive equation in ACI 318 was relatively accurate and conservative under various conditions including high-strength strands. However, the transfer lengths based on the strand strains rather than the conventional surface strains of concrete require further investigation depending on the bonding behavior between the strand and the surrounding concrete inside a member. Thus, this study also introduces a new sensing technology utilizing the Smart Strand to reliably measure the strain distribution along a strand.

Transfer lengths of pretensioned concrete members reinforced with 2400 MPa high-strength prestressing tendons

한선진,이득행,오재열,김강수,이성태 사단법인 한국계산역학회 2016 Computers and Concrete, An International Journal Vol.18 No.4

High-strength prestressing tendons with a tensile strength of 2400 MPa have been recently developed in the steel industry of South Korea, and is currently being mass produced for common commercial applications in structural engineering practices. Accordingly, since most of the existing transfer length estimation models were derived based on the test results of the specimens having the prestressing tendons with a tensile strength of 1860 MPa or less, modifications of the transfer length models are now required to consider the effect of the enhanced tensile strength of the prestressing tendons. In this study, six pretensioned concrete specimens reinforced with 2400 MPa tensile strength prestressing tendons were fabricated and tested to investigate their transfer lengths. In addition, a simplified design equation for the transfer length was developed based on the assumption of the linear strain profile curves of the prestressing tendon and surrounding concrete in transfer length zone. The accuracy of the proposed equation was verified in detail by comparing a total of 215 transfer length test results with analysis results. The simplified design equation provided very accurate results on the transfer lengths of all the test specimens, regardless of the tensile strength grades of prestressing tendons.

Experimental and Numerical Study of the Critical Length of Short Kenaf Fiber Reinforced Polypropylene Composites

Mohammad Nematollahi,Mehdi Karevan,Marzieh Fallah,Mahmoud Farzin 한국섬유공학회 2020 Fibers and polymers Vol.21 No.4

Widespread attention to make use of biodegradable resources as a replacement for petroleum products leads to theexploitation of natural fiber reinforced composites. Natural fiber reinforced polymer composites usually exhibit lowermechanical properties than synthetic fiber ones. Thus, understanding key factors affecting the overall mechanical propertiesin order to increase them is crucial. One underlying factor is the length of fiber highly contributing to the extent of matrix/fiber interfacial load transfer at the interface. However, the concurrent examination of the load transfer mechanism at theinterface of fiber/matrix in terms of fiber length has not been well performed using computational, analytical andexperimental approaches. This work is aimed at the determination of the critical fiber length associated with a full loadtransfer condition using various methods to better understand their accuracy and the interfacial load transfer mechanism. Forthis purpose, specimens of neat polypropylene (PP) and 20 wt% kenaf/PP composites were fabricated using extrusioninjection molding. Tensile testing, scanning electron microscopy and density measurements were conducted to incorporatethe obtained results into the models and to verify the results predicted by the models. A three dimensional representativevolume element (RVE) representing the filler content of fabricated specimens was assumed. A micromechanical model wasemployed to make the results of analysis independent of the RVE dimensions. The critical fiber length for a full load transferwas determined by evaluating the stored elastic strain energy changes against the fiber length. The results showed that thekenaf fiber length is critical to both the load transfer efficiency and stiffening of composites. The results further revealed thatto obtain the full interfacial load transfer, the length of kenaf fibers needs to be greater than the critical length being ~2.4 mmprovided that perfect kenaf/PP interfacial interaction exists.

Frequency of and Reasons for Unplanned Transfers From the Inpatient Rehabilitation Facility in a Tertiary Hospital

Soobin Im,Da Young Lim,Min Kyun Sohn,김영욱 대한재활의학회 2020 Annals of Rehabilitation Medicine Vol.44 No.2

Objective To characterize the patients in the inpatient rehabilitation facility who were transferred to acute care facilities and identify the frequency of and reasons for the unplanned transfer. Methods Medical records of patients admitted to the inpatient rehabilitation facility from October 2017 to December 2018 were reviewed. Patients were categorized according to their diagnoses. The included patients were divided into the unplanned transfer and control groups based on whether they required to transfer to another department for acute care before completing an uninterrupted rehabilitation course. The groups were compared in terms of sex, age, length of stay, admission sources, and disease groups. The reasons for unplanned transfers were classified based on medical or surgical conditions. Results Of the 1,378 patients were admitted to the inpatient rehabilitation facility, 1,301 satisfied inclusion criteria. Among them, 121 (9.3%) were unexpectedly transferred to the medical or surgical department. The unplanned transfer group had a higher age (69.54±12.53 vs. 64.39±15.32 years; p=0.001) and longer length of stay (85.69±66.08 vs. 37.81±31.13 days; p<0.001) than the control group. The top 3 reasons for unplanned transfers were infectious disease, cardiopulmonary disease, and orthopedic problem. Conclusion The unplanned transfer group had a significantly higher age and longer length of stay. The most common reason for the unplanned transfer was infectious disease. However, the proportions of those with orthopedic and neurological problems were relatively high. Therefore, further studies of these patient populations may help organize systematic strategies that are needed to reduce unplanned transfers to acute facilities for patients in rehabilitation facilities.

Bond Behavior of Pretensioned Strand Embedded in Ultra-High-Performance Fiber-Reinforced Concrete

Hyun-Oh Shin,Seung-Jung Lee,Doo-Yeol Yoo 한국콘크리트학회 2018 International Journal of Concrete Structures and M Vol.12 No.4

This study aimed to investigate the bond properties of prestressing strands embedded in ultra-high-performance fiberreinforced concrete (UHPFRC). Toward this end, two types of prestressing strands with diameters of 12.7 and 15.2 mm were considered, along with various concrete cover depths and initial prestressing force magnitudes. The average bond strength of the strands in UHPFRC was estimated by using pullout tests, and the transfer length was evaluated based on a 95% average maximum strain method. Test results indicated that the average bond strength of the pretensioned strand reduced as the diameter of the strand increased, and was between the bond strengths of round and deformed steel rebars. Higher bond strength was also obtained with a lower embedment length. Based on a comparison of p value, the bar diameter and embedment length most significantly influenced the bond strength of strands in UHPFRC, compared to a ratio of cover depth to diameter and initial prestressing force. Pretensioned strands in UHPFRC exhibited much higher bond strength and shorter transfer length compared with strands embedded in ordinary high-strength concrete. Lastly, ACI 318 and AASHTO LRFD codes significantly overestimated the transfer length of the strands embedded in UHPFRC.

Transfer learning for vehicle detection using two cameras with different focal lengths

Quang Dinh, Vinh,Munir, Farzeen,Azam, Shoaib,Yow, Kin-Choong,Jeon, Moongu Elsevier science 2020 Information sciences Vol.514 No.-

<P><B>Abstract</B></P> <P>This paper proposes a vehicle detection method using transfer learning for two cameras with different focal lengths. A detected vehicle region in an image of one camera is transformed into a binary map. After that, the map is used to filter convolutional neural network (CNN) feature maps which are computed for the other camera’s image. We also introduce a robust evolutionary algorithm that is used to compute the relationship between the two cameras in an off-line mode efficiently. We capture video sequences and sample them to make a dataset that includes images with different focal lengths for vehicle detection. We compare the proposed vehicle detection method with baseline detection methods, including faster region proposal networks (Faster-RCNN), single-shot-multi-Box detector (SSD), and detector using recurrent rolling convolution (RRC), in the same experimental context. The experimental results show that the proposed method can detect vehicles at a wide range of distances accurately and robustly, and significantly outperforms the baseline detection methods.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A transfer learning based vehicle detection method is proposed for two cameras with different focal lengths and effectively solves tiny object size problems. </LI> <LI> REAL is introduced to compute relationship between two cameras effectively. </LI> <LI> Vehicle datasets using cameras with different focal lengths were captured and labeled to evaluate vehicle detection methods. Experimental results show the proposed vehicle detection method significantly outperforms baseline methods. </LI> </UL> </P>

Bond mechanism of 18-mm prestressing strands: New insights and design applications

Canh N. Dang,José R. Martí-Vargas,W. Micah Hale 국제구조공학회 2020 Structural Engineering and Mechanics, An Int'l Jou Vol.76 No.1

Pretensioned concrete (PC) is widely used in contemporary construction. Bond of prestressing strand is significant for composite-action between the strand and concrete in the transfer and flexural-bond zones of PC members. This study develops a new methodology for quantifying the bond of 18-mm prestressing strand in PC members based on results of a pullout test, the Standard Test for Strand Bond (STSB). The experimental program includes: (a) twenty-four pretensioned concrete beams, using a wide range of concrete compressive strength; and (b) twelve untensioned pullout specimens. By testing beams, the transfer length, flexural-bond length, and development length were all measured. In the STSB, the pullout forces for the strands were measured. Experimental results indicate a significant relationship between the bond of prestressing strand to the code-established design parameters, such as transfer length and development length. However, the code-predictions can be unconservative for the prestressing strands having a low STSB pullout force. Three simplified bond equations are proposed for the design applications of PC members.

FCAW에서의 아크 길이 추정 방법 개발에 관한 연구

배광무,조상명,Bae, Kwang-Moo,Cho, Sang-Myung 대한용접접합학회 2009 대한용접·접합학회지 Vol.27 No.3

The flux cored arc welding (FCAW) process is one of the most frequently employed and important welding process due to high productivity and excellent workability. The process is performed either as an automated process or as a semi-automatic process. In FCAW process, welding voltage has been considered as a qualitative indication of arc length. But it is necessary to let welding operators know, maintain and manage the arc length directly by estimating and displaying it. In this study, to develop arc length estimation technique, we measured a welding circuit resistance($R_sc$) and then we calculated welding circuit voltage drop($V_sc$). Also, we measured arc peak voltage($V_ap$). By subtracting $V_sc$ from $V_arc$, we can easily calculate net arc voltage drop($V_arc$). Consequently, we suggested arc length estimating equation and basic algorithm by regressive analyzing the relationship between net arc voltage drop($V_arc$) and real arc length(Larc) measured by high speed camera. Therefore, arc length can be predicted by just monitoring welding current and voltage.

사각 마이크로 채널의 단상 유동 열전달 특성 연구

문지현(Ji Hyun Mun),김선창(Seon-Chang Kim) 대한기계학회 2011 大韓機械學會論文集B Vol.35 No.9

본 연구에서는 사각 마이크로 채널의 열전달 특성을 연구하기 위한 실험을 수행하였다. 실험에 사용된 시료의 채널 수력직경은 700 ㎛이며, 채널의 개수는 20개이다. 작동유체는 물이며, 작동유체의 입구 온도는 20 이다. 실험 변수는 Reynolds 수 400 ~ 800 및 열 유속 35 ~ 85 ㎾/㎡ 이다. 결과로, Reynolds 수가 큰 경우일수록 대류 열전달 계수가 증가하는 것으로 나타났으며, 열적으로 완전히 발달된 영역에 대하여 대류 열전달 계수는 약 4.6 ~ 6.4 ㎾/㎡ 로 나타났다. 또한, 사각 마이크로 채널에서의 열적 입구길이는 Reynolds 수가 커지는 경우일수록 길어지는 것을 알 수 있었으나, 열 유속의 변화는 입구길이에 영향을 미치지 않는 것으로 나타났다. 본 연구의 결과로 완전히 발달된 유동영역에 대하여 사각 마이크로 채널의 열적 특성을 나타내기 위한 Nusselt 수 상관식을 제안하였다. In this study, experiments were carried out to investigate the convective heat transfer characteristics of rectangular microchannels. The sample used in the experiments contained 20 rectangular microchannels in parallel. The channels had a hydraulic diameter of 700 ㎛. Distilled water was used as the working fluid. In the experiments, the Reynolds number ranged from 400 to 800, heat flux ranged from 35 to 85 ㎾/㎡, and the inlet fluid temperature was 20℃. As a result, the convective heat transfer coefficient increased upon increasing the Reynolds number and ranged from 4.6 to 6.4 ㎾/㎡/℃ in the thermally fully developed region. Moreover, the higher the Reynolds number, the longer the thermal entry length in the rectangular microchannels. However, it was observed that a variable heat flux did not affect the thermal entry length. In conclusion, a correlation was proposed to indicate the heat transfer characteristics in a thermally fully developed region.